From: Jason Merrill <jason@redhat.com>
To: Nathaniel Shead <nathanieloshead@gmail.com>
Cc: gcc-patches@gcc.gnu.org
Subject: Re: [PATCH v2] c++: Strengthen checks on 'main'
Date: Mon, 20 May 2024 18:03:38 -0400 [thread overview]
Message-ID: <5904df4f-9594-4ae2-8a00-6e0fa6972847@redhat.com> (raw)
In-Reply-To: <6646fd7e.170a0220.376e4.b72c@mx.google.com>
On 5/17/24 02:47, Nathaniel Shead wrote:
> On Tue, May 14, 2024 at 06:25:29PM -0400, Jason Merrill wrote:
>> On 5/11/24 08:32, Nathaniel Shead wrote:
>>> I wasn't entirely sure what to do with the 'abi/main.C' testcase here;
>>> is this OK, or should I e.g. lower the linkage error to a pedwarn for
>>> the purposes of this test?
>>
>> I think it should be a pedwarn anyway, since it's harmless. The others can
>> still be errors.
>
> Fair enough; how about this? OK for trunk if bootstrap + regtest
> succeeds?
OK.
> -- >8 --
>
> This patch adds some missing requirements for legal main declarations,
> as according to [basic.start.main] p2.
>
> gcc/cp/ChangeLog:
>
> * decl.cc (grokfndecl): Check for main functions with language
> linkage or module attachment.
> (grokvardecl): Check for extern 'C' entities named main.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/abi/main.C: Check pedwarn for main with linkage-spec.
> * g++.dg/modules/contracts-1_b.C: Don't declare main in named
> module.
> * g++.dg/modules/contracts-3_b.C: Likewise.
> * g++.dg/modules/contracts-4_d.C: Likewise.
> * g++.dg/modules/horcrux-1_a.C: Export declarations, so that...
> * g++.dg/modules/horcrux-1_b.C: Don't declare main in named
> module.
> * g++.dg/modules/main-1.C: New test.
> * g++.dg/parse/linkage5.C: New test.
> * g++.dg/parse/linkage6.C: New test.
>
> Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
> ---
> gcc/cp/decl.cc | 19 +++++++++++++++----
> gcc/testsuite/g++.dg/abi/main.C | 3 ++-
> gcc/testsuite/g++.dg/modules/contracts-1_b.C | 4 ----
> gcc/testsuite/g++.dg/modules/contracts-3_b.C | 4 ----
> gcc/testsuite/g++.dg/modules/contracts-4_d.C | 2 --
> gcc/testsuite/g++.dg/modules/horcrux-1_a.C | 3 +++
> gcc/testsuite/g++.dg/modules/horcrux-1_b.C | 2 +-
> gcc/testsuite/g++.dg/modules/main-1.C | 5 +++++
> gcc/testsuite/g++.dg/parse/linkage5.C | 14 ++++++++++++++
> gcc/testsuite/g++.dg/parse/linkage6.C | 13 +++++++++++++
> 10 files changed, 53 insertions(+), 16 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/modules/main-1.C
> create mode 100644 gcc/testsuite/g++.dg/parse/linkage5.C
> create mode 100644 gcc/testsuite/g++.dg/parse/linkage6.C
>
> diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
> index 6fcab615d55..a992d54dc8f 100644
> --- a/gcc/cp/decl.cc
> +++ b/gcc/cp/decl.cc
> @@ -10788,6 +10788,11 @@ grokfndecl (tree ctype,
> "cannot declare %<::main%> to be %qs", "consteval");
> if (!publicp)
> error_at (location, "cannot declare %<::main%> to be static");
> + if (current_lang_depth () != 0)
> + pedwarn (location, OPT_Wpedantic, "cannot declare %<::main%> with a"
> + " linkage specification");
> + if (module_attach_p ())
> + error_at (location, "cannot attach %<::main%> to a named module");
> inlinep = 0;
> publicp = 1;
> }
> @@ -11287,10 +11292,16 @@ grokvardecl (tree type,
> DECL_INTERFACE_KNOWN (decl) = 1;
>
> if (DECL_NAME (decl)
> - && MAIN_NAME_P (DECL_NAME (decl))
> - && scope == global_namespace)
> - error_at (DECL_SOURCE_LOCATION (decl),
> - "cannot declare %<::main%> to be a global variable");
> + && MAIN_NAME_P (DECL_NAME (decl)))
> + {
> + if (scope == global_namespace)
> + error_at (DECL_SOURCE_LOCATION (decl),
> + "cannot declare %<::main%> to be a global variable");
> + else if (DECL_EXTERN_C_P (decl))
> + error_at (DECL_SOURCE_LOCATION (decl),
> + "an entity named %<main%> cannot be declared with "
> + "C language linkage");
> + }
>
> /* Check that the variable can be safely declared as a concept.
> Note that this also forbids explicit specializations. */
> diff --git a/gcc/testsuite/g++.dg/abi/main.C b/gcc/testsuite/g++.dg/abi/main.C
> index 4c5f1ea213c..2797a16df5b 100644
> --- a/gcc/testsuite/g++.dg/abi/main.C
> +++ b/gcc/testsuite/g++.dg/abi/main.C
> @@ -1,10 +1,11 @@
> /* { dg-do compile } */
> +/* { dg-additional-options "-Wno-error=pedantic" }
>
> /* Check if entry points get implicit C linkage. If they don't, compiler will
> * error on incompatible declarations */
>
> int main();
> -extern "C" int main();
> +extern "C" int main(); // { dg-warning "linkage specification" }
>
> #ifdef __MINGW32__
>
> diff --git a/gcc/testsuite/g++.dg/modules/contracts-1_b.C b/gcc/testsuite/g++.dg/modules/contracts-1_b.C
> index 30c15f6928b..aa36c8d6b1b 100644
> --- a/gcc/testsuite/g++.dg/modules/contracts-1_b.C
> +++ b/gcc/testsuite/g++.dg/modules/contracts-1_b.C
> @@ -1,15 +1,11 @@
> // { dg-module-do run }
> // { dg-additional-options "-fmodules-ts -fcontracts -fcontract-continuation-mode=on" }
> -module;
> #include <cstdio>
> -export module bar;
> -// { dg-module-cmi bar }
> import foo;
>
> template<typename T>
> bool bar_fn_pre(T n) { printf("bar fn pre(%d)\n", n); return true; }
>
> -export
> template<typename T>
> T bar_fn(T n)
> [[ pre: bar_fn_pre(n) && n > 0 ]]
> diff --git a/gcc/testsuite/g++.dg/modules/contracts-3_b.C b/gcc/testsuite/g++.dg/modules/contracts-3_b.C
> index b1d6375391b..1a29e2c3e5d 100644
> --- a/gcc/testsuite/g++.dg/modules/contracts-3_b.C
> +++ b/gcc/testsuite/g++.dg/modules/contracts-3_b.C
> @@ -1,15 +1,11 @@
> // { dg-module-do run }
> // { dg-additional-options "-fmodules-ts -fcontracts -fcontract-role=default:ignore,ignore,ignore" }
> -module;
> #include <cstdio>
> -export module bar;
> -// { dg-module-cmi bar }
> import foo;
>
> template<typename T>
> bool bar_fn_pre(T n) { printf("bar fn pre(%d)\n", n); return true; }
>
> -export
> template<typename T>
> T bar_fn(T n)
> [[ pre: bar_fn_pre(n) && n > 0 ]]
> diff --git a/gcc/testsuite/g++.dg/modules/contracts-4_d.C b/gcc/testsuite/g++.dg/modules/contracts-4_d.C
> index dc56251d1d8..9e6b7c3d4de 100644
> --- a/gcc/testsuite/g++.dg/modules/contracts-4_d.C
> +++ b/gcc/testsuite/g++.dg/modules/contracts-4_d.C
> @@ -1,8 +1,6 @@
> // { dg-module-do run }
> // { dg-additional-options "-fmodules-ts -fcontracts" }
> -module;
> #include <cstdio>
> -export module baz;
> import foo;
> import bar;
>
> diff --git a/gcc/testsuite/g++.dg/modules/horcrux-1_a.C b/gcc/testsuite/g++.dg/modules/horcrux-1_a.C
> index ff548d039ea..c115bd2965b 100644
> --- a/gcc/testsuite/g++.dg/modules/horcrux-1_a.C
> +++ b/gcc/testsuite/g++.dg/modules/horcrux-1_a.C
