From be0905a333d6f7c4d7f5c70c18211463e53473cd Mon Sep 17 00:00:00 2001
From: Jun Zhang <jun@junz.org>
Date: Fri, 15 Apr 2022 15:14:38 +0800
Subject: [PATCH] [Clang][Sema] Fix invalid redefinition error in if/switch/for
 statement

Clang should no longer incorrectly diagnose a variable declaration inside of a
lambda expression that shares the name of a variable in a containing
if/while/for/switch init statement as a redeclaration.

After this patch, clang is supposed to accept code below:

void foo() {
  for (int x = [] { int x = 0; return x; }(); ;) ;
}

Fixes https://github.com/llvm/llvm-project/issues/54913

Differential Revision: https://reviews.llvm.org/D123840
---
 clang/docs/ReleaseNotes.rst                 |  4 ++++
 clang/lib/Sema/IdentifierResolver.cpp       |  5 ++++-
 clang/test/SemaCXX/cxx1z-init-statement.cpp | 15 +++++++++++++++
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index f5d3793..2497280 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -119,6 +119,10 @@ Bug Fixes
   This fixes Issue `Issue 52802 <https://github.com/llvm/llvm-project/issues/52802>`_.
 - Unknown type attributes with a ``[[]]`` spelling are no longer diagnosed twice.
   This fixes Issue `Issue 54817 <https://github.com/llvm/llvm-project/issues/54817>`_.
+- Clang should no longer incorrectly diagnose a variable declaration inside of
+  a lambda expression that shares the name of a variable in a containing
+  if/while/for/switch init statement as a redeclaration.
+  This fixes `Issue 54913 <https://github.com/llvm/llvm-project/issues/54913>`_.
 
 Improvements to Clang's diagnostics
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/IdentifierResolver.cpp b/clang/lib/Sema/IdentifierResolver.cpp
index 333f4d7..9c5d78f 100644
--- a/clang/lib/Sema/IdentifierResolver.cpp
+++ b/clang/lib/Sema/IdentifierResolver.cpp
@@ -121,7 +121,10 @@ bool IdentifierResolver::isDeclInScope(Decl *D, DeclContext *Ctx, Scope *S,
       // of the controlled statement.
       //
       assert(S->getParent() && "No TUScope?");
-      if (S->getParent()->getFlags() & Scope::ControlScope) {
+      // If the current decl is in a lambda, we shouldn't consider this is a
+      // redefinition as lambda has its own scope.
+      if (S->getParent()->getFlags() & Scope::ControlScope &&
+          !S->isFunctionScope()) {
         S = S->getParent();
         if (S->isDeclScope(D))
           return true;
diff --git a/clang/test/SemaCXX/cxx1z-init-statement.cpp b/clang/test/SemaCXX/cxx1z-init-statement.cpp
index eea2589..b963c9e 100644
--- a/clang/test/SemaCXX/cxx1z-init-statement.cpp
+++ b/clang/test/SemaCXX/cxx1z-init-statement.cpp
@@ -90,3 +90,18 @@ void test_constexpr_init_stmt() {
   static_assert(constexpr_switch_init(-2) == 0, "");
   static_assert(constexpr_switch_init(-5) == -1, "");
 }
+
+int test_lambda_init() {
+  if (int x = []() {int x = 42; return x; }(); x) {
+  };
+
+  switch (int y = []() {int y = 42; return y; }(); y) {
+  case 42:
+    return 1;
+  }
+
+  for (int x = [] { int x = 0; return x; }();;)
+    ;
+
+  return 0;
+}
-- 
2.7.4