Fixes a couple of issues around import scope compilation

7dffad1a · Tomas Matousek · c7ab77d0 · 7dffad1a · 7dffad1a · 7dffad1a
32 changed file
--- a/src/Compilers/CSharp/Portable/Binder/Binder_Initializers.cs
+++ b/src/Compilers/CSharp/Portable/Binder/Binder_Initializers.cs
@@ -23,7 +23,6 @@ internal struct ProcessedFieldInitializers
            SourceMemberContainerTypeSymbol typeSymbol,
            MethodSymbol scriptCtor,
            ImmutableArray<ImmutableArray<FieldOrPropertyInitializer>> fieldInitializers,
-            bool generateDebugInfo,
            DiagnosticBag diagnostics,
            ref ProcessedFieldInitializers processedInitializers) //by ref so that we can store the results of lowering
        {
@@ -33,7 +32,7 @@ internal struct ProcessedFieldInitializers
                ImportChain firstImportChain;
                processedInitializers.BoundInitializers = BindFieldInitializers(typeSymbol, scriptCtor, fieldInitializers,
-                    diagsForInstanceInitializers, generateDebugInfo, out firstImportChain);
+                    diagsForInstanceInitializers, out firstImportChain);
                processedInitializers.HasErrors = diagsForInstanceInitializers.HasAnyErrors();
                processedInitializers.FirstImportChain = firstImportChain;
@@ -50,7 +49,6 @@ internal struct ProcessedFieldInitializers
            MethodSymbol scriptCtor,
            ImmutableArray<ImmutableArray<FieldOrPropertyInitializer>> initializers,
            DiagnosticBag diagnostics,
-            bool generateDebugInfo,
            out ImportChain firstImportChain)
        {
            if (initializers.IsEmpty)
@@ -64,11 +62,11 @@ internal struct ProcessedFieldInitializers
            if ((object)scriptCtor == null)
            {
-                BindRegularCSharpFieldInitializers(compilation, initializers, boundInitializers, diagnostics, generateDebugInfo, out firstImportChain);
+                BindRegularCSharpFieldInitializers(compilation, initializers, boundInitializers, diagnostics, out firstImportChain);
            }
            else
            {
-                BindScriptFieldInitializers(compilation, scriptCtor, initializers, boundInitializers, diagnostics, generateDebugInfo, out firstImportChain);
+                BindScriptFieldInitializers(compilation, scriptCtor, initializers, boundInitializers, diagnostics, out firstImportChain);
            }
            return boundInitializers.ToImmutableAndFree();
@@ -83,7 +81,6 @@ internal struct ProcessedFieldInitializers
            ImmutableArray<ImmutableArray<FieldOrPropertyInitializer>> initializers,
            ArrayBuilder<BoundInitializer> boundInitializers,
            DiagnosticBag diagnostics,
-            bool generateDebugInfo,
            out ImportChain firstDebugImports)
        {
            firstDebugImports = null;
@@ -118,7 +115,7 @@ internal struct ProcessedFieldInitializers
                        Debug.Assert(parentBinder.ContainingMemberOrLambda == fieldSymbol.ContainingType || //should be the binder for the type
                                fieldSymbol.ContainingType.IsImplicitClass); //however, we also allow fields in namespaces to help support script scenarios
-                        if (generateDebugInfo && firstDebugImports == null)
+                        if (firstDebugImports == null)
                        {
                            firstDebugImports = parentBinder.ImportChain;
                        }
@@ -138,7 +135,7 @@ internal struct ProcessedFieldInitializers
        /// </summary>
        private static void BindScriptFieldInitializers(CSharpCompilation compilation, MethodSymbol scriptCtor,
            ImmutableArray<ImmutableArray<FieldOrPropertyInitializer>> initializers, ArrayBuilder<BoundInitializer> boundInitializers, DiagnosticBag diagnostics,
-            bool generateDebugInfo, out ImportChain firstDebugImports)
+            out ImportChain firstDebugImports)
        {
            Debug.Assert((object)scriptCtor != null);
@@ -177,7 +174,7 @@ internal struct ProcessedFieldInitializers
                    Binder scriptClassBinder = binderFactory.GetBinder(initializerNode);
                    Debug.Assert(((ImplicitNamedTypeSymbol)scriptClassBinder.ContainingMemberOrLambda).IsScriptClass);
-                    if (generateDebugInfo && firstDebugImports == null)
+                    if (firstDebugImports == null)
                    {
                        firstDebugImports = scriptClassBinder.ImportChain;
                    }

--- a/src/Compilers/CSharp/Portable/Binder/ImportChain.cs
+++ b/src/Compilers/CSharp/Portable/Binder/ImportChain.cs
 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
-using System;
-using System.Collections;
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Diagnostics;
-using System.Linq;
-using System.Threading;
 using Microsoft.CodeAnalysis.CSharp.Symbols;
-using Microsoft.CodeAnalysis.Emit;
 namespace Microsoft.CodeAnalysis.CSharp
 {
@@ -27,17 +22,29 @@ public ImportChain(Imports imports, ImportChain parentOpt)
            ParentOpt = parentOpt;
        }
-        ImmutableArray<Cci.UsedNamespaceOrType> Cci.IImportScope.GetUsedNamespaces(EmitContext context)
+        ImmutableArray<Cci.UsedNamespaceOrType> Cci.IImportScope.GetUsedNamespaces()
        {
-            if (_lazyTranslatedImports.IsDefault)
+            // The imports should have been translated during code gen.
+            Debug.Assert(!_lazyTranslatedImports.IsDefault);
+            return _lazyTranslatedImports;
+        }
+        public Cci.IImportScope Translate(Emit.PEModuleBuilder moduleBuilder, DiagnosticBag diagnostics)
+        {
+            for (var scope = this; scope != null; scope = scope.ParentOpt)
            {
-                ImmutableInterlocked.InterlockedInitialize(ref _lazyTranslatedImports, TranslateImports(context));
+                if (!scope._lazyTranslatedImports.IsDefault)
+                {
+                    break;
                }
-            return _lazyTranslatedImports;
+                ImmutableInterlocked.InterlockedInitialize(ref scope._lazyTranslatedImports, scope.TranslateImports(moduleBuilder, diagnostics));
+            }
+            return this;
        }
-        private ImmutableArray<Cci.UsedNamespaceOrType> TranslateImports(EmitContext context)
+        private ImmutableArray<Cci.UsedNamespaceOrType> TranslateImports(Emit.PEModuleBuilder moduleBuilder, DiagnosticBag diagnostics)
        {
            var usedNamespaces = ArrayBuilder<Cci.UsedNamespaceOrType>.GetInstance();
@@ -61,12 +68,13 @@ private ImmutableArray<Cci.UsedNamespaceOrType> TranslateImports(EmitContext con
                    if (namespaceOrType.IsNamespace)
                    {
                        var ns = (NamespaceSymbol)namespaceOrType;
-                        var assemblyRef = TryGetAssemblyScope(context, ns);
+                        var assemblyRef = TryGetAssemblyScope(ns, moduleBuilder, diagnostics);
                        usedNamespaces.Add(Cci.UsedNamespaceOrType.CreateNamespace(ns, assemblyRef));
                    }
-                    else
+                    else if (!namespaceOrType.ContainingAssembly.IsLinked)
                    {
-                        var typeRef = GetTypeReference(context, (TypeSymbol)namespaceOrType);
+                        // We skip alias imports of embedded types to be consistent with imports of aliased embedded types and with VB.
+                        var typeRef = GetTypeReference((TypeSymbol)namespaceOrType, nsOrType.UsingDirective, moduleBuilder, diagnostics);
                        usedNamespaces.Add(Cci.UsedNamespaceOrType.CreateType(typeRef));
                    }
                }
@@ -79,18 +87,21 @@ private ImmutableArray<Cci.UsedNamespaceOrType> TranslateImports(EmitContext con
                {
                    var alias = pair.Key;
                    var symbol = pair.Value.Alias;
+                    var syntax = pair.Value.UsingDirective;
                    Debug.Assert(!symbol.IsExtern);
                    NamespaceOrTypeSymbol target = symbol.Target;
                    if (target.Kind == SymbolKind.Namespace)
                    {
                        var ns = (NamespaceSymbol)target;
-                        var assemblyRef = TryGetAssemblyScope(context, ns);
+                        var assemblyRef = TryGetAssemblyScope(ns, moduleBuilder, diagnostics);
                        usedNamespaces.Add(Cci.UsedNamespaceOrType.CreateNamespace(ns, assemblyRef, alias));
                    }
-                    else
+                    else if (!target.ContainingAssembly.IsLinked)
                    {
-                        var typeRef = GetTypeReference(context, (TypeSymbol)target);
+                        // We skip alias imports of embedded types to avoid breaking existing code that
+                        // imports types that can't be embedded but doesn't use them anywhere else in the code.
+                        var typeRef = GetTypeReference((TypeSymbol)target, syntax, moduleBuilder, diagnostics);
                        usedNamespaces.Add(Cci.UsedNamespaceOrType.CreateType(typeRef, alias));
                    }
                }
@@ -99,17 +110,17 @@ private ImmutableArray<Cci.UsedNamespaceOrType> TranslateImports(EmitContext con
            return usedNamespaces.ToImmutableAndFree();
        }
-        private static Cci.ITypeReference GetTypeReference(EmitContext context, TypeSymbol type)
+        private static Cci.ITypeReference GetTypeReference(TypeSymbol type, SyntaxNode syntaxNode, Emit.PEModuleBuilder moduleBuilder, DiagnosticBag diagnostics)
        {
-            return context.ModuleBuilder.Translate(type, context.SyntaxNodeOpt, context.Diagnostics);
+            return moduleBuilder.Translate(type, syntaxNode, diagnostics);
        }
-        private Cci.IAssemblyReference TryGetAssemblyScope(EmitContext context, NamespaceSymbol @namespace)
+        private Cci.IAssemblyReference TryGetAssemblyScope(NamespaceSymbol @namespace, Emit.PEModuleBuilder moduleBuilder, DiagnosticBag diagnostics)
        {
            AssemblySymbol containingAssembly = @namespace.ContainingAssembly;
-            if ((object)containingAssembly != null && (object)containingAssembly != context.ModuleBuilder.CommonCompilation.Assembly)
+            if ((object)containingAssembly != null && (object)containingAssembly != moduleBuilder.CommonCompilation.Assembly)
            {
-                var referenceManager = ((CSharpCompilation)context.ModuleBuilder.CommonCompilation).GetBoundReferenceManager();
+                var referenceManager = ((CSharpCompilation)moduleBuilder.CommonCompilation).GetBoundReferenceManager();
                foreach (var referencedAssembly in referenceManager.ReferencedAssembliesMap.Values)
                {
@@ -117,7 +128,7 @@ private Cci.IAssemblyReference TryGetAssemblyScope(EmitContext context, Namespac
                    {
                        if (!referencedAssembly.DeclarationsAccessibleWithoutAlias())
                        {
-                            return context.ModuleBuilder.Translate(containingAssembly, context.Diagnostics);
+                            return moduleBuilder.Translate(containingAssembly, diagnostics);
                        }
                    }
                }

