* cp-tree.h (struct lang_decl_decomp): New type.
(struct lang_decl): Add u.decomp.
(LANG_DECL_DECOMP_CHECK): Define.
(DECL_DECOMPOSITION_P): Note it is set also on the vars
for user identifiers.
(DECL_DECOMP_BASE): Define.
(retrofit_lang_decl): Add extra int = 0 argument.
* lex.c (retrofit_lang_decl): Add SEL argument, if non-zero
use it to influence the selector choices and for selector
0 to non-zero transition copy old content.
(cxx_dup_lang_specific_decl): Handle DECL_DECOMPOSITION_P.
* decl.c (poplevel): For DECL_DECOMPOSITION_P, check
!DECL_DECOMP_BASE instead of !DECL_VALUE_EXPR. Adjust warning
wording if decl is a structured binding.
(cp_finish_decomp): Pass 4 as the new argument to retrofit_lang_decl.
Set DECL_DECOMP_BASE. Ignore DECL_READ_P sets from initialization
of individual variables for tuple structured bindings.
(grokdeclarator): Pass 4 as the new argument to retrofit_lang_decl.
Clear DECL_DECOMP_BASE.
* decl2.c (mark_used): Mark DECL_DECOMP_BASE TREE_USED as well.
* pt.c (tsubst_decomp_names): Assert DECL_DECOMP_BASE matches what
is expected.
* expr.c (mark_exp_read): Recurse on DECL_DECOMP_BASE instead of
DECL_VALUE_EXPR.
* g++.dg/cpp1z/decomp29.C (p): New variable.
(main): Add further tests.
From-SVN: r248483
