Add a misc-unused-parameters.CommentOutUnusedParameters to clang-tidy

[mehdi_amini]

Summary

This option allows to eliminate parameter names instead of commenting
them out.

[jpienaar]

clang-tools-extra/docs/clang-tidy/checks/misc-unused-parameters.rst

25

OOC why the extra space after the type?

[mehdi_amini]

clang-tools-extra/docs/clang-tidy/checks/misc-unused-parameters.rst

25

The space is in the original code, the fix only touches the name (clang-format is expected to fix it afterward)

[Mogball]

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

157

Oh I was thinking that the option would disable editing the parameter at all. I.e. it would leave unused parameters untouched or remove the parameter from the function signature altogether (if it can).

[jpienaar]

Looks reasonable as an option/this is another way to make it explicit that param is unused.

clang-tools-extra/docs/clang-tidy/checks/misc-unused-parameters.rst

48

Could we flip this? ElideUnusedParameterNames with default value false: eliding drops local information and I'd rather that be explicit in the name. CommentOut is still the default with the current naming, but it feels more optional for some reason to me. WDYT?

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

if (Function->isExternallyVisible() ||
     // It is illegal to omit parameter name here in C code, so early-out.
     if (!Result.Context->getLangOpts().CPlusPlus)
       return;
 
     SourceRange RemovalRange(Param->getLocation());
     // Note: We always add a space before the '/*' to not accidentally create
     // a '*/*' for pointer types, which doesn't start a comment. clang-format
     // will clean this up afterwards.
+    if (Options.get("CommentOutUnusedParameters", true))
       MyDiag << FixItHint::CreateReplacement(
           RemovalRange, (Twine(" /*") + Param->getName() + "*/").str());
+    else
+      MyDiag << FixItHint::CreateReplacement(RemovalRange, "");
     return;
   }
 
   // Fix all redeclarations.
   for (const FunctionDecl *FD : Function->redecls())
     if (FD->param_size())
       MyDiag << removeParameter(Result, FD, ParamIndex);
 

clang-tools-extra/docs/clang-tidy/checks/misc-unused-parameters.rst

 .. code-block:: c++
 
   void a(int i) { /*some code that doesn't use `i`*/ }
 
   // becomes
 
   void a(int  /*i*/) { /*some code that doesn't use `i`*/ }
 
+  // or if the CommentOutUnusedParameters is set to false:
+
+  void a(int ) { /*some code that doesn't use `i`*/ }
+
 .. code-block:: c++
 
   static void staticFunctionA(int i);
   static void staticFunctionA(int i) { /*some code that doesn't use `i`*/ }
 
   // becomes
 
   static void staticFunctionA()
   static void staticFunctionA() { /*some code that doesn't use `i`*/ }
 
 Options
 -------
 
 .. option:: StrictMode
 
    When `false` (default value), the check will ignore trivially unused parameters,
    i.e. when the corresponding function has an empty body (and in case of
    constructors - no constructor initializers). When the function body is empty,
    an unused parameter is unlikely to be unnoticed by a human reader, and
    there's basically no place for a bug to hide.
+
+.. option:: misc-unused-parameters.CommentOutUnusedParameters
+
+   When `true` (default value), the suggest fix will comment out the parameter name
+   instead of removing them.

clang-tools-extra/test/clang-tidy/checkers/misc-unused-parameters-no-comment.cpp

+// RUN: %check_clang_tidy %s misc-unused-parameters %t -- \
+// RUN:   -config="{CheckOptions: [{key: misc-unused-parameters.CommentOutUnusedParameters, value: false}]}" --
+
+// Check that we eliminate parameters instead of commenting them out.
+class SomeClass {
+  static void f(int i) { ; }
+  // CHECK-MESSAGES: :[[@LINE-1]]:21: warning
+  // CHECK-FIXES: static void f(int ) {;}
+  static void g(int i = 1) { ; }
+  // CHECK-MESSAGES: :[[@LINE-1]]:21: warning
+  // CHECK-FIXES: static void g(int = 1) {;}
+  static void h(int i[]) { ; }
+  // CHECK-MESSAGES: :[[@LINE-1]]:21: warning
+  // CHECK-FIXES: static void h(int []) {;}
+  static void s(void (*fn)()) { ; }
+  // CHECK-MESSAGES: :[[@LINE-1]]:24: warning
+  // CHECK-FIXES: static void s(void (*)()) {;}
+};