Fine tuning of what types of project update affect what state (#11213)

Follow up to #11191 which caused RPS
regressions.

There were some edge-y things I papered over in that PR, assuming they
were unnecessary over-complications, but given the RPS regression I had
a closer look, and they could have caused re-compilation of closed
documents when only tag helpers changed, which would be new behaviour.
Not _entirely_ convinced the re-compilation is all unnecessary (if a
document used a Tag Helper that has only just been discovered, then its
code gen would legitimately change) but it's hard to justify when I
can't point to any tooling for the closed files that would actually
benefit from the extra work.

The key thing is not changing `DocumentCollectionVersion` when only
`ProjectWorkspaceState` changes. Not re-calculating import documents was
just a little extra amuse-bouche, and not caching the computed state
tracker is pure paranoia.

Author: davidwengier

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/ProjectSystem/DocumentState.cs

@@ -160,12 +160,14 @@ public virtual DocumentState WithImportsChange()
         return state;
     }
 
-    public virtual DocumentState WithProjectChange()
+    public virtual DocumentState WithProjectChange(bool cacheComputedState)
     {
         var state = new DocumentState(HostDocument, Version + 1, _textAndVersion, _textLoader);
 
-        // Optimistically cache the computed state
-        state._computedState = new ComputedStateTracker(_computedState);
+        if (cacheComputedState)
+        {
+            state._computedState = new ComputedStateTracker(_computedState);
+        }
 
         return state;
     }

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/ProjectSystem/ProjectState.cs

@@ -274,26 +274,36 @@ public ProjectState WithChangedHostDocument(HostDocument hostDocument, TextLoade
 
     public ProjectState WithHostProjectAndWorkspaceState(HostProject hostProject, ProjectWorkspaceState projectWorkspaceState)
     {
-        if (HostProject.Configuration.Equals(hostProject.Configuration) &&
-            HostProject.RootNamespace == hostProject.RootNamespace &&
-            ProjectWorkspaceState.Equals(projectWorkspaceState))
+        var configUnchanged = (HostProject.Configuration.Equals(hostProject.Configuration) &&
+            HostProject.RootNamespace == hostProject.RootNamespace);
+
+        if (configUnchanged && ProjectWorkspaceState.Equals(projectWorkspaceState))
         {
             return this;
         }
 
-        var documents = Documents.ToImmutableDictionary(kvp => kvp.Key, kvp => kvp.Value.WithProjectChange(), FilePathNormalizingComparer.Instance);
+        var documents = Documents.ToImmutableDictionary(kvp => kvp.Key, kvp => kvp.Value.WithProjectChange(cacheComputedState: configUnchanged), FilePathNormalizingComparer.Instance);
 
         // If the host project has changed then we need to recompute the imports map
-        var importsToRelatedDocuments = s_emptyImportsToRelatedDocuments;
+        var importsToRelatedDocuments = configUnchanged
+            ? ImportsToRelatedDocuments
+            : ComputeImportsToRelatedDocuments(documents);
+
+        var state = new ProjectState(this, numberOfDocumentsMayHaveChanged: !configUnchanged, hostProject, projectWorkspaceState, documents, importsToRelatedDocuments);
+        return state;
 
-        foreach (var document in documents)
+        ImmutableDictionary<string, ImmutableArray<string>> ComputeImportsToRelatedDocuments(ImmutableDictionary<string, DocumentState> documents)
         {
-            var importTargetPaths = GetImportDocumentTargetPaths(document.Value.HostDocument);
-            importsToRelatedDocuments = AddToImportsToRelatedDocuments(importsToRelatedDocuments, document.Value.HostDocument.FilePath, importTargetPaths);
-        }
+            var importsToRelatedDocuments = s_emptyImportsToRelatedDocuments;
 
-        var state = new ProjectState(this, numberOfDocumentsMayHaveChanged: true, hostProject, projectWorkspaceState, documents, importsToRelatedDocuments);
-        return state;
+            foreach (var document in documents)
+            {
+                var importTargetPaths = GetImportDocumentTargetPaths(document.Value.HostDocument);
+                importsToRelatedDocuments = AddToImportsToRelatedDocuments(importsToRelatedDocuments, document.Value.HostDocument.FilePath, importTargetPaths);
+            }
+
+            return importsToRelatedDocuments;
+        }
     }
 
     internal static ImmutableDictionary<string, ImmutableArray<string>> AddToImportsToRelatedDocuments(

src/Razor/test/Microsoft.CodeAnalysis.Razor.Workspaces.Test/ProjectSystem/DocumentStateTest.cs

@@ -70,7 +70,7 @@ public void DocumentState_WithProjectChange_CachesSnapshotText()
             .WithText(_text, VersionStamp.Create());
 
         // Act
-        var state = original.WithProjectChange();
+        var state = original.WithProjectChange(cacheComputedState: false);
 
         // Assert
         Assert.True(state.TryGetText(out _));
@@ -87,7 +87,7 @@ public async Task DocumentState_WithProjectChange_CachesLoadedText()
         await original.GetTextAsync(DisposalToken);
 
         // Act
-        var state = original.WithProjectChange();
+        var state = original.WithProjectChange(cacheComputedState: false);
 
         // Assert
         Assert.True(state.TryGetText(out _));

src/Razor/test/Microsoft.CodeAnalysis.Razor.Workspaces.Test/ProjectSystem/ProjectStateTest.cs

