[clang] [Clang] fixes false-positive lambda shadow diagnostics in explicit object member functions (PR #165919)

[Oleksandr T. via cfe-commits]

https://github.com/a-tarasyuk created https://github.com/llvm/llvm-project/pull/165919

Fixes #163731

---

This PR addresses false-positive shadow diagnostics for lambdas inside explicit object member functions

```cpp
struct S {
  int x;
  void m(this S &self) {
    auto lambda = [](int x) { return x; }; // ok
  }
};
```



>From 9b2073d5b4b6c3654560676f257f4041ada2fb1f Mon Sep 17 00:00:00 2001
From: Oleksandr Tarasiuk <oleksandr.tarasiuk at outlook.com>
Date: Fri, 31 Oct 2025 22:54:53 +0200
Subject: [PATCH] [Clang] fixes false-positive lambda shadow diagnostics in
 explicit-object member functions

---
 clang/docs/ReleaseNotes.rst                   |  1 +
 clang/lib/Sema/SemaDecl.cpp                   |  5 ++++
 clang/test/SemaCXX/warn-shadow-in-lambdas.cpp | 28 +++++++++++++++++++
 3 files changed, 34 insertions(+)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 92fc9381a5868..593e117777314 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -432,6 +432,7 @@ Bug Fixes in This Version
 - Fixed a failed assertion with empty filename arguments in ``__has_embed``. (#GH159898)
 - Fixed a failed assertion with empty filename in ``#embed`` directive. (#GH162951)
 - Fixed a crash triggered by unterminated ``__has_embed``. (#GH162953)
+- Fixed false-positive shadow diagnostics for lambdas in explicit object member functions. (#GH163731)
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index fc3aabf5741ca..96aea9877719e 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -8640,6 +8640,11 @@ void Sema::DiagnoseShadowingLambdaDecls(const LambdaScopeInfo *LSI) {
             << Shadow.VD->getDeclName() << /*explicitly*/ 0;
       Diag(ShadowedDecl->getLocation(), diag::note_previous_declaration);
     } else if (isa<FieldDecl>(ShadowedDecl)) {
+      if (CXXMethodDecl *MD =
+              dyn_cast<CXXMethodDecl>(getFunctionLevelDeclContext()))
+        if (MD->isExplicitObjectMemberFunction())
+          continue;
+
       Diag(Shadow.VD->getLocation(),
            LSI->isCXXThisCaptured() ? diag::warn_decl_shadow
                                     : diag::warn_decl_shadow_uncaptured_local)
diff --git a/clang/test/SemaCXX/warn-shadow-in-lambdas.cpp b/clang/test/SemaCXX/warn-shadow-in-lambdas.cpp
index 0042ef035c84c..47653a9c39d15 100644
--- a/clang/test/SemaCXX/warn-shadow-in-lambdas.cpp
+++ b/clang/test/SemaCXX/warn-shadow-in-lambdas.cpp
@@ -3,6 +3,7 @@
 // RUN: %clang_cc1 -std=c++14 -verify=expected,cxx14 -fsyntax-only -Wshadow-all %s
 // RUN: %clang_cc1 -std=c++17 -verify -fsyntax-only -Wshadow-all %s
 // RUN: %clang_cc1 -std=c++20 -verify -fsyntax-only -Wshadow-all %s
+// RUN: %clang_cc1 -std=c++23 -verify -fsyntax-only -Wshadow-all %s
 
 void foo(int param) { // expected-note 1+ {{previous declaration is here}}
   int var = 0; // expected-note 1+ {{previous declaration is here}}
@@ -268,5 +269,32 @@ int foo() {
   }();
 #endif
 }
+}
+
+#if __cplusplus >= 202302L
+namespace GH163731 {
+struct S1 {
+  int a;
+  void m(this S1 &self) {
+    auto lambda = [](int a) { return a; };
+  }
+};
+
+struct S2 {
+  int a;
+  void m(this S2 &self) {
+    int a = 1;                // expected-note {{previous declaration is here}}
+    auto lambda = [](int a) { // expected-warning {{declaration shadows a local variable}}
+      return a;
+    };
+  }
+};
 
+struct S3 {
+  int a;
+  void m(this S3 &self) {
+    auto lambda = [self](int a) { return a + self.a; };
+  }
+};
 }
+#endif