[clang-tools-extra] [clang-tidy] Workaround for cppcoreguidelines-pro-type-union-access if memLoc is invalid (PR #104540)

[Konstantin Romanov via cfe-commits]

https://github.com/ksromanov created https://github.com/llvm/llvm-project/pull/104540

Fixes #102945

>From 5c5f8496341e7b97faf62dad2ba7e0b210bde11b Mon Sep 17 00:00:00 2001
From: Konstantin Romanov <konstantinsromanov at gmail.com>
Date: Fri, 9 Aug 2024 23:40:07 -0400
Subject: [PATCH] Workaround for cppcoreguidelines-pro-type-union-access if
 member location is invalid.

---
 .../cppcoreguidelines/ProTypeUnionAccessCheck.cpp         | 8 ++++++--
 .../checkers/cppcoreguidelines/pro-type-union-access.cpp  | 7 +++++++
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeUnionAccessCheck.cpp b/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeUnionAccessCheck.cpp
index 1ed444e630ec25..0e9185956b7aa8 100644
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeUnionAccessCheck.cpp
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeUnionAccessCheck.cpp
@@ -23,8 +23,12 @@ void ProTypeUnionAccessCheck::registerMatchers(MatchFinder *Finder) {
 
 void ProTypeUnionAccessCheck::check(const MatchFinder::MatchResult &Result) {
   const auto *Matched = Result.Nodes.getNodeAs<MemberExpr>("expr");
-  diag(Matched->getMemberLoc(),
-       "do not access members of unions; use (boost::)variant instead");
+  if (auto MemberLoc = Matched->getMemberLoc(); MemberLoc.isValid())
+    diag(MemberLoc,
+         "do not access members of unions; use (boost::)variant instead");
+  else
+    diag(Matched->getBeginLoc(),
+         "do not access members of unions; use (boost::)variant instead");
 }
 
 } // namespace clang::tidy::cppcoreguidelines
diff --git a/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/pro-type-union-access.cpp b/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/pro-type-union-access.cpp
index 6abc22b9e4345e..46bb06ba2c8fbe 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/pro-type-union-access.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/pro-type-union-access.cpp
@@ -5,6 +5,10 @@ union U {
   char union_member2;
 } u;
 
+union W {
+  template <class TP> operator TP *() const;
+};
+
 struct S {
   int non_union_member;
   union {
@@ -20,6 +24,7 @@ void f(char);
 void f2(U);
 void f3(U&);
 void f4(U*);
+W f5();
 
 void check()
 {
@@ -38,4 +43,6 @@ void check()
   f2(u); // OK
   f3(u); // OK
   f4(&u); // OK
+  void *ret = f5();
+  // CHECK-MESSAGES: :[[@LINE-1]]:15: warning: do not access members of unions; use (boost::)variant instead
 }