Expose generator internals: (#46296)

* Expose generator internals:
- Add a new api + result objects to return generator driver internals
- Rework the way we handle exceptions, especially for syntax walk based operations
- Ensure we don't mix up generator and driver exceptions

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -6436,4 +6436,4 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="IDS_FeatureExtensionGetEnumerator" xml:space="preserve">
     <value>extension GetEnumerator</value>
   </data>
-</root>
+</root>
\ No newline at end of file

src/Compilers/CSharp/Test/Semantic/SourceGeneration/GeneratorDriverTests.cs

@@ -16,6 +16,7 @@
 using Microsoft.CodeAnalysis.Diagnostics;
 using Microsoft.CodeAnalysis.PooledObjects;
 using Microsoft.CodeAnalysis.Text;
+using Roslyn.Test.Utilities;
 using Roslyn.Test.Utilities.TestGenerators;
 using Xunit;
 
@@ -698,6 +699,209 @@ class C { }
                 $"{generator2.GetType().Module.ModuleVersionId}_{generator2.GetType().FullName}_source.cs"
             }, filePaths);
         }
+
+        [Fact]
+        public void RunResults_Are_Empty_Before_Generation()
+        {
+            GeneratorDriver driver = new CSharpGeneratorDriver(TestOptions.Regular, ImmutableArray<ISourceGenerator>.Empty, CompilerAnalyzerConfigOptionsProvider.Empty, ImmutableArray<AdditionalText>.Empty);
+            var results = driver.GetRunResult();
+
+            Assert.Empty(results.GeneratedTrees);
+            Assert.Empty(results.Diagnostics);
+            Assert.Empty(results.Results);
+        }
+
+        [Fact]
+        public void RunResults_Are_Available_After_Generation()
+        {
+            var source = @"
+class C { }
+";
+            var parseOptions = TestOptions.Regular;
+            Compilation compilation = CreateCompilation(source, options: TestOptions.DebugDll, parseOptions: parseOptions);
+            compilation.VerifyDiagnostics();
+            Assert.Single(compilation.SyntaxTrees);
+
+            var generator = new CallbackGenerator((ic) => { }, (sgc) => { sgc.AddSource("test", SourceText.From("public class D {}", Encoding.UTF8)); });
+
+            GeneratorDriver driver = new CSharpGeneratorDriver(parseOptions, ImmutableArray.Create<ISourceGenerator>(generator), CompilerAnalyzerConfigOptionsProvider.Empty, ImmutableArray<AdditionalText>.Empty);
+            driver = driver.RunGenerators(compilation);
+
+            var results = driver.GetRunResult();
+
+            Assert.Single(results.GeneratedTrees);
+            Assert.Single(results.Results);
+            Assert.Empty(results.Diagnostics);
+
+            var result = results.Results.Single();
+
+            Assert.Null(result.Exception);
+            Assert.Empty(result.Diagnostics);
+            Assert.Single(result.GeneratedSources);
+            Assert.Equal(results.GeneratedTrees.Single(), result.GeneratedSources.Single().SyntaxTree);
+        }
+
+        [Fact]
+        public void RunResults_Combine_SyntaxTrees()
+        {
+            var source = @"
+class C { }
+";
+            var parseOptions = TestOptions.Regular;
+            Compilation compilation = CreateCompilation(source, options: TestOptions.DebugDll, parseOptions: parseOptions);
+            compilation.VerifyDiagnostics();
+            Assert.Single(compilation.SyntaxTrees);
+
+            var generator = new CallbackGenerator((ic) => { }, (sgc) => { sgc.AddSource("test", SourceText.From("public class D {}", Encoding.UTF8)); sgc.AddSource("test2", SourceText.From("public class E {}", Encoding.UTF8)); });
+            var generator2 = new SingleFileTestGenerator("public class F{}");
+            var generator3 = new SingleFileTestGenerator2("public class G{}");
+
+            GeneratorDriver driver = new CSharpGeneratorDriver(parseOptions, ImmutableArray.Create<ISourceGenerator>(generator, generator2, generator3), CompilerAnalyzerConfigOptionsProvider.Empty, ImmutableArray<AdditionalText>.Empty);
+            driver = driver.RunGenerators(compilation);
+
+            var results = driver.GetRunResult();
+
+            Assert.Equal(4, results.GeneratedTrees.Length);
+            Assert.Equal(3, results.Results.Length);
+            Assert.Empty(results.Diagnostics);
+
+            var result1 = results.Results[0];
+            var result2 = results.Results[1];
+            var result3 = results.Results[2];
+
+            Assert.Null(result1.Exception);
+            Assert.Empty(result1.Diagnostics);
+            Assert.Equal(2, result1.GeneratedSources.Length);
+            Assert.Equal(results.GeneratedTrees[0], result1.GeneratedSources[0].SyntaxTree);
+            Assert.Equal(results.GeneratedTrees[1], result1.GeneratedSources[1].SyntaxTree);
+
+            Assert.Null(result2.Exception);
+            Assert.Empty(result2.Diagnostics);
+            Assert.Single(result2.GeneratedSources);
+            Assert.Equal(results.GeneratedTrees[2], result2.GeneratedSources[0].SyntaxTree);
+
+            Assert.Null(result3.Exception);
+            Assert.Empty(result3.Diagnostics);
+            Assert.Single(result3.GeneratedSources);
+            Assert.Equal(results.GeneratedTrees[3], result3.GeneratedSources[0].SyntaxTree);
+        }
+
+        [Fact]
+        public void RunResults_Combine_Diagnostics()
+        {
+            var source = @"
+class C { }
+";
+            var parseOptions = TestOptions.Regular;
+            Compilation compilation = CreateCompilation(source, options: TestOptions.DebugDll, parseOptions: parseOptions);
+            compilation.VerifyDiagnostics();
+            Assert.Single(compilation.SyntaxTrees);
+
+            string description = "This is a test diagnostic";
+            DiagnosticDescriptor generatorDiagnostic1 = new DiagnosticDescriptor("TG001", "Test Diagnostic", description, "Generators", DiagnosticSeverity.Warning, isEnabledByDefault: true, description: description);
+            DiagnosticDescriptor generatorDiagnostic2 = new DiagnosticDescriptor("TG002", "Test Diagnostic", description, "Generators", DiagnosticSeverity.Warning, isEnabledByDefault: true, description: description);
+            DiagnosticDescriptor generatorDiagnostic3 = new DiagnosticDescriptor("TG003", "Test Diagnostic", description, "Generators", DiagnosticSeverity.Warning, isEnabledByDefault: true, description: description);
+
+            var diagnostic1 = Microsoft.CodeAnalysis.Diagnostic.Create(generatorDiagnostic1, Location.None);
+            var diagnostic2 = Microsoft.CodeAnalysis.Diagnostic.Create(generatorDiagnostic2, Location.None);
+            var diagnostic3 = Microsoft.CodeAnalysis.Diagnostic.Create(generatorDiagnostic3, Location.None);
+
+            var generator = new CallbackGenerator((ic) => { }, (sgc) => { sgc.ReportDiagnostic(diagnostic1); sgc.ReportDiagnostic(diagnostic2); });
+            var generator2 = new CallbackGenerator2((ic) => { }, (sgc) => { sgc.ReportDiagnostic(diagnostic3); });
+
+            GeneratorDriver driver = new CSharpGeneratorDriver(parseOptions, ImmutableArray.Create<ISourceGenerator>(generator, generator2), CompilerAnalyzerConfigOptionsProvider.Empty, ImmutableArray<AdditionalText>.Empty);
+            driver = driver.RunGenerators(compilation);
+
+            var results = driver.GetRunResult();
+
+            Assert.Equal(2, results.Results.Length);
+            Assert.Equal(3, results.Diagnostics.Length);
+            Assert.Empty(results.GeneratedTrees);
+
+            var result1 = results.Results[0];
+            var result2 = results.Results[1];
+
+            Assert.Null(result1.Exception);
+            Assert.Equal(2, result1.Diagnostics.Length);
+            Assert.Empty(result1.GeneratedSources);
+            Assert.Equal(results.Diagnostics[0], result1.Diagnostics[0]);
+            Assert.Equal(results.Diagnostics[1], result1.Diagnostics[1]);
+
+            Assert.Null(result2.Exception);
+            Assert.Single(result2.Diagnostics);
+            Assert.Empty(result2.GeneratedSources);
+            Assert.Equal(results.Diagnostics[2], result2.Diagnostics[0]);
+        }
+
+        [Fact]
+        public void FullGeneration_Diagnostics_AreSame_As_RunResults()
+        {
+            var source = @"
+class C { }
+";
+            var parseOptions = TestOptions.Regular;
+            Compilation compilation = CreateCompilation(source, options: TestOptions.DebugDll, parseOptions: parseOptions);
+            compilation.VerifyDiagnostics();
+            Assert.Single(compilation.SyntaxTrees);
+
+            string description = "This is a test diagnostic";
+            DiagnosticDescriptor generatorDiagnostic1 = new DiagnosticDescriptor("TG001", "Test Diagnostic", description, "Generators", DiagnosticSeverity.Warning, isEnabledByDefault: true, description: description);
+            DiagnosticDescriptor generatorDiagnostic2 = new DiagnosticDescriptor("TG002", "Test Diagnostic", description, "Generators", DiagnosticSeverity.Warning, isEnabledByDefault: true, description: description);
+            DiagnosticDescriptor generatorDiagnostic3 = new DiagnosticDescriptor("TG003", "Test Diagnostic", description, "Generators", DiagnosticSeverity.Warning, isEnabledByDefault: true, description: description);
+
+            var diagnostic1 = Microsoft.CodeAnalysis.Diagnostic.Create(generatorDiagnostic1, Location.None);
+            var diagnostic2 = Microsoft.CodeAnalysis.Diagnostic.Create(generatorDiagnostic2, Location.None);
+            var diagnostic3 = Microsoft.CodeAnalysis.Diagnostic.Create(generatorDiagnostic3, Location.None);
+
+            var generator = new CallbackGenerator((ic) => { }, (sgc) => { sgc.ReportDiagnostic(diagnostic1); sgc.ReportDiagnostic(diagnostic2); });
+            var generator2 = new CallbackGenerator2((ic) => { }, (sgc) => { sgc.ReportDiagnostic(diagnostic3); });
+
+            GeneratorDriver driver = new CSharpGeneratorDriver(parseOptions, ImmutableArray.Create<ISourceGenerator>(generator, generator2), CompilerAnalyzerConfigOptionsProvider.Empty, ImmutableArray<AdditionalText>.Empty);
+            driver = driver.RunFullGeneration(compilation, out _, out var fullDiagnostics);
+
+            var results = driver.GetRunResult();
+
+            Assert.Equal(3, results.Diagnostics.Length);
+            Assert.Equal(3, fullDiagnostics.Length);
+            AssertEx.Equal(results.Diagnostics, fullDiagnostics);
+        }
+
+        [Fact]
+        public void Cancellation_During_Execution_Doesnt_Report_As_Generator_Error()
+        {
+            var source = @"
+class C 
+{
+}
+";
+            var parseOptions = TestOptions.Regular;
+            Compilation compilation = CreateCompilation(source, options: TestOptions.DebugDll, parseOptions: parseOptions);
+            compilation.VerifyDiagnostics();
+
+            Assert.Single(compilation.SyntaxTrees);
+
+            CancellationTokenSource cts = new CancellationTokenSource();
+
+            var testGenerator = new CallbackGenerator(
+                onInit: (i) => { },
+                onExecute: (e) => { cts.Cancel(); }
+                );
+
+            // test generator cancels the token. Check that the call to this generator doesn't make it look like it errored.
+            var testGenerator2 = new CallbackGenerator2(
+                onInit: (i) => { },
+                onExecute: (e) => { e.AddSource("a", SourceText.From("public class E {}", Encoding.UTF8)); }
+                );
+
+
+            GeneratorDriver driver = new CSharpGeneratorDriver(parseOptions, ImmutableArray.Create<ISourceGenerator>(testGenerator, testGenerator2), CompilerAnalyzerConfigOptionsProvider.Empty, ImmutableArray<AdditionalText>.Empty);
+            var oldDriver = driver;
+
+            Assert.Throws<OperationCanceledException>(() =>
+               driver = driver.RunFullGeneration(compilation, out var outputCompilation, out var outputDiagnostics, cts.Token)
+               );
+            Assert.Same(oldDriver, driver);
+        }
     }
 }
 

