https://gcc.gnu.org/g:a21847acb8bb1101c15deef1b55d929e65c9ada4
commit r15-7988-ga21847acb8bb1101c15deef1b55d929e65c9ada4
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Sat Mar 8 11:58:49 2025 +0000
libstdc++: Reject basic_format_parse_context::check_dynamic_spec<>(n)
LWG 4142 (approved in Wrocław, November 2024) made it ill-formed to call
basic_format_parse_context::check_dynamic_spec with an empty template
argument list.
This adds a static_assert to enforce that, and adjusts the tests.
libstdc++-v3/ChangeLog:
* include/std/format
(basic_format_parse_context::check_dynamic_spec): Require a
non-empty parameter pack, as per LWG 4142.
* testsuite/std/format/parse_ctx.cc: Remove call of
check_dynamic_spec with empty template argument list.
* testsuite/std/format/parse_ctx_neg.cc: Add dg-error to call of
check_dynamic_spec with empty template argument list.
Reviewed-by: Tomasz Kamiński <tkami...@redhat.com>
Diff:
---
libstdc++-v3/include/std/format | 3 +++
libstdc++-v3/testsuite/std/format/parse_ctx.cc | 1 -
libstdc++-v3/testsuite/std/format/parse_ctx_neg.cc | 8 ++++++--
3 files changed, 9 insertions(+), 3 deletions(-)
diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format
index e7e0d2d142bb..0d6cc7f6bef4 100644
--- a/libstdc++-v3/include/std/format
+++ b/libstdc++-v3/include/std/format
@@ -4338,6 +4338,9 @@ namespace __format
constexpr void
basic_format_parse_context<_CharT>::check_dynamic_spec(size_t __id)
noexcept
{
+ // _GLIBCXX_RESOLVE_LIB_DEFECTS
+ // 4142. check_dynamic_spec should require at least one type
+ static_assert(sizeof...(_Ts) >= 1);
// This call enforces the Mandates: condition that _Ts contains valid
// types and each type appears at most once. It could be a static_assert
// but this way failures give better diagnostics, due to calling the
diff --git a/libstdc++-v3/testsuite/std/format/parse_ctx.cc
b/libstdc++-v3/testsuite/std/format/parse_ctx.cc
index 88ffd77debe0..b5dd7cdba782 100644
--- a/libstdc++-v3/testsuite/std/format/parse_ctx.cc
+++ b/libstdc++-v3/testsuite/std/format/parse_ctx.cc
@@ -491,7 +491,6 @@ test_dynamic_type_check()
std::format_parse_context pc("{1}.{2}");
// None of these calls should do anything at runtime, only during consteval:
- pc.check_dynamic_spec<>(0);
pc.check_dynamic_spec<int, const char*>(0);
pc.check_dynamic_spec_integral(0);
pc.check_dynamic_spec_string(0);
diff --git a/libstdc++-v3/testsuite/std/format/parse_ctx_neg.cc
b/libstdc++-v3/testsuite/std/format/parse_ctx_neg.cc
index f19107c886fc..d83fd8c7a7b0 100644
--- a/libstdc++-v3/testsuite/std/format/parse_ctx_neg.cc
+++ b/libstdc++-v3/testsuite/std/format/parse_ctx_neg.cc
@@ -12,8 +12,9 @@ test_invalid()
pc.check_dynamic_spec<bool, char, int, unsigned, long long,
unsigned long long, float, double, long double,
const char*, std::string_view, const void*>(0);
- // For some reason, an empty pack of types is valid:
- pc.check_dynamic_spec<>(0);
+
+ // LWG 4142. check_dynamic_spec should require at least one type
+ pc.check_dynamic_spec<>(0); // { dg-error "here" }
pc.check_dynamic_spec<void>(0); // { dg-error "here" }
// const void* is allowed, but void* is not
@@ -25,6 +26,7 @@ test_invalid()
pc.check_dynamic_spec<char8_t>(0); // { dg-error "here" }
// std::string_view is allowed, but std::string is not
pc.check_dynamic_spec<std::string>(0); // { dg-error "here" }
+ // The types in the pack must be unique.
pc.check_dynamic_spec<int, bool, int>(0); // { dg-error "here" }
std::wformat_parse_context wpc(L"");
@@ -38,3 +40,5 @@ test_invalid()
// Each failure above will point to a call to this non-constexpr function:
// { dg-error "__invalid_dynamic_spec" "" { target *-*-* } 0 }
+// Except the check_dynamic_spec<>(0) one for LWG 4142 which matches this:
+// { dg-error "static assertion failed" "" { target *-*-* } 0 }
