[clang-tidy] No misc-definitions-in-headers warning on C++14 variable templates.

[gribozavr2]

clang-tools-extra/docs/clang-tidy/checks/misc-definitions-in-headers.rst

86

s/is allowed/are inline/

clang-tools-extra/test/clang-tidy/checkers/misc-definitions-in-headers-1z.hpp

14

I would prefer if you could make the test compatible with all language modes after C++11. You can do it by wrapping the variable template in #ifs on the __cplusplus macro that contains the language version.

[hokein]

Address review comments.

clang-tools-extra/test/clang-tidy/checkers/misc-definitions-in-headers-1z.hpp

14

I'd prefer keep it as it-is. using __cplusplus seems a bit hacky to me, and I think it only works for non-CHECK-MESSAGES cases.

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

diag(FD->getLocation(),
          "%select{function|full function template specialization}0 %1 defined "
          "in a header file; function definitions in header files can lead to "
          "ODR violations")
         << IsFullSpec << FD;
     diag(FD->getLocation(), /*FixDescription=*/"make as 'inline'",
          DiagnosticIDs::Note)
         << FixItHint::CreateInsertion(FD->getInnerLocStart(), "inline ");
   } else if (const auto *VD = dyn_cast<VarDecl>(ND)) {
+    // C++14 variable templates are allowed.
+    if (VD->getDescribedVarTemplate())
+      return;
     // Static data members of a class template are allowed.
     if (VD->getDeclContext()->isDependentContext() && VD->isStaticDataMember())
       return;
     // Ignore instantiated static data members of classes.
     if (isTemplateInstantiation(VD->getTemplateSpecializationKind()))
       return;
     // Ignore variable definition within function scope.
     if (VD->hasLocalStorage() || VD->isStaticLocal())

clang-tools-extra/docs/clang-tidy/checks/misc-definitions-in-headers.rst

.. code-block:: c++
    class CE {
      constexpr static int i = 5; // OK: inline variable definition.
    };
 
    inline int i = 5; // OK: inline variable definition.
 
    constexpr int f10() { return 0; } // OK: constexpr function implies inline.
 
+   // OK: C++14 variable templates are inline.
+   template <class T>
+   constexpr T pi = T(3.1415926L);
+
 Options
 -------
 
 .. option:: HeaderFileExtensions
 
    A comma-separated list of filename extensions of header files (the filename
    extensions should not include "." prefix). Default is "h,hh,hpp,hxx".
    For header files without an extension, use an empty string (if there are no
    other desired extensions) or leave an empty element in the list. e.g.,
    "h,hh,hpp,hxx," (note the trailing comma).
 
 .. option:: UseHeaderFileExtension
 
    When non-zero, the check will use the file extension to distinguish header
    files. Default is `1`.

clang-tools-extra/test/clang-tidy/checkers/misc-definitions-in-headers-1z.hpp

-// RUN: %check_clang_tidy %s misc-definitions-in-headers %t -- -- -std=c++1z
+// RUN: %check_clang_tidy -std=c++17-or-later %s misc-definitions-in-headers %t
 
 class CE {
   constexpr static int i = 5; // OK: inline variable definition.
 };
 
 inline int i = 5; // OK: inline variable definition.
 
 int b = 1;
 // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: variable 'b' defined in a header file; variable definitions in header files can lead to ODR violations [misc-definitions-in-headers]
+
+// OK: C++14 variable template.
+template <class T>
+constexpr T pi = T(3.1415926L);