src/Compilers/CSharp/Test/Semantic/SourceGeneration/SyntaxAwareGeneratorTests.cs

@@ -5,11 +5,13 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
+using System.Linq;
 using System.Text;
 using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.CSharp.Test.Utilities;
 using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis.Text;
 using Roslyn.Test.Utilities.TestGenerators;
 using Xunit;
 
@@ -84,14 +86,14 @@ class C { }
             Assert.Single(compilation.SyntaxTrees);
 
             var testGenerator = new CallbackGenerator(
-                onInit: Initialize,
+                onInit: initialize,
                 onExecute: (e) => { }
                 );
 
             GeneratorDriver driver = new CSharpGeneratorDriver(parseOptions, ImmutableArray.Create<ISourceGenerator>(testGenerator), CompilerAnalyzerConfigOptionsProvider.Empty, ImmutableArray<AdditionalText>.Empty);
             driver.RunFullGeneration(compilation, out _, out _);
 
-            void Initialize(InitializationContext initContext)
+            void initialize(InitializationContext initContext)
             {
                 initContext.RegisterForSyntaxNotifications(() => new TestSyntaxReceiver());
                 Assert.Throws<InvalidOperationException>(() =>
@@ -192,21 +194,248 @@ void Function()
             Assert.IsType<CompilationUnitSyntax>(testReceiver.VisitedNodes[0]);
         }
 
