[clang-format] Fix a crash (assertion) in qualifier alignment when matching template closer is null

[MyDeveloperDay]

Summary

https://github.com/llvm/llvm-project/issues/53008

template <class Id> using A = quantity /**/<kind<Id>, 1>;

the presence of the comment between identifier and template opener seems to be causing the qualifier alignment to fail

[MyDeveloperDay]

The cause is because Next is a comment, not a template opener, handle that case.

[curdeius]

clang/unittests/Format/QualifierFixerTest.cpp

830

Could you test with a line comment too?

830

And what about multiple comments? Maybe we need a while loop instead of if?

[curdeius]

clang/unittests/Format/QualifierFixerTest.cpp

830

And test with non-empty comments too.

[MyDeveloperDay]

Use getNextNonComment() which has some const-ness knock ons (but probably not a bad thing)

address the review concerns by adding more tests (which indeed highlighted new failure scenarios! Thanks @curdeius)

[curdeius]

LGTM! Thanks :).

[curdeius]

Just a last thought, you can maybe minimize some of the test cases.
It seems that even:

using X = Y /**/ <>;

reproduces the issue.

[MyDeveloperDay]

Simplify down the test to make it easier to read, keep perhaps slightly duplicated tests to just ensure we have the coverage

[curdeius]

Cool. Thanks!

clang/lib/Format/QualifierAlignmentFixer.cpp

if (Tok->startsSequence(tok::identifier) && Tok->Next) {
     FormatToken *Next = Tok->Next;
     // The case  `std::Foo<T> const` -> `const std::Foo<T> &&`
     while (Next && Next->isOneOf(tok::identifier, tok::coloncolon))
       Next = Next->Next;
     if (Next && Next->Previous &&
         Next->Previous->startsSequence(tok::identifier, TT_TemplateOpener)) {
       // Read from to the end of the TemplateOpener to
       // TemplateCloser const ArrayRef<int> a; const ArrayRef<int> &a;
-      assert(Next->MatchingParen && "Missing template closer");
+      if (!Next->MatchingParen)
+        return Next;
       Next = Next->MatchingParen->Next;
 
       // Move to the end of any template class members e.g.
       // `Foo<int>::iterator`.
       if (Next && Next->startsSequence(tok::coloncolon, tok::identifier))
         Next = Next->Next->Next;
       if (Next && Next->is(QualifierType)) {
         // Remove the const.

clang/unittests/Format/QualifierFixerTest.cpp

TEST_F(QualifierFixerTest, NoOpQualifierReplacements) {
   Style.QualifierOrder = {"static", "const", "type"};
 
   ReplacementCount = 0;
   EXPECT_EQ(ReplacementCount, 0);
   verifyFormat("static const uint32 foo[] = {0, 31};", Style);
   EXPECT_EQ(ReplacementCount, 0);
 }
 
+TEST_F(QualifierFixerTest, QualifierTemplates) {
+
+  FormatStyle Style = getLLVMStyle();
+  Style.QualifierAlignment = FormatStyle::QAS_Custom;
+  Style.QualifierOrder = {"static", "const", "type"};
+
+  ReplacementCount = 0;
+  EXPECT_EQ(ReplacementCount, 0);
+  verifyFormat("template <class Id> using A = quantity /**/<kind<Id>, 1>;",
+               Style);
+  EXPECT_EQ(ReplacementCount, 0);
+}
+
 } // namespace format
 } // namespace clang