--- a/src/Compilers/CSharp/Portable/CodeGen/CodeGenerator.cs
+++ b/src/Compilers/CSharp/Portable/CodeGen/CodeGenerator.cs
@@ -70,7 +70,7 @@ private enum IndirectReturnState : byte
            PEModuleBuilder moduleBuilder,
            DiagnosticBag diagnostics,
            OptimizationLevel optimizations,
-            bool emittingPdbs)
+            bool emittingPdb)
        {
            Debug.Assert((object)method != null);
            Debug.Assert(boundBody != null);
@@ -98,7 +98,7 @@ private enum IndirectReturnState : byte
            //   user code that can be stepped thru, or changed during EnC.
            // 
            // This setting only affects generating PDB sequence points, it shall not affect generated IL in any way.
-            _emitPdbSequencePoints = emittingPdbs && method.GenerateDebugInfo;
+            _emitPdbSequencePoints = emittingPdb && method.GenerateDebugInfo;
            if (_optimizations == OptimizationLevel.Release)
            {

--- a/src/Compilers/CSharp/Portable/Compilation/CSharpCompilation.cs
+++ b/src/Compilers/CSharp/Portable/Compilation/CSharpCompilation.cs
@@ -2322,7 +2322,7 @@ internal override StrongNameKeys StrongNameKeys
            CommonPEModuleBuilder moduleBuilder,
            Stream win32Resources,
            Stream xmlDocStream,
-            bool generateDebugInfo,
+            bool emittingPdb,
            DiagnosticBag diagnostics,
            Predicate<ISymbol> filterOpt,
            CancellationToken cancellationToken)
@@ -2354,13 +2354,10 @@ internal override StrongNameKeys StrongNameKeys
            }
            else
            {
-                if (generateDebugInfo && moduleBeingBuilt != null)
+                if (emittingPdb && !StartSourceChecksumCalculation(moduleBeingBuilt, diagnostics))
-                {
-                    if (!StartSourceChecksumCalculation(moduleBeingBuilt, diagnostics))
                {
                    return false;
                }
-                }
                // Perform initial bind of method bodies in spite of earlier errors. This is the same
                // behavior as when calling GetDiagnostics()
@@ -2371,7 +2368,7 @@ internal override StrongNameKeys StrongNameKeys
                MethodCompiler.CompileMethodBodies(
                    this,
                    moduleBeingBuilt,
-                    generateDebugInfo,
+                    emittingPdb,
                    hasDeclarationErrors,
                    diagnostics: methodBodyDiagnosticBag,
                    filterOpt: filterOpt,

--- a/src/Compilers/CSharp/Portable/Compiler/MethodCompiler.cs
+++ b/src/Compilers/CSharp/Portable/Compiler/MethodCompiler.cs
@@ -21,7 +21,7 @@ namespace Microsoft.CodeAnalysis.CSharp
    internal sealed class MethodCompiler : CSharpSymbolVisitor<TypeCompilationState, object>
    {
        private readonly CSharpCompilation _compilation;
-        private readonly bool _generateDebugInfo;
+        private readonly bool _emittingPdb;
        private readonly CancellationToken _cancellationToken;
        private readonly DiagnosticBag _diagnostics;
        private readonly bool _hasDeclarationErrors;
@@ -73,7 +73,7 @@ private void SetGlobalErrorIfTrue(bool arg)
        }
        // Internal for testing only.
-        internal MethodCompiler(CSharpCompilation compilation, PEModuleBuilder moduleBeingBuiltOpt, bool generateDebugInfo, bool hasDeclarationErrors,
+        internal MethodCompiler(CSharpCompilation compilation, PEModuleBuilder moduleBeingBuiltOpt, bool emittingPdb, bool hasDeclarationErrors,
            DiagnosticBag diagnostics, Predicate<Symbol> filterOpt, CancellationToken cancellationToken)
        {
            Debug.Assert(compilation != null);
@@ -81,7 +81,7 @@ private void SetGlobalErrorIfTrue(bool arg)
            _compilation = compilation;
            _moduleBeingBuiltOpt = moduleBeingBuiltOpt;
-            _generateDebugInfo = generateDebugInfo;
+            _emittingPdb = emittingPdb;
            _cancellationToken = cancellationToken;
            _diagnostics = diagnostics;
            _filterOpt = filterOpt;
@@ -89,7 +89,7 @@ private void SetGlobalErrorIfTrue(bool arg)
            _hasDeclarationErrors = hasDeclarationErrors;
            SetGlobalErrorIfTrue(hasDeclarationErrors);
-            if (generateDebugInfo)
+            if (emittingPdb)
            {
                _debugDocumentProvider = (path, basePath) => moduleBeingBuiltOpt.GetOrAddDebugDocument(path, basePath, CreateDebugDocumentForFile);
            }
@@ -233,7 +233,7 @@ internal static MethodSymbol DefineScriptEntryPoint(CSharpCompilation compilatio
                    diagnostics: diagnostics,
                    debugDocumentProvider: null,
                    importChainOpt: null,
-                    generateDebugInfo: false);
+                    emittingPdb: false);
                moduleBeingBuilt.SetMethodBody(scriptEntryPoint, emittedBody);
                moduleBeingBuilt.AddSynthesizedDefinition(compilation.ScriptClass, scriptEntryPoint);
@@ -376,10 +376,10 @@ private void CompileNamedType(NamedTypeSymbol symbol)
            if ((object)sourceTypeSymbol != null)
            {
                _cancellationToken.ThrowIfCancellationRequested();
-                Binder.BindFieldInitializers(sourceTypeSymbol, scriptCtor, sourceTypeSymbol.StaticInitializers, _generateDebugInfo, _diagnostics, ref processedStaticInitializers);
+                Binder.BindFieldInitializers(sourceTypeSymbol, scriptCtor, sourceTypeSymbol.StaticInitializers, _diagnostics, ref processedStaticInitializers);
                _cancellationToken.ThrowIfCancellationRequested();
-                Binder.BindFieldInitializers(sourceTypeSymbol, scriptCtor, sourceTypeSymbol.InstanceInitializers, _generateDebugInfo, _diagnostics, ref processedInstanceInitializers);
+                Binder.BindFieldInitializers(sourceTypeSymbol, scriptCtor, sourceTypeSymbol.InstanceInitializers, _diagnostics, ref processedInstanceInitializers);
                if (compilationState.Emitting)
                {
@@ -625,7 +625,7 @@ private void CompileSynthesizedMethods(TypeCompilationState compilationState)
                        diagnosticsThisMethod,
                        _debugDocumentProvider,
                        methodWithBody.ImportChainOpt,
-                        generateDebugInfo: _generateDebugInfo && method.GenerateDebugInfo);
+                        emittingPdb: _emittingPdb);
                }
                _diagnostics.AddRange(diagnosticsThisMethod);
@@ -719,7 +719,7 @@ private void CompileFieldLikeEventAccessor(SourceEventSymbol eventSymbol, bool i
                        diagnostics: diagnosticsThisMethod,
                        debugDocumentProvider: _debugDocumentProvider,
                        importChainOpt: null,
-                        generateDebugInfo: false);
+                        emittingPdb: false);
                    _moduleBeingBuiltOpt.SetMethodBody(accessor, emittedBody);
                    // Definition is already in the symbol table, so don't call moduleBeingBuilt.AddCompilerGeneratedDefinition
@@ -841,7 +841,7 @@ public override object VisitField(FieldSymbol symbol, TypeCompilationState argum
                    includeInitializersInBody = !processedInitializers.BoundInitializers.IsDefaultOrEmpty &&
                                                !HasThisConstructorInitializer(methodSymbol);
-                    body = BindMethodBody(methodSymbol, compilationState, diagsForCurrentMethod, _generateDebugInfo, out importChain);
+                    body = BindMethodBody(methodSymbol, compilationState, diagsForCurrentMethod, out importChain);
                    // lower initializers just once. the lowered tree will be reused when emitting all constructors 
                    // with field initializers. Once lowered, these initializers will be stashed in processedInitializers.LoweredInitializers
@@ -869,12 +869,9 @@ public override object VisitField(FieldSymbol symbol, TypeCompilationState argum
                    }
                }
 #if DEBUG
                // If the method is a synthesized static or instance constructor, then debugImports will be null and we will use the value
                // from the first field initializer.
-                if (_generateDebugInfo)
-                {
                if ((methodSymbol.MethodKind == MethodKind.Constructor || methodSymbol.MethodKind == MethodKind.StaticConstructor) &&
                    methodSymbol.IsImplicitlyDeclared && body == null)
                {
@@ -884,7 +881,6 @@ public override object VisitField(FieldSymbol symbol, TypeCompilationState argum
                // Either there were no field initializers or we grabbed debug imports from the first one.
                Debug.Assert(processedInitializers.BoundInitializers.IsDefaultOrEmpty || processedInitializers.FirstImportChain != null);
-                }
 #endif
                importChain = importChain ?? processedInitializers.FirstImportChain;
@@ -1082,7 +1078,7 @@ public override object VisitField(FieldSymbol symbol, TypeCompilationState argum
                            diagsForCurrentMethod,
                            _debugDocumentProvider,
                            importChain,
-                            _generateDebugInfo && methodSymbol.GenerateDebugInfo);
+                            _emittingPdb);
                        _moduleBeingBuiltOpt.SetMethodBody(methodSymbol.PartialDefinitionPart ?? methodSymbol, emittedBody);
                    }
@@ -1242,7 +1238,7 @@ private BoundStatement ChainImplicitStructConstructor(MethodSymbol methodSymbol,
            DiagnosticBag diagnostics,
            DebugDocumentProvider debugDocumentProvider,
            ImportChain importChainOpt,
-            bool generateDebugInfo)
+            bool emittingPdb)
        {
            // Note: don't call diagnostics.HasAnyErrors() in release; could be expensive if compilation has many warnings.
            Debug.Assert(!diagnostics.HasAnyErrors(), "Running code generator when errors exist might be dangerous; code generator not expecting errors");
@@ -1257,7 +1253,7 @@ private BoundStatement ChainImplicitStructConstructor(MethodSymbol methodSymbol,
            {
                Cci.AsyncMethodBodyDebugInfo asyncDebugInfo = null;
-                var codeGen = new CodeGen.CodeGenerator(method, block, builder, moduleBuilder, diagnosticsForThisMethod, optimizations, generateDebugInfo);
+                var codeGen = new CodeGen.CodeGenerator(method, block, builder, moduleBuilder, diagnosticsForThisMethod, optimizations, emittingPdb);
                // We need to save additional debugging information for MoveNext of an async state machine.
                var stateMachineMethod = method as SynthesizedStateMachineMethod;
@@ -1284,6 +1280,11 @@ private BoundStatement ChainImplicitStructConstructor(MethodSymbol methodSymbol,
                    codeGen.Generate();
                }
+                // Translate the imports even if we are not writing PDBs. The translation has an impact on generated metadata 
+                // and we don't want to emit different metadata depending on whether or we emit with PDB stream.
+                // TODO (https://github.com/dotnet/roslyn/issues/2846): This will need to change for member initializers in partial class.
+                var importScopeOpt = importChainOpt?.Translate(moduleBuilder, diagnosticsForThisMethod);
                var localVariables = builder.LocalSlotManager.LocalsInOrder();
                if (localVariables.Length > 0xFFFE)
@@ -1329,7 +1330,7 @@ private BoundStatement ChainImplicitStructConstructor(MethodSymbol methodSymbol,
                    builder.RealizedExceptionHandlers,
                    builder.GetAllScopes(),
                    builder.HasDynamicLocal,
-                    importChainOpt,
+                    importScopeOpt,
                    lambdaDebugInfo,
                    closureDebugInfo,
                    stateMachineTypeOpt?.Name,
@@ -1395,11 +1396,11 @@ private BoundStatement ChainImplicitStructConstructor(MethodSymbol methodSymbol,
        internal static BoundBlock BindMethodBody(MethodSymbol method, TypeCompilationState compilationState, DiagnosticBag diagnostics)
        {
            ImportChain unused;
-            return BindMethodBody(method, compilationState, diagnostics, false, out unused);
+            return BindMethodBody(method, compilationState, diagnostics, out unused);
        }
        // NOTE: can return null if the method has no body.
-        private static BoundBlock BindMethodBody(MethodSymbol method, TypeCompilationState compilationState, DiagnosticBag diagnostics, bool generateDebugInfo, out ImportChain importChain)
+        private static BoundBlock BindMethodBody(MethodSymbol method, TypeCompilationState compilationState, DiagnosticBag diagnostics, out ImportChain importChain)
        {
            importChain = null;
@@ -1457,10 +1458,7 @@ private static BoundBlock BindMethodBody(MethodSymbol method, TypeCompilationSta
                    Binder binder = new ExecutableCodeBinder(blockSyntax, sourceMethod, inMethodBinder);
                    body = binder.BindBlock(blockSyntax, diagnostics);
-                    if (generateDebugInfo)
-                    {
                    importChain = binder.ImportChain;
-                    }
                    if (inMethodBinder.IsDirectlyInIterator)
                    {