+        [Fact]
+        public void Syntax_Receiver_Exception_During_Creation()
+        {
+            var source = @"
+class C 
+{
+    int Property { get; set; }
+
+    void Function()
+    {
+        var x = 5;
+        x += 4;
+    }
+}
+";
+            var parseOptions = TestOptions.Regular;
+            Compilation compilation = CreateCompilation(source, options: TestOptions.DebugDll, parseOptions: parseOptions);
+            compilation.VerifyDiagnostics();
+
+            Assert.Single(compilation.SyntaxTrees);
+
+            var testGenerator = new CallbackGenerator(
+                onInit: (i) => i.RegisterForSyntaxNotifications(() => throw new Exception("Test Exception")),
+                onExecute: (e) => { Assert.True(false); }
+                );
+
+            GeneratorDriver driver = new CSharpGeneratorDriver(parseOptions, ImmutableArray.Create<ISourceGenerator>(testGenerator), CompilerAnalyzerConfigOptionsProvider.Empty, ImmutableArray<AdditionalText>.Empty);
+            driver = driver.RunFullGeneration(compilation, out var outputCompilation, out var outputDiagnostics);
+            var results = driver.GetRunResult();
+
+            Assert.Empty(results.GeneratedTrees);
+            Assert.Single(results.Diagnostics);
+            Assert.Single(results.Results);
+            Assert.Single(results.Results[0].Diagnostics);
+
+            Assert.NotNull(results.Results[0].Exception);
+            Assert.Equal("Test Exception", results.Results[0].Exception?.Message);
+
+            outputDiagnostics.Verify(
+                Diagnostic(ErrorCode.WRN_GeneratorFailedDuringGeneration).WithArguments("CallbackGenerator").WithLocation(1, 1)
+                );
+        }
+
+        [Fact]
+        public void Syntax_Receiver_Exception_During_Visit()
+        {
+            var source = @"
+class C 
+{
+    int Property { get; set; }
+
+    void Function()
+    {
+        var x = 5;
+        x += 4;
+    }
+}
+";
+            var parseOptions = TestOptions.Regular;
+            Compilation compilation = CreateCompilation(source, options: TestOptions.DebugDll, parseOptions: parseOptions);
+            compilation.VerifyDiagnostics();
+
+            Assert.Single(compilation.SyntaxTrees);
+
+            var testGenerator = new CallbackGenerator(
+                onInit: (i) => i.RegisterForSyntaxNotifications(() => new TestSyntaxReceiver(tag: 0, callback: (a) => { if (a is AssignmentExpressionSyntax) throw new Exception("Test Exception"); })),
+                onExecute: (e) => { e.AddSource("test", SourceText.From("public class D{}", Encoding.UTF8)); }
+                );
+
+            GeneratorDriver driver = new CSharpGeneratorDriver(parseOptions, ImmutableArray.Create<ISourceGenerator>(testGenerator), CompilerAnalyzerConfigOptionsProvider.Empty, ImmutableArray<AdditionalText>.Empty);
+            driver = driver.RunFullGeneration(compilation, out var outputCompilation, out var outputDiagnostics);
+            var results = driver.GetRunResult();
+
+            Assert.Empty(results.GeneratedTrees);
+            Assert.Single(results.Diagnostics);
+            Assert.Single(results.Results);
+            Assert.Single(results.Results[0].Diagnostics);
+
+            Assert.NotNull(results.Results[0].Exception);
+            Assert.Equal("Test Exception", results.Results[0].Exception?.Message);
+
+            outputDiagnostics.Verify(
+                Diagnostic(ErrorCode.WRN_GeneratorFailedDuringGeneration).WithArguments("CallbackGenerator").WithLocation(1, 1)
+                );
+        }
+
+        [Fact]
+        public void Syntax_Receiver_Exception_During_Visit_Stops_Visits_On_Other_Trees()
+        {
+            var source1 = @"
+class C 
+{
+    int Property { get; set; }
+}
+";
+            var source2 = @"
+class D
+{
+    public void Method() { }
+}
+";
+            var parseOptions = TestOptions.Regular;
+            Compilation compilation = CreateCompilation(new[] { source1, source2 }, options: TestOptions.DebugDll, parseOptions: parseOptions);
+            compilation.VerifyDiagnostics();
+
+            Assert.Equal(2, compilation.SyntaxTrees.Count());
+
+            TestSyntaxReceiver receiver1 = new TestSyntaxReceiver(tag: 0, callback: (a) => { if (a is PropertyDeclarationSyntax) throw new Exception("Test Exception"); });
+            var testGenerator1 = new CallbackGenerator(
+                onInit: (i) => i.RegisterForSyntaxNotifications(() => receiver1),
+                onExecute: (e) => { }
+                );
+
+            TestSyntaxReceiver receiver2 = new TestSyntaxReceiver(tag: 1);
+            var testGenerator2 = new CallbackGenerator2(
+                onInit: (i) => i.RegisterForSyntaxNotifications(() => receiver2),
+                onExecute: (e) => { }
+                );
+
+            GeneratorDriver driver = new CSharpGeneratorDriver(parseOptions, ImmutableArray.Create<ISourceGenerator>(testGenerator1, testGenerator2), CompilerAnalyzerConfigOptionsProvider.Empty, ImmutableArray<AdditionalText>.Empty);
+            driver = driver.RunFullGeneration(compilation, out var outputCompilation, out var outputDiagnostics);
+            var results = driver.GetRunResult();
+
+            Assert.DoesNotContain(receiver1.VisitedNodes, n => n is MethodDeclarationSyntax);
+            Assert.Contains(receiver2.VisitedNodes, n => n is MethodDeclarationSyntax);
+
+        }
+
+        [Fact]
+        public void Syntax_Receiver_Exception_During_Visit_Doesnt_Stop_Other_Receivers()
+        {
+            var source = @"
+class C 
+{
+    int Property { get; set; }
+
+    void Function()
+    {
+        var x = 5;
+        x += 4;
+    }
+}
+";
+            var parseOptions = TestOptions.Regular;
+            Compilation compilation = CreateCompilation(source, options: TestOptions.DebugDll, parseOptions: parseOptions);
+            compilation.VerifyDiagnostics();
+
+            Assert.Single(compilation.SyntaxTrees);
+
+            var testGenerator = new CallbackGenerator(
+                onInit: (i) => i.RegisterForSyntaxNotifications(() => new TestSyntaxReceiver(tag: 0, callback: (a) => { if (a is AssignmentExpressionSyntax) throw new Exception("Test Exception"); })),
+                onExecute: (e) => { }
+                );
+
+            ISyntaxReceiver? receiver = null;
+            var testGenerator2 = new CallbackGenerator2(
+                onInit: (i) => i.RegisterForSyntaxNotifications(() => new TestSyntaxReceiver(tag: 1)),
+                onExecute: (e) => { receiver = e.SyntaxReceiver; e.AddSource("test", SourceText.From("public class D{}", Encoding.UTF8)); }
+                );
+
+            GeneratorDriver driver = new CSharpGeneratorDriver(parseOptions, ImmutableArray.Create<ISourceGenerator>(testGenerator, testGenerator2), CompilerAnalyzerConfigOptionsProvider.Empty, ImmutableArray<AdditionalText>.Empty);
+            driver = driver.RunFullGeneration(compilation, out var outputCompilation, out var outputDiagnostics);
+            var results = driver.GetRunResult();
+
+            Assert.Single(results.GeneratedTrees);
+            Assert.Single(results.Diagnostics);
+            Assert.Equal(2, results.Results.Length);
+
+            Assert.Single(results.Results[0].Diagnostics);
+            Assert.NotNull(results.Results[0].Exception);
+            Assert.Equal("Test Exception", results.Results[0].Exception?.Message);
+
+            Assert.Empty(results.Results[1].Diagnostics);
+
+            var testReceiver = (TestSyntaxReceiver)receiver!;
+            Assert.Equal(1, testReceiver.Tag);
+            Assert.Equal(21, testReceiver.VisitedNodes.Count);
+
+            outputDiagnostics.Verify(
+                Diagnostic(ErrorCode.WRN_GeneratorFailedDuringGeneration).WithArguments("CallbackGenerator").WithLocation(1, 1)
+                );
+        }
+
+        [Fact]
+        public void Syntax_Receiver_Is_Not_Created_If_Exception_During_Initialize()
+        {
+            var source = @"
+class C 
+{
+    int Property { get; set; }
+
+    void Function()
+    {
+        var x = 5;
+        x += 4;
+    }
+}
+";
+            var parseOptions = TestOptions.Regular;
+            Compilation compilation = CreateCompilation(source, options: TestOptions.DebugDll, parseOptions: parseOptions);
+            compilation.VerifyDiagnostics();
+
+            Assert.Single(compilation.SyntaxTrees);
+
+            TestSyntaxReceiver? receiver = null;
+            var testGenerator = new CallbackGenerator(
+                onInit: (i) => { i.RegisterForSyntaxNotifications(() => receiver = new TestSyntaxReceiver()); throw new Exception("test exception"); },
+                onExecute: (e) => { Assert.True(false); }
+                );
+
+            GeneratorDriver driver = new CSharpGeneratorDriver(parseOptions, ImmutableArray.Create<ISourceGenerator>(testGenerator), CompilerAnalyzerConfigOptionsProvider.Empty, ImmutableArray<AdditionalText>.Empty);
+            driver = driver.RunFullGeneration(compilation, out var outputCompilation, out var outputDiagnostics);
+            var results = driver.GetRunResult();
+
+            Assert.Null(receiver);
+
+            outputDiagnostics.Verify(
+                Diagnostic(ErrorCode.WRN_GeneratorFailedDuringInitialization).WithArguments("CallbackGenerator").WithLocation(1, 1)
+                );
+        }
 
