Re: "WARNING: parenthesis in function name" correctness

[Ingo Schwarze <schwarze@usta.de>]

Hi Yuri,

Yuri Pankov wrote on Tue, Sep 10, 2019 at 11:20:24AM +0300:

> I'm looking into fixing sbuf.9 which currently has somewhat unreadable:
> 
> .Ft typedef\ int ( sbuf_drain_func ) ( void\ *arg, const\ char\ *data, 
> int\ len ) ;

Indeed, that is horrible and should be fixed.

> ...into somewhat nicer:
> 
> .Ft typedef int
> .Fo (sbuf_drain_func)
> .Fa "void *arg"
> .Fa "const char *data"
> .Fa "int len"
> .Fc
> 
> ...but that gives me a:
> 
> mandoc: share/man/man9/sbuf.9:69:5: WARNING: parenthesis in function 
> name: (sbuf_drain_func)
> 
> Looking at the code, parenthesis are only allowed in the following form:
> 
> .Ft (*func_ptr)

I think you mean .Fo/.Fn, not .Ft, right?

> ...while here we don't have a "*" -- it's the way it's typedef'ed in the 
> source, and I want to follow it, so I wonder if that check/warning is 
> really useful.

If i understand the C standard correctly (otherwise, please somebody
correct me!), we have:

  int (f)()    --  function returning int
  int (*fp)()  --  pointer to function returning int

In many situations, both can be used interchangeably, consider for
example C89 3.2.2.1: "A function designator is an expression that
has function type.  Except when it is the operand of the sizeof
operator or the unary & operator, a function designator with type
``function returning type'' is converted to an expression that has
type ``pointer to function returning type.''"

Then again, it seems for sizeof(), it may make a difference whether
a type is a function type or a function pointer type, and maybe there
are also other situations where that matters.

So i suspect you are right there are legitimate reasons for making
the difference in the documentation, too,
and saying ".Fo (sbuf_drain_func)" looks reasonable.
Do others agree?

I plan to suppress the warning for ".Fo (f)" just like for ".Fo (*f)"
in the future.  The likely typo that should be warned about
is ".Fo f()", and that warning will still work.

Yours,
  Ingo
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