--- a/src/Compilers/CSharp/Portable/Emitter/EditAndContinue/EmitHelpers.cs
+++ b/src/Compilers/CSharp/Portable/Emitter/EditAndContinue/EmitHelpers.cs
@@ -72,7 +72,7 @@ internal static class EmitHelpers
                moduleBeingBuilt,
                win32Resources: null,
                xmlDocStream: null,
-                generateDebugInfo: true,
+                emittingPdb: true,
                diagnostics: diagnostics,
                filterOpt: changes.RequiresCompilation,
                cancellationToken: cancellationToken))

--- a/src/Compilers/CSharp/Portable/Emitter/Model/PEModuleBuilder.cs
+++ b/src/Compilers/CSharp/Portable/Emitter/Model/PEModuleBuilder.cs
@@ -117,7 +117,7 @@ internal sealed override AssemblySymbol CorLibrary
        protected sealed override IEnumerable<string> LinkedAssembliesDebugInfo => SpecializedCollections.EmptyEnumerable<string>();
        // C# currently doesn't emit compilation level imports (TODO: scripting).
-        protected override ImmutableArray<Cci.UsedNamespaceOrType> GetImports(EmitContext context) => ImmutableArray<Cci.UsedNamespaceOrType>.Empty;
+        protected override ImmutableArray<Cci.UsedNamespaceOrType> GetImports() => ImmutableArray<Cci.UsedNamespaceOrType>.Empty;
        // C# doesn't allow to define default namespace for compilation.
        protected override string DefaultNamespace => null;

--- a/src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenTests.cs
+++ b/src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenTests.cs
@@ -12570,7 +12570,7 @@ static System.Action M()
            var methodBodyCompiler = new MethodCompiler(
                compilation: compilation,
                moduleBeingBuiltOpt: module,
-                generateDebugInfo: false,
+                emittingPdb: false,
                hasDeclarationErrors: false,
                diagnostics: diagnostics,
                filterOpt: null,

--- a/src/Compilers/CSharp/Test/Emit/PDB/PDBUsingTests.cs
+++ b/src/Compilers/CSharp/Test/Emit/PDB/PDBUsingTests.cs
@@ -3,9 +3,13 @@
 using System.Collections.Immutable;
 using System.IO;
 using System.Linq;
+using System.Reflection.Metadata;
 using System.Reflection.Metadata.Ecma335;
+using System.Reflection.PortableExecutable;
+using System.Text;
 using Microsoft.CodeAnalysis.CSharp.Test.Utilities;
 using Microsoft.CodeAnalysis.Test.Utilities;
+using Roslyn.Test.MetadataUtilities;
 using Roslyn.Test.Utilities;
 using Xunit;
 using ProprietaryTestResources = Microsoft.CodeAnalysis.Test.Resources.Proprietary;
@@ -2130,5 +2134,208 @@ static void Main()
                Assert.Equal(1, reader.GetTableRowCount(TableIndex.TypeSpec));
            });
        }
+        [Fact]
+        public void EmittingPdbVsNot()
+        {
+            string source = @"
+using System;
+using X = System.IO.FileStream;
+class C
+{
+    int x = 1;
+    static int y = 1;
+    C()
+    {
+        Console.WriteLine();
+    }
+}
+";
+            var c = CreateCompilationWithMscorlib(source, assemblyName: "EmittingPdbVsNot", options: TestOptions.ReleaseDll);
+            var peStream1 = new MemoryStream();
+            var peStream2 = new MemoryStream();
+            var pdbStream = new MemoryStream();
+            var emitResult1 = c.Emit(peStream: peStream1, pdbStream: pdbStream);
+            var emitResult2 = c.Emit(peStream: peStream2);
+            SharedCompilationUtils.VerifyMetadataEqualModuloMvid(peStream1, peStream2);
+        }
+        [Fact]
+        public void ImportedNoPiaTypes()
+        {
+            var sourceLib = @"
+using System;
+using System.Reflection;
+using System.Runtime.InteropServices;
+[assembly: Guid(""11111111-1111-1111-1111-111111111111"")]
+[assembly: ImportedFromTypeLib(""Foo"")]
+[assembly: TypeLibVersion(1, 0)]
+namespace N
+{
+    public enum E
+    {
+        Value1 = 1
+    }
+    public struct S1
+    {
+        public int A1;
+        public int A2;
+    }
+    public struct S2
+    {
+        public const int Value2 = 2;
+    }
+    public struct SBad
+    {
+        public int A3;
+        public const int Value3 = 3;
+    }
+    [ComImport, Guid(""22222222-2222-2222-2222-222222222222"")]
+    public interface I
+    {
+        void F();
+    }
+    public interface IBad
+    {
+        void F();
+    }
+}
+";
+            var source = @"
+using System;
+using static N.E;
+using static N.SBad;
+using Z1 = N.S1;
+using Z2 = N.S2;
+using ZBad = N.SBad;
+using NI = N.I;
+using NIBad = N.IBad;
+class C
+{
+    NI i;
+    void M()
+    {
+        Console.WriteLine(Value1);
+        Console.WriteLine(Z2.Value2);
+        Console.WriteLine(new Z1());
+    }
+}
+";
+            var libRef = CreateCompilationWithMscorlib(sourceLib, assemblyName: "ImportedNoPiaTypesAssemblyName").EmitToImageReference(embedInteropTypes: true);
+            var compilation = CreateCompilationWithMscorlib(source, new[] { libRef });
+            var v = CompileAndVerify(compilation);
+            v.Diagnostics.Verify(
+                // (14,8): warning CS0169: The field 'C.i' is never used
+                //     NI i;
+                Diagnostic(ErrorCode.WRN_UnreferencedField, "i").WithArguments("C.i"),
+                // (5,1): hidden CS8019: Unnecessary using directive.
+                // using static N.SBad;
+                Diagnostic(ErrorCode.HDN_UnusedUsingDirective, "using static N.SBad;"),
+                // (10,1): hidden CS8019: Unnecessary using directive.
+                // using NIBad = N.IBad;
+                Diagnostic(ErrorCode.HDN_UnusedUsingDirective, "using NIBad = N.IBad;"),
+                // (8,1): hidden CS8019: Unnecessary using directive.
+                // using ZBad = N.SBad;
+                Diagnostic(ErrorCode.HDN_UnusedUsingDirective, "using ZBad = N.SBad;"));
+            // Usings of embedded types are currently ommitted:
+            v.VerifyPdb("C.M", @"
+<symbols>
+  <methods>
+    <method containingType=""C"" name=""M"">
+      <customDebugInfo>
+        <using>
+          <namespace usingCount=""1"" />
+        </using>
+      </customDebugInfo>
+      <sequencePoints>
+        <entry offset=""0x0"" startLine=""18"" startColumn=""9"" endLine=""18"" endColumn=""35"" document=""0"" />
+        <entry offset=""0xb"" startLine=""19"" startColumn=""9"" endLine=""19"" endColumn=""38"" document=""0"" />
+        <entry offset=""0x11"" startLine=""20"" startColumn=""9"" endLine=""20"" endColumn=""37"" document=""0"" />
+        <entry offset=""0x24"" startLine=""21"" startColumn=""5"" endLine=""21"" endColumn=""6"" document=""0"" />
+      </sequencePoints>
+      <scope startOffset=""0x0"" endOffset=""0x25"">
+        <namespace name=""System"" />
+      </scope>
+    </method>
+  </methods>
+</symbols>");
+        }
+        [Fact]
+        public void ImportedTypeWithUnknownBase()
+        {
+            var sourceLib1 = @"
+namespace N
+{
+    public class A { }
+}
+";
+            var sourceLib2 = @"
+namespace N
+{
+    public class B : A { }
+}
+";
+            var source = @"
+using System;
+using X = N.B;
+class C
+{
+    void M()
+    {
+        Console.WriteLine();
+    }
+}
+";
+            var libRef1 = CreateCompilationWithMscorlib(sourceLib1).EmitToImageReference();
+            var libRef2 = CreateCompilationWithMscorlib(sourceLib2, new[] { libRef1 }, assemblyName: "LibRef2").EmitToImageReference();
+            var compilation = CreateCompilationWithMscorlib(source, new[] { libRef2 });
+            var v = CompileAndVerify(compilation, emitters: TestEmitters.CCI);
+            v.Diagnostics.Verify(
+                // (3,1): hidden CS8019: Unnecessary using directive.
+                // using X = N.B;
+                Diagnostic(ErrorCode.HDN_UnusedUsingDirective, "using X = N.B;"));
+            v.VerifyPdb("C.M", @"
+<symbols>
+  <methods>
+    <method containingType=""C"" name=""M"">
+      <customDebugInfo>
+        <using>
+          <namespace usingCount=""2"" />
+        </using>
+      </customDebugInfo>
+      <sequencePoints>
+        <entry offset=""0x0"" startLine=""9"" startColumn=""9"" endLine=""9"" endColumn=""29"" document=""0"" />
+        <entry offset=""0x5"" startLine=""10"" startColumn=""5"" endLine=""10"" endColumn=""6"" document=""0"" />
+      </sequencePoints>
+      <scope startOffset=""0x0"" endOffset=""0x6"">
+        <namespace name=""System"" />
+        <alias name=""X"" target=""N.B, LibRef2, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null"" kind=""type"" />
+      </scope>
+    </method>
+  </methods>
+</symbols>");
+        }
    }
 }
--- a/src/Compilers/CSharp/Test/Semantic/Semantics/FieldInitializerBindingTests.cs
+++ b/src/Compilers/CSharp/Test/Semantic/Semantics/FieldInitializerBindingTests.cs
@@ -293,16 +293,9 @@ private static ImmutableArray<BoundInitializer> BindInitializersWithoutDiagnosti
                    scriptCtor: null,
                    initializers: initializers,
                    diagnostics: diagnostics,
-                    generateDebugInfo: false,
                    firstImportChain: out unused);
-                var filteredDiag = diagnostics.AsEnumerable();
+                diagnostics.Verify();
-                foreach (var diagnostic in filteredDiag)
-                {
-                    Console.WriteLine(diagnostic);
-                }
-                Assert.True(filteredDiag.IsEmpty());
                return boundInitializers;
            }