         class TestSyntaxReceiver : ISyntaxReceiver
         {
+            private readonly Action<SyntaxNode>? _callback;
+
             public List<SyntaxNode> VisitedNodes { get; } = new List<SyntaxNode>();
 
             public int Tag { get; }
 
-            public TestSyntaxReceiver(int tag = 0)
+            public TestSyntaxReceiver(int tag = 0, Action<SyntaxNode>? callback = null)
             {
                 Tag = tag;
+                _callback = callback;
             }
 
             public void OnVisitSyntaxNode(SyntaxNode syntaxNode)
             {
                 VisitedNodes.Add(syntaxNode);
+                if (_callback is object)
+                {
+                    _callback(syntaxNode);
+                }
             }
         }
     }

src/Compilers/Core/Portable/PublicAPI.Unshipped.txt

@@ -9,10 +9,14 @@ Microsoft.CodeAnalysis.Diagnostics.CompilationWithAnalyzers.GetAnalysisResultAsy
 Microsoft.CodeAnalysis.Diagnostics.CompilationWithAnalyzers.GetAnalysisResultAsync(Microsoft.CodeAnalysis.AdditionalText file, System.Threading.CancellationToken cancellationToken) -> System.Threading.Tasks.Task<Microsoft.CodeAnalysis.Diagnostics.AnalysisResult>
 Microsoft.CodeAnalysis.Diagnostics.Telemetry.AnalyzerTelemetryInfo.AdditionalFileActionsCount.get -> int
 Microsoft.CodeAnalysis.Diagnostics.Telemetry.AnalyzerTelemetryInfo.AdditionalFileActionsCount.set -> void
+Microsoft.CodeAnalysis.GeneratorDriverRunResult.Diagnostics.get -> System.Collections.Immutable.ImmutableArray<Microsoft.CodeAnalysis.Diagnostic>
+Microsoft.CodeAnalysis.GeneratorDriverRunResult.GeneratedTrees.get -> System.Collections.Immutable.ImmutableArray<Microsoft.CodeAnalysis.SyntaxTree>
+Microsoft.CodeAnalysis.GeneratorDriverRunResult.Results.get -> System.Collections.Immutable.ImmutableArray<Microsoft.CodeAnalysis.GeneratorRunResult>
 Microsoft.CodeAnalysis.SyntaxTreeOptionsProvider
 Microsoft.CodeAnalysis.SyntaxTreeOptionsProvider.SyntaxTreeOptionsProvider() -> void
 abstract Microsoft.CodeAnalysis.SyntaxTreeOptionsProvider.IsGenerated(Microsoft.CodeAnalysis.SyntaxTree tree) -> bool?
 abstract Microsoft.CodeAnalysis.SyntaxTreeOptionsProvider.TryGetDiagnosticValue(Microsoft.CodeAnalysis.SyntaxTree tree, string diagnosticId, out Microsoft.CodeAnalysis.ReportDiagnostic severity) -> bool
+Microsoft.CodeAnalysis.GeneratorRunResult.GeneratedSources.get -> System.Collections.Immutable.ImmutableArray<Microsoft.CodeAnalysis.GeneratedSourceResult>
 const Microsoft.CodeAnalysis.WellKnownMemberNames.TopLevelStatementsEntryPointMethodName = "<Main>$" -> string
 const Microsoft.CodeAnalysis.WellKnownMemberNames.TopLevelStatementsEntryPointTypeName = "<Program>$" -> string
 Microsoft.CodeAnalysis.CompilationOptions.SyntaxTreeOptionsProvider.get -> Microsoft.CodeAnalysis.SyntaxTreeOptionsProvider
@@ -20,3 +24,14 @@ Microsoft.CodeAnalysis.CompilationOptions.WithSyntaxTreeOptionsProvider(Microsof
 Microsoft.CodeAnalysis.Operations.IPatternOperation.NarrowedType.get -> Microsoft.CodeAnalysis.ITypeSymbol
 virtual Microsoft.CodeAnalysis.Diagnostics.AnalysisContext.RegisterAdditionalFileAction(System.Action<Microsoft.CodeAnalysis.Diagnostics.AdditionalFileAnalysisContext> action) -> void
 virtual Microsoft.CodeAnalysis.Diagnostics.CompilationStartAnalysisContext.RegisterAdditionalFileAction(System.Action<Microsoft.CodeAnalysis.Diagnostics.AdditionalFileAnalysisContext> action) -> void
+Microsoft.CodeAnalysis.GeneratedSourceResult
+Microsoft.CodeAnalysis.GeneratedSourceResult.HintName.get -> string
+Microsoft.CodeAnalysis.GeneratedSourceResult.SourceText.get -> Microsoft.CodeAnalysis.Text.SourceText
+Microsoft.CodeAnalysis.GeneratedSourceResult.SyntaxTree.get -> Microsoft.CodeAnalysis.SyntaxTree
+Microsoft.CodeAnalysis.GeneratorDriver.GetRunResult() -> Microsoft.CodeAnalysis.GeneratorDriverRunResult
+Microsoft.CodeAnalysis.GeneratorDriver.RunGenerators(Microsoft.CodeAnalysis.Compilation compilation, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> Microsoft.CodeAnalysis.GeneratorDriver
+Microsoft.CodeAnalysis.GeneratorDriverRunResult
+Microsoft.CodeAnalysis.GeneratorRunResult
+Microsoft.CodeAnalysis.GeneratorRunResult.Diagnostics.get -> System.Collections.Immutable.ImmutableArray<Microsoft.CodeAnalysis.Diagnostic>
+Microsoft.CodeAnalysis.GeneratorRunResult.Exception.get -> System.Exception
+Microsoft.CodeAnalysis.GeneratorRunResult.Generator.get -> Microsoft.CodeAnalysis.ISourceGenerator
\ No newline at end of file

src/Compilers/Core/Portable/SourceGeneration/GeneratorDriver.cs

@@ -9,7 +9,6 @@
 using System.Threading;
 using Microsoft.CodeAnalysis.Diagnostics;
 using Microsoft.CodeAnalysis.PooledObjects;
-using Roslyn.Utilities;
 
 #nullable enable
 namespace Microsoft.CodeAnalysis
@@ -46,80 +45,19 @@ internal GeneratorDriver(ParseOptions parseOptions, ImmutableArray<ISourceGenera
             _state = new GeneratorDriverState(parseOptions, optionsProvider, generators, additionalTexts, ImmutableArray.Create(new GeneratorState[generators.Length]), ImmutableArray<PendingEdit>.Empty, editsFailed: true);
         }
 
