Minor SourceFileResolver fixups...

- Undo some refactoring of CommonCompiler.ReadFileContent
- Remove LoadDirectiveResolver
- Make SourceReferenceResolver.ReadText detect encoding
- Make SourceReferenceResolver.ReadText Dispose its Stream
- Generate Diagnostic if source contains #load and SourceReferenceResolver
  is not specified in ParseOptions

src/Compilers/CSharp/Portable/CSharpResources.Designer.cs

@@ -5588,7 +5588,7 @@ internal class CSharpResources {
         }
         
         /// <summary>
-        ///   Looks up a localized string similar to Metadata references not supported..
+        ///   Looks up a localized string similar to Metadata references are not supported..
         /// </summary>
         internal static string ERR_MetadataReferencesNotSupported {
             get {
@@ -7765,6 +7765,15 @@ internal class CSharpResources {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to Source file references are not supported..
+        /// </summary>
+        internal static string ERR_SourceFileReferencesNotSupported {
+            get {
+                return ResourceManager.GetString("ERR_SourceFileReferencesNotSupported", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Instance of type &apos;{0}&apos; cannot be used inside an anonymous function, query expression, iterator block or async method.
         /// </summary>

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -373,7 +373,7 @@
     <value>Metadata file '{0}' could not be found</value>
   </data>
   <data name="ERR_MetadataReferencesNotSupported" xml:space="preserve">
-    <value>Metadata references not supported.</value>
+    <value>Metadata references are not supported.</value>
   </data>
   <data name="FTL_MetadataCantOpenFile" xml:space="preserve">
     <value>Metadata file '{0}' could not be opened -- {1}</value>
@@ -4651,4 +4651,7 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="SyntaxTreeFromLoadNoRemoveReplace" xml:space="preserve">
     <value>SyntaxTree '{0}' resulted from a #load directive and cannot be removed or replaced directly.</value>
   </data>
+  <data name="ERR_SourceFileReferencesNotSupported" xml:space="preserve">
+    <value>Source file references are not supported.</value>
+  </data>
 </root>
\ No newline at end of file

src/Compilers/CSharp/Portable/Compilation/SyntaxAndDeclarationManager.cs

@@ -187,55 +187,66 @@ public SyntaxAndDeclarationManager AddSyntaxTrees(IEnumerable<SyntaxTree> trees)
                 }
 
                 var diagnostics = DiagnosticBag.GetInstance();
-                var resolvedFilePath = resolver.ResolveReference(path, baseFilePath: tree.FilePath);
-                if (resolvedFilePath == null)
+                string resolvedFilePath = null;
+                if (resolver == null)
                 {
                     diagnostics.Add(
                         messageProvider.CreateDiagnostic(
-                            (int)ErrorCode.ERR_NoSourceFile,
-                            fileToken.GetLocation(),
-                            path,
-                            CSharpResources.CouldNotFindFile));
+                            (int)ErrorCode.ERR_SourceFileReferencesNotSupported,
+                            directive.Location));
                 }
-                else if (!loadedSyntaxTreeMapBuilder.ContainsKey(resolvedFilePath))
+                else
                 {
-                    try
+                    resolvedFilePath = resolver.ResolveReference(path, baseFilePath: tree.FilePath);
+                    if (resolvedFilePath == null)
                     {
-                        var code = resolver.ReadText(resolvedFilePath);
-                        var loadedTree = SyntaxFactory.ParseSyntaxTree(
-                            code,
-                            tree.Options, // Use ParseOptions propagated from "external" tree.
-                            resolvedFilePath);
+                        diagnostics.Add(
+                            messageProvider.CreateDiagnostic(
+                                (int)ErrorCode.ERR_NoSourceFile,
+                                fileToken.GetLocation(),
+                                path,
+                                CSharpResources.CouldNotFindFile));
+                    }
+                    else if (!loadedSyntaxTreeMapBuilder.ContainsKey(resolvedFilePath))
+                    {
+                        try
+                        {
+                            var code = resolver.ReadText(resolvedFilePath);
+                            var loadedTree = SyntaxFactory.ParseSyntaxTree(
+                                code,
+                                tree.Options, // Use ParseOptions propagated from "external" tree.
+                                resolvedFilePath);
 
