[Macros] Fix name lookup in macro expansion declaration arguments.

Teach ASTScope to create child nodes for each of the arguments of a
macro expansion declaration, so that we can perform name lookup into
them. Otherwise, we cannot have nontrivial closures in arguments to a
macro expansion declaration.

Fixes rdar://107388151.

Author: DougGregor

include/swift/AST/ASTScope.h

@@ -1237,6 +1237,32 @@ class MacroDefinitionScope final : public ASTScopeImpl {
   ASTScopeImpl *expandSpecifically(ScopeCreator &scopeCreator) override;
 };
 
+class MacroExpansionDeclScope final : public ASTScopeImpl {
+public:
+  MacroExpansionDecl *const decl;
+
+  MacroExpansionDeclScope(MacroExpansionDecl *e) : decl(e) {}
+  virtual ~MacroExpansionDeclScope() {}
+
+protected:
+  ASTScopeImpl *expandSpecifically(ScopeCreator &scopeCreator) override;
+
+private:
+  void expandAScopeThatDoesNotCreateANewInsertionPoint(ScopeCreator &);
+
+public:
+  std::string getClassName() const override;
+  SourceRange
+  getSourceRangeOfThisASTNode(bool omitAssertions = false) const override;
+
+protected:
+  void printSpecifics(llvm::raw_ostream &out) const override;
+
+public:
+  virtual NullablePtr<Decl> getDeclIfAny() const override { return decl; }
+  Decl *getDecl() const { return decl; }
+};
+
 class AbstractStmtScope : public ASTScopeImpl {
 public:
   SourceRange

lib/AST/ASTScope.cpp

@@ -152,6 +152,7 @@ DEFINE_GET_CLASS_NAME(SubscriptDeclScope)
 DEFINE_GET_CLASS_NAME(EnumElementScope)
 DEFINE_GET_CLASS_NAME(MacroDeclScope)
 DEFINE_GET_CLASS_NAME(MacroDefinitionScope)
+DEFINE_GET_CLASS_NAME(MacroExpansionDeclScope)
 DEFINE_GET_CLASS_NAME(IfStmtScope)
 DEFINE_GET_CLASS_NAME(WhileStmtScope)
 DEFINE_GET_CLASS_NAME(GuardStmtScope)

lib/AST/ASTScopeCreation.cpp

@@ -317,7 +317,6 @@ class NodeAdder
   VISIT_AND_IGNORE(PoundDiagnosticDecl)
   VISIT_AND_IGNORE(MissingDecl)
   VISIT_AND_IGNORE(MissingMemberDecl)
-  VISIT_AND_IGNORE(MacroExpansionDecl)
 
   // Only members of the active clause are in scope, and those
   // are visited separately.
@@ -353,6 +352,7 @@ class NodeAdder
   VISIT_AND_CREATE(CaseStmt, CaseStmtScope)
   VISIT_AND_CREATE(AbstractFunctionDecl, AbstractFunctionDeclScope)
   VISIT_AND_CREATE(MacroDecl, MacroDeclScope)
+  VISIT_AND_CREATE(MacroExpansionDecl, MacroExpansionDeclScope)
 
 #undef VISIT_AND_CREATE
 
@@ -724,6 +724,7 @@ NO_NEW_INSERTION_POINT(RepeatWhileScope)
 NO_NEW_INSERTION_POINT(SubscriptDeclScope)
 NO_NEW_INSERTION_POINT(MacroDeclScope)
 NO_NEW_INSERTION_POINT(MacroDefinitionScope)
+NO_NEW_INSERTION_POINT(MacroExpansionDeclScope)
 NO_NEW_INSERTION_POINT(SwitchStmtScope)
 NO_NEW_INSERTION_POINT(WhileStmtScope)
 
@@ -1131,6 +1132,16 @@ MacroDefinitionScope::expandAScopeThatDoesNotCreateANewInsertionPoint(
   scopeCreator.addToScopeTree(ASTNode(definition), this);
 }
 
+void MacroExpansionDeclScope::expandAScopeThatDoesNotCreateANewInsertionPoint(
+    ScopeCreator &scopeCreator) {
+  // FIXME: If we get attributes on macro expansions, visit them here.
+  if (auto argList = decl->getArgs()) {
+    for (const auto &arg : *argList) {
+      scopeCreator.addExprToScopeTree(arg.getExpr(), this);
+    }
+  }
+}
+
 void CaptureListScope::expandAScopeThatDoesNotCreateANewInsertionPoint(
     ScopeCreator &scopeCreator) {
   auto *closureExpr = expr->getClosureBody();

lib/AST/ASTScopePrinting.cpp

@@ -182,6 +182,10 @@ void MacroDeclScope::printSpecifics(llvm::raw_ostream &out) const {
   decl->dumpRef(out);
 }
 
+void MacroExpansionDeclScope::printSpecifics(llvm::raw_ostream &out) const {
+  out << decl->getMacroName();
+}
+
 void ConditionalClausePatternUseScope::printSpecifics(
     llvm::raw_ostream &out) const {
   sec.getPattern()->print(out);

lib/AST/ASTScopeSourceRange.cpp

@@ -148,6 +148,11 @@ SourceRange MacroDefinitionScope::getSourceRangeOfThisASTNode(
   return definition->getSourceRange();
 }
 
+SourceRange MacroExpansionDeclScope::getSourceRangeOfThisASTNode(
+    const bool omitAssertions) const {
+  return decl->getSourceRangeIncludingAttrs();
+}
+
 SourceRange
 EnumElementScope::getSourceRangeOfThisASTNode(const bool omitAssertions) const {
   return decl->getSourceRange();

test/Macros/Inputs/syntax_macro_definitions.swift

@@ -208,6 +208,15 @@ enum CustomError: Error, CustomStringConvertible {
   }
 }
 
+public struct EmptyDeclarationMacro: DeclarationMacro {
+  public static func expansion(
+    of node: some FreestandingMacroExpansionSyntax,
+    in context: some MacroExpansionContext
+  ) throws -> [DeclSyntax] {
+    return []
+  }
+}
+
 public struct DefineBitwidthNumberedStructsMacro: DeclarationMacro {
   public static func expansion(
     of node: some FreestandingMacroExpansionSyntax,

test/Macros/macro_expand.swift

@@ -334,3 +334,16 @@ func testFreestandingMacroExpansion() {
   #anonymousTypes { "hello" }
 }
 testFreestandingMacroExpansion()
+
+// Avoid re-type-checking declaration macro arguments.
+@freestanding(declaration)
+macro freestandingWithClosure<T>(_ value: T, body: (T) -> T) = #externalMacro(module: "MacroDefinition", type: "EmptyDeclarationMacro")
+
+func testFreestandingWithClosure(i: Int) {
+  #freestandingWithClosure(i) { x in x }
+
+  #freestandingWithClosure(i) {
+    let x = $0
+    return x
+  }
+}

test/Macros/top_level_freestanding.swift

@@ -35,3 +35,14 @@ struct Main {
     lookupGlobalFreestandingExpansion()
   }
 }
+
+@freestanding(declaration)
+macro freestandingWithClosure<T>(_ value: T, body: (T) -> T) = #externalMacro(module: "MacroDefinition", type: "EmptyDeclarationMacro")
+
+// Unqualified lookup for names defined within macro arguments.
+#freestandingWithClosure(0) { x in x }
+
+#freestandingWithClosure(1) {
+  let x = $0
+  return x
+}