Re: [RFC] c++: Print function template parms when relevant (was: [PATCH v4] c++: Add gnu::diagnose_as attribute)

[Matthias Kretz <m.kretz@gsi.de>]

On Friday, 19 November 2021 23:26:57 CET Jason Merrill wrote:
> On 11/19/21 04:53, Matthias Kretz wrote:
> > My motivation for printing a function template specialization differently
> > is:
> > 
> > 1. It's a different function definition that's being called. The user
> > (caller) might be surprised to realize this is the case as he forgot
> > about the specialization and was expecting his change to the general
> > template to make a difference.
> > 
> > 2. There's no T in
> > 
> > template <> void f<int>() {
> > // no T here, but of course I can define one:
> > using T = int;
> > }
> > 
> > so presenting the function that was called as 'void f<T>() [with T = int]'
> > is not exactly correct. In this case it wasn't even the case that T was
> > deduced to be 'int', which we could argue to be useful information that
> > might get lost.
> 
> On the other hand, this tells us what template this specialization is
> specializing, which could be unclear if there are multiple overloaded
> function templates.

I don't disagree that printing the primary template + substitution has value. 
I just believe that being more explicit about a function specialization 
getting called has more value. But I guess we'll just have to live with our 
disagreement.

I'll re-add the condition for "pretty-printing" specialized functions for the 
next patch revision, unless someone else wants to & can convince you. :)

> There's always -fno-pretty-templates if you want the form without
> template args.
> 
> Incidentally, the contents of __PRETTY_FUNCTION__ probably shouldn't
> vary with that flag...

That ship is sailing since -fpretty-templates was implemented AFAICS. Do you 
want it to come back? ;)

> >> That sounds good: omit defaulted parms only if they don't appear in the
> >> signature (other than as another default template argument).
> >
> > Let me check whether I have the right idea:
> > 
> > I could extend find_typenames (which walks the complete) tree to look for
> > TEMPLATE_TYPE_PARM (and the 3 others I don't recall right now). But since
> > that walks the *complete* tree, it'll simply find all parms with no
> > indication
> > whether they appear in the signature. Ideas:
>
> Hmm, since it walks DECL_TEMPLATE_RESULT, I wouldn't expect it to find
> template parms that aren't in the function signature.

Maybe I made an error elsewhere, but that's what I saw when I tried it. I'll 
try again (next week, I think).

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 Dr. Matthias Kretz                           https://mattkretz.github.io
 GSI Helmholtz Centre for Heavy Ion Research               https://gsi.de
 stdₓ::simd
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