-                        // All #load'ed trees should have unique path information.
-                        loadedSyntaxTreeMapBuilder.Add(loadedTree.FilePath, loadedTree);
+                            // All #load'ed trees should have unique path information.
+                            loadedSyntaxTreeMapBuilder.Add(loadedTree.FilePath, loadedTree);
 
-                        AppendAllSyntaxTrees(
-                            treesBuilder,
-                            loadedTree,
-                            scriptClassName,
-                            resolver,
-                            messageProvider,
-                            isSubmission,
-                            ordinalMapBuilder,
-                            loadDirectiveMapBuilder,
-                            loadedSyntaxTreeMapBuilder,
-                            declMapBuilder,
-                            ref declTable);
+                            AppendAllSyntaxTrees(
+                                treesBuilder,
+                                loadedTree,
+                                scriptClassName,
+                                resolver,
+                                messageProvider,
+                                isSubmission,
+                                ordinalMapBuilder,
+                                loadDirectiveMapBuilder,
+                                loadedSyntaxTreeMapBuilder,
+                                declMapBuilder,
+                                ref declTable);
+                        }
+                        catch (Exception e)
+                        {
+                            diagnostics.Add(
+                                CommonCompiler.ToFileReadDiagnostics(messageProvider, e, resolvedFilePath),
+                                fileToken.GetLocation());
+                        }
                     }
-                    catch (Exception e)
+                    else
                     {
-                        diagnostics.Add(
-                            CommonCompiler.ToFileReadDiagnostics(messageProvider, e, resolvedFilePath),
-                            fileToken.GetLocation());
+                        // The path resolved, but we've seen this file before,
+                        // so don't attempt to load it again.
+                        Debug.Assert(diagnostics.IsEmptyWithoutResolution);
                     }
                 }
-                else
-                {
-                    // The path resolved, but we've seen this file before,
-                    // so don't attempt to load it again.
-                    Debug.Assert(diagnostics.IsEmptyWithoutResolution);
-                }
 
                 if (loadDirectives == null)
                 {

src/Compilers/CSharp/Portable/Errors/ErrorCode.cs

@@ -1314,5 +1314,6 @@ internal enum ErrorCode
         ERR_DebugEntryPointNotSourceMethodDefinition = 8096,
         ERR_LoadDirectiveOnlyAllowedInScripts = 8097,
         ERR_PPLoadFollowsToken = 8098,
+        ERR_SourceFileReferencesNotSupported = 8099,
     }
 }

src/Compilers/CSharp/Test/Symbol/Compilation/LoadDirectiveTests.cs

@@ -62,6 +62,19 @@ void FileWithErrors()
                 Diagnostic(ErrorCode.ERR_NameNotInContext, "asdf").WithArguments("asdf").WithLocation(3, 21));
         }
 
+        [Fact]
+        void NoSourceReferenceResolver()
+        {
+            var code = "#load \"test\"";
+            var compilation = CreateCompilationWithMscorlib(code, parseOptions: TestOptions.Script);
+
+            Assert.Single(compilation.SyntaxTrees);
+            compilation.GetDiagnostics().Verify(
+                // (1,1): error CS8099: Source file references not supported
+                // #load "test"
+                Diagnostic(ErrorCode.ERR_SourceFileReferencesNotSupported, @"#load ""test""").WithLocation(1, 1));
+        }
+
         private static CSharpCompilation CreateCompilation(string code, SourceReferenceResolver sourceReferenceResolver = null)
         {
             var options = new CSharpCompilationOptions(

src/Compilers/Core/Portable/CommandLine/CommonCompiler.cs

@@ -153,7 +153,14 @@ internal SourceText ReadFileContent(CommandLineSourceFile file, IList<Diagnostic
             var filePath = file.Path;
             try
             {
-                return ReadFileContentHelper(filePath, encoding, checksumAlgorithm, out normalizedFilePath);
+                // PERF: Using a very small buffer size for the FileStream opens up an optimization within EncodedStringText where
+                // we read the entire FileStream into a byte array in one shot. For files that are actually smaller than the buffer
+                // size, FileStream.Read still allocates the internal buffer.
+                using (var data = PortableShim.FileStream.Create(filePath, PortableShim.FileMode.Open, PortableShim.FileAccess.Read, PortableShim.FileShare.ReadWrite, bufferSize: 1, options: PortableShim.FileOptions.None))
+                {
+                    normalizedFilePath = (string)PortableShim.FileStream.Name.GetValue(data);
+                    return EncodedStringText.Create(data, encoding, checksumAlgorithm);
+                }
             }
             catch (Exception e)
             {
@@ -163,18 +170,6 @@ internal SourceText ReadFileContent(CommandLineSourceFile file, IList<Diagnostic
             }
         }
 
