[Analyzer] Add a custom semantic tokens modifier to named parameter labels

Change-Id: I5b5e4030a17bd894872884960d11eaa748c12e5c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/179769
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>

Author: DanTup

pkg/analysis_server/lib/src/computer/computer_highlights.dart

@@ -380,7 +380,9 @@ class DartUnitHighlightsComputer {
     var type = node.inDeclarationContext()
         ? HighlightRegionType.PARAMETER_DECLARATION
         : HighlightRegionType.PARAMETER_REFERENCE;
-    return _addRegion_node(node, type);
+    var modifiers =
+        node.parent is Label ? {CustomSemanticTokenModifiers.label} : null;
+    return _addRegion_node(node, type, semanticTokenModifiers: modifiers);
   }
 
   bool _addIdentifierRegion_typeParameter(SimpleIdentifier node) {
@@ -459,10 +461,21 @@ class DartUnitHighlightsComputer {
     }
   }
 
-  bool _addRegion_node(AstNode node, HighlightRegionType type) {
+  bool _addRegion_node(
+    AstNode node,
+    HighlightRegionType type, {
+    SemanticTokenTypes semanticTokenType,
+    Set<SemanticTokenModifiers> semanticTokenModifiers,
+  }) {
     var offset = node.offset;
     var length = node.length;
-    _addRegion(offset, length, type);
+    _addRegion(
+      offset,
+      length,
+      type,
+      semanticTokenType: semanticTokenType,
+      semanticTokenModifiers: semanticTokenModifiers,
+    );
     return true;
   }
 

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

@@ -100,15 +100,23 @@ abstract class CustomMethods {
 }
 
 abstract class CustomSemanticTokenModifiers {
-  // A modifier applied to control keywords like if/for/etc. so they can be
-  // coloured differently to other keywords (void, import, etc), matching the
-  // original Dart textmate grammar.
-  // https://github.com/dart-lang/dart-syntax-highlight/blob/84a8e84f79bc917ebd959a4587349c865dc945e0/grammars/dart.json#L244-L261
+  /// A modifier applied to control keywords like if/for/etc. so they can be
+  /// coloured differently to other keywords (void, import, etc), matching the
+  /// original Dart textmate grammar.
+  /// https://github.com/dart-lang/dart-syntax-highlight/blob/84a8e84f79bc917ebd959a4587349c865dc945e0/grammars/dart.json#L244-L261
   static const control = SemanticTokenModifiers('control');
 
+  /// A modifier applied to parameter references to indicate they are the name/label
+  /// to allow theming them differently to the values. For example in the code
+  /// `foo({String a}) => foo(a: a)` the a's will be differentiated as:
+  /// - parameter.declaration
+  /// - parameter.label
+  /// - parameter
+  static const label = SemanticTokenModifiers('label');
+
   /// All custom semantic token modifiers, used to populate the LSP Legend which must
   /// include all used modifiers.
-  static const values = [control];
+  static const values = [control, label];
 }
 
 abstract class CustomSemanticTokenTypes {

pkg/analysis_server/test/lsp/semantic_tokens_test.dart

@@ -600,6 +600,33 @@ class MyClass {}
     expect(decoded, equals(expected));
   }
 
+  Future<void> test_namedArguments() async {
+    final content = '''
+    f({String a}) {
+      f(a: a);
+    }    
+    ''';
+
+    final expected = [
+      _Token('f', SemanticTokenTypes.function,
+          [SemanticTokenModifiers.declaration, SemanticTokenModifiers.static]),
+      _Token('String', SemanticTokenTypes.class_),
+      _Token('a', SemanticTokenTypes.parameter,
+          [SemanticTokenModifiers.declaration]),
+      _Token('f', SemanticTokenTypes.function),
+      _Token('a', SemanticTokenTypes.parameter,
+          [CustomSemanticTokenModifiers.label]),
+      _Token('a', SemanticTokenTypes.parameter),
+    ];
+
+    await initialize();
+    await openFile(mainFileUri, withoutMarkers(content));
+
+    final tokens = await getSemanticTokens(mainFileUri);
+    final decoded = decodeSemanticTokens(content, tokens);
+    expect(decoded, equals(expected));
+  }
+
   Future<void> test_range() async {
     final content = '''
     /// class docs