[clang] [clang][Sema] Fix false-positive -Wshadow for friend functions (PR #221249)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: ahmed mohamed kamel (AhmedKamel10)

<details>
<summary>Changes</summary>

A friend function defined inline in a class body has no implicit 'this', so a parameter with the same name as a field cannot actually shadow it. CheckShadow only exempted static members and members with an explicit object parameter (via a valid CXXMethodDecl cast); it never handled the case where the enclosing function isn't a member function at all, which silently fell through to the generic diagnostic. Extend the exemption to cover that case.

Fixes #<!-- -->221190

---
Full diff: https://github.com/llvm/llvm-project/pull/221249.diff


3 Files Affected:

- (modified) clang/docs/ReleaseNotes.md (+2) 
- (modified) clang/lib/Sema/SemaDecl.cpp (+5-7) 
- (modified) clang/test/SemaCXX/warn-shadow.cpp (+11) 


``````````diff
diff --git a/clang/docs/ReleaseNotes.md b/clang/docs/ReleaseNotes.md
index ca5c63fbaa17d..398b1eec0aee0 100644
--- a/clang/docs/ReleaseNotes.md
+++ b/clang/docs/ReleaseNotes.md
@@ -469,6 +469,8 @@ features cannot lower the translation-unit ABI level;
   dimension that is a zero integer constant, as in `struct Empty vla[n]` or
   `int vla[n][0]`. (#GH28328)
 
+- Fixed a false-positive `-Wshadow` warning when a function parameter in an inline-defined friend function shares the name of a non-static class member variable. (#GH221190)
+
 ### Improvements to Clang's time-trace
 
 ### Improvements to Coverage Mapping
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index ccdc33d6fa39b..3339acb3bead4 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -8623,13 +8623,11 @@ void Sema::CheckShadow(NamedDecl *D, NamedDecl *ShadowedDecl,
   DeclContext *NewDC = D->getDeclContext();
 
   if (FieldDecl *FD = dyn_cast<FieldDecl>(ShadowedDecl)) {
-    if (const auto *MD =
-            dyn_cast<CXXMethodDecl>(getFunctionLevelDeclContext())) {
-      // Fields aren't shadowed in C++ static members or in member functions
-      // with an explicit object parameter.
-      if (MD->isStatic() || MD->isExplicitObjectMemberFunction())
-        return;
-    }
+    const auto *MD = dyn_cast<CXXMethodDecl>(getFunctionLevelDeclContext());
+    // Fields aren't shadowed in C++ static members or in member functions
+    // with an explicit object parameter.
+    if (!MD || MD->isStatic() || MD->isExplicitObjectMemberFunction())
+      return;
     // Fields shadowed by constructor parameters are a special case. Usually
     // the constructor initializes the field with the parameter.
     if (isa<CXXConstructorDecl>(NewDC))
diff --git a/clang/test/SemaCXX/warn-shadow.cpp b/clang/test/SemaCXX/warn-shadow.cpp
index 98a235a73c7e5..766766e465bdf 100644
--- a/clang/test/SemaCXX/warn-shadow.cpp
+++ b/clang/test/SemaCXX/warn-shadow.cpp
@@ -90,6 +90,17 @@ class A {
   }
 };
 
+class FriendFunction {
+  int x; // expected-note {{previous declaration is here}}
+
+  friend bool operator==(const FriendFunction &f, int x) {
+    return f.x == x;
+  }
+
+  void test(int x) { // expected-warning {{declaration shadows a field of 'FriendFunction'}}
+  }
+};
+
 struct path {
   using value_type = char;
   typedef char value_type2;

``````````

</details>


https://github.com/llvm/llvm-project/pull/221249