Warning for C Parameter Name Mismatch

Warning for C Parameter Name Mismatch

[Joel Sherrill]

Hi

This may be just an ignorant user question on my part.

Can gcc report when the parameter name in a C prototype
does not match that used in the implementation?

int f(int x);

int f(int y) {...}

We try to fix every warning gcc reports but this is one that gcc
doesn't report for us. It could be we need an extra -Wxxx but
we end up spotting these with Doxygen.

Anything we are missing?

Thanks.

--joel

Re: Warning for C Parameter Name Mismatch

[Joseph Myers]

On Fri, 8 Mar 2019, Joel Sherrill wrote:

> Can gcc report when the parameter name in a C prototype
> does not match that used in the implementation?
> 
> int f(int x);
> 
> int f(int y) {...}

I think this would be normal and expected - an installed header would use 
a reserved-namespace name for the parameter while the implementation uses 
a non-reserved name that's more convenient for use within the 
implementation.  (Thus anything like this would only be useful if it can 
know that it's e.g. OK to have __y and y as the names, and some code no 
doubt uses other such conventions relating the two names.)

-- 
Joseph S. Myers
joseph@codesourcery.com

Re: Warning for C Parameter Name Mismatch

[David Brown]

On 09/03/2019 00:06, Joseph Myers wrote:
> On Fri, 8 Mar 2019, Joel Sherrill wrote:
> 
>> Can gcc report when the parameter name in a C prototype
>> does not match that used in the implementation?
>>
>> int f(int x);
>>
>> int f(int y) {...}
> 
> I think this would be normal and expected - an installed header would use
> a reserved-namespace name for the parameter while the implementation uses
> a non-reserved name that's more convenient for use within the
> implementation.  (Thus anything like this would only be useful if it can
> know that it's e.g. OK to have __y and y as the names, and some code no
> doubt uses other such conventions relating the two names.)
> 

I can appreciate that a warning like this is not for everyone.  But /I/ 
would like and use such a warning for my own code.

The kind of headers which would specifically use reserved or otherwise 
unusual parameter names are things like library headers - and you will 
not be compiling the implementation source code, and thus won't get a 
mismatch.  A warning like this would be used with your own header/source 
combinations - where your implementation is #include'ing the unit's 
header as a way of checking that you've got the function name and 
parameter types correct.  This warning would add parameter names to the 
things that are checked.

Re: Warning for C Parameter Name Mismatch

[Eric Gallager]

On 3/8/19, David Brown <david.brown@hesbynett.no> wrote:
> On 09/03/2019 00:06, Joseph Myers wrote:
>> On Fri, 8 Mar 2019, Joel Sherrill wrote:
>>
>>> Can gcc report when the parameter name in a C prototype
>>> does not match that used in the implementation?
>>>
>>> int f(int x);
>>>
>>> int f(int y) {...}
>>
>> I think this would be normal and expected - an installed header would use
>> a reserved-namespace name for the parameter while the implementation uses
>> a non-reserved name that's more convenient for use within the
>> implementation.  (Thus anything like this would only be useful if it can
>> know that it's e.g. OK to have __y and y as the names, and some code no
>> doubt uses other such conventions relating the two names.)
>>
>
> I can appreciate that a warning like this is not for everyone.  But /I/
> would like and use such a warning for my own code.
>
> The kind of headers which would specifically use reserved or otherwise
> unusual parameter names are things like library headers - and you will
> not be compiling the implementation source code, and thus won't get a
> mismatch.  A warning like this would be used with your own header/source
> combinations - where your implementation is #include'ing the unit's
> header as a way of checking that you've got the function name and
> parameter types correct.  This warning would add parameter names to the
> things that are checked.
>
>

How would it handle the case where the parameter name is missing
entirely from the prototype? I see a lot of header files with their
prototypes written like that.

e.g.

int f(int);

int f(int y) {...}

Re: Warning for C Parameter Name Mismatch

[Jonathan Wakely]

On Sat, 9 Mar 2019, 02:23 Eric Gallager, <egall@gwmail.gwu.edu> wrote:

