[Bug c++/57012] pretty-printer does not handle well template parameter packs

[Bug c++/57012] pretty-printer does not handle well template parameter packs

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57012

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2021-08-10
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=54948

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
GCC improved error recovery with r219067 so that now it just prints one error:

gcc/testsuite/g++.dg/cpp0x/pr31432.C:2:10: error: parameter pack
‘<template-parameter-1-1>’ must be at the end of the template parameter list
    2 | template<typename..., typename> struct A // { dg-error "parameter pack"
}
      |          ^~~~~~~~

Printing "<template-parameter-1-1>" is still not pretty.

See also PR 54948 and PR 101844.

If the template parameter (or template parameter pack) hasn't got a name, maybe
we should not try to print it. The caret location already shows which pack
we're talking about.

If it's unnamed, maybe special case the diagnostic so it just says "parameter
pack must be at the end ..." instead of making up a name which doesn't appear
in the source code.