--- a/src/Compilers/Core/Portable/Compilation/Compilation.cs
+++ b/src/Compilers/Core/Portable/Compilation/Compilation.cs
@@ -1250,7 +1250,7 @@ internal bool IsRealSigned
            CommonPEModuleBuilder moduleBuilder,
            Stream win32Resources,
            Stream xmlDocStream,
-            bool generateDebugInfo,
+            bool emittingPdb,
            DiagnosticBag diagnostics,
            Predicate<ISymbol> filterOpt,
            CancellationToken cancellationToken);
@@ -1259,7 +1259,7 @@ internal bool IsRealSigned
            CommonPEModuleBuilder moduleBuilder,
            Stream win32Resources,
            Stream xmlDocStream,
-            bool generateDebugInfo,
+            bool emittingPdb,
            DiagnosticBag diagnostics,
            Predicate<ISymbol> filterOpt,
            CancellationToken cancellationToken)
@@ -1270,7 +1270,7 @@ internal bool IsRealSigned
                    moduleBuilder,
                    win32Resources,
                    xmlDocStream,
-                    generateDebugInfo,
+                    emittingPdb,
                    diagnostics,
                    filterOpt,
                    cancellationToken);
@@ -1303,7 +1303,7 @@ internal void EnsureAnonymousTypeTemplates(CancellationToken cancellationToken)
                            moduleBeingBuilt,
                            win32Resources: null,
                            xmlDocStream: null,
-                            generateDebugInfo: false,
+                            emittingPdb: false,
                            diagnostics: discardedDiagnostics,
                            filterOpt: null,
                            cancellationToken: cancellationToken);
@@ -1576,7 +1576,7 @@ internal void EnsureAnonymousTypeTemplates(CancellationToken cancellationToken)
                moduleBeingBuilt,
                win32Resources,
                xmlDocumentationStream,
-                generateDebugInfo: pdbStreamProvider != null,
+                emittingPdb: pdbStreamProvider != null,
                diagnostics: diagnostics,
                filterOpt: null,
                cancellationToken: cancellationToken))

--- a/src/Compilers/Core/Portable/Emit/CommonPEModuleBuilder.cs
+++ b/src/Compilers/Core/Portable/Emit/CommonPEModuleBuilder.cs
@@ -8,6 +8,7 @@
 using System.Linq;
 using System.Threading;
 using Microsoft.CodeAnalysis.CodeGen;
+using Microsoft.CodeAnalysis.Emit.NoPia;
 using Roslyn.Utilities;
 namespace Microsoft.CodeAnalysis.Emit
@@ -24,6 +25,7 @@ internal abstract class CommonPEModuleBuilder
        internal abstract CommonModuleCompilationState CommonModuleCompilationState { get; }
        internal abstract void CompilationFinished();
        internal abstract ImmutableDictionary<Cci.ITypeDefinition, ImmutableArray<Cci.ITypeDefinitionMember>> GetSynthesizedMembers();
+        internal abstract CommonEmbeddedTypesManager CommonEmbeddedTypesManagerOpt { get; }
    }
    /// <summary>
@@ -237,54 +239,16 @@ internal sealed override Cci.ITypeReference Translate(ITypeSymbol symbol, Syntax
            return Translate((TTypeSymbol)symbol, (TSyntaxNode)syntaxNodeOpt, diagnostics);
        }
-        internal OutputKind OutputKind
+        internal OutputKind OutputKind => _outputKind;
-        {
+        internal TSourceModuleSymbol SourceModule => _sourceModule;
-            get
+        internal TCompilation Compilation => _compilation;
-            {
-                return _outputKind;
-            }
-        }
-        internal TSourceModuleSymbol SourceModule
+        internal sealed override Compilation CommonCompilation => _compilation;
-        {
+        internal sealed override CommonModuleCompilationState CommonModuleCompilationState => CompilationState;
-            get
+        internal sealed override CommonEmbeddedTypesManager CommonEmbeddedTypesManagerOpt => EmbeddedTypesManagerOpt;
-            {
-                return _sourceModule;
-            }
-        }
-        internal TCompilation Compilation
-        {
-            get
-            {
-                return _compilation;
-            }
-        }
-        internal override Compilation CommonCompilation
-        {
-            get
-            {
-                return _compilation;
-            }
-        }
-        internal override CommonModuleCompilationState CommonModuleCompilationState
-        {
-            get
-            {
-                return this.CompilationState;
-            }
-        }
        // General entry point method. May be a PE entry point or a submission entry point.
-        internal sealed override Cci.IMethodReference EntryPoint
+        internal sealed override Cci.IMethodReference EntryPoint => _entryPoint;
-        {
-            get
-            {
-                return _entryPoint;
-            }
-        }
        internal void SetEntryPoint(TMethodSymbol value)
        {
@@ -778,8 +742,8 @@ ImmutableArray<Cci.AssemblyReferenceAlias> Cci.IModule.GetAssemblyReferenceAlias
        IEnumerable<string> Cci.IModule.LinkedAssembliesDebugInfo => LinkedAssembliesDebugInfo;
        protected abstract IEnumerable<string> LinkedAssembliesDebugInfo { get; }
-        ImmutableArray<Cci.UsedNamespaceOrType> Cci.IModule.GetImports(EmitContext context) => GetImports(context);
+        ImmutableArray<Cci.UsedNamespaceOrType> Cci.IModule.GetImports() => GetImports();
-        protected abstract ImmutableArray<Cci.UsedNamespaceOrType> GetImports(EmitContext context);
+        protected abstract ImmutableArray<Cci.UsedNamespaceOrType> GetImports();
        string Cci.IModule.DefaultNamespace => DefaultNamespace;
        protected abstract string DefaultNamespace { get; }

--- a/src/Compilers/Core/Portable/NativePdbWriter/PdbWriter.cs
+++ b/src/Compilers/Core/Portable/NativePdbWriter/PdbWriter.cs
@@ -305,7 +305,7 @@ public void SerializeDebugInfo(IMethodBody methodBody, uint localSignatureToken,
            // NOTE: This is an attempt to match Dev10's apparent behavior.  For iterator methods (i.e. the method
            // that appears in source, not the synthesized ones), Dev10 only emits the ForwardIterator and IteratorLocal
            // custom debug info (e.g. there will be no information about the usings that were in scope).
-            if (!isIterator)
+            if (!isIterator && methodBody.ImportScope != null)
            {
                IMethodDefinition forwardToMethod;
                if (customDebugInfoWriter.ShouldForwardNamespaceScopes(Context, methodBody, methodToken, out forwardToMethod))
@@ -375,7 +375,7 @@ private void DefineNamespaceScopes(IMethodBody methodBody)
            {
                for (var scope = namespaceScopes; scope != null; scope = scope.Parent)
                {
-                    foreach (var import in scope.GetUsedNamespaces(Context))
+                    foreach (var import in scope.GetUsedNamespaces())
                    {
                        if (import.TargetNamespaceOpt == null && import.TargetTypeOpt == null)
                        {
@@ -396,7 +396,7 @@ private void DefineNamespaceScopes(IMethodBody methodBody)
            // file and namespace level
            for (IImportScope scope = namespaceScopes; scope != null; scope = scope.Parent)
            {
-                foreach (UsedNamespaceOrType import in scope.GetUsedNamespaces(Context))
+                foreach (UsedNamespaceOrType import in scope.GetUsedNamespaces())
                {
                    var importString = TryEncodeImport(import, lazyDeclaredExternAliases, isProjectLevel: false);
                    if (importString != null)
@@ -424,7 +424,7 @@ private void DefineNamespaceScopes(IMethodBody methodBody)
                    UsingNamespace("&" + assemblyName, module);
                }
-                foreach (UsedNamespaceOrType import in module.GetImports(Context))
+                foreach (UsedNamespaceOrType import in module.GetImports())
                {
                    var importString = TryEncodeImport(import, null, isProjectLevel: true);
                    if (importString != null)

--- a/src/Compilers/Core/Portable/PEWriter/CustomDebugInfoWriter.cs
+++ b/src/Compilers/Core/Portable/PEWriter/CustomDebugInfoWriter.cs
@@ -34,7 +34,7 @@ public CustomDebugInfoWriter(PdbWriter pdbWriter)
        /// </summary>
        public bool ShouldForwardNamespaceScopes(EmitContext context, IMethodBody methodBody, uint methodToken, out IMethodDefinition forwardToMethod)
        {
-            if (ShouldForwardToPreviousMethodWithUsingInfo(context, methodBody) || methodBody.ImportScope == null)
+            if (ShouldForwardToPreviousMethodWithUsingInfo(context, methodBody))
            {
                // SerializeNamespaceScopeMetadata will do the actual forwarding in case this is a CSharp method.
                // VB on the other hand adds a "@methodtoken" to the scopes instead.
@@ -351,7 +351,7 @@ private void SerializeNamespaceScopeMetadata(EmitContext context, IMethodBody me
            BinaryWriter cmw = new BinaryWriter(customMetadata);
            for (IImportScope scope = methodBody.ImportScope; scope != null; scope = scope.Parent)
            {
-                usingCounts.Add((ushort)scope.GetUsedNamespaces(context).Length);
+                usingCounts.Add((ushort)scope.GetUsedNamespaces().Length);
            }
            // ACASEY: This originally wrote (uint)12, (ushort)1, (ushort)0 in the
@@ -414,7 +414,7 @@ private bool ShouldForwardToPreviousMethodWithUsingInfo(EmitContext context, IMe
            var s2 = previousScopes;
            while (s1 != null && s2 != null)
            {
-                if (!s1.GetUsedNamespaces(context).SequenceEqual(s2.GetUsedNamespaces(context)))
+                if (!s1.GetUsedNamespaces().SequenceEqual(s2.GetUsedNamespaces()))
                {
                    return false;
                }

--- a/src/Compilers/Core/Portable/PEWriter/IImportScope.cs
+++ b/src/Compilers/Core/Portable/PEWriter/IImportScope.cs
 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 using System.Collections.Immutable;
-using Microsoft.CodeAnalysis.Emit;
 namespace Microsoft.Cci
 {
@@ -13,7 +12,7 @@ internal interface IImportScope
        /// <summary>
        /// Zero or more used namespaces. These correspond to using directives in C# or Imports syntax in VB.
        /// </summary>
-        ImmutableArray<UsedNamespaceOrType> GetUsedNamespaces(EmitContext context);
+        ImmutableArray<UsedNamespaceOrType> GetUsedNamespaces();
        /// <summary>
        /// Parent import scope, or null.