> On 3/8/19, David Brown <david.brown@hesbynett.no> wrote:
> > On 09/03/2019 00:06, Joseph Myers wrote:
> >> On Fri, 8 Mar 2019, Joel Sherrill wrote:
> >>
> >>> Can gcc report when the parameter name in a C prototype
> >>> does not match that used in the implementation?
> >>>
> >>> int f(int x);
> >>>
> >>> int f(int y) {...}
> >>
> >> I think this would be normal and expected - an installed header would
> use
> >> a reserved-namespace name for the parameter while the implementation
> uses
> >> a non-reserved name that's more convenient for use within the
> >> implementation.  (Thus anything like this would only be useful if it can
> >> know that it's e.g. OK to have __y and y as the names, and some code no
> >> doubt uses other such conventions relating the two names.)
> >>
> >
> > I can appreciate that a warning like this is not for everyone.  But /I/
> > would like and use such a warning for my own code.
> >
> > The kind of headers which would specifically use reserved or otherwise
> > unusual parameter names are things like library headers - and you will
> > not be compiling the implementation source code, and thus won't get a
> > mismatch.  A warning like this would be used with your own header/source
> > combinations - where your implementation is #include'ing the unit's
> > header as a way of checking that you've got the function name and
> > parameter types correct.  This warning would add parameter names to the
> > things that are checked.
> >
> >
>
> How would it handle the case where the parameter name is missing
> entirely from the prototype? I see a lot of header files with their
> prototypes written like that.
>
> e.g.
>
> int f(int);
>
> int f(int y) {...}
>

I don't think that's valid in C, only C++, and I would expect no warning
for such cases. But I don't see much value in the suggested warning at all.

Re: Warning for C Parameter Name Mismatch

[Segher Boessenkool]

On Sat, Mar 09, 2019 at 08:30:19AM +0000, Jonathan Wakely wrote:
> On Sat, 9 Mar 2019, 02:23 Eric Gallager, <egall@gwmail.gwu.edu> wrote:
> > How would it handle the case where the parameter name is missing
> > entirely from the prototype? I see a lot of header files with their
> > prototypes written like that.
> >
> > e.g.
> >
> > int f(int);
> >
> > int f(int y) {...}
> 
> I don't think that's valid in C, only C++, and I would expect no warning
> for such cases. But I don't see much value in the suggested warning at all.

This is perfectly fine C.  Parameter names are optional in prototypes.
It's different if it is the function definition, I think that is what
you mean?


Segher

Re: Warning for C Parameter Name Mismatch

[Joel Sherrill]

On Sat, Mar 9, 2019, 11:27 AM Segher Boessenkool <segher@kernel.crashing.org>
wrote:

> On Sat, Mar 09, 2019 at 08:30:19AM +0000, Jonathan Wakely wrote:
> > On Sat, 9 Mar 2019, 02:23 Eric Gallager, <egall@gwmail.gwu.edu> wrote:
> > > How would it handle the case where the parameter name is missing
> > > entirely from the prototype? I see a lot of header files with their
> > > prototypes written like that.
> > >
> > > e.g.
> > >
> > > int f(int);
> > >
> > > int f(int y) {...}
> >
> > I don't think that's valid in C, only C++, and I would expect no warning
> > for such cases. But I don't see much value in the suggested warning at
> all.
>
> This is perfectly fine C.  Parameter names are optional in prototypes.
> It's different if it is the function definition, I think that is what
> you mean?
>

That's how I read it and that would not be a warning IMO.

Back to a point in my original email that seems to have been missed.
Doxygen reports this as a warning. I would just like the option to find it
with gcc as well.

And not checking system headers is reasonable in general. For RTEMS though,
we are implementing those system headers and do follow the names in the
standards for parameter names in the implementation.

--joel

>
>
> Segher
>

Re: Warning for C Parameter Name Mismatch

[Jonathan Wakely]

On Sat, 9 Mar 2019 at 17:51, Joel Sherrill wrote:
> And not checking system headers is reasonable in general. For RTEMS though, we are implementing those system headers and do follow the names in the standards for parameter names in the implementation.

