From a6a15bc5b77c8703a95130f410a944f5408a5cc4 Mon Sep 17 00:00:00 2001 From: Nathaniel Shead Date: Thu, 7 Nov 2024 21:37:28 +1100 Subject: c++: Disallow decomposition of lambda bases [PR90321] Decomposition of lambda closure types is not allowed by [dcl.struct.bind] p6, since members of a closure have no name. r244909 made this an error, but missed the case where a lambda is used as a base. This patch moves the check to find_decomp_class_base to handle this case. As a drive-by improvement, we also slightly improve the diagnostics to indicate why a base class was being inspected. Ideally the diagnostic would point directly at the relevant base, but there doesn't seem to be an easy way to get this location just from the binfo so I don't worry about that here. PR c++/90321 gcc/cp/ChangeLog: * decl.cc (find_decomp_class_base): Check for decomposing a lambda closure type. Report base class chains if needed. (cp_finish_decomp): Remove no-longer-needed check. gcc/testsuite/ChangeLog: * g++.dg/cpp1z/decomp62.C: New test. Signed-off-by: Nathaniel Shead Reviewed-by: Marek Polacek --- gcc/cp/decl.cc | 19 +++++++++++++------ gcc/testsuite/g++.dg/cpp1z/decomp62.C | 12 ++++++++++++ 2 files changed, 25 insertions(+), 6 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp1z/decomp62.C (limited to 'gcc') diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc index 4ba6e37..a1b9957 100644 --- a/gcc/cp/decl.cc +++ b/gcc/cp/decl.cc @@ -9405,6 +9405,14 @@ cp_finish_decl (tree decl, tree init, bool init_const_expr_p, static tree find_decomp_class_base (location_t loc, tree type, tree ret) { + if (LAMBDA_TYPE_P (type)) + { + auto_diagnostic_group d; + error_at (loc, "cannot decompose lambda closure type %qT", type); + inform (location_of (type), "lambda declared here"); + return error_mark_node; + } + bool member_seen = false; for (tree field = TYPE_FIELDS (type); field; field = DECL_CHAIN (field)) if (TREE_CODE (field) != FIELD_DECL @@ -9447,9 +9455,13 @@ find_decomp_class_base (location_t loc, tree type, tree ret) for (binfo = TYPE_BINFO (type), i = 0; BINFO_BASE_ITERATE (binfo, i, base_binfo); i++) { + auto_diagnostic_group d; tree t = find_decomp_class_base (loc, TREE_TYPE (base_binfo), ret); if (t == error_mark_node) - return error_mark_node; + { + inform (location_of (type), "in base class of %qT", type); + return error_mark_node; + } if (t != NULL_TREE && t != ret) { if (ret == type) @@ -9905,11 +9917,6 @@ cp_finish_decomp (tree decl, cp_decomp *decomp, bool test_p) error_at (loc, "cannot decompose non-array non-class type %qT", type); goto error_out; } - else if (LAMBDA_TYPE_P (type)) - { - error_at (loc, "cannot decompose lambda closure type %qT", type); - goto error_out; - } else if (processing_template_decl && complete_type (type) == error_mark_node) goto error_out; else if (processing_template_decl && !COMPLETE_TYPE_P (type)) diff --git a/gcc/testsuite/g++.dg/cpp1z/decomp62.C b/gcc/testsuite/g++.dg/cpp1z/decomp62.C new file mode 100644 index 0000000..b0ce105 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1z/decomp62.C @@ -0,0 +1,12 @@ +// PR c++/90321 +// { dg-do compile { target c++17 } } + +template struct hack : F { }; +template hack(F) -> hack; + +int main() +{ + auto f = [x = 1, y = 2]() { }; + auto [a, b] = hack { f }; // { dg-error "cannot decompose lambda closure type" } + return b; +} -- cgit v1.1