-        public GeneratorDriver RunFullGeneration(Compilation compilation, out Compilation outputCompilation, out ImmutableArray<Diagnostic> diagnostics, CancellationToken cancellationToken = default)
+        public GeneratorDriver RunGenerators(Compilation compilation, CancellationToken cancellationToken = default)
         {
-            // with no generators, there is no work to do
-            if (_state.Generators.Length == 0)
-            {
-                outputCompilation = compilation;
-                diagnostics = ImmutableArray<Diagnostic>.Empty;
-                return this;
-            }
-
-            // run the actual generation
-            var state = StateWithPendingEditsApplied(_state);
-            var stateBuilder = ArrayBuilder<GeneratorState>.GetInstance();
-            var receivers = PooledDictionary<ISourceGenerator, ISyntaxReceiver>.GetInstance();
-            var diagnosticsBag = new DiagnosticBag();
-
-            for (int i = 0; i < state.Generators.Length; i++)
-            {
-                var generator = state.Generators[i];
-                var generatorState = state.GeneratorStates[i];
-
-                // initialize the generator if needed
-                if (!generatorState.Info.Initialized)
-                {
-                    generatorState = InitializeGenerator(generator, diagnosticsBag, cancellationToken);
-                }
-                stateBuilder.Add(generatorState);
-
-                // create the syntax receiver if requested
-                if (generatorState.Info.SyntaxReceiverCreator is object)
-                {
-                    var rx = generatorState.Info.SyntaxReceiverCreator();
-                    receivers.Add(generator, rx);
-                }
-            }
-
-            // Run a syntax walk if any of the generators requested it
-            if (receivers.Count > 0)
-            {
-                GeneratorSyntaxWalker walker = new GeneratorSyntaxWalker(receivers.Values.ToImmutableArray());
-                foreach (var syntaxTree in compilation.SyntaxTrees)
-                {
-                    walker.Visit(syntaxTree.GetRoot(cancellationToken));
-                }
-            }
-
-            // https://github.com/dotnet/roslyn/issues/42629: should be possible to parallelize this
-            for (int i = 0; i < state.Generators.Length; i++)
-            {
-                var generator = state.Generators[i];
-                var generatorState = stateBuilder[i];
-                try
-                {
-                    // don't try and generate if initialization failed
-                    if (!generatorState.Info.Initialized)
-                    {
-                        continue;
-                    }
+            var state = RunGeneratorsCore(compilation, diagnosticsBag: null, cancellationToken); //don't directly collect diagnostics on this path
+            return FromState(state);
+        }
 
-                    // we create a new context for each run of the generator. We'll never re-use existing state, only replace anything we have
-                    _ = receivers.TryGetValue(generator, out var syntaxReceiverOpt);
-                    var context = new SourceGeneratorContext(compilation, state.AdditionalTexts.NullToEmpty(), state.OptionsProvider, syntaxReceiverOpt, diagnosticsBag);
-                    generator.Execute(context);
-                    stateBuilder[i] = generatorState.WithSources(ParseAdditionalSources(generator, context.AdditionalSources.ToImmutableAndFree(), cancellationToken));
-                }
-                catch
-                {
-                    diagnosticsBag.Add(Diagnostic.Create(MessageProvider, MessageProvider.WRN_GeneratorFailedDuringGeneration, generator.GetType().Name));
-                }
-            }
-            state = state.With(generatorStates: stateBuilder.ToImmutableAndFree());
-            diagnostics = diagnosticsBag.ToReadOnlyAndFree();
+        public GeneratorDriver RunFullGeneration(Compilation compilation, out Compilation outputCompilation, out ImmutableArray<Diagnostic> diagnostics, CancellationToken cancellationToken = default)
+        {
+            var diagnosticsBag = DiagnosticBag.GetInstance();
+            var state = RunGeneratorsCore(compilation, diagnosticsBag, cancellationToken);
 
             // build the final state, and return 
+            diagnostics = diagnosticsBag.ToReadOnlyAndFree();
             return BuildFinalCompilation(compilation, out outputCompilation, state, cancellationToken);
         }
 
@@ -183,6 +121,138 @@ public GeneratorDriver AddAdditionalTexts(ImmutableArray<AdditionalText> additio
             return FromState(newState);
         }
 
+        public GeneratorDriverRunResult GetRunResult()
+        {
+            var results = _state.Generators.ZipAsArray(
+                            _state.GeneratorStates,
+                            (generator, generatorState)
+                                => new GeneratorRunResult(generator,
+                                                          diagnostics: generatorState.Diagnostics,
+                                                          exception: generatorState.Exception,
+                                                          generatedSources: generatorState.SourceTexts.ZipAsArray(
+                                                                                generatorState.Trees,
+                                                                                (sourceText, tree) => new GeneratedSourceResult(tree, sourceText.Text, sourceText.HintName))));
+            return new GeneratorDriverRunResult(results);
+        }
+
+        internal GeneratorDriverState RunGeneratorsCore(Compilation compilation, DiagnosticBag? diagnosticsBag, CancellationToken cancellationToken = default)
+        {
+            // with no generators, there is no work to do
+            if (_state.Generators.IsEmpty)
+            {
+                return _state;
+            }
+
+            // run the actual generation
+            var state = StateWithPendingEditsApplied(_state);
+            var stateBuilder = ArrayBuilder<GeneratorState>.GetInstance(state.Generators.Length);
+            var walkerBuilder = ArrayBuilder<GeneratorSyntaxWalker?>.GetInstance(state.Generators.Length, fillWithValue: null); // we know there is at max 1 per generator
+            int receiverCount = 0;
+
+            for (int i = 0; i < state.Generators.Length; i++)
+            {
+                var generator = state.Generators[i];
+                var generatorState = state.GeneratorStates[i];
+
+                // initialize the generator if needed
+                if (!generatorState.Info.Initialized)
+                {
+                    InitializationContext context = new InitializationContext(cancellationToken);
+                    Exception? ex = null;
+                    try
+                    {
+                        generator.Initialize(context);
+                    }
+                    catch (Exception e)
+                    {
+                        ex = e;
+                    }
+                    generatorState = ex is null
+                                     ? new GeneratorState(context.InfoBuilder.ToImmutable())
+                                     : SetGeneratorException(MessageProvider, GeneratorState.Uninitialized, generator, ex, diagnosticsBag, isInit: true);
+                }
+
+                // create the syntax receiver if requested
+                if (generatorState.Info.SyntaxReceiverCreator is object)
+                {
+                    try
+                    {
+                        var rx = generatorState.Info.SyntaxReceiverCreator();
+                        walkerBuilder.SetItem(i, new GeneratorSyntaxWalker(rx));
+                        generatorState = generatorState.WithReceiver(rx);
+                        receiverCount++;
+                    }
+                    catch (Exception e)
+                    {
+                        generatorState = SetGeneratorException(MessageProvider, generatorState, generator, e, diagnosticsBag);
+                    }
+                }
+
+                stateBuilder.Add(generatorState);
+            }
+
+
+            // Run a syntax walk if any of the generators requested it
+            if (receiverCount > 0)
+            {
+                foreach (var tree in compilation.SyntaxTrees)
+                {
+                    var root = tree.GetRoot(cancellationToken);
+
+                    // https://github.com/dotnet/roslyn/issues/42629: should be possible to parallelize this
+                    for (int i = 0; i < walkerBuilder.Count; i++)
+                    {
+                        var walker = walkerBuilder[i];
+                        if (walker is object)
+                        {
+                            try
+                            {
+                                walker.Visit(root);
+                            }
+                            catch (Exception e)
+                            {
+                                stateBuilder[i] = SetGeneratorException(MessageProvider, stateBuilder[i], state.Generators[i], e, diagnosticsBag);
+                                walkerBuilder.SetItem(i, null); // don't re-visit this walker for any other trees
+                            }
+                        }
+                    }
+                }
+            }
+            walkerBuilder.Free();
+
+            // https://github.com/dotnet/roslyn/issues/42629: should be possible to parallelize this
+            for (int i = 0; i < state.Generators.Length; i++)
+            {
+                var generator = state.Generators[i];
+                var generatorState = stateBuilder[i];
+
+                // don't try and generate if initialization or syntax walk failed
+                if (generatorState.Exception is object)
+                {
+                    continue;
+                }
+                Debug.Assert(generatorState.Info.Initialized);
+
+                // we create a new context for each run of the generator. We'll never re-use existing state, only replace anything we have 
+                var context = new SourceGeneratorContext(compilation, state.AdditionalTexts.NullToEmpty(), state.OptionsProvider, generatorState.SyntaxReceiver);
+                try
+                {
+                    generator.Execute(context);
+                }
+                catch (Exception e)
+                {
+                    stateBuilder[i] = SetGeneratorException(MessageProvider, generatorState, generator, e, diagnosticsBag);
+                    continue;
+                }
+
+                (var sources, var diagnostics) = context.ToImmutableAndFree();
+                stateBuilder[i] = new GeneratorState(generatorState.Info, sources, ParseAdditionalSources(generator, sources, cancellationToken), diagnostics);
+                diagnosticsBag?.AddRange(diagnostics);
+            }
+            state = state.With(generatorStates: stateBuilder.ToImmutableAndFree());
+            return state;
+        }
+
         // When we expose this publicly, remove arbitrary edit adding and replace with dedicated edit types
         internal GeneratorDriver WithPendingEdits(ImmutableArray<PendingEdit> edits)
         {
@@ -203,7 +273,7 @@ private GeneratorDriverState ApplyPartialEdit(GeneratorDriverState state, Pendin
                 if (edit.AcceptedBy(generatorState.Info))
                 {
                     // attempt to apply the edit
-                    var context = new EditContext(generatorState.Sources.Keys.ToImmutableArray(), cancellationToken);
+                    var context = new EditContext(generatorState.SourceTexts.ToImmutableArray(), cancellationToken);
                     var succeeded = edit.TryApply(generatorState.Info, context);
                     if (!succeeded)
                     {
@@ -213,7 +283,8 @@ private GeneratorDriverState ApplyPartialEdit(GeneratorDriverState state, Pendin
                     }
 