-        internal static SourceText ReadFileContentHelper(string filePath, Encoding encoding, SourceHashAlgorithm checksumAlgorithm, out string normalizedFilePath)
-        {
-            // PERF: Using a very small buffer size for the FileStream opens up an optimization within EncodedStringText where
-            // we read the entire FileStream into a byte array in one shot. For files that are actually smaller than the buffer
-            // size, FileStream.Read still allocates the internal buffer.
-            using (var data = PortableShim.FileStream.Create(filePath, PortableShim.FileMode.Open, PortableShim.FileAccess.Read, PortableShim.FileShare.ReadWrite, bufferSize: 1, options: PortableShim.FileOptions.None))
-            {
-                normalizedFilePath = (string)PortableShim.FileStream.Name.GetValue(data);
-                return EncodedStringText.Create(data, encoding, checksumAlgorithm);
-            }
-        }
-
         internal static DiagnosticInfo ToFileReadDiagnostics(CommonMessageProvider messageProvider, Exception e, string filePath)
         {
             DiagnosticInfo diagnosticInfo;

src/Compilers/Core/Portable/Compilation/CommonSyntaxAndDeclarationManager.cs

@@ -30,7 +30,7 @@ internal abstract class CommonSyntaxAndDeclarationManager
         {
             this.ExternalSyntaxTrees = externalSyntaxTrees;
             this.ScriptClassName = scriptClassName ?? "";
-            this.Resolver = resolver; // TODO: What if SourceReferenceResolver is null?
+            this.Resolver = resolver;
             this.MessageProvider = messageProvider;
             this.IsSubmission = isSubmission;
         }

src/Compilers/Core/Portable/Compilation/SourceReferenceResolver.cs

@@ -62,7 +62,10 @@ internal Stream OpenReadChecked(string fullPath)
         /// <param name="resolvedPath">Path returned by <see cref="ResolveReference(string, string)"/>.</param>
         public virtual SourceText ReadText(string resolvedPath)
         {
-            return SourceText.From(OpenRead(resolvedPath));
+            using (var stream = OpenRead(resolvedPath))
+            {
+                return EncodedStringText.Create(stream);
+            }
         }
     }
 }

src/Scripting/CSharp/CSharpScriptCompiler.cs

@@ -51,7 +51,7 @@ public override Compilation CreateSubmission(Script script)
                     platform: Platform.AnyCpu,
                     warningLevel: 4,
                     xmlReferenceResolver: null, // don't support XML file references in interactive (permissions & doc comment includes)
-                    sourceReferenceResolver: LoadDirectiveResolver.Default,
+                    sourceReferenceResolver: null,
                     metadataReferenceResolver: script.Options.ReferenceResolver,
                     assemblyIdentityComparer: DesktopAssemblyIdentityComparer.Default
                 ),
@@ -62,25 +62,5 @@ public override Compilation CreateSubmission(Script script)
 
             return compilation;
         }
-
-        private class LoadDirectiveResolver : SourceFileResolver
-        {
-            public static new LoadDirectiveResolver Default { get; } = new LoadDirectiveResolver();
-
-            private LoadDirectiveResolver()
-                : base(ImmutableArray<string>.Empty, baseDirectory: null)
-            {
-            }
-
-            public override SourceText ReadText(string resolvedPath)
-            {
-                string unused;
-                return CommonCompiler.ReadFileContentHelper(
-                    resolvedPath,
-                    encoding: null,
-                    checksumAlgorithm: SourceHashAlgorithm.Sha1, // TODO: Should we be fetching the checksum algorithm from somewhere?
-                    normalizedFilePath: out unused);
-            }
-        }
     }
 }