[clang] Add option to opt out of the missing_dependent_template_keyword diagnostic

[hokein]

After commit ce4aada, we observed many warnings in our internal codebase. It is
infeasible to fix all at once.

Currently, there is no way to disable this warning. This patch provides a way to disable it using the -Wno-missing-dependent-template-keyword flag.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Haojian Wu (hokein)

Changes

After commit ce4aada, we observed many warnings in our internal codebase. It is
infeasible to fix all at once.

Currently, there is no way to disable this warning. This patch provides a way to disable it using the -Wno-missing-dependent-template-keyword flag.

---

Full diff: https://github.com/llvm/llvm-project/pull/98613.diff

2 Files Affected:

• (modified) clang/include/clang/Basic/DiagnosticParseKinds.td (+2-1)
• (modified) clang/test/Misc/warning-flags.c (+1-2)

diff --git a/clang/include/clang/Basic/DiagnosticParseKinds.td b/clang/include/clang/Basic/DiagnosticParseKinds.td
index 0bd2e35bf2e31..e00cd47411cb3 100644
--- a/clang/include/clang/Basic/DiagnosticParseKinds.td
+++ b/clang/include/clang/Basic/DiagnosticParseKinds.td
@@ -896,7 +896,8 @@ def missing_template_arg_list_after_template_kw : Extension<
   DefaultError;
 
 def ext_missing_dependent_template_keyword : ExtWarn<
-  "use 'template' keyword to treat '%0' as a dependent template name">;
+  "use 'template' keyword to treat '%0' as a dependent template name">,
+  InGroup<DiagGroup<"missing-dependent-template-keyword">>;
 
 def ext_extern_template : Extension<
   "extern templates are a C++11 extension">, InGroup<CXX11>;
diff --git a/clang/test/Misc/warning-flags.c b/clang/test/Misc/warning-flags.c
index 651a86fb6e226..7b993f6849363 100644
--- a/clang/test/Misc/warning-flags.c
+++ b/clang/test/Misc/warning-flags.c
@@ -18,10 +18,9 @@ This test serves two purposes:
 
 The list of warnings below should NEVER grow.  It should gradually shrink to 0.
 
-CHECK: Warnings without flags (65):
+CHECK: Warnings without flags (64):
 
 CHECK-NEXT:   ext_expected_semi_decl_list
-CHECK-NEXT:   ext_missing_dependent_template_keyword
 CHECK-NEXT:   ext_missing_whitespace_after_macro_name
 CHECK-NEXT:   ext_new_paren_array_nonconst
 CHECK-NEXT:   ext_plain_complex

[sdkrystian]

Reasonable, LGTM. Perhaps a release note should be added?

[hokein]

Reasonable, LGTM. Perhaps a release note should be added?

Thanks for the review. Done.

[pranavk]

This doesn't seem to handle all the cases? See abseil/abseil-cpp#1711 for absl build failures that are not silenced by using this option.

[hokein]

It does filter out the missing-dependent-template-keyword warnings, but doesn't fix the absl case.

With ce4aada, there is a behavior change in clang. Clang reject the following code which was accepted before by emitting a hard error err_no_member.

#define TYPE_OR_NONTYPE int

template<TYPE_OR_NONTYPE T>
struct BaseT {
  void Foo();
};

template<TYPE_OR_NONTYPE T>
struct DerivedT : BaseT<T> {
  void Inner();
};

template<TYPE_OR_NONTYPE T>
void DerivedT<T>::Inner() {
  this->BaseT<T>::Foo();
}

• If the TYPE_OR_NONTYPE is typename (type template parameter case), clang emits a missing-dependent-template-keyword warning, which can be suppressed;
• If the TYPE_OR_NONTYPE is int (non-type template parameter case), clang emits a hard error err_no_member;