                     // update the state with the new edits
-                    state = state.With(generatorStates: state.GeneratorStates.SetItem(i, generatorState.WithSources(ParseAdditionalSources(generator, context.AdditionalSources.ToImmutableAndFree(), cancellationToken))));
+                    var additionalSources = context.AdditionalSources.ToImmutableAndFree();
+                    state = state.With(generatorStates: state.GeneratorStates.SetItem(i, new GeneratorState(generatorState.Info, sourceTexts: additionalSources, trees: ParseAdditionalSources(generator, additionalSources, cancellationToken), diagnostics: ImmutableArray<Diagnostic>.Empty)));
                 }
             }
             state = edit.Commit(state);
@@ -234,28 +305,12 @@ private static GeneratorDriverState StateWithPendingEditsApplied(GeneratorDriver
             return state.With(edits: ImmutableArray<PendingEdit>.Empty, editsFailed: false);
         }
 
-        private GeneratorState InitializeGenerator(ISourceGenerator generator, DiagnosticBag diagnostics, CancellationToken cancellationToken)
-        {
-            GeneratorInfo info = default;
-            try
-            {
-                InitializationContext context = new InitializationContext(cancellationToken);
-                generator.Initialize(context);
-                info = context.InfoBuilder.ToImmutable();
-            }
-            catch
-            {
-                diagnostics.Add(Diagnostic.Create(MessageProvider, MessageProvider.WRN_GeneratorFailedDuringInitialization, generator.GetType().Name));
-            }
-            return new GeneratorState(info);
-        }
-
         private static Compilation RemoveGeneratedSyntaxTrees(GeneratorDriverState state, Compilation compilation)
         {
             ArrayBuilder<SyntaxTree> trees = ArrayBuilder<SyntaxTree>.GetInstance();
             foreach (var generatorState in state.GeneratorStates)
             {
-                foreach (var (_, tree) in generatorState.Sources)
+                foreach (var tree in generatorState.Trees)
                 {
                     if (tree is object && compilation.ContainsSyntaxTree(tree))
                     {
@@ -269,16 +324,16 @@ private static Compilation RemoveGeneratedSyntaxTrees(GeneratorDriverState state
             return comp;
         }
 
-        private ImmutableDictionary<GeneratedSourceText, SyntaxTree> ParseAdditionalSources(ISourceGenerator generator, ImmutableArray<GeneratedSourceText> generatedSources, CancellationToken cancellationToken)
+        private ImmutableArray<SyntaxTree> ParseAdditionalSources(ISourceGenerator generator, ImmutableArray<GeneratedSourceText> generatedSources, CancellationToken cancellationToken)
         {
-            var trees = PooledDictionary<GeneratedSourceText, SyntaxTree>.GetInstance();
+            var trees = ArrayBuilder<SyntaxTree>.GetInstance(generatedSources.Length);
             var type = generator.GetType();
             var prefix = $"{type.Module.ModuleVersionId}_{type.FullName}";
             foreach (var source in generatedSources)
             {
-                trees.Add(source, ParseGeneratedSourceText(source, $"{prefix}_{source.HintName}", cancellationToken));
+                trees.Add(ParseGeneratedSourceText(source, $"{prefix}_{source.HintName}", cancellationToken));
             }
-            return trees.ToImmutableDictionaryAndFree();
+            return trees.ToImmutableAndFree();
         }
 
         private GeneratorDriver BuildFinalCompilation(Compilation compilation, out Compilation outputCompilation, GeneratorDriverState state, CancellationToken cancellationToken)
@@ -286,7 +341,7 @@ private GeneratorDriver BuildFinalCompilation(Compilation compilation, out Compi
             ArrayBuilder<SyntaxTree> trees = ArrayBuilder<SyntaxTree>.GetInstance();
             foreach (var generatorState in state.GeneratorStates)
             {
-                trees.AddRange(generatorState.Sources.Values);
+                trees.AddRange(generatorState.Trees);
             }
             outputCompilation = compilation.AddSyntaxTrees(trees);
             trees.Free();
@@ -296,6 +351,14 @@ private GeneratorDriver BuildFinalCompilation(Compilation compilation, out Compi
             return FromState(state);
         }
 
+        private static GeneratorState SetGeneratorException(CommonMessageProvider provider, GeneratorState generatorState, ISourceGenerator generator, Exception e, DiagnosticBag? diagnosticBag, bool isInit = false)
+        {
+            var message = isInit ? provider.WRN_GeneratorFailedDuringInitialization : provider.WRN_GeneratorFailedDuringGeneration;
+            var diagnostic = Diagnostic.Create(provider, message, generator.GetType().Name);
+            diagnosticBag?.Add(diagnostic);
+            return new GeneratorState(generatorState.Info, e, diagnostic);
+        }
+
         internal abstract CommonMessageProvider MessageProvider { get; }
 
         internal abstract GeneratorDriver FromState(GeneratorDriverState state);

src/Compilers/Core/Portable/SourceGeneration/GeneratorState.cs

@@ -2,31 +2,81 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using System.Collections.Immutable;
+using System.Diagnostics;
 