--- a/src/Compilers/Core/Portable/PEWriter/ReferenceIndexer.cs
+++ b/src/Compilers/Core/Portable/PEWriter/ReferenceIndexer.cs
@@ -47,7 +47,7 @@ public override void Visit(IModule module)
                this.Visit(module.GetResources(Context));
            }
-            VisitImports(module.GetImports(Context));
+            VisitImports(module.GetImports());
        }
        public void VisitMethodBodyReference(IReference reference)
@@ -101,7 +101,7 @@ protected override void ProcessMethodBody(IMethodDefinition method)
                    {
                        if (_alreadySeenScopes.Add(scope))
                        {
-                            VisitImports(scope.GetUsedNamespaces(Context));
+                            VisitImports(scope.GetUsedNamespaces());
                        }
                        else
                        {

--- a/src/Compilers/Core/Portable/PEWriter/Units.cs
+++ b/src/Compilers/Core/Portable/PEWriter/Units.cs
@@ -414,7 +414,7 @@ ulong SizeOfStackReserve
        /// <summary>
        /// Project level imports (VB only, TODO: C# scripts).
        /// </summary>
-        ImmutableArray<UsedNamespaceOrType> GetImports(EmitContext context);
+        ImmutableArray<UsedNamespaceOrType> GetImports();
        /// <summary>
        /// Default namespace (VB only).

--- a/src/Compilers/VisualBasic/Portable/CodeGen/CodeGenerator.vb
+++ b/src/Compilers/VisualBasic/Portable/CodeGen/CodeGenerator.vb
@@ -47,7 +47,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.CodeGen
                       moduleBuilder As PEModuleBuilder,
                       diagnostics As DiagnosticBag,
                       optimizations As OptimizationLevel,
-                       emittingPdbs As Boolean)
+                       emittingPdb As Boolean)
            Debug.Assert(method IsNot Nothing)
            Debug.Assert(boundBody IsNot Nothing)
@@ -55,14 +55,14 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.CodeGen
            Debug.Assert(moduleBuilder IsNot Nothing)
            Debug.Assert(diagnostics IsNot Nothing)
-            Me._method = method
+            _method = method
-            Me._block = boundBody
+            _block = boundBody
-            Me._builder = builder
+            _builder = builder
-            Me._module = moduleBuilder
+            _module = moduleBuilder
-            Me._diagnostics = diagnostics
+            _diagnostics = diagnostics
            ' Always optimize synthesized methods that don't contain user code.
-            Me._optimizations = If(method.GenerateDebugInfo, optimizations, OptimizationLevel.Release)
+            _optimizations = If(method.GenerateDebugInfo, optimizations, OptimizationLevel.Release)
            ' Emit sequence points unless
            ' - the PDBs are not being generated
@@ -70,14 +70,14 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.CodeGen
            '   user code that can be stepped thru, or changed during EnC.
            ' 
            ' This setting only affects generating PDB sequence points, it shall Not affect generated IL in any way.
-            Me._emitPdbSequencePoints = emittingPdbs AndAlso method.GenerateDebugInfo
+            _emitPdbSequencePoints = emittingPdb AndAlso method.GenerateDebugInfo
-            If Me._optimizations = OptimizationLevel.Release Then
+            If _optimizations = OptimizationLevel.Release Then
-                Me._block = Optimizer.Optimize(method, boundBody, Me._stackLocals)
+                _block = Optimizer.Optimize(method, boundBody, _stackLocals)
            End If
-            Me._checkCallsForUnsafeJITOptimization = (Me._method.ImplementationAttributes And MethodSymbol.DisableJITOptimizationFlags) <> MethodSymbol.DisableJITOptimizationFlags
+            _checkCallsForUnsafeJITOptimization = (_method.ImplementationAttributes And MethodSymbol.DisableJITOptimizationFlags) <> MethodSymbol.DisableJITOptimizationFlags
-            Debug.Assert(Not Me._module.JITOptimizationIsDisabled(Me._method))
+            Debug.Assert(Not _module.JITOptimizationIsDisabled(_method))
        End Sub
        Public Sub Generate()

--- a/src/Compilers/VisualBasic/Portable/Compilation/MethodCompiler.vb
+++ b/src/Compilers/VisualBasic/Portable/Compilation/MethodCompiler.vb
@@ -20,7 +20,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
        Private ReadOnly _compilation As VisualBasicCompilation
        Private ReadOnly _cancellationToken As CancellationToken
-        Private ReadOnly _generateDebugInfo As Boolean
+        Private ReadOnly _emittingPdb As Boolean
        Private ReadOnly _diagnostics As DiagnosticBag
        Private ReadOnly _hasDeclarationErrors As Boolean
        Private ReadOnly _namespaceScopeBuilder As NamespaceScopeBuilder
@@ -78,28 +78,28 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
        ' moduleBeingBuilt can be Nothing in order to just analyze methods for errors.
        Private Sub New(compilation As VisualBasicCompilation,
                       moduleBeingBuiltOpt As PEModuleBuilder,
-                       generateDebugInfo As Boolean,
+                       emittingPdb As Boolean,
                       doEmitPhase As Boolean,
                       hasDeclarationErrors As Boolean,
                       diagnostics As DiagnosticBag,
                       filter As Predicate(Of Symbol),
                       cancellationToken As CancellationToken)
-            Me._compilation = compilation
+            _compilation = compilation
-            Me._moduleBeingBuiltOpt = moduleBeingBuiltOpt
+            _moduleBeingBuiltOpt = moduleBeingBuiltOpt
-            Me._diagnostics = diagnostics
+            _diagnostics = diagnostics
-            Me._hasDeclarationErrors = hasDeclarationErrors
+            _hasDeclarationErrors = hasDeclarationErrors
-            Me._cancellationToken = cancellationToken
+            _cancellationToken = cancellationToken
-            Me._doEmitPhase = doEmitPhase
+            _doEmitPhase = doEmitPhase
-            Me._generateDebugInfo = generateDebugInfo
+            _emittingPdb = emittingPdb
-            Me._filterOpt = filter
+            _filterOpt = filter
-            If generateDebugInfo Then
+            If emittingPdb Then
-                Me._debugDocumentProvider = Function(path As String, basePath As String) moduleBeingBuiltOpt.GetOrAddDebugDocument(path, basePath, AddressOf CreateDebugDocumentForFile)
+                _debugDocumentProvider = Function(path As String, basePath As String) moduleBeingBuiltOpt.GetOrAddDebugDocument(path, basePath, AddressOf CreateDebugDocumentForFile)
            End If
            If compilation.Options.ConcurrentBuild Then
-                Me._compilerTasks = New ConcurrentStack(Of Task)()
+                _compilerTasks = New ConcurrentStack(Of Task)()
            End If
        End Sub
@@ -155,7 +155,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
            Dim compiler = New MethodCompiler(compilation,
                                              moduleBeingBuiltOpt:=Nothing,
-                                              generateDebugInfo:=False,
+                                              emittingPdb:=False,
                                              doEmitPhase:=doEmitPhase,
                                              hasDeclarationErrors:=hasDeclarationErrors,
                                              diagnostics:=diagnostics,
@@ -187,7 +187,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
        ''' </summary>
        Friend Shared Sub CompileMethodBodies(compilation As VisualBasicCompilation,
                                              moduleBeingBuiltOpt As PEModuleBuilder,
-                                              generateDebugInfo As Boolean,
+                                              emittingPdb As Boolean,
                                              hasDeclarationErrors As Boolean,
                                              filter As Predicate(Of Symbol),
                                              diagnostics As DiagnosticBag,
@@ -209,7 +209,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
            Dim compiler = New MethodCompiler(compilation,
                                              moduleBeingBuiltOpt,
-                                                  generateDebugInfo,
+                                              emittingPdb,
                                              doEmitPhase:=True,
                                              hasDeclarationErrors:=hasDeclarationErrors,
                                              diagnostics:=diagnostics,
@@ -305,7 +305,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                                                     variableSlotAllocatorOpt:=Nothing,
                                                     debugDocumentProvider:=Nothing,
                                                     diagnostics:=diagnostics,
-                                                     generateDebugInfo:=False)
+                                                     emittingPdb:=False)
                moduleBeingBuilt.SetMethodBody(scriptEntryPoint, emittedBody)
                moduleBeingBuilt.AddSynthesizedDefinition(compilation.ScriptClass, scriptEntryPoint)
@@ -855,7 +855,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                                                     variableSlotAllocatorOpt:=Nothing,
                                                     debugDocumentProvider:=Nothing,
                                                     diagnostics:=diagnosticsThisMethod,
-                                                     generateDebugInfo:=False)
+                                                     emittingPdb:=False)
                _diagnostics.AddRange(diagnosticsThisMethod)
                diagnosticsThisMethod.Free()
@@ -919,7 +919,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                                                             lazyVariableSlotAllocator,
                                                             debugDocumentProvider:=Nothing,
                                                             diagnostics:=diagnosticsThisMethod,
-                                                             generateDebugInfo:=False)
+                                                             emittingPdb:=False)
                        End If
                        lambdaDebugInfoBuilder.Free()
@@ -968,7 +968,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                                                         variableSlotAllocatorOpt:=Nothing,
                                                         debugDocumentProvider:=_debugDocumentProvider,
                                                         diagnostics:=diagnosticsThisMethod,
-                                                         generateDebugInfo:=_generateDebugInfo AndAlso method.GenerateDebugInfo)
+                                                         emittingPdb:=_emittingPdb)
                    _diagnostics.AddRange(diagnosticsThisMethod)
                    diagnosticsThisMethod.Free()
@@ -1451,7 +1451,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                                                              lazyVariableSlotAllocator,
                                                              _debugDocumentProvider,
                                                              diagnostics,
-                                                              generateDebugInfo:=_generateDebugInfo AndAlso method.GenerateDebugInfo)
+                                                              emittingPdb:=_emittingPdb)
            If diagnostics IsNot diagsForCurrentMethod Then
                DirectCast(method.AssociatedSymbol, SynthesizedMyGroupCollectionPropertySymbol).RelocateDiagnostics(diagnostics, diagsForCurrentMethod)
@@ -1474,10 +1474,10 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                                                  variableSlotAllocatorOpt As VariableSlotAllocator,
                                                  debugDocumentProvider As DebugDocumentProvider,
                                                  diagnostics As DiagnosticBag,
-                                                  generateDebugInfo As Boolean) As MethodBody
+                                                  emittingPdb As Boolean) As MethodBody
            Dim compilation = moduleBuilder.Compilation
-            Dim localSlotManager = New localSlotManager(variableSlotAllocatorOpt)
+            Dim localSlotManager = New LocalSlotManager(variableSlotAllocatorOpt)
            Dim optimizations = compilation.Options.OptimizationLevel
            If method.IsEmbedded Then
@@ -1490,7 +1490,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                Debug.Assert(Not diagnostics.HasAnyErrors)
                Dim asyncDebugInfo As Cci.AsyncMethodBodyDebugInfo = Nothing
-                Dim codeGen = New codeGen.CodeGenerator(method, block, builder, moduleBuilder, diagnostics, optimizations, generateDebugInfo)
+                Dim codeGen = New CodeGen.CodeGenerator(method, block, builder, moduleBuilder, diagnostics, optimizations, emittingPdb)
                ' We need to save additional debugging information for MoveNext of an async state machine.
                Dim stateMachineMethod = TryCast(method, SynthesizedStateMachineMethod)
@@ -1523,6 +1523,13 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                    codeGen.Generate()
                End If
+                ' Translate the imports even if we are not writing PDBs. The translation has an impact on generated metadata 
+                ' and we don't want to emit different metadata depending on whether or we emit with PDB stream.
+                ' TODO (https://github.com/dotnet/roslyn/issues/2846): This will need to change for member initializers in partial class.
+                Dim importScopeOpt = If(method.Syntax IsNot Nothing AndAlso method.Syntax.SyntaxTree IsNot VisualBasicSyntaxTree.DummySyntaxTree.Dummy,
+                                        moduleBuilder.SourceModule.GetSourceFile(method.Syntax.SyntaxTree).Translate(moduleBuilder, diagnostics),
+                                        Nothing)
                If diagnostics.HasAnyErrors() Then
                    Return Nothing
                End If
@@ -1539,29 +1546,6 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                    GetStateMachineSlotDebugInfo(moduleBuilder.GetSynthesizedFields(stateMachineTypeOpt), stateMachineHoistedLocalSlots, stateMachineAwaiterSlots)
                End If
-                Dim namespaceScopes = If(generateDebugInfo, moduleBuilder.SourceModule.GetSourceFile(method.Syntax.SyntaxTree), Nothing)
-                ' edgeInclusive must be true as that is what VB EE expects.
-                '<PdbUtil.cpp>
-                'HRESULT()
-                'PdbUtil::IsScopeInOffset(
-                '    _In_ ISymUnmanagedScope* pScope,
-                '    _In_ DWORD offset,
-                '    _Out_ bool* inOffset)
-                '{
-                '    VerifyInPtr(pScope);
-                '    VerifyOutPtr(inOffset);
-                '    HRESULT hr;
-                '    ULONG32 start, end;
-                '    IfFailGo( pScope->GetStartOffset(&start) );
-                '    IfFailGo( pScope->GetEndOffset(&end) );
-                '    *inOffset = (end >= offset) && (offset >= start);      <====  HERE
-                'Error:
-                '    return hr;
-                '}
                Dim localScopes = builder.GetAllScopes()
                Return New MethodBody(builder.RealizedIL,
@@ -1574,7 +1558,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                                      builder.RealizedExceptionHandlers,
                                      localScopes,
                                      hasDynamicLocalVariables:=False,
-                                      importScopeOpt:=namespaceScopes,
+                                      importScopeOpt:=importScopeOpt,
                                      lambdaDebugInfo:=lambdaDebugInfo,
                                      closureDebugInfo:=closureDebugInfo,
                                      stateMachineTypeNameOpt:=stateMachineTypeOpt?.Name, ' TODO: remove or update AddedOrChangedMethodInfo

