Switch MacroExpansionContext to an protocol

The macros design has moved to having `MacroExpansionContext` be a
class-bound protocol. Adjust the implementation accordingly, and add a
`TestingMacroExpansionContext` for a concrete implementation to use in
test cases.

And since I didn't want to break the `#fileID` macro that used to work,
implement a general scheme for getting the location of a syntax node :).

Author: DougGregor

Sources/_SwiftSyntaxMacros/MacroExpansionContext.swift

@@ -13,56 +13,85 @@
 import SwiftSyntax
 import SwiftDiagnostics
 
-/// System-supplied structure that provides information about the context in
-/// which a given macro is being expanded.
-public struct MacroExpansionContext {
-  /// The name of the module in which the macro is being evaluated.
-  public let moduleName: String
-
-  /// The name of the source file in which the macro is being evaluated,
-  /// without any path information.
+/// Interface to extract information about the context in which a given
+/// macro is expanded.
+public protocol MacroExpansionContext: AnyObject {
+  /// Generate a unique name for use in the macro.
+  ///
+  /// - Parameters:
+  ///   - name: The name to use as a basis for the uniquely-generated name,
+  ///     which will appear in the unique name that's produced here.
   ///
-  /// Swift prevents two files within the same module from having the same
-  /// name, so the combination of file and module name is unique.
-  public let fileName: String
+  /// - Returns: an identifier token containing a unique name that will not
+  ///   conflict with any other name in a well-formed program.
+  func createUniqueName(_ name: String) -> TokenSyntax
 
-  /// Counter used to generate names local to the macro.
-  var localNameCounter = 0
+  /// Produce a diagnostic while expanding the macro.
+  func diagnose(_ diagnostic: Diagnostic)
 
-  /// The set of diagnostics that were emitted as part of expanding the
-  /// macro.
-  public private(set) var diagnostics: [Diagnostic] = []
+  /// Retrieve a source location for the given syntax node.
+  ///
+  /// - Parameters:
+  ///   - node: The syntax node whose source location to produce.
+  ///   - position: The position within the syntax node for the resulting
+  ///     location.
+  ///   - filePathMode: How the file name contained in the source location is
+  ///     formed.
+  ///
+  /// - Returns: the source location within the given node, or `nil` if the
+  ///   given syntax node is not rooted in a source file that the macro
+  ///   expansion context knows about.
+  func location<Node: SyntaxProtocol> (
+    of node: Node,
+    at position: PositionInSyntaxNode,
+    filePathMode: SourceLocationFilePathMode
+  ) -> SourceLocation?
+}
 
-  /// Create a new macro evaluation context.
-  public init(moduleName: String, fileName: String) {
-    self.moduleName = moduleName
-    self.fileName = fileName
+extension MacroExpansionContext {
+  /// Retrieve a source location for the given syntax node's starting token
+  /// (after leading trivia) using file naming according to `#fileID`.
+  ///
+  /// - Parameters:
+  ///   - node: The syntax node whose source location to produce.
+  ///
+  /// - Returns: the source location within the given node, or `nil` if the
+  ///   given syntax node is not rooted in a source file that the macro
+  ///   expansion context knows about.
+  public func location<Node: SyntaxProtocol> (
+    of node: Node
+  ) -> SourceLocation? {
+    return location(of: node, at: .afterLeadingTrivia, filePathMode: .fileID)
   }
+}
 
-  /// Generate a unique local name for use in the macro.
-  public mutating func createUniqueLocalName() -> TokenSyntax {
-    let name = "__macro_local_\(localNameCounter)"
-    let token = TokenSyntax(.identifier(name), presence: .present)
-    localNameCounter += 1
-    return token
-  }
+/// Describe the position within a syntax node that can be used to compute
+/// source locations.
+public enum PositionInSyntaxNode {
+  /// Refers to the start of the syntax node's leading trivia, which is
+  /// the first source location covered by the syntax node.
+  case beforeLeadingTrivia
 
-  /// Create a new macro evaluation context.
-  @available(*, deprecated, message: "Use init(moduleName:fileName:)")
-  public init(
-    moduleName: String,
-    sourceLocationConverter: SourceLocationConverter
-  ) {
-    let fileName =
-      sourceLocationConverter.location(
-        for: AbsolutePosition(utf8Offset: -1)
-      ).file ?? "unknown.swift"
+  /// Refers to the start of the syntax node's first token, which
+  /// immediately follows the leading trivia.
+  case afterLeadingTrivia
 
-    self.init(moduleName: moduleName, fileName: fileName)
-  }
+  /// Refers to the end of the syntax node's last token, right before the
+  /// trailing trivia.
+  case beforeTrailingTrivia
 