 #nullable enable
 namespace Microsoft.CodeAnalysis
 {
+    /// <summary>
+    /// Represents the current state of a generator
+    /// </summary>
     internal readonly struct GeneratorState
     {
+        /// <summary>
+        /// Gets an uninitalized generator state
+        /// </summary>
+        internal static GeneratorState Uninitialized;
+
+        /// <summary>
+        /// Creates a new generator state that just contains information
+        /// </summary>
         public GeneratorState(GeneratorInfo info)
-            : this(info, ImmutableDictionary<GeneratedSourceText, SyntaxTree>.Empty)
+            : this(info, ImmutableArray<GeneratedSourceText>.Empty, ImmutableArray<SyntaxTree>.Empty, ImmutableArray<Diagnostic>.Empty, syntaxReceiver: null, exception: null)
+        {
+        }
+
+        /// <summary>
+        /// Creates a new generator state that contains an exception and the associated diagnostic
+        /// </summary>
+        public GeneratorState(GeneratorInfo info, Exception e, Diagnostic error)
+            : this(info, ImmutableArray<GeneratedSourceText>.Empty, ImmutableArray<SyntaxTree>.Empty, ImmutableArray.Create(error), syntaxReceiver: null, exception: e)
         {
         }
 
-        private GeneratorState(GeneratorInfo info, ImmutableDictionary<GeneratedSourceText, SyntaxTree> sources)
+        /// <summary>
+        /// Creates a generator state that contains results
+        /// </summary>
+        public GeneratorState(GeneratorInfo info, ImmutableArray<GeneratedSourceText> sourceTexts, ImmutableArray<SyntaxTree> trees, ImmutableArray<Diagnostic> diagnostics)
+            : this(info, sourceTexts, trees, diagnostics, syntaxReceiver: null, exception: null)
         {
-            this.Sources = sources;
+        }
+
+        private GeneratorState(GeneratorInfo info, ImmutableArray<GeneratedSourceText> sourceTexts, ImmutableArray<SyntaxTree> trees, ImmutableArray<Diagnostic> diagnostics, ISyntaxReceiver? syntaxReceiver, Exception? exception)
+        {
+            this.SourceTexts = sourceTexts;
+            this.Trees = trees;
             this.Info = info;
+            this.Diagnostics = diagnostics;
+            this.SyntaxReceiver = syntaxReceiver;
+            this.Exception = exception;
         }
 
-        internal ImmutableDictionary<GeneratedSourceText, SyntaxTree> Sources { get; }
+        internal ImmutableArray<GeneratedSourceText> SourceTexts { get; }
+
+        internal ImmutableArray<SyntaxTree> Trees { get; }
 
         internal GeneratorInfo Info { get; }
 
-        internal GeneratorState WithSources(ImmutableDictionary<GeneratedSourceText, SyntaxTree> sources)
+        internal ISyntaxReceiver? SyntaxReceiver { get; }
+
+        internal Exception? Exception { get; }
+
+        internal ImmutableArray<Diagnostic> Diagnostics { get; }
+
+        /// <summary>
+        /// Adds an <see cref="ISyntaxReceiver"/> to this generator state
+        /// </summary>
+        internal GeneratorState WithReceiver(ISyntaxReceiver syntaxReceiver)
         {
-            return new GeneratorState(this.Info, sources);
+            Debug.Assert(this.Exception is null);
+            return new GeneratorState(this.Info,
+                                      sourceTexts: this.SourceTexts,
+                                      trees: this.Trees,
+                                      diagnostics: this.Diagnostics,
+                                      syntaxReceiver: syntaxReceiver,
+                                      exception: null);
         }
     }
 }

src/Compilers/Core/Portable/SourceGeneration/GeneratorSyntaxWalker.cs

@@ -2,28 +2,22 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-using System.Collections.Immutable;
-
 #nullable enable
 namespace Microsoft.CodeAnalysis
 {
     internal sealed class GeneratorSyntaxWalker : SyntaxWalker
     {
-        private readonly ImmutableArray<ISyntaxReceiver> _syntaxReceivers;
+        private readonly ISyntaxReceiver _syntaxReceiver;
 
-        public GeneratorSyntaxWalker(ImmutableArray<ISyntaxReceiver> syntaxReceivers)
+        internal GeneratorSyntaxWalker(ISyntaxReceiver syntaxReceiver)
         {
-            _syntaxReceivers = syntaxReceivers;
+            _syntaxReceiver = syntaxReceiver;
         }
 
         public override void Visit(SyntaxNode node)
         {
-            foreach (var receiver in _syntaxReceivers)
-            {
-                receiver.OnVisitSyntaxNode(node);
-            }
+            _syntaxReceiver.OnVisitSyntaxNode(node);
             base.Visit(node);
         }
     }
-
 }

src/Compilers/Core/Portable/SourceGeneration/RunResults.cs

+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Immutable;
+using System.Diagnostics;
+using System.Linq;
+using System.Threading;
+using Microsoft.CodeAnalysis.Text;
+
+#nullable enable
+
+namespace Microsoft.CodeAnalysis
+{
+    /// <summary>
+    /// Represents the results of running a generation pass over a set of <see cref="ISourceGenerator"/>s.
+    /// </summary>
+    public class GeneratorDriverRunResult
+    {
+        private ImmutableArray<Diagnostic> _lazyDiagnostics;
+
+        private ImmutableArray<SyntaxTree> _lazyGeneratedTrees;
+
+        internal GeneratorDriverRunResult(ImmutableArray<GeneratorRunResult> results)
+        {
+            this.Results = results;
+        }
+
+        /// <summary>
+        /// The individual result of each <see cref="ISourceGenerator"/> that was run in this generator pass, one per generator.
+        /// </summary>
+        public ImmutableArray<GeneratorRunResult> Results { get; }
+
+        /// <summary>
+        /// The <see cref="Diagnostic"/>s produced by all generators run during this generation pass.
+        /// </summary>
+        /// <remarks>
+        /// This is equivalent to the union of all <see cref="GeneratorRunResult.Diagnostics"/> in <see cref="Results"/>.
+        /// </remarks>
+        public ImmutableArray<Diagnostic> Diagnostics
+        {
+            get
+            {
+                if (_lazyDiagnostics.IsDefault)
+                {
+                    ImmutableInterlocked.InterlockedInitialize(ref _lazyDiagnostics, Results.SelectMany(r => r.Diagnostics).ToImmutableArray());
+                }
+                return _lazyDiagnostics;
+            }
+        }
+
+        /// <summary>
+        /// The <see cref="SyntaxTree"/>s produced during this generation pass by parsing each <see cref="SourceText"/> added by each generator.
+        /// </summary>
+        /// <remarks>
+        /// This is equivalent to the union of all <see cref="GeneratedSourceResult.SyntaxTree"/>s in each <see cref="GeneratorRunResult.GeneratedSources"/> in each <see cref="Results"/>
+        /// </remarks>
+        public ImmutableArray<SyntaxTree> GeneratedTrees
+        {
+            get
+            {
+                if (_lazyGeneratedTrees.IsDefault)
+                {
+                    ImmutableInterlocked.InterlockedInitialize(ref _lazyGeneratedTrees, Results.SelectMany(r => r.GeneratedSources.Select(g => g.SyntaxTree)).ToImmutableArray());
+                }
+                return _lazyGeneratedTrees;
+            }
+        }
+    }
+
+    /// <summary>
+    /// Represents the results of a single <see cref="ISourceGenerator"/> generation pass.
+    /// </summary>
+    public readonly struct GeneratorRunResult
+    {
+        internal GeneratorRunResult(ISourceGenerator generator, ImmutableArray<GeneratedSourceResult> generatedSources, ImmutableArray<Diagnostic> diagnostics, Exception? exception)
+        {
+            Debug.Assert(exception is null || (generatedSources.IsEmpty && diagnostics.Length == 1));
+
+            this.Generator = generator;
+            this.GeneratedSources = generatedSources;
+            this.Diagnostics = diagnostics;
+            this.Exception = exception;
+        }
+
+        /// <summary>
+        /// The <see cref="ISourceGenerator"/> that produced this result.
+        /// </summary>
+        public ISourceGenerator Generator { get; }
+
+        /// <summary>
+        /// The sources that were added by <see cref="Generator"/> during the generation pass this result represents.
+        /// </summary>
+        public ImmutableArray<GeneratedSourceResult> GeneratedSources { get; }
+
+        /// <summary>
+        /// A collection of <see cref="Diagnostic"/>s reported by <see cref="Generator"/> 
+        /// </summary>
+        /// <remarks>
+        /// When generation fails due to an <see cref="Exception"/> being thrown, a single diagnostic is added
+        /// to represent the failure. Any generator reported diagnostics up to the failure point are not included.
+        /// </remarks>
+        public ImmutableArray<Diagnostic> Diagnostics { get; }
+
+        /// <summary>
+        /// An <see cref="System.Exception"/> instance that was thrown by the generator, or <c>null</c> if the generator completed without error.
+        /// </summary>
+        /// <remarks>
+        /// When this property has a value, <see cref="GeneratedSources"/> property is guaranteed to be empty, and the <see cref="Diagnostics"/>
+        /// collection will contain a single diagnostic indicating that the generator failed.
+        /// </remarks>
+        public Exception? Exception { get; }
+    }
+
+    /// <summary>
+    /// Represents the results of an <see cref="ISourceGenerator"/> calling <see cref="SourceGeneratorContext.AddSource(string, SourceText)"/>.
+    /// </summary>
+    /// <remarks>
+    /// This contains the original <see cref="SourceText"/> added by the generator, along with the parsed representation of that text in <see cref="SyntaxTree"/>.
+    /// </remarks>
+    public readonly struct GeneratedSourceResult
+    {
+        internal GeneratedSourceResult(SyntaxTree tree, SourceText text, string hintName)
+        {
+            this.SyntaxTree = tree;
+            this.SourceText = text;
+            this.HintName = hintName;
+        }
+
+        /// <summary>
+        /// The <see cref="SyntaxTree"/> that was produced from parsing the <see cref="GeneratedSourceResult.SourceText"/>.
+        /// </summary>
+        public SyntaxTree SyntaxTree { get; }
+
+        /// <summary>
+        /// The <see cref="SourceText"/> that was added by the generator.
+        /// </summary>
+        public SourceText SourceText { get; }
+
+        /// <summary>
+        /// An identifier provided by the generator that identifies the added <see cref="SourceText"/>.
+        /// </summary>
+        public string HintName { get; }
+    }
+}

