Add symbolName property for some syntax nodes

`FunctionDecl`, `InitializerDecl`, `SubscriptDecl`, `EnumCaseElement`, and `MacroDecl` gained a new computed property: `symbolName`

The `symbolName` property provides a string representation of the declaration's name along with its parameter labels. For example, a function `func greet(name: String)` will have the symbol name `greet(name:)`.

Release Notes/601.md

@@ -2,6 +2,11 @@
 
 ## New APIs
 
+- `FunctionDecl`, `InitializerDecl`, `SubscriptDecl`, `EnumCaseElement`, and `MacroDecl` gained a new computed property: `symbolName`
+  - Description: The `symbolName` property provides a string representation of the declaration's name along with its parameter labels. For example, a function `func greet(name: String)` will have the symbol name `greet(name:)`.
+  - Issue: https://github.com/apple/swift-syntax/issues/2488
+  - Pull Request: https://github.com/apple/swift-syntax/pull/2583
+
 ## API Behavior Changes
 
 ## Deprecations

Sources/SwiftSyntax/SymbolName.swift

@@ -0,0 +1,139 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2024 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+extension FunctionDeclSyntax {
+  /// The symbol name of the function declaration.
+  ///
+  /// The symbol name is a string representation of the function name along with its parameter labels.
+  /// For example, a function `func greet(name: String)` will have the symbol name `greet(name:)`.
+  public var symbolName: String {
+    SwiftSyntax.symbolName(
+      fromBaseName: name.text,
+      parameters: signature.parameterClause
+    )
+  }
+}
+
+extension InitializerDeclSyntax {
+  /// The symbol name of the initializer declaration.
+  ///
+  /// The symbol name is a string representation of the initializer along with its parameter labels.
+  /// For example, an initializer `init(name: String)` will have the symbol name `init(name:)`.
+  public var symbolName: String {
+    SwiftSyntax.symbolName(
+      fromBaseName: initKeyword.text,
+      parameters: signature.parameterClause
+    )
+  }
+}
+
+extension SubscriptDeclSyntax {
+  /// The symbol name of the subscript declaration.
+  ///
+  /// The symbol name is a string representation of the subscript along with its parameter labels.
+  /// For example, a subscript `subscript(index: Int)` will have the symbol name `subscript(_:)`.
+  public var symbolName: String {
+    SwiftSyntax.symbolName(
+      fromBaseName: subscriptKeyword.text,
+      parameters: parameterClause,
+      isForSubscript: true
+    )
+  }
+}
+
+extension EnumCaseElementSyntax {
+  /// The symbol name of the enum case element.
+  ///
+  /// The symbol name is a string representation of the enum case name along with its associated value labels (if any).
+  /// For example, an enum case `case foo(bar: Int)` will have the symbol name `foo(bar:)`.
+  public var symbolName: String {
+    let caseName = name.text
+
+    guard let associatedValues = parameterClause else {
+      return caseName
+    }
+
+    let argumentLabels = associatedValues.parameters
+      .map { parameter in
+        guard let firstName = parameter.firstName else {
+          return "_:"
+        }
+
+        return firstName.text + ":"
+      }
+      .joined()
+
+    return "\(caseName)(\(argumentLabels))"
+  }
+}
+
+extension MacroDeclSyntax {
+  /// The symbol name of the macro declaration.
+  ///
+  /// The symbol name is a string representation of the macro name along with its parameter labels.
+  /// For example, a macro `macro greet(name: String)` will have the symbol name `greet(name:)`.
+  public var symbolName: String {
+    SwiftSyntax.symbolName(
+      fromBaseName: name.text,
+      parameters: signature.parameterClause
+    )
+  }
+}
+
+/// Generates the symbol name by combining the base name and parameter labels.
+///
+/// If the parameter has two names (e.g., `external internal: Int`), the first name is considered the argument label.
+/// If the parameter has only one name and it's not a subscript parameter, it is considered the argument label.
+///
+/// - Parameters:
+///   - baseName: The base name of the symbol (e.g., function name, initializer, subscript).
+///   - parameters: The function parameter clause containing the parameter labels.
+/// - Returns: The symbol name with the base name and parameter labels combined.
+private func symbolName(
+  fromBaseName baseName: String,
+  parameters: FunctionParameterClauseSyntax,
+  isForSubscript: Bool = false
+) -> String {
+  let argumentLabels = parameters.parameters
+    .map { parameter in
+      let argumentLabelText = parameter.argumentName(isForSubscript: isForSubscript) ?? "_"
+      return argumentLabelText + ":"
+    }
+    .joined()
+
+  return "\(baseName)(\(argumentLabels))"
+}
+
+extension FunctionParameterSyntax {
+  /// The argument name (label) of the function parameter.
+  fileprivate func argumentName(isForSubscript: Bool = false) -> String? {
+    // If we have two names, the first one is the argument label
+    if secondName != nil {
+      return firstName.asIdentifierToken
+    }
+
+    if isForSubscript {
+      return nil
+    }
+
+    return firstName.asIdentifierToken
+  }
+}
+
+extension TokenSyntax {
+  fileprivate var asIdentifierToken: String? {
+    switch tokenKind {
+    case .identifier: return self.text
+    default: return nil
+    }
+  }
+}