Add support for lineFoldingOnly folding ranges

src/LanguageServer/Protocol/Handler/FoldingRanges/FoldingRangesHandler.cs

@@ -42,12 +42,14 @@ public FoldingRangesHandler(IGlobalOptionService globalOptions)
         if (document is null)
             return SpecializedTasks.Null<FoldingRange[]>();
 
-        return SpecializedTasks.AsNullable(GetFoldingRangesAsync(_globalOptions, document, cancellationToken));
+        var lineFoldingOnly = context.GetRequiredClientCapabilities().TextDocument?.FoldingRange?.LineFoldingOnly == true;
+        return SpecializedTasks.AsNullable(GetFoldingRangesAsync(_globalOptions, document, lineFoldingOnly, cancellationToken));
     }
 
     internal static Task<FoldingRange[]> GetFoldingRangesAsync(
         IGlobalOptionService globalOptions,
         Document document,
+        bool lineFoldingOnly,
         CancellationToken cancellationToken)
     {
         var options = globalOptions.GetBlockStructureOptions(document.Project) with
@@ -59,7 +61,7 @@ internal static Task<FoldingRange[]> GetFoldingRangesAsync(
             ShowBlockStructureGuidesForCodeLevelConstructs = true
         };
 
-        return GetFoldingRangesAsync(document, options, cancellationToken);
+        return GetFoldingRangesAsync(document, options, lineFoldingOnly, cancellationToken);
     }
 
     /// <summary>
@@ -68,6 +70,7 @@ internal static Task<FoldingRange[]> GetFoldingRangesAsync(
     public static async Task<FoldingRange[]> GetFoldingRangesAsync(
         Document document,
         BlockStructureOptions options,
+        bool lineFoldingOnly,
         CancellationToken cancellationToken)
     {
         var blockStructureService = document.GetRequiredLanguageService<BlockStructureService>();
@@ -76,10 +79,10 @@ public static async Task<FoldingRange[]> GetFoldingRangesAsync(
             return [];
 
         var text = await document.GetValueTextAsync(cancellationToken).ConfigureAwait(false);
-        return GetFoldingRanges(blockStructure, text);
+        return GetFoldingRanges(blockStructure, text, lineFoldingOnly);
     }
 
-    private static FoldingRange[] GetFoldingRanges(BlockStructure blockStructure, SourceText text)
+    private static FoldingRange[] GetFoldingRanges(BlockStructure blockStructure, SourceText text, bool lineFoldingOnly)
     {
         if (blockStructure.Spans.IsEmpty)
         {
@@ -103,8 +106,6 @@ private static FoldingRange[] GetFoldingRanges(BlockStructure blockStructure, So
                 continue;
             }
 
-            // TODO - Figure out which blocks should be returned as a folding range (and what kind).
-            // https://github.com/dotnet/roslyn/projects/45#card-20049168
             FoldingRangeKind? foldingRangeKind = span.Type switch
             {
                 BlockTypes.Comment => FoldingRangeKind.Comment,
@@ -123,8 +124,62 @@ private static FoldingRange[] GetFoldingRanges(BlockStructure blockStructure, So
                 Kind = foldingRangeKind,
                 CollapsedText = span.BannerText
             });
+
+            if (lineFoldingOnly)
+            {
+                foldingRanges = AdjustToEnsureNonOverlappingLines(foldingRanges);
+            }
         }
 
         return foldingRanges.ToArray();
+
+        static ArrayBuilder<FoldingRange> AdjustToEnsureNonOverlappingLines(ArrayBuilder<FoldingRange> foldingRanges)
+        {
+            using var _ = PooledDictionary<int, FoldingRange>.GetInstance(out var startLineToFoldingRange);
+
+            // Spans are sorted in descending order by start position (the span starting closer to the end of the file is first).
+            foreach (var foldingRange in foldingRanges)
+            {
+                var updatedRange = foldingRange;
+                // Check if another span starts on the same line.
+                if (startLineToFoldingRange.ContainsKey(foldingRange.StartLine))
+                {
+                    // There's already a span that starts on this line.  We want to keep the innermost span, which is the one
+                    // we already have in the dictionary (as it started later in the file).  Skip this one.
+                    continue;
+                }
+
+                var endLine = foldingRange.EndLine;
+
+                // Check if this span ends on the same line another span starts.
+                // Since we're iterating bottom up, if there is a span that starts on this end line, it will be in the dictionary.
+                if (startLineToFoldingRange.ContainsKey(endLine))
+                {
+                    // The end line of this span overlaps with the start line of another span - attempt to adjust this one
+                    // to the prior line.
+                    var adjustedEndLine = endLine - 1;
+
+                    // If the adjusted end line is now at or before the start line, there's no folding range possible without line overlapping another span.
+                    if (adjustedEndLine <= foldingRange.StartLine)
+                    {
+                        continue;
+                    }
+
+                    updatedRange = new FoldingRange
+                    {
+                        StartLine = foldingRange.StartLine,
+                        StartCharacter = foldingRange.StartCharacter,
+                        EndLine = adjustedEndLine,
+                        EndCharacter = foldingRange.EndCharacter,
+                        Kind = foldingRange.Kind,
+                        CollapsedText = foldingRange.CollapsedText
+                    };
+                }
+
+                startLineToFoldingRange[foldingRange.StartLine] = updatedRange;
+            }
+
+            return [.. startLineToFoldingRange.Values];
+        }
     }
 }

src/LanguageServer/ProtocolUnitTests/FoldingRanges/FoldingRangesTests.cs

@@ -4,6 +4,7 @@
 
 #nullable disable
 
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
@@ -64,9 +65,89 @@ private Action<int> Foo(){|implementation: => i =>{|foldingRange:
             }|}
             """);
 