src/Compilers/Core/Portable/SourceGeneration/SourceGeneratorContext.cs

@@ -18,15 +18,17 @@ namespace Microsoft.CodeAnalysis
     {
         private readonly DiagnosticBag _diagnostics;
 
-        internal SourceGeneratorContext(Compilation compilation, ImmutableArray<AdditionalText> additionalTexts, AnalyzerConfigOptionsProvider optionsProvider, ISyntaxReceiver? syntaxReceiver, DiagnosticBag diagnostics, CancellationToken cancellationToken = default)
+        private readonly AdditionalSourcesCollection _additionalSources;
+
+        internal SourceGeneratorContext(Compilation compilation, ImmutableArray<AdditionalText> additionalTexts, AnalyzerConfigOptionsProvider optionsProvider, ISyntaxReceiver? syntaxReceiver, CancellationToken cancellationToken = default)
         {
             Compilation = compilation;
             AdditionalFiles = additionalTexts;
             AnalyzerConfigOptions = optionsProvider;
             SyntaxReceiver = syntaxReceiver;
             CancellationToken = cancellationToken;
-            AdditionalSources = new AdditionalSourcesCollection();
-            _diagnostics = diagnostics;
+            _additionalSources = new AdditionalSourcesCollection();
+            _diagnostics = new DiagnosticBag();
         }
 
         /// <summary>
@@ -59,14 +61,12 @@ internal SourceGeneratorContext(Compilation compilation, ImmutableArray<Addition
         /// </summary>
         public CancellationToken CancellationToken { get; }
 
-        internal AdditionalSourcesCollection AdditionalSources { get; }
-
         /// <summary>
         /// Adds a <see cref="SourceText"/> to the compilation
         /// </summary>
         /// <param name="hintName">An identifier that can be used to reference this source text, must be unique within this generator</param>
         /// <param name="sourceText">The <see cref="SourceText"/> to add to the compilation</param>
-        public void AddSource(string hintName, SourceText sourceText) => AdditionalSources.Add(hintName, sourceText);
+        public void AddSource(string hintName, SourceText sourceText) => _additionalSources.Add(hintName, sourceText);
 
         /// <summary>
         /// Adds a <see cref="Diagnostic"/> to the users compilation 
@@ -76,6 +76,9 @@ internal SourceGeneratorContext(Compilation compilation, ImmutableArray<Addition
         /// The severity of the diagnostic may cause the compilation to fail, depending on the <see cref="Compilation"/> settings.
         /// </remarks>
         public void ReportDiagnostic(Diagnostic diagnostic) => _diagnostics.Add(diagnostic);
+
+        internal (ImmutableArray<GeneratedSourceText> sources, ImmutableArray<Diagnostic> diagnostics) ToImmutableAndFree()
+            => (_additionalSources.ToImmutableAndFree(), _diagnostics.ToReadOnlyAndFree());
     }
 
     /// <summary>

src/Test/Utilities/Portable/SourceGeneration/TestGenerators.cs

@@ -26,7 +26,7 @@ public SingleFileTestGenerator(string content, string hintName = "generatedFile"
 
         public void Execute(SourceGeneratorContext context)
         {
-            context.AdditionalSources.Add(this._hintName, SourceText.From(_content, Encoding.UTF8));
+            context.AddSource(this._hintName, SourceText.From(_content, Encoding.UTF8));
         }
 
         public void Initialize(InitializationContext context)
@@ -59,7 +59,7 @@ public void Execute(SourceGeneratorContext context)
             _onExecute(context);
             if (!string.IsNullOrWhiteSpace(_source))
             {
-                context.AdditionalSources.Add("source.cs", SourceText.From(_source, Encoding.UTF8));
+                context.AddSource("source.cs", SourceText.From(_source, Encoding.UTF8));
             }
         }
         public void Initialize(InitializationContext context) => _onInit(context);
@@ -80,7 +80,7 @@ public void Execute(SourceGeneratorContext context)
         {
             foreach (var file in context.AdditionalFiles)
             {
-                AddSourceForAdditionalFile(context.AdditionalSources, file);
+                context.AddSource(GetGeneratedFileName(file.Path), SourceText.From("", Encoding.UTF8));
             }
         }
 
@@ -93,14 +93,12 @@ bool UpdateContext(EditContext context, AdditionalFileEdit edit)
         {
             if (edit is AdditionalFileAddedEdit add && CanApplyChanges)
             {
-                AddSourceForAdditionalFile(context.AdditionalSources, add.AddedText);
+                context.AdditionalSources.Add(GetGeneratedFileName(add.AddedText.Path), SourceText.From("", Encoding.UTF8));
                 return true;
             }
             return false;
         }
 
-        private void AddSourceForAdditionalFile(AdditionalSourcesCollection sources, AdditionalText file) => sources.Add(GetGeneratedFileName(file.Path), SourceText.From("", Encoding.UTF8));
-
         private string GetGeneratedFileName(string path) => $"{Path.GetFileNameWithoutExtension(path.Replace('\\', Path.DirectorySeparatorChar))}.generated";
     }