[AST] Treat semantic form of InitListExpr as implicit code in traversals

Summary:
In particular, do not traverse the semantic form if shouldVisitImplicitCode()
returns false.

This simplifies the common case of traversals, avoiding the need to
worry about some expressions being traversed twice.

No tests break after the change, the change would allow to simplify at
least one of the usages, i.e. r366070 which had to handle this in
clangd.

Reviewers: gribozavr

Reviewed By: gribozavr

Subscribers: kadircet, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D64762

llvm-svn: 366672

clang/include/clang/AST/RecursiveASTVisitor.h

@@ -2308,19 +2308,30 @@ bool RecursiveASTVisitor<Derived>::TraverseSynOrSemInitListExpr(
   return true;
 }
 
-// This method is called once for each pair of syntactic and semantic
+// If shouldVisitImplicitCode() returns false, this method traverses only the
-// InitListExpr, and it traverses the subtrees defined by the two forms. This
+// syntactic form of InitListExpr.
-// may cause some of the children to be visited twice, if they appear both in
+// If shouldVisitImplicitCode() return true, this method is called once for
-// the syntactic and the semantic form.
+// each pair of syntactic and semantic InitListExpr, and it traverses the
+// subtrees defined by the two forms. This may cause some of the children to be
+// visited twice, if they appear both in the syntactic and the semantic form.
 //
 // There is no guarantee about which form \p S takes when this method is called.
 template <typename Derived>
 bool RecursiveASTVisitor<Derived>::TraverseInitListExpr(
     InitListExpr *S, DataRecursionQueue *Queue) {
+  if (S->isSemanticForm() && S->isSyntacticForm()) {
+    // `S` does not have alternative forms, traverse only once.
+    TRY_TO(TraverseSynOrSemInitListExpr(S, Queue));
+    return true;
+  }
   TRY_TO(TraverseSynOrSemInitListExpr(
       S->isSemanticForm() ? S->getSyntacticForm() : S, Queue));
-  TRY_TO(TraverseSynOrSemInitListExpr(
+  if (getDerived().shouldVisitImplicitCode()) {
-      S->isSemanticForm() ? S : S->getSemanticForm(), Queue));
+    // Only visit the semantic form if the clients are interested in implicit
+    // compiler-generated.
+    TRY_TO(TraverseSynOrSemInitListExpr(
+        S->isSemanticForm() ? S : S->getSemanticForm(), Queue));
+  }
   return true;
 }
 

clang/unittests/Tooling/RecursiveASTVisitorTests/InitListExprPreOrder.cpp

@@ -17,14 +17,22 @@ namespace {
 class InitListExprPreOrderVisitor
     : public ExpectedLocationVisitor<InitListExprPreOrderVisitor> {
 public:
+  InitListExprPreOrderVisitor(bool VisitImplicitCode)
+      : VisitImplicitCode(VisitImplicitCode) {}
+
+  bool shouldVisitImplicitCode() const { return VisitImplicitCode; }
+
   bool VisitInitListExpr(InitListExpr *ILE) {
     Match(ILE->isSemanticForm() ? "semantic" : "syntactic", ILE->getBeginLoc());
     return true;
   }
+
+private:
+  bool VisitImplicitCode;
 };
 
 TEST(RecursiveASTVisitor, InitListExprIsPreOrderVisitedTwice) {
-  InitListExprPreOrderVisitor Visitor;
+  InitListExprPreOrderVisitor Visitor(/*VisitImplicitCode=*/true);
   Visitor.ExpectMatch("syntactic", 2, 21);
   Visitor.ExpectMatch("semantic", 2, 21);
   EXPECT_TRUE(Visitor.runOver("struct S { int x; };\n"
@@ -32,4 +40,13 @@ TEST(RecursiveASTVisitor, InitListExprIsPreOrderVisitedTwice) {
                               InitListExprPreOrderVisitor::Lang_C));
 }
 
+TEST(RecursiveASTVisitor, InitListExprVisitedOnceWhenNoImplicit) {
+  InitListExprPreOrderVisitor Visitor(/*VisitImplicitCode=*/false);
+  Visitor.ExpectMatch("syntactic", 2, 21);
+  Visitor.DisallowMatch("semantic", 2, 21);
+  EXPECT_TRUE(Visitor.runOver("struct S { int x; };\n"
+                              "static struct S s = {.x = 0};\n",
+                              InitListExprPreOrderVisitor::Lang_C));
+}
+
 } // end anonymous namespace