-  /// Produce a diagnostic while expanding the macro.
-  public mutating func diagnose(_ diagnostic: Diagnostic) {
-    diagnostics.append(diagnostic)
-  }
+  /// Refers just past the end of the source text that is covered by the
+  /// syntax node, after all trailing trivia.
+  case afterTrailingTrivia
+}
+
+/// Describes how the a source location file path
+public enum SourceLocationFilePathMode {
+  /// A file ID consisting of the module name and file name (without full path),
+  /// as would be generated by the macro expansion `#fileID`.
+  case fileID
+
+  /// A full path name as would be generated by the macro expansion `#filePath`,
+  /// e.g., `/home/taylor/alison.swift`.
+  case filePath
 }

Sources/_SwiftSyntaxMacros/MacroProtocols/AccessorMacro.swift

@@ -17,7 +17,7 @@ public protocol AccessorMacro: AttachedMacro {
   static func expansion(
     of node: AttributeSyntax,
     attachedTo declaration: DeclSyntax,
-    in context: inout MacroExpansionContext
+    in context: any MacroExpansionContext
   ) throws -> [AccessorDeclSyntax]
 }
 

Sources/_SwiftSyntaxMacros/MacroProtocols/CodeItemMacro.swift

@@ -15,6 +15,6 @@ public protocol CodeItemMacro: FreestandingMacro {
   /// declaration within the given context to produce a set of declarations.
   static func expansion(
     of node: MacroExpansionDeclSyntax,
-    in context: inout MacroExpansionContext
+    in context: any MacroExpansionContext
   ) throws -> [CodeBlockItemSyntax]
 }

Sources/_SwiftSyntaxMacros/MacroProtocols/DeclarationMacro.swift

@@ -15,7 +15,7 @@ public protocol DeclarationMacro: FreestandingMacro {
   /// declaration within the given context to produce a set of declarations.
   static func expansion(
     of node: MacroExpansionDeclSyntax,
-    in context: inout MacroExpansionContext
+    in context: any MacroExpansionContext
   ) throws -> [DeclSyntax]
 }
 

Sources/_SwiftSyntaxMacros/MacroProtocols/ExpressionMacro.swift

@@ -18,6 +18,6 @@ public protocol ExpressionMacro: FreestandingMacro {
   /// within the given context to produce a replacement expression.
   static func expansion(
     of node: MacroExpansionExprSyntax,
-    in context: inout MacroExpansionContext
+    in context: any MacroExpansionContext
   ) throws -> ExprSyntax
 }

Sources/_SwiftSyntaxMacros/MacroProtocols/MemberAttributeMacro.swift

@@ -29,6 +29,6 @@ public protocol MemberAttributeMacro: AttachedMacro {
     of node: AttributeSyntax,
     attachedTo declaration: DeclSyntax,
     annotating member: DeclSyntax,
-    in context: inout MacroExpansionContext
+    in context: any MacroExpansionContext
   ) throws -> [AttributeSyntax]
 }

Sources/_SwiftSyntaxMacros/MacroProtocols/MemberMacro.swift

@@ -26,7 +26,7 @@ public protocol MemberMacro: AttachedMacro {
   static func expansion(
     of node: AttributeSyntax,
     attachedTo declaration: DeclSyntax,
-    in context: inout MacroExpansionContext
+    in context: any MacroExpansionContext
   ) throws -> [DeclSyntax]
 }
 

Sources/_SwiftSyntaxMacros/MacroProtocols/PeerMacro.swift

@@ -19,7 +19,7 @@ public protocol PeerMacro: AttachedMacro {
   static func expansion(
     of node: AttributeSyntax,
     attachedTo declaration: DeclSyntax,
-    in context: inout MacroExpansionContext
+    in context: any MacroExpansionContext
   ) throws -> [DeclSyntax]
 }
 

Sources/_SwiftSyntaxMacros/MacroSystem.swift

@@ -84,7 +84,7 @@ class MacroApplication: SyntaxRewriter {
     if node.evaluatedMacroName != nil {
       return node.evaluateMacro(
         with: macroSystem,
-        context: &context
+        context: context
       )
     }
 
@@ -135,7 +135,7 @@ class MacroApplication: SyntaxRewriter {
           if let macro = macro as? DeclarationMacro.Type {
             let expandedItemList = try macro.expansion(
               of: declExpansion,
-              in: &context
+              in: context
             )
             newItems.append(
               contentsOf: expandedItemList.map {
@@ -145,7 +145,7 @@ class MacroApplication: SyntaxRewriter {
           } else if let macro = macro as? ExpressionMacro.Type {
             let expandedExpr = try macro.expansion(
               of: declExpansion.asMacroExpansionExpr(),
-              in: &context
+              in: context
             )
             newItems.append(CodeBlockItemSyntax(item: .init(expandedExpr)))
           }
@@ -191,7 +191,7 @@ class MacroApplication: SyntaxRewriter {
         do {
           let expandedList = try freestandingMacro.expansion(
             of: declExpansion,
-            in: &context
+            in: context
           )
 
