[PATCH] D11940: don't diagnose -Wunused-parameter in virtual method or method that overrides base class method

[David Blaikie via cfe-commits]

On Tue, Aug 11, 2015 at 8:46 AM, Nico Weber via cfe-commits <
cfe-commits at lists.llvm.org> wrote:

> Can't you just change your signature to
>
>   virtual void a(int /* x */) {}
>
> in these cases?
>

You could - does it add much value to do that, though? (perhaps it does -
it means you express the intent that the parameter is not used and the
compiler helps you check that (so that for the parameters you think
/should/ be used (you haven't commented out their name but accidentally
shadow or otherwise fail to reference, you still get a warning))

- David


>
> On Tue, Aug 11, 2015 at 6:43 AM, Daniel Marjamäki <
> cfe-commits at lists.llvm.org> wrote:
>
>> danielmarjamaki created this revision.
>> danielmarjamaki added a reviewer: krememek.
>> danielmarjamaki added a subscriber: cfe-commits.
>>
>> Don't diagnose -Wunused-parameter in methods that override other methods
>> because the overridden methods might use the parameter
>>
>> Don't diagnose -Wunused-parameter in virtual methods because these might
>> be overriden by other methods that use the parameter.
>>
>> Such diagnostics could be more accurately written if they are based on
>> whole-program-analysis that establish if such parameter is unused in all
>> methods.
>>
>>
>>
>> http://reviews.llvm.org/D11940
>>
>> Files:
>>   lib/Sema/SemaDecl.cpp
>>   test/SemaCXX/warn-unused-parameters.cpp
>>
>> Index: test/SemaCXX/warn-unused-parameters.cpp
>> ===================================================================
>> --- test/SemaCXX/warn-unused-parameters.cpp
>> +++ test/SemaCXX/warn-unused-parameters.cpp
>> @@ -32,3 +32,20 @@
>>    auto l = [&t...]() { return sizeof...(s); };
>>    return l();
>>  }
>> +
>> +// Don't diagnose virtual methods or methods that override base class
>> +// methods.
>> +class Base {
>> +public:
>> +  virtual void f(int x);
>> +};
>> +
>> +class Derived : public Base {
>> +public:
>> +  // Don't warn in overridden methods.
>> +  virtual void f(int x) {}
>> +
>> +  // Don't warn in virtual methods.
>> +  virtual void a(int x) {}
>> +};
>> +
>> Index: lib/Sema/SemaDecl.cpp
>> ===================================================================
>> --- lib/Sema/SemaDecl.cpp
>> +++ lib/Sema/SemaDecl.cpp
>> @@ -10797,8 +10797,13 @@
>>
>>      if (!FD->isInvalidDecl()) {
>>        // Don't diagnose unused parameters of defaulted or deleted
>> functions.
>> -      if (!FD->isDeleted() && !FD->isDefaulted())
>> -        DiagnoseUnusedParameters(FD->param_begin(), FD->param_end());
>> +      if (!FD->isDeleted() && !FD->isDefaulted()) {
>> +        // Don't diagnose unused parameters in virtual methods or
>> +        // in methods that override base class methods.
>> +        const auto MD = dyn_cast<CXXMethodDecl>(FD);
>> +        if (!MD || (MD->size_overridden_methods() == 0U &&
>> !MD->isVirtual()))
>> +          DiagnoseUnusedParameters(FD->param_begin(), FD->param_end());
>> +      }
>>        DiagnoseSizeOfParametersAndReturnValue(FD->param_begin(),
>> FD->param_end(),
>>                                               FD->getReturnType(), FD);
>>
>>
>>
>>
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>>
>
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