@@ -558,6 +558,7 @@ public void ProjectState_WithHostProjectAndWorkspaceState_ConfigurationChange_Up
             Assert.Same(originalTagHelpers[i], actualTagHelpers[i]);
         }
 
+        Assert.NotEqual(original.DocumentCollectionVersion, state.DocumentCollectionVersion);
         Assert.NotEqual(originalProjectWorkspaceStateVersion, actualProjectWorkspaceStateVersion);
 
         Assert.NotSame(original.Documents[_documents[1].FilePath], state.Documents[_documents[1].FilePath]);
@@ -584,6 +585,7 @@ public void ProjectState_WithHostProjectAndWorkspaceState_RootNamespaceChange_Up
 
         // Assert
         Assert.NotSame(original, state);
+        Assert.NotEqual(original.DocumentCollectionVersion, state.DocumentCollectionVersion);
     }
 
     [Fact]
@@ -602,6 +604,7 @@ public void ProjectState_WithHostProjectAndWorkspaceState_NoConfigurationChange_
 
         // Assert
         Assert.Same(original, state);
+        Assert.Equal(original.DocumentCollectionVersion, state.DocumentCollectionVersion);
     }
 
     [Fact]
@@ -623,6 +626,7 @@ public void ProjectState_WithHostProjectAndWorkspaceState_CallsConfigurationChan
         // Assert
         Assert.NotEqual(original.Version, state.Version);
         Assert.Same(_hostProjectWithConfigurationChange, state.HostProject);
+        Assert.NotEqual(original.DocumentCollectionVersion, state.DocumentCollectionVersion);
         Assert.Equal(2, callCount);
     }
 
@@ -640,6 +644,38 @@ public void ProjectState_WithHostProjectAndWorkspaceState_ResetsImportedDocument
         var importMap = Assert.Single(state.ImportsToRelatedDocuments);
         var documentFilePath = Assert.Single(importMap.Value);
         Assert.Equal(TestProjectData.SomeProjectFile1.FilePath, documentFilePath);
+        Assert.NotSame(original.ImportsToRelatedDocuments, state.ImportsToRelatedDocuments);
+        Assert.NotEqual(original.DocumentCollectionVersion, state.DocumentCollectionVersion);
+    }
+
+    [Fact]
+    public void ProjectState_WithHostProjectAndWorkspaceState_ProjectWorkspaceStateChange_CachesImportedDocuments()
+    {
+        // Arrange
+        var original = ProjectState.Create(ProjectEngineFactoryProvider, LanguageServerFeatureOptions, _hostProject, _projectWorkspaceState);
+        original = original.WithAddedHostDocument(TestProjectData.SomeProjectFile1, DocumentState.EmptyLoader);
+
+        var changed = ProjectWorkspaceState.Default;
+
+        // Act
+        var state = original.WithHostProjectAndWorkspaceState(_hostProject, changed);
+
+        // Assert
+        Assert.Same(original.ImportsToRelatedDocuments, state.ImportsToRelatedDocuments);
+    }
+
+    [Fact]
+    public void ProjectState_WithHostProjectAndWorkspaceState_HostProjectChange_DoesntCacheImportedDocuments()
+    {
+        // Arrange
+        var original = ProjectState.Create(ProjectEngineFactoryProvider, LanguageServerFeatureOptions, _hostProject, _projectWorkspaceState);
+        original = original.WithAddedHostDocument(TestProjectData.SomeProjectFile1, DocumentState.EmptyLoader);
+
+        // Act
+        var state = original.WithHostProjectAndWorkspaceState(_hostProjectWithConfigurationChange, _projectWorkspaceState);
+
+        // Assert
+        Assert.NotSame(original.ImportsToRelatedDocuments, state.ImportsToRelatedDocuments);
     }
 
     [Fact]
@@ -679,6 +715,8 @@ public void ProjectState_WithHostProjectAndWorkspaceState_Changed()
 
         Assert.NotSame(original.Documents[_documents[1].FilePath], state.Documents[_documents[1].FilePath]);
         Assert.NotSame(original.Documents[_documents[2].FilePath], state.Documents[_documents[2].FilePath]);
+
+        Assert.Equal(original.DocumentCollectionVersion, state.DocumentCollectionVersion);
     }
 
     [Fact]
@@ -713,6 +751,8 @@ public void ProjectState_WithHostProjectAndWorkspaceState_Changed_TagHelpersChan
 
         Assert.NotSame(original.Documents[_documents[1].FilePath], state.Documents[_documents[1].FilePath]);
         Assert.NotSame(original.Documents[_documents[2].FilePath], state.Documents[_documents[2].FilePath]);
+
+        Assert.Equal(original.DocumentCollectionVersion, state.DocumentCollectionVersion);
     }
 
     [Fact]
@@ -756,6 +796,7 @@ public void ProjectState_WithHostProjectAndWorkspaceState_CallsWorkspaceProjectC
 
         // Assert
         Assert.NotEqual(original.Version, state.Version);
+        Assert.Equal(original.DocumentCollectionVersion, state.DocumentCollectionVersion);
         Assert.Equal(2, callCount);
     }
 
@@ -1034,10 +1075,10 @@ public override DocumentState WithTextLoader(TextLoader loader)
             return base.WithTextLoader(loader);
         }
 
-        public override DocumentState WithProjectChange()
+        public override DocumentState WithProjectChange(bool cacheComputedState)
         {
             _onConfigurationChange?.Invoke();
-            return base.WithProjectChange();
+            return base.WithProjectChange(cacheComputedState);
         }
 
         public override DocumentState WithImportsChange()