Using exactly the names from the standard is non-conforming, because
they aren't reserved names and so this valid code would fail to
compile:

#define format 1
#include <stdio.h>
int main() { printf("%d\n", format); }

Re: Warning for C Parameter Name Mismatch

[Jonathan Wakely]

On Sat, 9 Mar 2019 at 17:27, Segher Boessenkool
<segher@kernel.crashing.org> wrote:
>
> On Sat, Mar 09, 2019 at 08:30:19AM +0000, Jonathan Wakely wrote:
> > On Sat, 9 Mar 2019, 02:23 Eric Gallager, <egall@gwmail.gwu.edu> wrote:
> > > How would it handle the case where the parameter name is missing
> > > entirely from the prototype? I see a lot of header files with their
> > > prototypes written like that.
> > >
> > > e.g.
> > >
> > > int f(int);
> > >
> > > int f(int y) {...}
> >
> > I don't think that's valid in C, only C++, and I would expect no warning
> > for such cases. But I don't see much value in the suggested warning at all.
>
> This is perfectly fine C.  Parameter names are optional in prototypes.
> It's different if it is the function definition, I think that is what
> you mean?

Ah yes, sorry for the noise.

Re: Warning for C Parameter Name Mismatch

[David Brown]

On 09/03/2019 03:23, Eric Gallager wrote:
> On 3/8/19, David Brown <david.brown@hesbynett.no> wrote:
>> On 09/03/2019 00:06, Joseph Myers wrote:
>>> On Fri, 8 Mar 2019, Joel Sherrill wrote:
>>>
>>>> Can gcc report when the parameter name in a C prototype
>>>> does not match that used in the implementation?
>>>>
>>>> int f(int x);
>>>>
>>>> int f(int y) {...}
>>>
>>> I think this would be normal and expected - an installed header would use
>>> a reserved-namespace name for the parameter while the implementation uses
>>> a non-reserved name that's more convenient for use within the
>>> implementation.  (Thus anything like this would only be useful if it can
>>> know that it's e.g. OK to have __y and y as the names, and some code no
>>> doubt uses other such conventions relating the two names.)
>>>
>>
>> I can appreciate that a warning like this is not for everyone.  But /I/
>> would like and use such a warning for my own code.
>>
>> The kind of headers which would specifically use reserved or otherwise
>> unusual parameter names are things like library headers - and you will
>> not be compiling the implementation source code, and thus won't get a
>> mismatch.  A warning like this would be used with your own header/source
>> combinations - where your implementation is #include'ing the unit's
>> header as a way of checking that you've got the function name and
>> parameter types correct.  This warning would add parameter names to the
>> things that are checked.
>>
>>
> 
> How would it handle the case where the parameter name is missing
> entirely from the prototype? I see a lot of header files with their
> prototypes written like that.
> 
> e.g.
> 
> int f(int);
> 
> int f(int y) {...}
> 

That would be a warning, I would say.

	int f(int);

	int f(int) { ... }

would be fine in C++.  (And maybe allowed as a gcc extension in C?)


To me, this whole thing has two purposes.  It is to encourage 
consistency and avoid errors like having "moveto(int x, int y)" in the 
header and "moveto(int y, int x)" in the implementation file.  It is not 
nearly as good as named parameters would be, but it's a step forward.

The other point is to make headers more self-documenting.  I see a 
missing parameter name in a declaration as missing essential 
information, and I don't want to see that in headers for code I am 
writing or responsible for.  (The exception being when the parameter is 
not actually used, but exists for overloading or for compatibility with 
specific function types - in which case it is good that it is unnamed.)

(This is just what /I/ want - I know other people might want different 
things.)