-    private async Task AssertFoldingRanges(bool mutatingLspWorkspace, string markup, string collapsedText = null)
+    [Theory, CombinatorialData, WorkItem("https://github.com/dotnet/vscode-csharp/issues/7974")]
+    public Task TestGetFoldingRangeAsync_LineFoldingOnly_NoOverlappingRanges(bool mutatingLspWorkspace)
+        => AssertFoldingRanges(mutatingLspWorkspace, """
+            class C{|foldingRange:
+            {
+                public void M1(){|implementation:
+                {
+                    var x = 1;
+                }|}
+                public void M2(){|implementation:
+                {
+                    var y = 2;
+                }|}
+            }|}
+            """, lineFoldingOnly: true);
+
+    [Theory, CombinatorialData, WorkItem("https://github.com/dotnet/vscode-csharp/issues/7974")]
+    public Task TestGetFoldingRangeAsync_LineFoldingOnly_StartLineOverlapsChoosesInner(bool mutatingLspWorkspace)
+        => AssertFoldingRanges(mutatingLspWorkspace, """
+            class C { public void M1() {|implementation:{
+                    var x = 1;
+                }|}
+            }
+            """, lineFoldingOnly: true);
+
+    [Theory, CombinatorialData, WorkItem("https://github.com/dotnet/vscode-csharp/issues/7974")]
+    public Task TestGetFoldingRangeAsync_LineFoldingOnly_EndLineOverlaps(bool mutatingLspWorkspace)
+        => AssertFoldingRanges(mutatingLspWorkspace, """
+            class C{|foldingRange:
+            {
+                void M(){|implementation:
+                {
+                    void Local(){|foldingRange:
+                    {
+                    }|}}|}}|}
+            """, lineFoldingOnly: true);
+
+    [Theory, CombinatorialData, WorkItem("https://github.com/dotnet/vscode-csharp/issues/7974")]
+    public Task TestGetFoldingRangeAsync_LineFoldingOnly_EndLineOverlapsStartLine(bool mutatingLspWorkspace)
+        => AssertFoldingRanges(mutatingLspWorkspace, """
+            class C{|foldingRange:
+            {
+                void M(){|implementation:
+                {
+                    if (true){|foldingRange:
+                    {|}
+                    } else{|foldingRange: {
+                    }|}
+                }|}
+            }|}
+            """, lineFoldingOnly: true);
+
+    [Theory, CombinatorialData, WorkItem("https://github.com/dotnet/vscode-csharp/issues/7974")]
+    public Task TestGetFoldingRangeAsync_WithoutLineFoldingOnly_AllowsRangesOnSameLine(bool mutatingLspWorkspace)
+        => AssertFoldingRanges(mutatingLspWorkspace, """
+            class C {|foldingRange:{ public void M1() {|implementation:{
+                    if (true){|foldingRange:
+                    {
+                    }|} else{|foldingRange: {
+                    }|}
+                }|}
+            }|}
+            """, lineFoldingOnly: false);
+
+    private async Task AssertFoldingRanges(
+        bool mutatingLspWorkspace,
+        [StringSyntax(PredefinedEmbeddedLanguageNames.CSharpTest)] string markup,
+        string collapsedText = null,
+        bool lineFoldingOnly = false)
     {
-        var testLspServer = await CreateTestLspServerAsync(markup, mutatingLspWorkspace);
+        var clientCapabilities = new LSP.ClientCapabilities();
+        if (lineFoldingOnly)
+        {
+            clientCapabilities.TextDocument = new LSP.TextDocumentClientCapabilities
+            {
+                FoldingRange = new LSP.FoldingRangeSetting
+                {
+                    LineFoldingOnly = true
+                }
+            };
+        }
+
+        var testLspServer = await CreateTestLspServerAsync(markup, mutatingLspWorkspace, clientCapabilities);
         var expected = testLspServer.GetLocations()
             .SelectMany(kvp => kvp.Value.Select(location => CreateFoldingRange(kvp.Key, location.Range, collapsedText ?? "...")))
             .OrderByDescending(range => range.StartLine)

src/Tools/ExternalAccess/Razor/Features/Cohost/Handlers/FoldingRanges.cs

@@ -18,6 +18,6 @@ public static Task<FoldingRange[]> GetFoldingRangesAsync(Document document, Canc
         // composition so can't import it (and its internal anyway)
         var globalOptions = document.Project.Solution.Services.ExportProvider.GetService<IGlobalOptionService>();
 
-        return FoldingRangesHandler.GetFoldingRangesAsync(globalOptions, document, cancellationToken);
+        return FoldingRangesHandler.GetFoldingRangesAsync(globalOptions, document, lineFoldingOnly: false, cancellationToken);
     }
 }