[clang][Sema] Fix diagnostic message for unused constant varialbe templates

[hazohelet]

Summary

BEFORE this patch, unused const-qualified variable templates such as template <typename T> const double var_t = 0; were diagnosed as unused variable 'var_t'
This patch fixes this message to unused variable template 'var_t'

[tbaeder]

Makes sense. LGTM provided precommit CI comes back green.

[shafik]

clang/lib/Sema/Sema.cpp

1385

Sorry for late review but we should conform to bugprone-argument-comment for these.

[hazohelet]

clang/lib/Sema/Sema.cpp

1385

Thanks. Fixed in 940c94e1c1b99511630b6f61890ac54161b5829c

clang/docs/ReleaseNotes.rst

- Clang will now show a margin with line numbers to the left of each line
   of code it prints for diagnostics. This can be disabled using
   ``-fno-diagnostics-show-line-numbers``. At the same time, the maximum
   number of code lines it prints has been increased from 1 to 16. This
   can be controlled using ``-fcaret-diagnostics-max-lines=``.
 - Clang no longer emits ``-Wunused-variable`` warnings for variables declared
   with ``__attribute__((cleanup(...)))`` to match GCC's behavior.
 - Clang now issues expected warnings for situations of comparing with NULL pointers.
   (`#42992: <https://github.com/llvm/llvm-project/issues/42992>`_)
+- Clang now diagnoses unused const-qualified variable template as
+  "unused variable template" rather than "unused variable".
 
 Bug Fixes in This Version
 -------------------------
 
 - Fix segfault while running clang-rename on a non existing file.
   (`#36471 <https://github.com/llvm/llvm-project/issues/36471>`_)
 - Fix crash when diagnosing incorrect usage of ``_Nullable`` involving alias
   templates.

clang/lib/Sema/Sema.cpp

for (UnusedFileScopedDeclsType::iterator
         }
       } else {
         const VarDecl *DiagD = cast<VarDecl>(*I)->getDefinition();
         if (!DiagD)
           DiagD = cast<VarDecl>(*I);
         if (DiagD->isReferenced()) {
           Diag(DiagD->getLocation(), diag::warn_unneeded_internal_decl)
               << /*variable*/ 1 << DiagD;
+        } else if (DiagD->getDescribedVarTemplate()) {
+          Diag(DiagD->getLocation(), diag::warn_unused_template)
+              << /*variable*/ 1 << DiagD;
         } else if (DiagD->getType().isConstQualified()) {
           const SourceManager &SM = SourceMgr;
           if (SM.getMainFileID() != SM.getFileID(DiagD->getLocation()) ||
               !PP.getLangOpts().IsHeaderFile)
             Diag(DiagD->getLocation(), diag::warn_unused_const_variable)
                 << DiagD;
         } else {
-          if (DiagD->getDescribedVarTemplate())
-            Diag(DiagD->getLocation(), diag::warn_unused_template)
-                << /*variable*/ 1 << DiagD;
-          else
-            Diag(DiagD->getLocation(), diag::warn_unused_variable) << DiagD;
         }
       }
     }
 
     emitAndClearUnusedLocalTypedefWarnings();
   }
 
   if (!Diags.isIgnored(diag::warn_unused_private_field, SourceLocation())) {

clang/test/SemaCXX/warn-unused-filescoped.cpp

namespace test5 {
 
   // FIXME: We should produce warnings for both of these.
   static const int m = n;
   int x = sizeof(m);
   static const double d = 0.0; // expected-warning{{variable 'd' is not needed and will not be emitted}}
   int y = sizeof(d);
 
   namespace {
-  // FIXME: Should be "unused variable template 'var_t'" instead.
-  template <typename T> const double var_t = 0; // expected-warning {{unused variable 'var_t'}}
+  template <typename T> const double var_t = 0; // expected-warning {{unused variable template 'var_t'}}
   template <> const double var_t<int> = 0;      // expected-warning {{variable 'var_t<int>' is not needed and will not be emitted}}
   int z = sizeof(var_t<int>);                   // expected-warning {{unused variable 'z'}}
   }                                             // namespace
 }
 
 namespace unused_nested {
   class outer {
     void func1();