Add parameterLabel modifier for argument labels in semantic tokens

Author: PhantomInTheWire

Sources/SourceKitLSP/SemanticTokensLegend+SourceKitLSPLegend.swift

@@ -22,10 +22,28 @@ extension SemanticTokenTypes {
   }
 }
 
+extension SemanticTokenModifiers {
+  // Argument labels are considered part of the function name, but this modifier
+  // allows themes to style them differently if desired.
+  package static var parameterLabel: Self { Self(rawValue: UInt32(1) << UInt32(SemanticTokenModifiers.all.count)) }
+
+  package static let allSourceKitLSPModifiers: [Self] = [
+    .parameterLabel
+  ]
+
+  package var sourceKitLSPName: String? {
+    switch self {
+    case .parameterLabel: return "parameterLabel"
+    default: return nil
+    }
+  }
+}
+
 extension SemanticTokensLegend {
   /// The semantic tokens legend that is used between SourceKit-LSP and the editor.
   package static let sourceKitLSPLegend = SemanticTokensLegend(
     tokenTypes: SemanticTokenTypes.all.map(\.name),
     tokenModifiers: SemanticTokenModifiers.all.compactMap(\.name)
+      + SemanticTokenModifiers.allSourceKitLSPModifiers.compactMap(\.sourceKitLSPName)
   )
 }

Sources/SwiftLanguageService/SemanticTokens.swift

@@ -161,7 +161,7 @@ extension SyntaxClassification {
     case .docLineComment, .docBlockComment:
       return (.comment, .documentation)
     case .argumentLabel:
-      return (.function, [])
+      return (.function, .parameterLabel)
     #if RESILIENT_LIBRARIES
     @unknown default:
       fatalError("Unknown case")

Sources/SwiftLanguageService/SyntaxHighlightingTokenParser.swift

@@ -172,7 +172,7 @@ struct SyntaxHighlightingTokenParser {
       // therefore we don't use .parameter here (which LSP clients like
       // VSCode seem to interpret as variable identifiers, however
       // causing a 'wrong highlighting' e.g. of `x` in `f(x y: Int) {}`)
-      return (.function, [.declaration])
+      return (.function, [.declaration, .parameterLabel])
     case values.refVarStatic,
       values.refVarClass,
       values.refVarInstance:

Tests/SourceKitLSPTests/SemanticTokensTests.swift

@@ -321,7 +321,7 @@ final class SemanticTokensTests: SourceKitLSPTestCase {
       expected: [
         TokenSpec(marker: "1️⃣", length: 4, kind: .keyword),
         TokenSpec(marker: "2️⃣", length: 1, kind: .identifier),
-        TokenSpec(marker: "3️⃣", length: 1, kind: .function),
+        TokenSpec(marker: "3️⃣", length: 1, kind: .function, modifiers: .parameterLabel),
         TokenSpec(marker: "4️⃣", length: 3, kind: .struct, modifiers: .defaultLibrary),
         TokenSpec(marker: "5️⃣", length: 1, kind: .identifier),
         TokenSpec(marker: "6️⃣", length: 6, kind: .struct, modifiers: .defaultLibrary),
@@ -844,7 +844,7 @@ final class SemanticTokensTests: SourceKitLSPTestCase {
         TokenSpec(marker: "2️⃣", length: 7, kind: .identifier),
         TokenSpec(marker: "3️⃣", length: 4, kind: .keyword),
         TokenSpec(marker: "4️⃣", length: 1, kind: .identifier),
-        TokenSpec(marker: "5️⃣", length: 1, kind: .function),
+        TokenSpec(marker: "5️⃣", length: 1, kind: .function, modifiers: .parameterLabel),
         TokenSpec(marker: "6️⃣", length: 7, kind: .actor),
       ]
     )
@@ -859,10 +859,10 @@ final class SemanticTokensTests: SourceKitLSPTestCase {
       expected: [
         TokenSpec(marker: "1️⃣", length: 4, kind: .keyword),
         TokenSpec(marker: "2️⃣", length: 3, kind: .identifier),
-        TokenSpec(marker: "3️⃣", length: 3, kind: .function),
+        TokenSpec(marker: "3️⃣", length: 3, kind: .function, modifiers: .parameterLabel),
         TokenSpec(marker: "4️⃣", length: 3, kind: .struct, modifiers: .defaultLibrary),
         TokenSpec(marker: "5️⃣", length: 3, kind: .function),
-        TokenSpec(marker: "6️⃣", length: 3, kind: .function),
+        TokenSpec(marker: "6️⃣", length: 3, kind: .function, modifiers: .parameterLabel),
         TokenSpec(marker: "7️⃣", length: 1, kind: .number),
       ]
     )
@@ -876,7 +876,7 @@ final class SemanticTokensTests: SourceKitLSPTestCase {
       expected: [
         TokenSpec(marker: "1️⃣", length: 4, kind: .keyword),
         TokenSpec(marker: "2️⃣", length: 3, kind: .identifier),
-        TokenSpec(marker: "3️⃣", length: 3, kind: .function),
+        TokenSpec(marker: "3️⃣", length: 3, kind: .function, modifiers: .parameterLabel),
         TokenSpec(marker: "4️⃣", length: 12, kind: .identifier),
         TokenSpec(marker: "5️⃣", length: 3, kind: .struct, modifiers: .defaultLibrary),
       ]