[clang-format] Fix a crash due to dereferencing null MatchingParen

[owenpan]

Summary

Fixes https://github.com/llvm/llvm-project/issues/59089.

[owenpan]

Added a test case.

[rymiel]

Could the check be hoisted to the top of the loop? could that possibly catch more cases?

[rymiel]

Oops, nevermind, I misunderstood the loop

[HazardyKnusperkeks]

In D138371#3939682, @rymiel wrote:

Oops, nevermind, I misunderstood the loop

To understand this is really a tough one. Took me some minutes too, to see why the return is needed.

[rymiel]

In D138371#3939938, @HazardyKnusperkeks wrote:

In D138371#3939682, @rymiel wrote:

Oops, nevermind, I misunderstood the loop

To understand this is really a tough one. Took me some minutes too, to see why the return is needed.

I think the fact that almost every word is "Next" doesn't help 😃

clang/lib/Format/TokenAnnotator.cpp

for (; Next; Next = Next->Next) {
         if (Next->is(tok::kw_operator)) {
           Next = skipOperatorName(Next->Next);
           break;
         }
         if (!Next->is(tok::identifier))
           return false;
       } else if (isCppAttribute(IsCpp, *Next)) {
         Next = Next->MatchingParen;
+        if (!Next)
+          return false;
       } else if (Next->is(tok::l_paren)) {
         break;
       } else {
         return false;
       }
     }
   }
 

clang/unittests/Format/FormatTest.cpp

verifyFormat("class Foo {\n"
                "  int getSomething() const { return something; };;\n"
                "};",
                Style);
 
   verifyFormat("for (;;) {\n"
                "}",
                Style);
 
+  verifyIncompleteFormat("class C final [[deprecated(l]] {});", Style);
+
   // These tests are here to show a problem that may not be easily
   // solved, our implementation to remove semicolons is only as good
   // as our FunctionLBrace detection and this fails for empty braces
   // because we can't distringuish this from a bracelist.
   // We will enable when that is resolved.
 #if 0
   verifyFormat("void main() {}", "void main() {};", Style);
   verifyFormat("void foo() {} //\n"