[analysis_server] Don't overlap folding regions when lineFoldingOnly

+ convert LSP folding tests to use TestCode parser.

A change in VS Code means two folding regions are no longer allowed to end/start on the same line (the second range is silently dropped). This truncates folding regions if they end on the same line that another starts to end on the line before (but only if a client only supports line-folding mode).

Fixes Dart-Code/Dart-Code#4121.

Change-Id: Ic26f58f84c44a01ae5157c336ed0f207d1c0eeb8
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/261900
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Brian Wilkerson <[email protected]>

Author: DanTup

pkg/analysis_server/lib/src/lsp/client_capabilities.dart

@@ -71,6 +71,7 @@ class LspClientCapabilities {
   final bool typeDefinitionLocationLink;
   final bool hierarchicalSymbols;
   final bool diagnosticCodeDescription;
+  final bool lineFoldingOnly;
   final Set<CodeActionKind> codeActionKinds;
   final Set<CompletionItemTag> completionItemTags;
   final Set<DiagnosticTag> diagnosticTags;
@@ -142,6 +143,8 @@ class LspClientCapabilities {
     final hoverContentFormats = _listToNullableSet(hover?.contentFormat);
     final insertReplaceCompletionRanges =
         completionItem?.insertReplaceSupport ?? false;
+    final lineFoldingOnly =
+        textDocument?.foldingRange?.lineFoldingOnly ?? false;
     final literalCodeActions = codeActionLiteral != null;
     final renameValidation = textDocument?.rename?.prepareSupport ?? false;
     final signatureHelpDocumentationFormats =
@@ -170,6 +173,7 @@ class LspClientCapabilities {
       definitionLocationLink: definitionLocationLink,
       typeDefinitionLocationLink: typeDefinitionLocationLink,
       hierarchicalSymbols: hierarchicalSymbols,
+      lineFoldingOnly: lineFoldingOnly,
       diagnosticCodeDescription: diagnosticCodeDescription,
       codeActionKinds: codeActionKinds,
       completionItemTags: completionItemTags,
@@ -204,6 +208,7 @@ class LspClientCapabilities {
     required this.definitionLocationLink,
     required this.typeDefinitionLocationLink,
     required this.hierarchicalSymbols,
+    required this.lineFoldingOnly,
     required this.diagnosticCodeDescription,
     required this.codeActionKinds,
     required this.completionItemTags,

pkg/analysis_server/lib/src/lsp/handlers/handler_folding.dart

@@ -22,6 +22,13 @@ class FoldingHandler
   @override
   Future<ErrorOr<List<FoldingRange>>> handle(FoldingRangeParams params,
       MessageInfo message, CancellationToken token) async {
+    final clientCapabilities = server.clientCapabilities;
+    if (clientCapabilities == null) {
+      // This should not happen unless a client misbehaves.
+      return serverNotInitializedError;
+    }
+
+    final lineFoldingOnly = clientCapabilities.lineFoldingOnly;
     final path = pathOfDoc(params.textDocument);
 
     return path.mapResult((path) async {
@@ -53,9 +60,71 @@ class FoldingHandler
       final regions =
           notificationManager.merger.mergeFoldingRegions(partialResults);
 
-      return success(
-        regions.map((region) => toFoldingRange(lineInfo!, region)).toList(),
-      );
+      // Ensure sorted by offset for when looking for overlapping ranges in
+      // line mode below.
+      regions.sort((r1, r2) => r1.offset.compareTo(r2.offset));
+
+      final foldingRanges = regions
+          .map((region) =>
+              _toFoldingRange(lineInfo!, region, lineOnly: lineFoldingOnly))
+          .toList();
+
+      // When in line-only mode, ranges that end on the same line that another
+      // ranges starts should be truncated to be on the line before (and if this
+      // leave them spanning only a single line, should be removed).
+      if (lineFoldingOnly) {
+        _compensateForLineFolding(foldingRanges);
+      }
+
+      return success(foldingRanges);
     });
   }
+
+  /// Adjust [foldingRanges] taking into count additional rules for line
+  /// folding.
+  ///
+  /// When character folding is supported, a range may start on the same line
+  /// that another ends (as long as they don't overlap).
+  ///
+  /// When only line folding is supported, ranges must not end on the same line
+  /// that another starts. In this case, we shrink the previous range (and if
+  /// this makes it a single line, remove it).
+  void _compensateForLineFolding(List<FoldingRange> foldingRanges) {
+    // Loop over items expect last (`-1`). We can skip the last item because
+    // it has no next item.
+    for (var i = 0; i < foldingRanges.length - 1; i++) {
+      final range = foldingRanges[i];
+      final next = foldingRanges[i + 1];
+      // If this item runs into the next...
+      if (range.endLine >= next.startLine) {
+        // Truncate it to end on the line before.
+        final newEndLine = next.startLine - 1;
+
+        // If it no longer needs to be a folding range at all, remove it.
+        if (newEndLine <= range.startLine) {
+          foldingRanges.removeAt(i);
+          i--;
+          continue;
+        }
+
+        foldingRanges[i] = FoldingRange(
+          startLine: range.startLine,
+          endLine: newEndLine,
+          kind: range.kind,
+        );
+      }
+    }
+  }
+
+  FoldingRange _toFoldingRange(LineInfo lineInfo, FoldingRegion region,
+      {required bool lineOnly}) {
+    final range = toRange(lineInfo, region.offset, region.length);
+    return FoldingRange(
+      startLine: range.start.line,
+      startCharacter: lineOnly ? null : range.start.character,
+      endLine: range.end.line,
+      endCharacter: lineOnly ? null : range.end.character,
+      kind: toFoldingRangeKind(region.kind),
+    );
+  }
 }

pkg/analysis_server/lib/src/lsp/mapping.dart

@@ -1079,17 +1079,6 @@ lsp.FlutterOutlineAttribute toFlutterOutlineAttribute(
           : null);
 }
 
-lsp.FoldingRange toFoldingRange(
-    server.LineInfo lineInfo, server.FoldingRegion region) {
-  final range = toRange(lineInfo, region.offset, region.length);
-  return lsp.FoldingRange(
-      startLine: range.start.line,
-      startCharacter: range.start.character,
-      endLine: range.end.line,
-      endCharacter: range.end.character,
-      kind: toFoldingRangeKind(region.kind));
-}
-
 lsp.FoldingRangeKind? toFoldingRangeKind(server.FoldingKind kind) {
   switch (kind) {
     case server.FoldingKind.COMMENT: