https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118698
--- Comment #11 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Patrick Palka from comment #8)
> Started with r14-9938, though I bet before this commit it only accidentally
> worked.
This failure does seem to be strongly connected to that commit.
When normalizing is_foo for <T>, we get to normalizing tt<decltype([]{}),T> for
<T,foo>, which means substituting <T,foo> into <decltype([]{}),T>.
Since r14-9938, because in_template_context is false we return the lambda
unchanged, just with LAMBDA_EXPR_EXTRA_ARGS set, so the closure type still
refers to the is_specialization_of tparms in its CLASSTYPE_TEMPLATE_INFO.
The first failure comes in normalization caching find_template_parameters
walking over the parameter mapping; any_template_parm_r walks into the
TREE_TYPE of a LAMBDA_EXPR without considering EXTRA_ARGS and finds a template
parm from the wrong parameter list.
If I prevent that by skipping caching of lambdas, I then hit another crash in
tsubst_lambda_expr during satisfaction, because add_extra_args expects
dependent EXTRA_ARGS to have been set with tf_partial, but the earlier
substitution correctly wasn't tf_partial, so the expectation is violated.
It seems to me that the underlying issue is the "in_template_context is false";
we're normalizing a concept, that is a template context. So I guess
normalize_concept_definition needs to set current_template_parms.
