[clang-tidy] Ignore variable template partial specializations in `misc-definitions-in-headers`

[Izaron]

Summary

Variable template partial specializations are inline and can't lead
to ODR-violations. The checker now ignores them.

Fixes https://github.com/llvm/llvm-project/issues/53519

[Izaron]

A copy-pasted message below, as usual =)

If this review is eventually approved, kindly please merge the commit on my behalf =) As I don't have merge access. My name is Evgeny Shulgin and email is [e-mail]. Sorry for inconvenience!

[hokein]

thanks!

clang-tools-extra/clang-tidy/misc/DefinitionsInHeadersCheck.cpp

if (const auto *FD = dyn_cast<FunctionDecl>(ND)) {
     if (isTemplateInstantiation(VD->getTemplateSpecializationKind()))
       return;
     // Ignore variable definition within function scope.
     if (VD->hasLocalStorage() || VD->isStaticLocal())
       return;
     // Ignore inline variables.
     if (VD->isInline())
       return;
+    // Ignore partial specializations.
+    if (isa<VarTemplatePartialSpecializationDecl>(VD))
+      return;
 
     diag(VD->getLocation(),
          "variable %0 defined in a header file; "
          "variable definitions in header files can lead to ODR violations")
         << VD;
   }
 }
 
 } // namespace misc
 } // namespace tidy
 } // namespace clang

clang-tools-extra/test/clang-tidy/checkers/misc-definitions-in-headers.hpp

 template <typename T>
 const T f12();
 
 template <>
 const int f12() { return 0; }
 // CHECK-MESSAGES: :[[@LINE-1]]:11: warning: full function template specialization 'f12<int>' defined in a header file;
 // CHECK-FIXES: inline const int f12() { return 0; }
 
+template <typename T1, typename T2>
+constexpr bool f13 = false;
+
+template <typename T>
+constexpr bool f13<T, int> = true; // OK: template partial specialization
+
+template <>
+constexpr bool f13<void, int> = false;
+// CHECK-MESSAGES: :[[@LINE-1]]:16: warning: variable 'f13<void, int>' defined in a header file;
+
 int main() {}
 // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: function 'main' defined in a header file;
 // CHECK-FIXES: {{^}}int main() {