[PR49761] Fix variadic arg handling in matcher

[chrish_ericsson_atx]

Summary

Mishandling of variadic arguments in a function call caused a crash
(runtime assert fail) in bugprone-infinite-loop tidy checker. Fix
is to limit argument matching to the lesser of the number of variadic
params in the prototype or the number of actual args in the call.

[aaron.ballman]

Thank you for the fix! LGTM with some minor nits.

clang/include/clang/ASTMatchers/ASTMatchers.h

4760–4765

[chrish_ericsson_atx]

clang/include/clang/ASTMatchers/ASTMatchers.h

4760–4765

Thanks Aaron! Nice simplification. I don't know why I can't remember the variable name style -- old habits die hard! :) Thanks for the feedback.

[chrish_ericsson_atx]

Addressed feedback from aaron.ballman.

clang-tools-extra/test/clang-tidy/checkers/bugprone-infinite-loop.cpp

 void evaluatable(bool CondVar) {
   for (; false && CondVar;) {
   }
   while (false && CondVar) {
   }
   do {
   } while (false && CondVar);
 }
+
+struct logger {
+  void (*debug)(struct logger *, const char *, ...);
+};
+
+int foo(void) {
+  struct logger *pl = 0;
+  int iterator = 0;
+  while (iterator < 10) {
+    char *l_tmp_msg = 0;
+    pl->debug(pl, "%d: %s\n", iterator, l_tmp_msg);
+    iterator++;
+  }
+  return 0;
+}

clang/include/clang/ASTMatchers/ASTMatchers.h

if (const auto *Value =
                "The call must have happened through a member function "
                "pointer");
       }
     }
   }
 
   int ParamIndex = 0;
   bool Matched = false;
+  unsigned NumArgs = Node.getNumArgs();
+  if (FProto && FProto->isVariadic())
+    NumArgs = std::min(NumArgs, FProto->getNumParams());
 
-  for (; ArgIndex < Node.getNumArgs(); ++ArgIndex, ++ParamIndex) {
+  for (; ArgIndex < NumArgs; ++ArgIndex, ++ParamIndex) {
     BoundNodesTreeBuilder ArgMatches(*Builder);
     if (ArgMatcher.matches(*(Node.getArg(ArgIndex)->IgnoreParenCasts()), Finder,
                            &ArgMatches)) {
       BoundNodesTreeBuilder ParamMatches(ArgMatches);
 
       // This test is cheaper compared to the big matcher in the next if.
       // Therefore, please keep this order.
       if (FProto) {
         QualType ParamType = FProto->getParamType(ParamIndex);