[clang] [clang] Don't use `VarDecl` of local variables as `ManglingContextDecl` for lambdas (PR #179035)

[Jan Kokemüller via cfe-commits]

https://github.com/jiixyj updated https://github.com/llvm/llvm-project/pull/179035

>From 72d814fb6d05ae529538d5b673277e6c065bbbb5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jan=20Kokem=C3=BCller?= <jan.kokemueller at gmail.com>
Date: Sat, 31 Jan 2026 14:26:59 +0100
Subject: [PATCH 1/3] Don't use VarDecl of local variables as
 ManglingContextDecl for lambdas

---
 clang/lib/Sema/SemaLambda.cpp    |  8 ++++++++
 clang/test/Modules/pr178893.cppm | 29 +++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)
 create mode 100644 clang/test/Modules/pr178893.cppm

diff --git a/clang/lib/Sema/SemaLambda.cpp b/clang/lib/Sema/SemaLambda.cpp
index e74fe02bd0cf5..24426259bf01c 100644
--- a/clang/lib/Sema/SemaLambda.cpp
+++ b/clang/lib/Sema/SemaLambda.cpp
@@ -294,6 +294,14 @@ Sema::getCurrentMangleNumberContext(const DeclContext *DC) {
   bool IsInNonspecializedTemplate =
       inTemplateInstantiation() || CurContext->isDependentContext();
 
+  // If we must allocate mangling numbers but the `ManglingContextDecl`
+  // is a local variable, use the `DeclContext` containing the lambda expression
+  // instead.
+  if (ManglingContextDecl)
+    if (VarDecl *Var = dyn_cast<VarDecl>(ManglingContextDecl);
+        Var && Var->isLocalVarDecl())
+      ManglingContextDecl = const_cast<Decl *>(cast<Decl>(DC));
+
   // Default arguments of member function parameters that appear in a class
   // definition, as well as the initializers of data members, receive special
   // treatment. Identify them.
diff --git a/clang/test/Modules/pr178893.cppm b/clang/test/Modules/pr178893.cppm
new file mode 100644
index 0000000000000..6d2a599588667
--- /dev/null
+++ b/clang/test/Modules/pr178893.cppm
@@ -0,0 +1,29 @@
+// RUN: %clang_cc1 -std=c++20 -triple x86_64-apple-macosx10.7.0 -fmodules -xc++ -emit-llvm -o - %s -w | FileCheck %s
+
+// CHECK-LABEL: define linkonce_odr noundef i32 @_ZZN8PR178893W3mod6format5parseEPiENKUlvE_clEv
+// CHECK-LABEL: define linkonce_odr noundef i32 @_ZZN8PR178893W3mod6format5parseEPiENKUlvE0_clEv
+
+export module mod;
+
+namespace PR178893 {
+  struct format {
+      static inline int parse(int* i)
+      {
+          int number;
+          number = [&]() -> int { return i[0]; }();
+
+          volatile bool b = true;
+          if (b) {
+              auto identifier = [&]() -> int { return i[1]; }();
+              return identifier;
+          }
+
+          return number;
+      }
+  };
+
+  int test_format() {
+      int n[2] = {1, 0};
+      return format::parse(n);
+  }
+}

>From d5dbb1738f1d2c90850d27ba5e3e7245e6f325ac Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jan=20Kokem=C3=BCller?= <jan.kokemueller at gmail.com>
Date: Sun, 1 Feb 2026 10:45:25 +0100
Subject: [PATCH 2/3] Use `dyn_cast_or_null` instead of null check plus
 `dyn_cast`

Co-authored-by: Corentin Jabot <corentinjabot at gmail.com>
---
 clang/lib/Sema/SemaLambda.cpp | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/clang/lib/Sema/SemaLambda.cpp b/clang/lib/Sema/SemaLambda.cpp
index 24426259bf01c..cdefd60508164 100644
--- a/clang/lib/Sema/SemaLambda.cpp
+++ b/clang/lib/Sema/SemaLambda.cpp
@@ -297,8 +297,7 @@ Sema::getCurrentMangleNumberContext(const DeclContext *DC) {
   // If we must allocate mangling numbers but the `ManglingContextDecl`
   // is a local variable, use the `DeclContext` containing the lambda expression
   // instead.
-  if (ManglingContextDecl)
-    if (VarDecl *Var = dyn_cast<VarDecl>(ManglingContextDecl);
+  if (VarDecl *Var = dyn_cast_or_null<VarDecl>(ManglingContextDecl);
         Var && Var->isLocalVarDecl())
       ManglingContextDecl = const_cast<Decl *>(cast<Decl>(DC));
 

>From 42bb683d0d44e008408f542b01e192a4d192e273 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jan=20Kokem=C3=BCller?= <jan.kokemueller at gmail.com>
Date: Sun, 1 Feb 2026 10:56:51 +0100
Subject: [PATCH 3/3] Autoformat

---
 clang/lib/Sema/SemaLambda.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/clang/lib/Sema/SemaLambda.cpp b/clang/lib/Sema/SemaLambda.cpp
index cdefd60508164..1066333722bd8 100644
--- a/clang/lib/Sema/SemaLambda.cpp
+++ b/clang/lib/Sema/SemaLambda.cpp
@@ -298,8 +298,8 @@ Sema::getCurrentMangleNumberContext(const DeclContext *DC) {
   // is a local variable, use the `DeclContext` containing the lambda expression
   // instead.
   if (VarDecl *Var = dyn_cast_or_null<VarDecl>(ManglingContextDecl);
-        Var && Var->isLocalVarDecl())
-      ManglingContextDecl = const_cast<Decl *>(cast<Decl>(DC));
+      Var && Var->isLocalVarDecl())
+    ManglingContextDecl = const_cast<Decl *>(cast<Decl>(DC));
 
   // Default arguments of member function parameters that appear in a class
   // definition, as well as the initializers of data members, receive special