Re: Warning for C Parameter Name Mismatch

[Eric Gallager]

On 3/8/19, Joel Sherrill <joel@rtems.org> wrote:
> Hi
>
> This may be just an ignorant user question on my part.
>
> Can gcc report when the parameter name in a C prototype
> does not match that used in the implementation?
>
> int f(int x);
>
> int f(int y) {...}
>
> We try to fix every warning gcc reports but this is one that gcc
> doesn't report for us. It could be we need an extra -Wxxx but
> we end up spotting these with Doxygen.
>
> Anything we are missing?
>
> Thanks.
>
> --joel
>

I found bug 79022 which seems relevant to this conversation:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79022

Re: Warning for C Parameter Name Mismatch

[Basile Starynkevitch]

(I am reading the GCC mailing list in digest mode)

On 3/9/19 10:58 PM, gcc-digest-help@gcc.gnu.org wrote:

>
> On Fri, 8 Mar 2019, Joel Sherrill wrote:
>
>> Can gcc report when the parameter name in a C prototype
>> does not match that used in the implementation?
>>
>> int f(int x);
>>
>> int f(int y) {...}
> I think this would be normal and expected - an installed header would use
> a reserved-namespace name for the parameter while the implementation uses
> a non-reserved name that's more convenient for use within the
> implementation.  (Thus anything like this would only be useful if it can
> know that it's e.g. OK to have __y and y as the names, and some code no
> doubt uses other such conventions relating the two names.)
> I can appreciate that a warning like this is not for everyone.  But 
> /I/ would like and use such a warning for my own code. 
May I remind to all that this is a typical case for you writing a GCC 
plugin. You want a warning that few other people want, and that warning 
is tied to your particular coding style.

You could avoid that warning by avoid naming the parameters in your 
header files, so you would declare
int f (int /*x*/); in your header file.

You might want to get a warning, but since it is not of general use (as 
many explained, not using the same name in the header and in the 
implementation of a given function parameter makes a lot of sense in 
general, even if you dislike such as style) you really should consider 
writing your own GCC plugin for that purpose.

How to write such a GCC plugin is a different question, and should be 
asked as such.

Cheers.

-- 
Basile STARYNKEVITCH   == http://starynkevitch.net/Basile
opinions are mine only - les opinions sont seulement miennes
Bourg La Reine, France

Re: Warning for C Parameter Name Mismatch

[David Brown]

On 10/03/2019 07:11, Basile Starynkevitch wrote:
> 
> (I am reading the GCC mailing list in digest mode)
> 
> On 3/9/19 10:58 PM, gcc-digest-help@gcc.gnu.org wrote:
> 
>>
>> On Fri, 8 Mar 2019, Joel Sherrill wrote:
>>
>>> Can gcc report when the parameter name in a C prototype
>>> does not match that used in the implementation?
>>>
>>> int f(int x);
>>>
>>> int f(int y) {...}
>> I think this would be normal and expected - an installed header would use
>> a reserved-namespace name for the parameter while the implementation uses
>> a non-reserved name that's more convenient for use within the
>> implementation.  (Thus anything like this would only be useful if it can
>> know that it's e.g. OK to have __y and y as the names, and some code no
>> doubt uses other such conventions relating the two names.)
>> I can appreciate that a warning like this is not for everyone.  But 
>> /I/ would like and use such a warning for my own code. 
> May I remind to all that this is a typical case for you writing a GCC 
> plugin. You want a warning that few other people want, and that warning 
> is tied to your particular coding style.
> 
> You could avoid that warning by avoid naming the parameters in your 
> header files, so you would declare
> int f (int /*x*/); in your header file.
> 
> You might want to get a warning, but since it is not of general use (as 
> many explained, not using the same name in the header and in the 
> implementation of a given function parameter makes a lot of sense in 
> general, even if you dislike such as style) you really should consider 
> writing your own GCC plugin for that purpose.
> 
> How to write such a GCC plugin is a different question, and should be 
> asked as such.
> 
> Cheers.
> 

I fully agree that this is not a warning everyone will want - but I 
disagree with the idea that it is a specialist or unusual warning. 
Remember, no one is asking for it to be in -Wall or -Wextra.  gcc has 
many, many warnings available, and a large proportion of them will only 
be useful to a small proportion of users.  You could certainly say that 
of things like "-Wmissing-prototypes", "-Wmissing-declarations" and 
"-Wredundant-decls".  I fail to see that this suggestion is at all 
different.

In particular, I see this warning being of little use for large C / C++ 
applications with code split into multiple libraries.  But I see it as 
being of a good deal of use in small-systems embedded programming where 
you have a smaller code base, all compiled together in one project, and 
where coding conventions and styles are often strict.  That will apply 
to only a very small proportion of people programming for x86-64 targets 
- but a very high proportion of those programming for AVR, msp430, ARM 
Cortex-M, and most of the other targets of gcc.  It is easy to forget or 
underestimate the huge range of types of programming done with gcc - 
there are many of us for whom warnings like this would be a useful tool.

