[clang-tidy] follow-up on misc-definitions-in-header check.

Summary:
A follow-up on D34449:
* add `-std=c++11` to `.hpp` file by default.
* add constexpr function to test and doc.

Reviewers: alexfh

Reviewed By: alexfh

Subscribers: JDevlieghere, xazax.hun, cfe-commits

Differential Revision: https://reviews.llvm.org/D34771

llvm-svn: 306650

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

@@ -82,6 +82,8 @@ from multiple translation units.
 
    constexpr int k = 1; // OK: constexpr variable has internal linkage.
 
+   constexpr int f10() { return 0; } // OK: constexpr function definition.
+
 Options
 -------
 

clang-tools-extra/test/clang-tidy/check_clang_tidy.py

@@ -58,8 +58,8 @@ def main():
 
   clang_tidy_extra_args = extra_args
   if len(clang_tidy_extra_args) == 0:
-    clang_tidy_extra_args = ['--', '--std=c++11'] if extension == '.cpp' \
-                       else ['--']
+    clang_tidy_extra_args = ['--', '--std=c++11'] \
+        if extension == '.cpp' or extension == '.hpp' else ['--']
 
   # Tests should not rely on STL being available, and instead provide mock
   # implementations of relevant APIs.

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

@@ -1,4 +1,4 @@
-// RUN: %check_clang_tidy %s misc-definitions-in-headers %t -- -- -std=c++11
+// RUN: %check_clang_tidy %s misc-definitions-in-headers %t
 
 int f() {
 // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: function 'f' defined in a header file; function definitions in header files can lead to ODR violations [misc-definitions-in-headers]
@@ -177,3 +177,5 @@ int CD<T, int>::f() { // OK: partial template specialization.
 }
 
 constexpr int k = 1; // OK: constexpr variable has internal linkage.
+
+constexpr int f10() { return 0; } // OK: constexpr function definition.