[clang-tidy] Improve diagnostic message for misc-definitions-in-header.

Summary:
Users might get confused easily when they see the check's message on
full template function speciliations.

Add a note to the output message, which mentions these kind of function
specializations are treated as regular functions.

Reviewers: alexfh

Reviewed By: alexfh

Subscribers: JDevlieghere, cfe-commits

Differential Revision: https://reviews.llvm.org/D29928

llvm-svn: 295048

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

@@ -122,10 +122,12 @@ void DefinitionsInHeadersCheck::check(const MatchFinder::MatchResult &Result) {
       }
     }
 
+    bool is_full_spec = FD->getTemplateSpecializationKind() != TSK_Undeclared;
     diag(FD->getLocation(),
-         "function %0 defined in a header file; "
-         "function definitions in header files can lead to ODR violations")
-        << FD << FixItHint::CreateInsertion(
+         "%select{function|full function template specialization}0 %1 defined "
+         "in a header file; function definitions in header files can lead to "
+         "ODR violations")
+        << is_full_spec << FD << FixItHint::CreateInsertion(
                      FD->getReturnTypeSourceRange().getBegin(), "inline ");
   } else if (const auto *VD = dyn_cast<VarDecl>(ND)) {
     // Static data members of a class template are allowed.

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

@@ -28,7 +28,7 @@ void CA::f2() { }
 
 template <>
 int CA::f3() {
-// CHECK-MESSAGES: :[[@LINE-1]]:9: warning: function 'f3<int>' defined in a header file;
+// CHECK-MESSAGES: :[[@LINE-1]]:9: warning: full function template specialization 'f3<int>' defined in a header file;
 // CHECK-FIXES: inline int CA::f3() {
   int a = 1;
   return a;
@@ -92,7 +92,7 @@ T f3() {
 
 template <>
 int f3() {
-// CHECK-MESSAGES: :[[@LINE-1]]:5: warning: function 'f3<int>' defined in a header file;
+// CHECK-MESSAGES: :[[@LINE-1]]:5: warning: full function template specialization 'f3<int>' defined in a header file;
 // CHECK-FIXES: inline int f3() {
   int a = 1;
   return a;