[clang] [clang] Fix friend declaration check (PR #132320)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Chongzhi Deng (BruceAko)

<details>
<summary>Changes</summary>

Fix a crash in `SemaDeclCXX.cpp` when defaulting a comparison operator that has been declared as a friend function alongside class friend declarations. When checking if a defaulted operator is a friend, the code would dereference the result of `FriendDecl::getFriendDecl()` without checking for nullptr, which occurs for class friend declarations.

The fix ensures we check that `getFriendDecl()` returns a non-null pointer before attempting to access its canonical declaration.

---
Full diff: https://github.com/llvm/llvm-project/pull/132320.diff


1 Files Affected:

- (modified) clang/lib/Sema/SemaDeclCXX.cpp (+2-2) 


``````````diff
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index a1551e8027cd3..eae2bbf65db31 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -9039,8 +9039,8 @@ bool Sema::CheckExplicitlyDefaultedComparison(Scope *S, FunctionDecl *FD,
       return true;
 
     if (llvm::none_of(RD->friends(), [&](const FriendDecl *F) {
-          return FD->getCanonicalDecl() ==
-                 F->getFriendDecl()->getCanonicalDecl();
+          NamedDecl *ND = F->getFriendDecl();
+          return ND && FD->getCanonicalDecl() == ND->getCanonicalDecl();
         })) {
       Diag(FD->getLocation(), diag::err_defaulted_comparison_not_friend)
           << int(DCK) << int(0) << RD;

``````````

</details>


https://github.com/llvm/llvm-project/pull/132320