--- a/src/Compilers/VisualBasic/Portable/Compilation/NamespaceScopeBuilder.vb
+++ b/src/Compilers/VisualBasic/Portable/Compilation/NamespaceScopeBuilder.vb
@@ -11,10 +11,11 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
        End Sub
        Public Shared Function BuildNamespaceScope(
-            context As EmitContext,
+            moduleBuilder As Emit.PEModuleBuilder,
            xmlNamespaces As Dictionary(Of String, XmlNamespaceAndImportsClausePosition),
            aliasImports As IEnumerable(Of AliasAndImportsClausePosition),
-            memberImports As ImmutableArray(Of NamespaceOrTypeAndImportsClausePosition)
+            memberImports As ImmutableArray(Of NamespaceOrTypeAndImportsClausePosition),
+            diagnostics As DiagnosticBag
        ) As ImmutableArray(Of Cci.UsedNamespaceOrType)
            Dim scopeBuilder = ArrayBuilder(Of Cci.UsedNamespaceOrType).GetInstance
@@ -31,8 +32,10 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                    Dim target = aliasImport.Alias.Target
                    If target.IsNamespace Then
                        scopeBuilder.Add(Cci.UsedNamespaceOrType.CreateNamespace(DirectCast(target, NamespaceSymbol), aliasOpt:=aliasImport.Alias.Name))
-                    Else
+                    ElseIf Not target.ContainingAssembly.IsLinked
-                        Dim typeRef = GetTypeReference(context, DirectCast(target, NamedTypeSymbol))
+                        ' We skip alias imports of embedded types to avoid breaking existing code that
+                        ' imports types that can't be embedded but doesn't use them anywhere else in the code.
+                        Dim typeRef = GetTypeReference(DirectCast(target, NamedTypeSymbol), moduleBuilder, diagnostics)
                        scopeBuilder.Add(Cci.UsedNamespaceOrType.CreateType(typeRef, aliasOpt:=aliasImport.Alias.Name))
                    End If
                Next
@@ -44,8 +47,10 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                    Dim target = import.NamespaceOrType
                    If target.IsNamespace Then
                        scopeBuilder.Add(Cci.UsedNamespaceOrType.CreateNamespace(DirectCast(target, NamespaceSymbol)))
-                    Else
+                    ElseIf Not target.ContainingAssembly.IsLinked
-                        Dim typeRef = GetTypeReference(context, DirectCast(target, NamedTypeSymbol))
+                        ' We skip imports of embedded types to avoid breaking existing code that
+                        ' imports types that can't be embedded but doesn't use them anywhere else in the code.
+                        Dim typeRef = GetTypeReference(DirectCast(target, NamedTypeSymbol), moduleBuilder, diagnostics)
                        scopeBuilder.Add(Cci.UsedNamespaceOrType.CreateType(typeRef))
                    End If
                Next
@@ -54,8 +59,8 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
            Return scopeBuilder.ToImmutableAndFree()
        End Function
-        Private Shared Function GetTypeReference(context As EmitContext, type As TypeSymbol) As Cci.ITypeReference
+        Private Shared Function GetTypeReference(type As TypeSymbol, moduleBuilder As CommonPEModuleBuilder, diagnostics As DiagnosticBag) As Cci.ITypeReference
-            Return context.ModuleBuilder.Translate(type, context.SyntaxNodeOpt, context.Diagnostics)
+            Return moduleBuilder.Translate(type, Nothing, diagnostics)
        End Function
    End Class
 End Namespace
--- a/src/Compilers/VisualBasic/Portable/Compilation/VisualBasicCompilation.vb
+++ b/src/Compilers/VisualBasic/Portable/Compilation/VisualBasicCompilation.vb
@@ -2207,7 +2207,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
            moduleBuilder As CommonPEModuleBuilder,
            win32Resources As Stream,
            xmlDocStream As Stream,
-            generateDebugInfo As Boolean,
+            emittingPdb As Boolean,
            diagnostics As DiagnosticBag,
            filterOpt As Predicate(Of ISymbol),
            cancellationToken As CancellationToken) As Boolean
@@ -2220,6 +2220,8 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
            Me.EmbeddedSymbolManager.MarkAllDeferredSymbolsAsReferenced(Me)
+            moduleBeingBuilt.TranslateImports(diagnostics)
            If moduleBeingBuilt.EmitOptions.EmitMetadataOnly Then
                If hasDeclarationErrors Then
                    Return False
@@ -2233,13 +2235,10 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                SynthesizedMetadataCompiler.ProcessSynthesizedMembers(Me, moduleBeingBuilt, cancellationToken)
            Else
                ' start generating PDB checksums if we need to emit PDBs
-                If generateDebugInfo AndAlso moduleBeingBuilt IsNot Nothing Then
+                If emittingPdb AndAlso Not StartSourceChecksumCalculation(moduleBeingBuilt, diagnostics) Then
-                    If Not StartSourceChecksumCalculation(moduleBeingBuilt, diagnostics) Then
                    Return False
                End If
-                End If
                ' Perform initial bind of method bodies in spite of earlier errors. This is the same
                ' behavior as when calling GetDiagnostics()
@@ -2250,13 +2249,12 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                MethodCompiler.CompileMethodBodies(
                    Me,
                    moduleBeingBuilt,
-                    generateDebugInfo,
+                    emittingPdb,
                    hasDeclarationErrors,
                    filterOpt,
                    methodBodyDiagnosticBag,
                    cancellationToken)
                Dim assemblyName = FileNameUtilities.ChangeExtension(moduleBeingBuilt.EmitOptions.OutputNameOverride, extension:=Nothing)
                DocumentationCommentCompiler.WriteDocumentationCommentXml(Me, assemblyName, xmlDocStream, methodBodyDiagnosticBag, cancellationToken)

--- a/src/Compilers/VisualBasic/Portable/Emit/EditAndContinue/EmitHelpers.vb
+++ b/src/Compilers/VisualBasic/Portable/Emit/EditAndContinue/EmitHelpers.vb
@@ -63,7 +63,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Emit
            If compilation.Compile(moduleBeingBuilt,
                                   win32Resources:=Nothing,
                                   xmlDocStream:=Nothing,
-                                   generateDebugInfo:=True,
+                                   emittingPdb:=True,
                                   diagnostics:=diagnostics,
                                   filterOpt:=AddressOf changes.RequiresCompilation,
                                   cancellationToken:=cancellationToken) Then

