[Macros] Pass MacroExpansionContext as inout through macro expansion.

This matches the current proposal, and makes it possible for mutations
to the context in the future.

Author: DougGregor

Sources/_SwiftSyntaxMacros/ExpressionMacro.swift

@@ -22,7 +22,7 @@ public protocol ExpressionMacro: Macro {
   /// Evaluate a macro described by the given macro expansion expression
   /// within the given context to produce a replacement expression.
   static func apply(
-    _ macro: MacroExpansionExprSyntax, in context: MacroExpansionContext
+    _ macro: MacroExpansionExprSyntax, in context: inout MacroExpansionContext
   ) -> MacroResult<ExprSyntax>
 }
 

Sources/_SwiftSyntaxMacros/MacroSystem+Builtin.swift

@@ -116,7 +116,7 @@ public struct FunctionMacro: ExpressionMacro {
   }
 
   public static func apply(
-    _ macro: MacroExpansionExprSyntax, in context: MacroExpansionContext
+    _ macro: MacroExpansionExprSyntax, in context: inout MacroExpansionContext
   ) -> MacroResult<ExprSyntax> {
     let name = findEnclosingName(macro) ?? context.moduleName
     let literal: ExprSyntax = "\(literal: name)"
@@ -143,7 +143,7 @@ private func replaceFirstLabel(
 
 public struct ColorLiteralMacro: ExpressionMacro {
   public static func apply(
-    _ macro: MacroExpansionExprSyntax, in context: MacroExpansionContext
+    _ macro: MacroExpansionExprSyntax, in context: inout MacroExpansionContext
   ) -> MacroResult<ExprSyntax> {
     let argList = replaceFirstLabel(
       of: macro.argumentList, with: "_colorLiteralRed"
@@ -158,7 +158,7 @@ public struct ColorLiteralMacro: ExpressionMacro {
 
 public struct FileLiteralMacro: ExpressionMacro {
   public static func apply(
-    _ macro: MacroExpansionExprSyntax, in context: MacroExpansionContext
+    _ macro: MacroExpansionExprSyntax, in context: inout MacroExpansionContext
   ) -> MacroResult<ExprSyntax> {
     let argList = replaceFirstLabel(
       of: macro.argumentList, with: "fileReferenceLiteralResourceName"
@@ -173,7 +173,7 @@ public struct FileLiteralMacro: ExpressionMacro {
 
 public struct ImageLiteralMacro: ExpressionMacro {
   public static func apply(
-    _ macro: MacroExpansionExprSyntax, in context: MacroExpansionContext
+    _ macro: MacroExpansionExprSyntax, in context: inout MacroExpansionContext
   ) -> MacroResult<ExprSyntax> {
     let argList = replaceFirstLabel(
       of: macro.argumentList, with: "imageLiteralResourceName"
@@ -188,7 +188,7 @@ public struct ImageLiteralMacro: ExpressionMacro {
 
 public struct FileIDMacro: ExpressionMacro {
   public static func apply(
-    _ macro: MacroExpansionExprSyntax, in context: MacroExpansionContext
+    _ macro: MacroExpansionExprSyntax, in context: inout MacroExpansionContext
   ) -> MacroResult<ExprSyntax> {
     // FIXME: Compiler has more sophisticated file ID computation
     let fileID = "\(context.moduleName)/\(context.fileName)"

Sources/_SwiftSyntaxMacros/MacroSystem+Examples.swift

@@ -16,7 +16,7 @@ import SwiftSyntaxBuilder
 // Macros used for testing purposes
 public struct StringifyMacro: ExpressionMacro {
   public static func apply(
-    _ macro: MacroExpansionExprSyntax, in context: MacroExpansionContext
+    _ macro: MacroExpansionExprSyntax, in context: inout MacroExpansionContext
   ) -> MacroResult<ExprSyntax> {
     guard let argument = macro.argumentList.first?.expression else {
       // FIXME: Create a diagnostic for the missing argument?

Sources/_SwiftSyntaxMacros/MacroSystem.swift

@@ -62,7 +62,7 @@ public struct MacroSystem {
 /// Syntax rewriter that evaluates any macros encountered along the way.
 class MacroApplication : SyntaxRewriter {
   let macroSystem: MacroSystem
-  let context: MacroExpansionContext
+  var context: MacroExpansionContext
   let errorHandler: (MacroSystemError) -> Void
 
   init(
@@ -81,7 +81,7 @@ class MacroApplication : SyntaxRewriter {
     }
 
     return node.evaluateMacro(
-      with: macroSystem, context: context, errorHandler: errorHandler
+      with: macroSystem, context: &context, errorHandler: errorHandler
     )
   }
 
@@ -113,7 +113,7 @@ extension MacroSystem {
   /// - Returns: the syntax tree with all macros evaluated.
   public func evaluateMacros<Node: SyntaxProtocol>(
     node: Node,
-    in context: MacroExpansionContext,
+    in context: inout MacroExpansionContext,
     errorHandler: (MacroSystemError) -> Void
   ) -> Syntax {
     return withoutActuallyEscaping(errorHandler) { errorHandler in

