[clang][AST] Fix crash getting name of a template decl

[tblah]

Summary

NamedDecl::getIdentifier can return a nullptr when DeclarationName::isIdentifier is false, which leads to a null pointer dereference when TypePrinter::printTemplateId calls ->getName().

NamedDecl::getName does the same thing in the successful case and returns an empty string in the failure case.

This crash affects the llvm 14 packages on llvm.org.

[aaron.ballman]

This looks good in general, but can you add a test case for the scenario which previously crashed and a release note for the fix?

[tblah]

Added a unit test

[tblah]

I'm not able to reproduce the test failure in CI. It looks spurious to me because I have not changed anything related to openmp. The only change in behaviour after my patch should be to avoid a null pointer dereference. In tests which did not hit that null pointer dereference before there should not be any change in behaviour.

What I tried:

• Use a debian 11 x64 base image
• Install a minimum set of required packages from debian repos (including clang and lld from debian)
• Run the commands listed under "Reproduce build locally" on the CI failure report

[aaron.ballman]

LGTM, with a commenting nit. The Precommit CI test failures look unrelated to me as well.

Do you need me to commit on your behalf? If so, what name and email address would you like me to use for patch attribution? (I can fix the commenting issue when I land, so don't worry about pushing up a new patch.)

clang/unittests/AST/TypePrinterTest.cpp

74–75 ↗

(On Diff #422906)

[tblah]

Yes please commit on my behalf. My details are

Tom Eccles

[e-mail]

Thanks

[aaron.ballman]

Thank you for the fix! I've commit on your behalf in 225b91e6cbba31ff1ce787a152a67977d08fdcab.

[tcanabrava]

This affects all released versions of llvm14, and potentially llvm13 too (I got a crash today on llvm13 hitting this exact code).
yet, this is not backported to llvm14 on the current 14.x github branch. Please backport so this is released on the next tarball.

[aaron.ballman]

In D123667#3524614, @tcanabrava wrote:

This affects all released versions of llvm14, and potentially llvm13 too (I got a crash today on llvm13 hitting this exact code).
yet, this is not backported to llvm14 on the current 14.x github branch. Please backport so this is released on the next tarball.

I filed https://github.com/llvm/llvm-project/issues/55585 to see if we can get this into the 14.x branch, thanks for the request!

[aaron.ballman]

In D123667#3524711, @aaron.ballman wrote:

In D123667#3524614, @tcanabrava wrote:

This affects all released versions of llvm14, and potentially llvm13 too (I got a crash today on llvm13 hitting this exact code).
yet, this is not backported to llvm14 on the current 14.x github branch. Please backport so this is released on the next tarball.

I filed https://github.com/llvm/llvm-project/issues/55585 to see if we can get this into the 14.x branch, thanks for the request!

And it looks like it was backported today.

[tcanabrava]

thank you, this is really appreciated.

clang/lib/AST/TypePrinter.cpp

void TypePrinter::printTemplateId(const TemplateSpecializationType *T,
                                   raw_ostream &OS, bool FullyQualify) {
   IncludeStrongLifetimeRAII Strong(Policy);
 
   TemplateDecl *TD = T->getTemplateName().getAsTemplateDecl();
   if (FullyQualify && TD) {
     if (!Policy.SuppressScope)
       AppendScope(TD->getDeclContext(), OS, TD->getDeclName());
 
-    IdentifierInfo *II = TD->getIdentifier();
-    OS << II->getName();
+    OS << TD->getName();
   } else {
     T->getTemplateName().print(OS, Policy);
   }
 
   printTemplateArgumentList(OS, T->template_arguments(), Policy);
   spaceBeforePlaceHolder(OS);
 }