--- a/src/Compilers/VisualBasic/Portable/Emit/PEModuleBuilder.vb
+++ b/src/Compilers/VisualBasic/Portable/Emit/PEModuleBuilder.vb
@@ -22,7 +22,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Emit
        Private ReadOnly _metadataName As String
        Private _lazyExportedTypes As ImmutableArray(Of TypeExport(Of NamedTypeSymbol))
-        Private _lazyImports As ImmutableArray(Of Cci.UsedNamespaceOrType)
+        Private _lazyTranslatedImports As ImmutableArray(Of Cci.UsedNamespaceOrType)
        Private _lazyDefaultNamespace As String
        ' These fields will only be set when running tests.  They allow realized IL for a given method to be looked up by method display name.
@@ -99,15 +99,19 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Emit
            End Get
        End Property
-        Protected NotOverridable Overrides Function GetImports(context As EmitContext) As ImmutableArray(Of Cci.UsedNamespaceOrType)
+        Protected NotOverridable Overrides Function GetImports() As ImmutableArray(Of Cci.UsedNamespaceOrType)
-            If _lazyImports.IsDefault Then
+            ' Imports should have been translated in code gen phase.
+            Debug.Assert(Not _lazyTranslatedImports.IsDefault)
+            Return _lazyTranslatedImports
+        End Function
+        Public Sub TranslateImports(diagnostics As DiagnosticBag)
+            If _lazyTranslatedImports.IsDefault Then
                ImmutableInterlocked.InterlockedInitialize(
-                    _lazyImports,
+                    _lazyTranslatedImports,
-                    NamespaceScopeBuilder.BuildNamespaceScope(context, SourceModule.XmlNamespaces, SourceModule.AliasImports, SourceModule.MemberImports))
+                    NamespaceScopeBuilder.BuildNamespaceScope(Me, SourceModule.XmlNamespaces, SourceModule.AliasImports, SourceModule.MemberImports, diagnostics))
            End If
+        End Sub
-            Return _lazyImports
-        End Function
        Protected NotOverridable Overrides ReadOnly Property DefaultNamespace As String
            Get

--- a/src/Compilers/VisualBasic/Portable/Symbols/Source/SourceFile.vb
+++ b/src/Compilers/VisualBasic/Portable/Symbols/Source/SourceFile.vb
@@ -430,19 +430,26 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Symbols
            End Get
        End Property
-        Public Function GetUsedNamespaces(context As EmitContext) As ImmutableArray(Of Cci.UsedNamespaceOrType) Implements Cci.IImportScope.GetUsedNamespaces
+        Public Function Translate(moduleBuilder As Emit.PEModuleBuilder, diagnostics As DiagnosticBag) As Cci.IImportScope
            If _lazyTranslatedImports.IsDefault Then
-                ImmutableInterlocked.InterlockedInitialize(_lazyTranslatedImports, TranslateImports(context))
+                ImmutableInterlocked.InterlockedInitialize(_lazyTranslatedImports, TranslateImports(moduleBuilder, diagnostics))
            End If
+            Return Me
+        End Function
+        Public Function GetUsedNamespaces() As ImmutableArray(Of Cci.UsedNamespaceOrType) Implements Cci.IImportScope.GetUsedNamespaces
+            ' The imports should have been translated during code gen.
+            Debug.Assert(Not _lazyTranslatedImports.IsDefault)
            Return _lazyTranslatedImports
        End Function
-        Private Function TranslateImports(context As EmitContext) As ImmutableArray(Of Cci.UsedNamespaceOrType)
+        Private Function TranslateImports(moduleBuilder As Emit.PEModuleBuilder, diagnostics As DiagnosticBag) As ImmutableArray(Of Cci.UsedNamespaceOrType)
-            Return NamespaceScopeBuilder.BuildNamespaceScope(context,
+            Return NamespaceScopeBuilder.BuildNamespaceScope(moduleBuilder,
                                                             XmlNamespaces,
                                                             If(AliasImports IsNot Nothing, AliasImports.Values, Nothing),
-                                                             MemberImports)
+                                                             MemberImports,
+                                                             diagnostics)
        End Function
    End Class
 End Namespace

--- a/src/Compilers/VisualBasic/Test/Emit/PDB/PDBNamespaceScopes.vb
+++ b/src/Compilers/VisualBasic/Test/Emit/PDB/PDBNamespaceScopes.vb
 ' Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+Imports System.IO
 Imports Microsoft.CodeAnalysis.Test.Utilities
 Namespace Microsoft.CodeAnalysis.VisualBasic.UnitTests.PDB
@@ -354,6 +355,207 @@ End Namespace
 </symbols>)
        End Sub
+        <Fact>
+        Public Sub EmittingPdbVsNot()
+            Dim source =
+<compilation name="EmittingPdbVsNot">
+    <file>
+Imports System
+Imports X = System.IO.FileStream
+Class C
+    Dim x As Integer = 1
+    Shared y As Integer = 1
+    Sub New()
+        Console.WriteLine()
+    End Sub
+End Class
+    </file>
+</compilation>
+            Dim c = CreateCompilationWithMscorlib(source, options:=TestOptions.ReleaseDll)
+            Dim peStream1 = New MemoryStream()
+            Dim peStream2 = New MemoryStream()
+            Dim pdbStream = New MemoryStream()
+            Dim emitResult1 = c.Emit(peStream:=peStream1, pdbStream:=pdbStream)
+            Dim emitResult2 = c.Emit(peStream:=peStream2)
+            SharedCompilationUtils.VerifyMetadataEqualModuloMvid(peStream1, peStream2)
+        End Sub
+        <Fact>
+        Public Sub ImportedNoPiaTypes()
+            Dim sourceLib =
+<compilation name="ImportedNoPiaTypesAssemblyName">
+    <file><![CDATA[
+Imports System
+Imports System.Reflection
+Imports System.Runtime.InteropServices
+<Assembly:Guid("11111111-1111-1111-1111-111111111111")>
+<Assembly:ImportedFromTypeLib("Foo")>
+<Assembly:TypeLibVersion(1, 0)>
+Namespace N
+    Public Enum E
+        Value1 = 1
+    End Enum
+    Public Structure S1
+        Public A1 As Integer
+        Public A2 As Integer
+    End Structure
+    Public Structure S2
+        Public Const Value2 As Integer = 2
+    End Structure
+    Public Structure SBad
+        Public A3 As Integer
+        Public Const Value3 As Integer = 3
+    End Structure
+    <ComImport, Guid("22222222-2222-2222-2222-222222222222")>
+    Public Interface I
+        Sub F()
+    End Interface
+    Public Interface IBad
+        Sub F()
+    End Interface
+End Namespace
+]]>
+    </file>
+</compilation>
+            Dim source =
+<compilation>
+    <file>
+Imports System
+Imports N.E
+Imports N.SBad
+Imports Z1 = N.S1
+Imports Z2 = N.S2
+Imports ZBad = N.SBad
+Imports NI = N.I
+Imports NIBad = N.IBad
+Class C
+    Dim i As NI 
+    Sub M
+        Console.WriteLine(Value1)
+        Console.WriteLine(Z2.Value2)
+        Console.WriteLine(New Z1())
+    End Sub
+End Class
+    </file>
+</compilation>
+            Dim globalImports = GlobalImport.Parse(
+                "GlobalNIBad = N.IBad",
+                "GlobalZ1 = N.S1",
+                "GlobalZ2 = N.S2",
+                "GlobalZBad = N.SBad",
+                "GlobalNI = N.I")
+            Dim libRef = CreateCompilationWithMscorlib(sourceLib).EmitToImageReference(embedInteropTypes:=True)
+            Dim compilation = CreateCompilationWithMscorlibAndReferences(source, {libRef}, options:=TestOptions.DebugDll.WithGlobalImports(globalImports))
+            Dim v = CompileAndVerify(compilation)
+            v.Diagnostics.Verify(
+                Diagnostic(ERRID.HDN_UnusedImportStatement, "Imports N.SBad"),
+                Diagnostic(ERRID.HDN_UnusedImportStatement, "Imports ZBad = N.SBad"),
+                Diagnostic(ERRID.HDN_UnusedImportStatement, "Imports NIBad = N.IBad"))
+            ' Imports of embedded types are currently ommitted:
+            v.VerifyPdb("C.M",
+<symbols>
+    <methods>
+        <method containingType="C" name="M">
+            <sequencePoints>
+                <entry offset="0x0" startLine="13" startColumn="5" endLine="13" endColumn="10" document="0"/>
+                <entry offset="0x1" startLine="14" startColumn="9" endLine="14" endColumn="34" document="0"/>
+                <entry offset="0x8" startLine="15" startColumn="9" endLine="15" endColumn="37" document="0"/>
+                <entry offset="0xf" startLine="16" startColumn="9" endLine="16" endColumn="36" document="0"/>
+                <entry offset="0x23" startLine="17" startColumn="5" endLine="17" endColumn="12" document="0"/>
+            </sequencePoints>
+            <scope startOffset="0x0" endOffset="0x24">
+                <namespace name="System" importlevel="file"/>
+                <defunct name="&amp;ImportedNoPiaTypesAssemblyName"/>
+                <currentnamespace name=""/>
+            </scope>
+        </method>
+    </methods>
+</symbols>)
+        End Sub
+        <Fact>
+        Public Sub ImportedTypeWithUnknownBase()
+            Dim sourceLib1 =
+<compilation>
+    <file>
+Namespace N
+    Public Class A
+    End Class
+End Namespace
+    </file>
+</compilation>
+            Dim sourceLib2 =
+<compilation name="LibRef2">
+    <file>
+Namespace N
+    Public Class B
+        Inherits A
+    End Class
+End Namespace
+    </file>
+</compilation>
+            Dim source =
+<compilation>
+    <file>
+Imports System
+Imports X = N.B
+Class C
+    Sub M()
+        Console.WriteLine()
+    End Sub
+End Class
+    </file>
+</compilation>
+            Dim libRef1 = CreateCompilationWithMscorlib(sourceLib1).EmitToImageReference()
+            Dim libRef2 = CreateCompilationWithMscorlibAndReferences(sourceLib2, {libRef1}).EmitToImageReference()
+            Dim compilation = CreateCompilationWithMscorlibAndReferences(source, {libRef2})
+            Dim v = CompileAndVerify(compilation, emitters:=TestEmitters.CCI)
+            v.Diagnostics.Verify(
+                Diagnostic(ERRID.HDN_UnusedImportStatement, "Imports X = N.B"))
+            v.VerifyPdb("C.M",
+<symbols>
+    <methods>
+        <method containingType="C" name="M">
+            <sequencePoints>
+                <entry offset="0x0" startLine="6" startColumn="9" endLine="6" endColumn="28" document="0"/>
+                <entry offset="0x5" startLine="7" startColumn="5" endLine="7" endColumn="12" document="0"/>
+            </sequencePoints>
+            <scope startOffset="0x0" endOffset="0x6">
+                <alias name="X" target="N.B" kind="namespace" importlevel="file"/>
+                <namespace name="System" importlevel="file"/>
+                <currentnamespace name=""/>
+            </scope>
+        </method>
+    </methods>
+</symbols>)
+        End Sub
    End Class
 End Namespace