           newItems.append(
@@ -305,7 +305,7 @@ class MacroApplication: SyntaxRewriter {
         let newAccessors = try accessorMacro.expansion(
           of: accessorAttr,
           attachedTo: DeclSyntax(visitedNode),
-          in: &context
+          in: context
         )
 
         accessors.append(contentsOf: newAccessors)
@@ -373,7 +373,7 @@ extension MacroApplication {
     let macroAttributes = getMacroAttributes(attachedTo: decl, ofType: PeerMacro.Type.self)
     for (attribute, peerMacro) in macroAttributes {
       do {
-        let newPeers = try peerMacro.expansion(of: attribute, attachedTo: decl, in: &context)
+        let newPeers = try peerMacro.expansion(of: attribute, attachedTo: decl, in: context)
         peers.append(contentsOf: newPeers)
       } catch {
         // Record the error
@@ -402,7 +402,7 @@ extension MacroApplication {
           contentsOf: memberMacro.expansion(
             of: attribute,
             attachedTo: DeclSyntax(decl),
-            in: &context
+            in: context
           )
         )
       } catch {
@@ -442,7 +442,7 @@ extension MacroApplication {
             of: attribute,
             attachedTo: DeclSyntax(decl),
             annotating: member.decl,
-            in: &context
+            in: context
           )
         )
       } catch {
@@ -470,7 +470,7 @@ extension SyntaxProtocol {
   /// node.
   public func expand(
     macros: [String: Macro.Type],
-    in context: inout MacroExpansionContext
+    in context: any MacroExpansionContext
   ) -> Syntax {
     // Build the macro system.
     var system = MacroSystem()
@@ -483,10 +483,6 @@ extension SyntaxProtocol {
       context: context
     )
 
-    defer {
-      context = applier.context
-    }
-
     return applier.visit(Syntax(self))
   }
 }

Sources/_SwiftSyntaxMacros/Syntax+MacroEvaluation.swift

@@ -49,20 +49,41 @@ extension MacroExpansionDeclSyntax {
   }
 }
 
+extension SyntaxProtocol {
+  /// Detach the current node and inform the macro expansion context,
+  /// if it needs to know.
+  fileprivate func detach(in context: MacroExpansionContext) -> Self {
+    let detached = detach()
+
+    // Testing contexts want to know where the detach occurred so they can
+    // track it.
+    //
+    // TODO: Should this be generalized?
+    if let testingContext = context as? TestingMacroExpansionContext,
+       let parentSourceFile = root.as(SourceFileSyntax.self) {
+      testingContext.addDisconnected(
+        Syntax(detached), at: position, in: parentSourceFile
+      )
+    }
+
+    return detached
+  }
+}
+
 extension MacroExpansionExprSyntax {
   /// Evaluate the given macro for this syntax node, producing the expanded
   /// result and (possibly) some diagnostics.
   func evaluateMacro(
     _ macro: Macro.Type,
-    in context: inout MacroExpansionContext
+    in context: any MacroExpansionContext
   ) -> ExprSyntax {
     guard let exprMacro = macro as? ExpressionMacro.Type else {
       return ExprSyntax(self)
     }
 
     // Handle the rewrite.
     do {
-      return try exprMacro.expansion(of: detach(), in: &context)
+      return try exprMacro.expansion(of: detach(in: context), in: context)
     } catch {
       // Record the error
       context.diagnose(
@@ -82,7 +103,7 @@ extension MacroExpansionDeclSyntax {
   /// result and (possibly) some diagnostics.
   func evaluateMacro(
     _ macro: Macro.Type,
-    in context: inout MacroExpansionContext
+    in context: any MacroExpansionContext
   ) -> Syntax {
     // TODO: declaration/statement macros
 
@@ -115,7 +136,7 @@ extension Syntax {
   /// some kind.
   func evaluateMacro(
     with macroSystem: MacroSystem,
-    context: inout MacroExpansionContext
+    context: any MacroExpansionContext
   ) -> Syntax {
     // If this isn't a macro evaluation node, do nothing.
     guard let macroName = evaluatedMacroName else {
@@ -129,11 +150,11 @@ extension Syntax {
 
     switch self.as(SyntaxEnum.self) {
     case .macroExpansionDecl(let expansion):
-      return expansion.evaluateMacro(macro, in: &context)
+      return expansion.evaluateMacro(macro, in: context)
 
     case .macroExpansionExpr(let expansion):
       return Syntax(
-        expansion.evaluateMacro(macro, in: &context)
+        expansion.evaluateMacro(macro, in: context)
       )
 
     default: