[PATCH] c++: Don't hide narrowing errors in system headers
Jason Merrill
jason@redhat.com
Fri Jul 16 13:01:27 GMT 2021
On 7/15/21 8:03 PM, Marek Polacek wrote:
> Jonathan pointed me at this issue where
>
> constexpr unsigned f() { constexpr int n = -1; return unsigned{n}; }
>
> is accepted in system headers, despite the narrowing conversion from
> a constant. I suspect that whereas narrowing warnings should be
> disabled, ill-formed narrowing of constants should be a hard error
> (which can still be disabled by -Wno-narrowing).
>
> Bootstrapped/regtested on {ppc64le,x86_64}-pc-linux-gnu, ok for trunk?
OK.
> gcc/cp/ChangeLog:
>
> * typeck2.c (check_narrowing): Don't suppress the pedantic error
> in system headers.
>
> libstdc++-v3/ChangeLog:
>
> * testsuite/20_util/ratio/operations/ops_overflow_neg.cc: Add
> dg-error.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp1y/Wnarrowing2.C: New test.
> * g++.dg/cpp1y/Wnarrowing2.h: New test.
> ---
> gcc/cp/typeck2.c | 1 +
> gcc/testsuite/g++.dg/cpp1y/Wnarrowing2.C | 4 ++++
> gcc/testsuite/g++.dg/cpp1y/Wnarrowing2.h | 2 ++
> .../testsuite/20_util/ratio/operations/ops_overflow_neg.cc | 2 ++
> 4 files changed, 9 insertions(+)
> create mode 100644 gcc/testsuite/g++.dg/cpp1y/Wnarrowing2.C
> create mode 100644 gcc/testsuite/g++.dg/cpp1y/Wnarrowing2.h
>
> diff --git a/gcc/cp/typeck2.c b/gcc/cp/typeck2.c
> index 6679e247816..dcfdff2f905 100644
> --- a/gcc/cp/typeck2.c
> +++ b/gcc/cp/typeck2.c
> @@ -986,6 +986,7 @@ check_narrowing (tree type, tree init, tsubst_flags_t complain,
> {
> int savederrorcount = errorcount;
> global_dc->pedantic_errors = 1;
> + auto s = make_temp_override (global_dc->dc_warn_system_headers, true);
> pedwarn (loc, OPT_Wnarrowing,
> "narrowing conversion of %qE from %qH to %qI",
> init, ftype, type);
> diff --git a/gcc/testsuite/g++.dg/cpp1y/Wnarrowing2.C b/gcc/testsuite/g++.dg/cpp1y/Wnarrowing2.C
> new file mode 100644
> index 00000000000..048d484f46f
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp1y/Wnarrowing2.C
> @@ -0,0 +1,4 @@
> +// { dg-do compile { target c++14 } }
> +
> +#include "Wnarrowing2.h"
> +// { dg-error "narrowing conversion" "" { target *-*-* } 0 }
> diff --git a/gcc/testsuite/g++.dg/cpp1y/Wnarrowing2.h b/gcc/testsuite/g++.dg/cpp1y/Wnarrowing2.h
> new file mode 100644
> index 00000000000..7dafa51af14
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp1y/Wnarrowing2.h
> @@ -0,0 +1,2 @@
> +#pragma GCC system_header
> +constexpr unsigned f() { constexpr int n = -1; return unsigned{n}; }
> diff --git a/libstdc++-v3/testsuite/20_util/ratio/operations/ops_overflow_neg.cc b/libstdc++-v3/testsuite/20_util/ratio/operations/ops_overflow_neg.cc
> index 47d3c3a037e..f120e599a33 100644
> --- a/libstdc++-v3/testsuite/20_util/ratio/operations/ops_overflow_neg.cc
> +++ b/libstdc++-v3/testsuite/20_util/ratio/operations/ops_overflow_neg.cc
> @@ -39,6 +39,7 @@ test02()
> }
>
> // { dg-error "required from here" "" { target *-*-* } 28 }
> +// { dg-error "expected initializer" "" { target *-*-* } 28 }
> // { dg-error "expected initializer" "" { target *-*-* } 35 }
> // { dg-error "expected initializer" "" { target *-*-* } 37 }
> // { dg-error "overflow in addition" "" { target *-*-* } 0 }
> @@ -46,5 +47,6 @@ test02()
> // { dg-error "overflow in multiplication" "" { target *-*-* } 100 }
> // { dg-error "overflow in multiplication" "" { target *-*-* } 102 }
> // { dg-error "overflow in constant expression" "" { target *-*-* } 0 }
> +// { dg-error "narrowing conversion" "" { target *-*-* } 0 }
> // { dg-prune-output "out of range" }
> // { dg-prune-output "not usable in a constant expression" }
>
> base-commit: f364cdffa47af574f90f671b2dcf5afa91442741
>
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