[AST] Avoid walking macro expanded bodies in non-expanded mode

Make sure we don't walk into the expansion of a body macro if the AST
walker is configured not to walk macro expansions.

Author: hamishknight

include/swift/AST/Decl.h

@@ -8065,6 +8065,11 @@ class AbstractFunctionDecl : public GenericContext, public ValueDecl {
   /// type-checked.
   BraceStmt *getMacroExpandedBody() const;
 
+  /// Whether the body of the function has been expanded from a body macro.
+  bool isBodyMacroExpanded() const {
+    return getBodyExpandedStatus() == BodyExpandedStatus::Expanded;
+  }
+
   /// Retrieve the type-checked body of the given function, or \c nullptr if
   /// there's no body available.
   BraceStmt *getTypecheckedBody() const;

lib/AST/ASTWalker.cpp

@@ -558,7 +558,12 @@ class Traversal : public ASTVisitor<Traversal, Expr*, Stmt*,
     if (WalkGenerics && visitTrailingRequirements(AFD))
       return true;
 
-    if (AFD->getBody(/*canSynthesize=*/false)) {
+    // If we're not walking macro expansions, avoid walking into a body if it
+    // was expanded from a macro.
+    auto SkipBody = !Walker.shouldWalkMacroArgumentsAndExpansion().second &&
+                    AFD->isBodyMacroExpanded();
+
+    if (!SkipBody && AFD->getBody(/*canSynthesize=*/false)) {
       AbstractFunctionDecl::BodyKind PreservedKind = AFD->getBodyKind();
       if (BraceStmt *S = cast_or_null<BraceStmt>(doIt(AFD->getBody())))
         AFD->setBody(S, PreservedKind);