Store and display the times when files were generated.

src/VisualStudio/Core/Def/ServicesVSResources.resx

@@ -1382,8 +1382,8 @@ Additional information: {1}</value>
   <data name="Extract_Base_Class" xml:space="preserve">
     <value>Extract Base Class</value>
   </data>
-  <data name="This_file_is_autogenerated_by_0_and_cannot_be_edited" xml:space="preserve">
-    <value>This file is auto-generated by the generator '{0}' and cannot be edited.</value>
+  <data name="This_file_was_generated_by_0_at_1_and_cannot_be_edited" xml:space="preserve">
+    <value>This file was generated by '{0}' at {1} and cannot be edited.</value>
   </data>
   <data name="generated_by_0_suffix" xml:space="preserve">
     <value>[generated by {0}]</value>

src/VisualStudio/Core/Def/Workspace/SourceGeneratedFileManager.cs

@@ -346,7 +346,10 @@ public async ValueTask RefreshFileAsync(CancellationToken cancellationToken)
                 generatedDocument = await project.GetSourceGeneratedDocumentAsync(_documentIdentity.DocumentId, cancellationToken).ConfigureAwait(false);
                 if (generatedDocument != null)
                 {
-                    windowFrameMessageToShow = string.Format(ServicesVSResources.This_file_is_autogenerated_by_0_and_cannot_be_edited, GeneratorDisplayName);
+                    windowFrameMessageToShow = string.Format(
+                        ServicesVSResources.This_file_was_generated_by_0_at_1_and_cannot_be_edited,
+                        GeneratorDisplayName,
+                        generatedDocument.GenerationDateTime.ToLocalTime());
                     windowFrameImageMonikerToShow = default;
                     generatedSource = await generatedDocument.GetValueTextAsync(cancellationToken).ConfigureAwait(false);
                 }

src/VisualStudio/Core/Test.Next/Services/SolutionServiceTests.cs

@@ -448,7 +448,7 @@ public async Task TestFrozenSourceGeneratedDocument()
             // Now freeze with some content
             var documentIdentity = (await solution.Projects.Single().GetSourceGeneratedDocumentsAsync()).First().Identity;
             var frozenText1 = SourceText.From("// Hello, World!");
-            var frozenSolution1 = solution.WithFrozenSourceGeneratedDocument(documentIdentity, frozenText1).Project.Solution;
+            var frozenSolution1 = solution.WithFrozenSourceGeneratedDocument(documentIdentity, DateTime.Now, frozenText1).Project.Solution;
 
             assetProvider = await GetAssetProviderAsync(workspace, remoteWorkspace, frozenSolution1);
             solutionChecksum = await frozenSolution1.CompilationState.GetChecksumAsync(CancellationToken.None);
@@ -457,7 +457,7 @@ public async Task TestFrozenSourceGeneratedDocument()
 
             // Try freezing with some different content from the original solution
             var frozenText2 = SourceText.From("// Hello, World! A second time!");
-            var frozenSolution2 = solution.WithFrozenSourceGeneratedDocument(documentIdentity, frozenText2).Project.Solution;
+            var frozenSolution2 = solution.WithFrozenSourceGeneratedDocument(documentIdentity, DateTime.Now, frozenText2).Project.Solution;
 
             assetProvider = await GetAssetProviderAsync(workspace, remoteWorkspace, frozenSolution2);
             solutionChecksum = await frozenSolution2.CompilationState.GetChecksumAsync(CancellationToken.None);

src/Workspaces/Core/Portable/SourceGeneration/IRemoteSourceGenerationService.cs

@@ -2,11 +2,12 @@
 // 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.Runtime.Serialization;
+using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
-using System.Text;
 using Microsoft.CodeAnalysis.Text;
 
 namespace Microsoft.CodeAnalysis.SourceGeneration;
@@ -28,7 +29,7 @@ internal interface IRemoteSourceGenerationService
     /// Should only be called by the host for documents it does not know about, or documents whose checksum contents are
     /// different than the last time the document was queried.
     /// </summary>
-    ValueTask<ImmutableArray<string>> GetContentsAsync(
+    ValueTask<ImmutableArray<(string contents, DateTime generationDateTime)>> GetContentsAsync(
         Checksum solutionChecksum, ProjectId projectId, ImmutableArray<DocumentId> documentIds, CancellationToken cancellationToken);
 }
 

src/Workspaces/Core/Portable/Workspace/Solution/Solution.cs

@@ -1586,9 +1586,10 @@ public Solution WithDocumentText(IEnumerable<DocumentId?> documentIds, SourceTex
     /// implementation of <see cref="TextExtensions.GetOpenDocumentInCurrentContextWithChanges"/> where if a user has a source
     /// generated file open, we need to make sure everything lines up.
     /// </summary>
-    internal Document WithFrozenSourceGeneratedDocument(SourceGeneratedDocumentIdentity documentIdentity, SourceText text)
+    internal Document WithFrozenSourceGeneratedDocument(
+        SourceGeneratedDocumentIdentity documentIdentity, DateTime generationDateTime, SourceText text)
     {
-        var newCompilationState = _compilationState.WithFrozenSourceGeneratedDocuments([(documentIdentity, text)]);
+        var newCompilationState = _compilationState.WithFrozenSourceGeneratedDocuments([(documentIdentity, generationDateTime, text)]);
         var newSolution = newCompilationState != _compilationState
             ? new Solution(newCompilationState)
             : this;
@@ -1600,7 +1601,8 @@ internal Document WithFrozenSourceGeneratedDocument(SourceGeneratedDocumentIdent
         return newProject.GetOrCreateSourceGeneratedDocument(newDocumentState);
     }
 
-    internal Solution WithFrozenSourceGeneratedDocuments(ImmutableArray<(SourceGeneratedDocumentIdentity documentIdentity, SourceText text)> documents)
+    internal Solution WithFrozenSourceGeneratedDocuments(
+        ImmutableArray<(SourceGeneratedDocumentIdentity documentIdentity, DateTime generationDateTime, SourceText text)> documents)
     {
         var newCompilationState = _compilationState.WithFrozenSourceGeneratedDocuments(documents);
         return newCompilationState != _compilationState