Re: [C++ PATCH] Don't reject auto deduction of multiple variables if some initializers were type dependent (PR c++/78693)

[Jason Merrill <jason at redhat dot com>]

OK.

On Mon, Jan 2, 2017 at 3:11 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> Hi!
>
> As the testcase shows, if some initializers are type dependent, auto_result
> is still using auto, is not yet deduced and the deduction will happen during
> instantiation.  So rejecting it due to inconsistent deduction when one
> type is int and another type auto (or vice versa) is wrong, during
> instantiation it could be still instantiated with initializers that are
> valid.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> Though, the PR also shows that we should do similar diagnostics about
> inconsistent auto deduction at instantiation time, but we don't have
> infrastructure for that (at tsubst time we don't know which variables
> were declared together in a single declaration, nor the auto_result
> for those vars where the auto deduction happened already during parsing).
> So I think further work is needed on this PR.
>
> 2017-01-02  Jakub Jelinek  <jakub@redhat.com>
>
>         PR c++/78693
>         * parser.c (cp_parser_simple_declaration): Only complain about
>         inconsistent auto deduction if auto_result doesn't use auto.
>
>         * g++.dg/cpp0x/pr78693.C: New test.
>
> --- gcc/cp/parser.c.jj  2017-01-01 12:45:44.000000000 +0100
> +++ gcc/cp/parser.c     2017-01-02 14:02:49.690859759 +0100
> @@ -12770,9 +12770,11 @@ cp_parser_simple_declaration (cp_parser*
>        if (cp_parser_error_occurred (parser))
>         goto done;
>
> -      if (auto_result)
> +      if (auto_result
> +         && (!processing_template_decl || !type_uses_auto (auto_result)))
>         {
> -         if (last_type && last_type != error_mark_node
> +         if (last_type
> +             && last_type != error_mark_node
>               && !same_type_p (auto_result, last_type))
>             {
>               /* If the list of declarators contains more than one declarator,
> --- gcc/testsuite/g++.dg/cpp0x/pr78693.C.jj     2017-01-02 14:05:45.494582539 +0100
> +++ gcc/testsuite/g++.dg/cpp0x/pr78693.C        2017-01-02 14:05:07.000000000 +0100
> @@ -0,0 +1,31 @@
> +// PR c++/78693
> +// { dg-do compile { target c++11 } }
> +
> +template <class T>
> +void
> +foo (T t)
> +{
> +  auto i = t, j = 1;           // { dg-bogus "inconsistent deduction" }
> +}
> +
> +template <class T>
> +void
> +bar (T t)
> +{
> +  auto i = 1, j = t, k = 2;    // { dg-bogus "inconsistent deduction" }
> +}
> +
> +template <class T, class U>
> +void
> +foo (T t, U u)
> +{
> +  auto i = t, j = u;           // { dg-bogus "inconsistent deduction" }
> +}
> +
> +void
> +foo ()
> +{
> +  foo (0);
> +  bar (0);
> +  foo (1, 2);
> +}
>
>         Jakub