[Bug c++/90538] [9/10 Regression] Redeclaration error when expanding parameter pack multiple times in a lambda

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90538

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Wed Jul 31 18:50:00 2019
New Revision: 273944

URL: https://gcc.gnu.org/viewcvs?rev=273944&root=gcc&view=rev
Log:
        PR c++/90538 - multiple expansions of capture packs

Previously, with init-capture the type of the closure field was a
DECLTYPE_TYPE of the initializer.  But since each time we tsubst a lambda we
get a different lambda, that meant that if the initializer is a lambda, we'd
end up with different closure types in the field and initializer after
substitution (PR 87322).  We dealt with this by remembering the lambda
instantiation within each pack expansion element, using
local_specialization_stack to separate the elements.  But that broke this
testcase, because it lost lambda capture proxies that also use
local_specializations.

So, this patch removes the local_specializations changes from that patch and
fixes 87322 differently, by giving init-capture fields 'auto' type and doing
deduction later.  There's a bit of a kludge to get the right number of
fields by pretending that 'auto...' uses the parameter packs from the
initializer, but it does the trick.

        * cp-tree.h (DECLTYPE_FOR_INIT_CAPTURE): Remove.
        * lambda.c (add_capture): Copy parameter packs from init.
        (lambda_capture_field_type): Always use auto for init-capture.
        * pt.c (uses_parameter_packs): Return tree.
        (tsubst) [DECLTYPE_TYPE]: Remove init-capture handling.
        (gen_elem_of_pack_expansion_instantiation): Don't push
        local_specialization_stack.
        (prepend_one_capture): New.
        (tsubst_lambda_expr): Use it.  Don't touch local_specializations.
        (do_auto_deduction): Avoid redundant error.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-variadic9.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/cp-tree.h
    trunk/gcc/cp/lambda.c
    trunk/gcc/cp/pt.c
    trunk/gcc/testsuite/g++.dg/cpp0x/range-for19.C
    trunk/gcc/testsuite/g++.dg/cpp1y/lambda-init16.C