Re: [PATCH] c: Improve build_component_ref diagnostics [PR91134]

[David Malcolm <dmalcolm@redhat.com>]

On Tue, 2022-05-24 at 09:57 -0400, David Malcolm wrote:
> On Tue, 2022-05-24 at 09:25 +0200, Jakub Jelinek via Gcc-patches
> wrote:
> > Hi!
> > 
> > On the following testcase (the first dg-error line) we emit a weird
> > diagnostics and even fixit on pointerpointer->member
> > where pointerpointer is pointer to pointer to struct and we say
> > 'pointerpointer' is a pointer; did you mean to use '->'?
> > The first part is indeed true, but suggesting -> when the code
> > already
> > does use -> is confusing.
> > The following patch adjusts callers so that they tell it if it is
> > from
> > . parsing or from -> parsing and in the latter case suggests to
> > dereference
> > the left operand instead by adding (* before it and ) after it
> > (before ->).
> > Or would a suggestion to add [0] before -> be better?
> > 
> > Bootstrapped/regtested on x86_64-linux and i686-linux, ok for
> > trunk?
> > 
> 
> [...snip implementation...]
> 
> >  
> > --- gcc/testsuite/gcc.dg/pr91134.c.jj   2022-05-23
> > 20:31:11.751001817
> > +0200
> > +++ gcc/testsuite/gcc.dg/pr91134.c      2022-05-23
> > 20:30:45.291268997
> > +0200
> > @@ -0,0 +1,13 @@
> > +/* PR c/91134 */
> > +
> > +struct X { int member; } x;
> > +
> > +int
> > +foo (void)
> > +{
> > +  struct X *pointer = &x;
> > +  struct X **pointerpointer = &pointer;
> > +  int i = *pointerpointer->member;     /* { dg-error
> > "'pointerpointer' is a pointer to pointer; did you mean to
> > dereference it before applying '->' to it\\\?" } */
> > +  int j = pointer.member;              /* { dg-error "'pointer' is
> > a
> > pointer; did you mean to use '->'\\\?" } */
> > +  return i + j;
> > +}
> 
> Ideally we'd have an automated check that the fix-it hint fixes the
> code, but failing that, I like to have at least some DejaGnu test
> coverage for fix-it hints - something like the tests in
> gcc.dg/fixits.c
> or gcc.dg/semicolon-fixits.c, perhaps?

Also, what does the output from:
  -fdiagnostics-generate-patch
look like?  That's usually the best way of checking if we're generating
good fix-it hints.

Dave