Re: [PATCH 1/2] c++: requires-exprs and partial constraint subst [PR112769]

[Jason Merrill <jason@redhat.com>]

On 2/2/24 14:41, Patrick Palka wrote:
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this
> look OK for trunk?
> 
> -- >8 --
> 
> In r11-3261-gb28b621ac67bee we made tsubst_requires_expr never partially
> substitute into a requires-expression so as to avoid checking its
> requirements out of order during e.g. generic lambda regeneration.
> 
> Unfortunately we still do need to partially substitute into a
> requires-expression in rare cases, in particular when it's used in
> associated constraints that we are directly substituting for sake of
> declaration matching or dguide constraint rewriting.  We can identify
> this situation by checking processing_constraint_expression_p, so this
> patch uses this predicate to control whether we defer substitution or
> partially substitute.  The entering_scope=true change in tsubst_baselink
> is needed to avoid ICEing from tsubst_baselink during name lookup when
> rewriting std::ranges::ref_view's dguide constraints.

Actually, I don't think we want to enter the scope when rewriting 
constraints.  Would tsubst_scope work instead?

Jason