[Macros] Fix an issue where the constraint system skipped local declarations

inside closures while type checking a macro expansion.

PreCheckExpr, ConstraintGenerator, and other walkers do not walk into macro
expansions. However, the implementation of this macro walking behavior in
ASTWalker would skip any declaration that appears inside any macro expansion
buffer. This is incorrect for cases where the parent is in the same macro
expansion buffer, because the local declaration is not inside a new macro
expansion. This caused bogus errors when type checking expanded macro expressions
containing closures with local declarations, because pre-check and constraint
generation mistakenly skipped local pattern bindings.

Author: hborla

include/swift/AST/Decl.h

@@ -935,9 +935,14 @@ class alignas(1 << DeclAlignInBits) Decl : public ASTAllocated<Decl> {
 
   SourceLoc TrailingSemiLoc;
 
-  /// Whether this declaration is within a generated buffer, \c false if this
-  /// declaration was constructed from a serialized module.
-  bool isInGeneratedBuffer() const;
+  /// Whether this declaration is within a macro expansion relative to
+  /// its decl context. If the decl context is itself in a macro expansion,
+  /// the method returns \c true if this decl is in a different macro
+  /// expansion buffer than the context.
+  ///
+  /// \Note this method returns \c false if this declaration was
+  /// constructed from a serialized module.
+  bool isInMacroExpansionInContext() const;
 
   /// Returns the appropriate kind of entry point to generate for this class,
   /// based on its attributes.

lib/AST/ASTWalker.cpp

@@ -1481,7 +1481,7 @@ class Traversal : public ASTVisitor<Traversal, Expr*, Stmt*,
 
   bool shouldSkip(Decl *D) {
     if (!Walker.shouldWalkMacroArgumentsAndExpansion().second &&
-        D->isInGeneratedBuffer())
+        D->isInMacroExpansionInContext())
       return true;
 
     if (auto *VD = dyn_cast<VarDecl>(D)) {

lib/AST/Decl.cpp

@@ -765,8 +765,22 @@ SourceRange Decl::getSourceRangeIncludingAttrs() const {
   return Range;
 }
 
-bool Decl::isInGeneratedBuffer() const {
-  return getModuleContext()->isInGeneratedBuffer(getStartLoc());
+bool Decl::isInMacroExpansionInContext() const {
+  auto *dc = getDeclContext();
+  auto parentFile = dc->getParentSourceFile();
+  auto *mod = getModuleContext();
+  auto *file = mod->getSourceFileContainingLocation(getStartLoc());
+
+  // Decls in macro expansions always have a source file. The source
+  // file can be null if the decl is implicit or has an invalid
+  // source location.
+  if (!parentFile || !file)
+    return false;
+
+  if (file->getBufferID() == parentFile->getBufferID())
+    return false;
+
+  return file->getFulfilledMacroRole() != None;
 }
 
 SourceLoc Decl::getLocFromSource() const {

lib/IDE/SourceEntityWalker.cpp

@@ -889,7 +889,7 @@ bool SemaAnnotator::shouldIgnore(Decl *D) {
   // by a member attribute expansion. Note that we would have already skipped
   // this decl if we were ignoring expansions, so no need to check that.
   if (auto *missing = dyn_cast<MissingDecl>(D)) {
-    if (D->isInGeneratedBuffer())
+    if (D->isInMacroExpansionInContext())
       return false;
   }
 

test/Macros/Inputs/syntax_macro_definitions.swift

@@ -1360,3 +1360,18 @@ public struct SimpleCodeItemMacro: CodeItemMacro {
     ]
   }
 }
+
+public struct MultiStatementClosure: ExpressionMacro {
+  public static func expansion(
+    of node: some FreestandingMacroExpansionSyntax,
+    in context: some MacroExpansionContext
+  ) throws -> ExprSyntax {
+    return """
+      {
+        let temp = 10
+        let result = temp
+        return result
+      }()
+      """
+  }
+}

test/Macros/macro_expand_closure.swift

@@ -0,0 +1,16 @@
+// REQUIRES: swift_swift_parser, executable_test
+
+// RUN: %empty-directory(%t)
+// RUN: %host-build-swift -swift-version 5 -emit-library -o %t/%target-library-name(MacroDefinition) -module-name=MacroDefinition %S/Inputs/syntax_macro_definitions.swift -g -no-toolchain-stdlib-rpath
+// RUN: %target-build-swift -swift-version 5 -load-plugin-library %t/%target-library-name(MacroDefinition) %s -o %t/main -module-name MacroUser -swift-version 5
+// RUN: %target-codesign %t/main
+// RUN: %target-run %t/main | %FileCheck %s
+
+@freestanding(expression) public macro multiStatement() -> Int = #externalMacro(module: "MacroDefinition", type: "MultiStatementClosure")
+
+func multiStatementInference() -> Int {
+  #multiStatement()
+}
+
+// CHECK: 10
+print(multiStatementInference())