Sources/_SwiftSyntaxMacros/Syntax+MacroEvaluation.swift

@@ -18,7 +18,7 @@ extension MacroExpansionExprSyntax {
   /// result and (possibly) some diagnostics.
   func evaluateMacro(
     _ macro: Macro.Type,
-    in context: MacroExpansionContext,
+    in context: inout MacroExpansionContext,
     errorHandler: (MacroSystemError) -> Void
   ) -> ExprSyntax {
     guard let exprMacro = macro as? ExpressionMacro.Type else {
@@ -27,7 +27,7 @@ extension MacroExpansionExprSyntax {
     }
 
     // Handle the rewrite.
-    let result = exprMacro.apply(self, in: context)
+    let result = exprMacro.apply(self, in: &context)
 
     // Report diagnostics, if there were any.
     if !result.diagnostics.isEmpty {
@@ -65,15 +65,15 @@ extension MacroExpansionDeclSyntax {
   /// result and (possibly) some diagnostics.
   func evaluateMacro(
     _ macro: Macro.Type,
-    in context: MacroExpansionContext,
+    in context: inout MacroExpansionContext,
     errorHandler: (MacroSystemError) -> Void
   ) -> Syntax {
     // TODO: declaration/statement macros
 
     // Fall back to evaluating as an expression macro.
     return Syntax(
       asMacroExpansionExpr().evaluateMacro(
-        macro, in: context, errorHandler: errorHandler
+        macro, in: &context, errorHandler: errorHandler
       )
     )
   }
@@ -104,7 +104,7 @@ extension Syntax {
   /// some kind.
   public func evaluateMacro(
     with macroSystem: MacroSystem,
-    context: MacroExpansionContext,
+    context: inout MacroExpansionContext,
     errorHandler: (MacroSystemError) -> Void
   ) -> Syntax {
     // If this isn't a macro evaluation node, do nothing.
@@ -121,13 +121,13 @@ extension Syntax {
     switch self.as(SyntaxEnum.self) {
     case .macroExpansionDecl(let expansion):
       return expansion.evaluateMacro(
-        macro, in: context, errorHandler: errorHandler
+        macro, in: &context, errorHandler: errorHandler
       )
 
     case .macroExpansionExpr(let expansion):
       return Syntax(
         expansion.evaluateMacro(
-          macro, in: context, errorHandler: errorHandler
+          macro, in: &context, errorHandler: errorHandler
         )
       )
 

Sources/swift-parser-cli/swift-parser-cli.swift

@@ -242,12 +242,12 @@ class ExpandMacros: ParsableCommand {
         resultTree = Syntax(tree)
       }
 
-      let context = MacroExpansionContext(
+      var context = MacroExpansionContext(
         moduleName: "MyModule", fileName: self.sourceFile.withoutPath()
       )
       var diags = ParseDiagnosticsGenerator.diagnostics(for: tree)
       let transformedTree = MacroSystem.exampleSystem.evaluateMacros(
-        node: resultTree, in: context
+        node: resultTree, in: &context
       ) { error in
         if case let .evaluationDiagnostics(_, diagnostics) = error {
           diags.append(contentsOf: diagnostics)

Tests/SwiftSyntaxMacrosTest/MacroSystemTests.swift

@@ -23,11 +23,11 @@ final class MacroSystemTests: XCTestCase {
       let b = #stringify(x + y)
       #colorLiteral(red: 0.5, green: 0.5, blue: 0.25, alpha: 1.0)
       """
-    let context = MacroExpansionContext(
+    var context = MacroExpansionContext(
       moduleName: "MyModule", fileName: "test.swift"
     )
     let transformedSF = MacroSystem.exampleSystem.evaluateMacros(
-      node: sf, in: context, errorHandler: { error in }
+      node: sf, in: &context, errorHandler: { error in }
     )
     AssertStringsEqualWithDiff(
       transformedSF.description,
@@ -46,11 +46,11 @@ final class MacroSystemTests: XCTestCase {
         return true
       })
       """
-    let context = MacroExpansionContext(
+    var context = MacroExpansionContext(
       moduleName: "MyModule", fileName: "test.swift"
     )
     let transformedSF = MacroSystem.exampleSystem.evaluateMacros(
-      node: sf, in: context, errorHandler: { error in }
+      node: sf, in: &context, errorHandler: { error in }
     )
     AssertStringsEqualWithDiff(
       transformedSF.description,
@@ -94,11 +94,11 @@ final class MacroSystemTests: XCTestCase {
         static var staticProp: String = #function
       }
       """
-    let context = MacroExpansionContext(
+    var context = MacroExpansionContext(
       moduleName: "MyModule", fileName: "test.swift"
     )
     let transformedSF = MacroSystem.exampleSystem.evaluateMacros(
-      node: sf, in: context, errorHandler: { error in }
+      node: sf, in: &context, errorHandler: { error in }
     )
     AssertStringsEqualWithDiff(
       transformedSF.description,
@@ -139,11 +139,11 @@ final class MacroSystemTests: XCTestCase {
       """
       let b = #fileID
       """
-    let context = MacroExpansionContext(
+    var context = MacroExpansionContext(
       moduleName: "MyModule", fileName: "taylor.swift"
     )
     let transformedSF = MacroSystem.exampleSystem.evaluateMacros(
-      node: sf, in: context, errorHandler: { error in }
+      node: sf, in: &context, errorHandler: { error in }
     )
     AssertStringsEqualWithDiff(
       transformedSF.description,