--- a/src/ExpressionEvaluator/CSharp/Source/ExpressionCompiler/CompilationContext.cs
+++ b/src/ExpressionEvaluator/CSharp/Source/ExpressionCompiler/CompilationContext.cs
@@ -157,7 +157,7 @@ internal sealed class CompilationContext
                module,
                win32Resources: null,
                xmlDocStream: null,
-                generateDebugInfo: false,
+                emittingPdb: false,
                diagnostics: diagnostics,
                filterOpt: null,
                cancellationToken: CancellationToken.None);
@@ -220,7 +220,7 @@ internal sealed class CompilationContext
                module,
                win32Resources: null,
                xmlDocStream: null,
-                generateDebugInfo: false,
+                emittingPdb: false,
                diagnostics: diagnostics,
                filterOpt: null,
                cancellationToken: CancellationToken.None);
@@ -405,7 +405,7 @@ private static string GetNextMethodName(ArrayBuilder<MethodSymbol> builder)
                module,
                win32Resources: null,
                xmlDocStream: null,
-                generateDebugInfo: false,
+                emittingPdb: false,
                diagnostics: diagnostics,
                filterOpt: null,
                cancellationToken: CancellationToken.None);

--- a/src/ExpressionEvaluator/VisualBasic/Source/ExpressionCompiler/CompilationContext.vb
+++ b/src/ExpressionEvaluator/VisualBasic/Source/ExpressionCompiler/CompilationContext.vb
@@ -154,7 +154,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.ExpressionEvaluator
                moduleBuilder,
                win32Resources:=Nothing,
                xmlDocStream:=Nothing,
-                generateDebugInfo:=False,
+                emittingPdb:=False,
                diagnostics:=diagnostics,
                filterOpt:=Nothing,
                cancellationToken:=CancellationToken.None)
@@ -327,7 +327,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.ExpressionEvaluator
                moduleBuilder,
                win32Resources:=Nothing,
                xmlDocStream:=Nothing,
-                generateDebugInfo:=False,
+                emittingPdb:=False,
                diagnostics:=diagnostics,
                filterOpt:=Nothing,
                cancellationToken:=CancellationToken.None)

--- a/src/Scripting/Core/Emit/CommonCompilationExtensions.cs
+++ b/src/Scripting/Core/Emit/CommonCompilationExtensions.cs
@@ -84,7 +84,7 @@ internal static class CommonCompilationExtensions
                moduleBeingBuilt,
                win32Resources: null,
                xmlDocStream: null,
-                generateDebugInfo: false,
+                emittingPdb: false,
                diagnostics: diagnostics,
                filterOpt: null,
                cancellationToken: cancellationToken))

--- a/src/Test/Utilities/AssertEx.cs
+++ b/src/Test/Utilities/AssertEx.cs
@@ -381,6 +381,7 @@ public static void ThrowsArgumentException(string parameterName, Action del)
            throw new Exception("No exception was thrown.");
        }
+        // compares against a baseline
        public static void AssertEqualToleratingWhitespaceDifferences(
            string expected,
            string actual,
@@ -397,6 +398,32 @@ public static void ThrowsArgumentException(string parameterName, Action del)
            }
        }
+        // compares two results (no baseline)
+        public static void AssertResultsEqual(string result1, string result2)
+        {
+            if (result1 != result2)
+            {
+                string message;
+                if (DiffToolAvailable)
+                {
+                    string file1 = Path.GetTempFileName();
+                    File.WriteAllText(file1, result1);
+                    string file2 = Path.GetTempFileName();
+                    File.WriteAllText(file2, result2);
+                    message = MakeDiffToolLink(file1, file2);
+                }
+                else
+                {
+                    message = GetAssertMessage(result1, result2);
+                }
+                Assert.True(false, message);
+            }
+        }
        public static void AssertContainsToleratingWhitespaceDifferences(string expectedSubString, string actualString)
        {
            expectedSubString = NormalizeWhitespace(expectedSubString);
@@ -481,7 +508,7 @@ public static string GetAssertMessage<T>(IEnumerable<T> expected, IEnumerable<T>
            message.AppendLine(DiffUtil.DiffReport(expected, actual, comparer, itemInspector, itemSeparator));
            string link;
-            if (TryGenerateExpectedSourceFielAndGetDiffLink(actualString, expected.Count(), expectedValueSourcePath, expectedValueSourceLine, out link))
+            if (TryGenerateExpectedSourceFileAndGetDiffLink(actualString, expected.Count(), expectedValueSourcePath, expectedValueSourceLine, out link))
            {
                message.AppendLine(link);
            }
@@ -489,10 +516,10 @@ public static string GetAssertMessage<T>(IEnumerable<T> expected, IEnumerable<T>
            return message.ToString();
        }
-        internal static bool TryGenerateExpectedSourceFielAndGetDiffLink(string actualString, int expectedLineCount, string expectedValueSourcePath, int expectedValueSourceLine, out string link)
+        internal static bool TryGenerateExpectedSourceFileAndGetDiffLink(string actualString, int expectedLineCount, string expectedValueSourcePath, int expectedValueSourceLine, out string link)
        {
            // add a link to a .cmd file that opens a diff tool:
-            if (!string.IsNullOrEmpty(s_diffToolPath) && expectedValueSourcePath != null && expectedValueSourceLine != 0)
+            if (DiffToolAvailable && expectedValueSourcePath != null && expectedValueSourceLine != 0)
            {
                var actualFile = Path.GetTempFileName();
                var testFileLines = File.ReadAllLines(expectedValueSourcePath);
@@ -501,10 +528,7 @@ internal static bool TryGenerateExpectedSourceFielAndGetDiffLink(string actualSt
                File.AppendAllText(actualFile, actualString);
                File.AppendAllLines(actualFile, testFileLines.Skip(expectedValueSourceLine + expectedLineCount));
-                var compareCmd = Path.GetTempFileName() + ".cmd";
+                link = MakeDiffToolLink(actualFile, expectedValueSourcePath);
-                File.WriteAllText(compareCmd, string.Format("\"{0}\" \"{1}\" \"{2}\"", s_diffToolPath, actualFile, expectedValueSourcePath));
-                link = "file://" + compareCmd;
                s_diffLinks.Value.Add(Tuple.Create(expectedValueSourcePath, expectedValueSourceLine, link));
                return true;
@@ -514,6 +538,16 @@ internal static bool TryGenerateExpectedSourceFielAndGetDiffLink(string actualSt
            return false;
        }
+        internal static bool DiffToolAvailable => !string.IsNullOrEmpty(s_diffToolPath);
+        internal static string MakeDiffToolLink(string actualFilePath, string expectedFilePath)
+        {
+            var compareCmd = Path.GetTempFileName() + ".cmd";
+            File.WriteAllText(compareCmd, string.Format("\"{0}\" \"{1}\" \"{2}\"", s_diffToolPath, actualFilePath, expectedFilePath));
+            return "file://" + compareCmd;
+        }
        private static readonly Lazy<List<Tuple<string, int, string>>> s_diffLinks = new Lazy<List<Tuple<string, int, string>>>(() =>
        {
            AppDomain.CurrentDomain.DomainUnload += (_, __) =>

--- a/src/Test/Utilities/AssertXml.cs
+++ b/src/Test/Utilities/AssertXml.cs
@@ -84,7 +84,7 @@ private static string GetXmlString(XElement node, bool expectedIsXmlLiteral)
            string expectedString = expectedIsXmlLiteral ? expected.Replace(" />\r\n", "/>\r\n") : string.Format("@\"{0}\"", expected.Replace("\"", "\"\""));
            string link;
-            if (AssertEx.TryGenerateExpectedSourceFielAndGetDiffLink(actualString, expectedString.Count(c => c == '\n') + 1, expectedValueSourcePath, expectedValueSourceLine, out link))
+            if (AssertEx.TryGenerateExpectedSourceFileAndGetDiffLink(actualString, expectedString.Count(c => c == '\n') + 1, expectedValueSourcePath, expectedValueSourceLine, out link))
            {
                assertText.AppendLine(link);
            }

--- a/src/Test/Utilities/CompilationExtensions.cs
+++ b/src/Test/Utilities/CompilationExtensions.cs
@@ -38,7 +38,7 @@ public static class CompilationExtensions
                getHostDiagnostics: null,
                cancellationToken: default(CancellationToken));
-            Assert.True(emitResult.Success, "Diagnostics:\r\n" + string.Join("\r\n, ", emitResult.Diagnostics.Select(d => d.ToString())));
+            Assert.True(emitResult.Success, "Diagnostics:\r\n" + string.Join("\r\n", emitResult.Diagnostics.Select(d => d.ToString())));
            if (expectedWarnings != null)
            {

--- a/src/Test/Utilities/SharedCompilationUtils.cs
+++ b/src/Test/Utilities/SharedCompilationUtils.cs
@@ -8,12 +8,14 @@
 using System.Linq;
 using System.Reflection;
 using System.Reflection.Metadata;
+using System.Reflection.Metadata.Ecma335;
 using System.Reflection.PortableExecutable;
 using System.Runtime.CompilerServices;
 using System.Text;
 using System.Xml.Linq;
 using Microsoft.CodeAnalysis.CodeGen;
 using Microsoft.CodeAnalysis.Emit;
+using PDB::Roslyn.Test.MetadataUtilities;
 using PDB::Roslyn.Test.PdbUtilities;
 using Roslyn.Test.Utilities;
 using Xunit;
@@ -194,6 +196,39 @@ public static void ValidateDebugDirectory(Stream peStream, string pdbPath)
            Assert.Equal(0, reader.ReadByte());
        }
+        public static void VerifyMetadataEqualModuloMvid(Stream peStream1, Stream peStream2)
+        {
+            peStream1.Position = 0;
+            peStream2.Position = 0;
+            var peReader1 = new PEReader(peStream1);
+            var peReader2 = new PEReader(peStream2);
+            var md1 = peReader1.GetMetadata().GetContent();
+            var md2 = peReader2.GetMetadata().GetContent();
+            var mdReader1 = peReader1.GetMetadataReader();
+            var mdReader2 = peReader2.GetMetadataReader();
+            var mvidIndex1 = mdReader1.GetModuleDefinition().Mvid;
+            var mvidIndex2 = mdReader2.GetModuleDefinition().Mvid;
+            var mvidOffset1 = mdReader1.GetHeapMetadataOffset(HeapIndex.Guid) + 16 * (MetadataTokens.GetHeapOffset(mvidIndex1) - 1);
+            var mvidOffset2 = mdReader2.GetHeapMetadataOffset(HeapIndex.Guid) + 16 * (MetadataTokens.GetHeapOffset(mvidIndex2) - 1);
+            if (!md1.RemoveRange(mvidOffset1, 16).SequenceEqual(md1.RemoveRange(mvidOffset2, 16)))
+            {
+                var mdw1 = new StringWriter();
+                var mdw2 = new StringWriter();
+                new MetadataVisualizer(mdReader1, mdw1).Visualize();
+                new MetadataVisualizer(mdReader2, mdw2).Visualize();
+                mdw1.Flush();
+                mdw2.Flush();
+                AssertEx.AssertResultsEqual(mdw1.ToString(), mdw2.ToString());
+            }
+        }
        internal static string GetMethodIL(this CompilationTestData.MethodData method)
        {
            return ILBuilderVisualizer.ILBuilderToString(method.ILBuilder);