On 1/22/25 6:11 PM, Jason Merrill wrote:
On 1/16/25 7:24 PM, Nathaniel Shead wrote:
On Thu, Jan 16, 2025 at 07:09:33PM -0500, Jason Merrill wrote:
On 1/6/25 7:22 AM, Nathaniel Shead wrote:
I'm not 100% sure I've handled this properly, any feedback welcome.
In particular, maybe should I use `DECL_IMPLICIT_TYPEDEF_P` in the
mangling logic instead of `!TYPE_DECL_ALIAS_P`? They both seem to work
in this case but not sure which would be clearer.
I also looked into trying do a limited form of 'start_decl' before
parsing the type but there were too many circular dependencies for
me to
work through, so I think any such changes would have to wait till GCC16
(if they're even possible at all).
-- >8 --
This adds mangling support for lambdas with a mangling context of an
alias template, and gives that context when instantiating such a
lambda.
I think this is wrong, an alias is not an entity so it is not a
definable
item.
The ABI change proposal also doesn't mention aliases.
Ah right, I see; I'd treated https://eel.is/c++draft/basic.def.odr#1.5
as being any template, but I see now it's "any templated entity" which
is different (since as you say an alias isn't an entity).
In that case, how do you think we should handle class-scope alias
templates of lambdas? Such a class is surely a definable item, and so
e.g.
struct S {
template <int I>
using X = decltype([]{ return I; });
};
using L1 = S::X<1>;
using L2 = S::X<2>;
should this work and declare L1 to be the same type across TUs?
Hmm, I suppose it should. So then using the alias template name in the
mangling is then not because it's a definable item, but just as a
convenient label to indicate where it appears in the class and what the
template arguments apply to.
Actually, on rereading I think my interpretation was wrong:
https://eel.is/c++draft/basic#pre-3 says a template is an entity.
https://eel.is/c++draft/temp.pre#8.1 says an entity is templated if it
is a template.
https://eel.is/c++draft/basic#def.odr-1.5 says a templated entity is a
definable item.
So, an alias template is a definable item even if a non-template alias
is not.
But a lambda in a namespace-scope alias template is still clearly
TU-local under https://eel.is/c++draft/basic#link-15.2 .
Jason