> @@ -3,13 +3,16 @@
> export module foo;
> // { dg-module-cmi foo }
>
> +export
> template<typename _Tp, _Tp __v>
> struct integral_constant
> {};
>
> +export
> template<bool __v>
> using __bool_constant = integral_constant<bool, __v>;
>
> +export
> template<typename _Tp, typename... _Args>
> struct __is_constructible_impl
> : public __bool_constant<__is_constructible(_Tp, _Args...)>
> diff --git a/gcc/testsuite/g++.dg/modules/horcrux-1_b.C b/gcc/testsuite/g++.dg/modules/horcrux-1_b.C
> index 842bf413585..54aa069436a 100644
> --- a/gcc/testsuite/g++.dg/modules/horcrux-1_b.C
> +++ b/gcc/testsuite/g++.dg/modules/horcrux-1_b.C
> @@ -1,6 +1,6 @@
> // { dg-additional-options -fmodules-ts }
>
> -module foo;
> +import foo;
>
> int main ()
> {
> diff --git a/gcc/testsuite/g++.dg/modules/main-1.C b/gcc/testsuite/g++.dg/modules/main-1.C
> new file mode 100644
> index 00000000000..0d79edddb75
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/main-1.C
> @@ -0,0 +1,5 @@
> +// { dg-additional-options "-fmodules-ts" }
> +// { dg-prune-output "not writing module" }
> +
> +export module M;
> +int main() {} // { dg-error "attach" }
> diff --git a/gcc/testsuite/g++.dg/parse/linkage5.C b/gcc/testsuite/g++.dg/parse/linkage5.C
> new file mode 100644
> index 00000000000..451406de69b
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/parse/linkage5.C
> @@ -0,0 +1,14 @@
> +// { dg-do compile }
> +// The main function shall not be declared with a linkage-specification.
> +
> +extern "C" {
> + int main(); // { dg-error "linkage" }
> +}
> +
> +namespace foo {
> + extern "C" int main(); // { dg-error "linkage" }
> +}
> +
> +extern "C++" int main(); // { dg-error "linkage" }
> +
> +extern "C" struct S { int main(); }; // OK
> diff --git a/gcc/testsuite/g++.dg/parse/linkage6.C b/gcc/testsuite/g++.dg/parse/linkage6.C
> new file mode 100644
> index 00000000000..44081c1544c
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/parse/linkage6.C
> @@ -0,0 +1,13 @@
> +// { dg-do compile }
> +// A program that declares an entity named main with C language linkage
> +// (in any namespace) is ill-formed.
> +
> +namespace foo {
> + extern "C" int main; // { dg-error "linkage" }
> + extern "C" struct A {
> + int main; // OK
> + };
> + extern "C" struct B {
> + int main(); // OK
> + };
> +}
prev parent reply other threads:[~2024-05-20 22:03 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-11 12:32 [PATCH] " Nathaniel Shead
2024-05-14 22:25 ` Jason Merrill
2024-05-17 6:47 ` [PATCH v2] " Nathaniel Shead
2024-05-20 22:03 ` Jason Merrill [this message]
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