However, you are right that plugins could be a way to achieve this.  I 
think the Python plugin could be a good way to prototype features like 
this - and if it is useful, then it could be moved into gcc main.

Re: Warning for C Parameter Name Mismatch

[Basile Starynkevitch]

On 3/10/19 12:54 PM, David Brown wrote:
> On 10/03/2019 07:11, Basile Starynkevitch wrote:
>>
>> (I am reading the GCC mailing list in digest mode)
>>
>> On 3/9/19 10:58 PM, gcc-digest-help@gcc.gnu.org wrote:
>>
>>>
>>> On Fri, 8 Mar 2019, Joel Sherrill wrote:
>>>
>>>> Can gcc report when the parameter name in a C prototype
>>>> does not match that used in the implementation?
>>>>
>>>> int f(int x);
>>>>
>>>> int f(int y) {...}
>>> I think this would be normal and expected - an installed header 
>>> would use
>>> a reserved-namespace name for the parameter while the implementation 
>>> uses
>>> a non-reserved name that's more convenient for use within the
>>> implementation.  (Thus anything like this would only be useful if it 
>>> can
>>> know that it's e.g. OK to have __y and y as the names, and some code no
>>> doubt uses other such conventions relating the two names.)
>>> I can appreciate that a warning like this is not for everyone.  But 
>>> /I/ would like and use such a warning for my own code. 
>> May I remind to all that this is a typical case for you writing a GCC 
>> plugin. You want a warning that few other people want, and that 
>> warning is tied to your particular coding style.
>>
>> You could avoid that warning by avoid naming the parameters in your 
>> header files, so you would declare
>> int f (int /*x*/); in your header file.
>>
>> You might want to get a warning, but since it is not of general use 
>> (as many explained, not using the same name in the header and in the 
>> implementation of a given function parameter makes a lot of sense in 
>> general, even if you dislike such as style) you really should 
>> consider writing your own GCC plugin for that purpose.
>>
>> How to write such a GCC plugin is a different question, and should be 
>> asked as such.
>>
>> Cheers.
>>
>
> I fully agree that this is not a warning everyone will want - but I 
> disagree with the idea that it is a specialist or unusual warning. 
> Remember, no one is asking for it to be in -Wall or -Wextra.  gcc has 
> many, many warnings available, and a large proportion of them will 
> only be useful to a small proportion of users.  You could certainly 
> say that of things like "-Wmissing-prototypes", 
> "-Wmissing-declarations" and "-Wredundant-decls".  I fail to see that 
> this suggestion is at all different.
>
> In particular, I see this warning being of little use for large C / 
> C++ applications with code split into multiple libraries.  But I see 
> it as being of a good deal of use in small-systems embedded 
> programming where you have a smaller code base, all compiled together 
> in one project, and where coding conventions and styles are often 
> strict.  That will apply to only a very small proportion of people 
> programming for x86-64 targets - but a very high proportion of those 
> programming for AVR, msp430, ARM Cortex-M, and most of the other 
> targets of gcc.  It is easy to forget or underestimate the huge range 
> of types of programming done with gcc - there are many of us for whom 
> warnings like this would be a useful tool.
>
> However, you are right that plugins could be a way to achieve this.  I 
> think the Python plugin could be a good way to prototype features like 
> this - and if it is useful, then it could be moved into gcc main.
>

In the long term, the question becomes philosophical. I would be really 
happy if every future GCC release would come with a small set of 
"example" plugins for various unusual warnings. And I even think that 
such an approach will favor outside people to write plugins for their needs.

I am not so sure that making an even larger cc1plus binary is wanted.

Of course, I am making the hypothesis that plugins are as necessary as 
directories to host GCC.

Cheers


-- 
Basile STARYNKEVITCH   == http://starynkevitch.net/Basile
opinions are mine only - les opinions sont seulement miennes
Bourg La Reine, France