[clang-tidy] Fix cppcoreguidelines-pro-type-union-access if memLoc is invalid (llvm#104540)

Fixes llvm#102945.

Author: ksromanov

clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeUnionAccessCheck.cpp

@@ -23,8 +23,11 @@ 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");
+  SourceLocation Loc = Matched->getMemberLoc();
+  if (Loc.isInvalid())
+    Loc = Matched->getBeginLoc();
+  diag(Loc, "do not access members of unions; consider using (boost::)variant "
+            "instead");
 }
 
 } // namespace clang::tidy::cppcoreguidelines

clang-tools-extra/docs/ReleaseNotes.rst

@@ -180,6 +180,10 @@ Changes in existing checks
   avoid false positive when member initialization depends on a structured
   binding variable.
 
+- Fixed :doc:`cppcoreguidelines-pro-type-union-access
+  <clang-tidy/checks/cppcoreguidelines/pro-type-union-access>` check to
+  report a location even when the member location is not valid.
+
 - Improved :doc:`misc-definitions-in-headers
   <clang-tidy/checks/misc/definitions-in-headers>` check by rewording the
   diagnostic note that suggests adding ``inline``.

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 {
@@ -20,22 +24,25 @@ void f(char);
 void f2(U);
 void f3(U&);
 void f4(U*);
+W f5();
 
 void check()
 {
   u.union_member1 = true;
-  // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: do not access members of unions; use (boost::)variant instead [cppcoreguidelines-pro-type-union-access]
+  // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: do not access members of unions; consider using (boost::)variant instead [cppcoreguidelines-pro-type-union-access]
   auto b = u.union_member2;
-  // CHECK-MESSAGES: :[[@LINE-1]]:14: warning: do not access members of unions; use (boost::)variant instead
+  // CHECK-MESSAGES: :[[@LINE-1]]:14: warning: do not access members of unions; consider using (boost::)variant instead
   auto a = &s.union_member;
-  // CHECK-MESSAGES: :[[@LINE-1]]:15: warning: do not access members of unions; use (boost::)variant instead
+  // CHECK-MESSAGES: :[[@LINE-1]]:15: warning: do not access members of unions; consider using (boost::)variant instead
   f(s.u.union_member2);
-  // CHECK-MESSAGES: :[[@LINE-1]]:9: warning: do not access members of unions; use (boost::)variant instead
+  // CHECK-MESSAGES: :[[@LINE-1]]:9: warning: do not access members of unions; consider using (boost::)variant instead
 
   s.non_union_member = 2; // OK
 
   U u2 = u; // OK
   f2(u); // OK
   f3(u); // OK
   f4(&u); // OK
+  void *ret = f5();
+  // CHECK-MESSAGES: :[[@LINE-1]]:15: warning: do not access members of unions; consider using (boost::)variant instead
 }