Fix misc-unused-parameters handling of function templates

[swallace]

Summary

The parameters of the function templates were being marked as incorrectly be marked as unused.
Added a test for this and changed the check to use the same isReferenced() || !getDeclName() logic as Sema::DiagnoseUnusedParameters.

[djasper]

Cool. Looks good. Wanna extend the test to ensure that we mark unused parameters of function templates? Do you have commit access?

[swallace]

I'll try and add a few more test cases.

I don't have commit access.

[swallace]

Add a couple of cases showing that unused parameters in function templates do correctly get removed.

[djasper]

Cool. Thank you. Submitted as r242912.

clang-tidy/misc/UnusedParametersCheck.cpp

   if (!Function->doesThisDeclarationHaveABody())
     return;
   const auto *Param = Result.Nodes.getNodeAs<ParmVarDecl>("x");
-  if (Param->isUsed())
+  if (Param->isUsed() || Param->isReferenced() || !Param->getDeclName() ||
+     Param->hasAttr<UnusedAttr>())
     return;
 
   auto MyDiag = diag(Param->getLocation(), "parameter '%0' is unused")

 
 } // namespace tidy
 } // namespace clang
-

test/clang-tidy/misc-unused-parameters.cpp

 }
 
 } // end namespace
+
+template <typename T> void someFunctionTemplate(T b, T e) { (void)b; (void)e; }
+
+template <typename T> void someFunctionTemplateOneUnusedParam(T b, T e) { (void)e; }
+// CHECK-MESSAGES: :[[@LINE-1]]:65: warning
+// CHECK-FIXES: {{^}}template <typename T> void someFunctionTemplateOneUnusedParam(T  /*b*/, T e) { (void)e; }
+
+template <typename T> void someFunctionTemplateAllUnusedParams(T b, T e) {}
+// CHECK-MESSAGES: :[[@LINE-1]]:66: warning
+// CHECK-MESSAGES: :[[@LINE-2]]:71: warning
+// CHECK-FIXES: {{^}}template <typename T> void someFunctionTemplateAllUnusedParams(T  /*b*/, T  /*e*/) {}