c++: fix truncated diagnostic in C++23 [PR111272]
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Commit Message
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >8 --
In C++23, since P2448, a constexpr function F that calls a non-constexpr
function N is OK as long as we don't actually call F in a constexpr
context. So instead of giving an error in maybe_save_constexpr_fundef,
we only give an error when evaluating the call. Unfortunately, as shown
in this PR, the diagnostic can be truncated:
z.C:10:13: note: 'constexpr Jam::Jam()' is not usable as a 'constexpr' function because:
10 | constexpr Jam() { ft(); }
| ^~~
...because what? With this patch, we say:
z.C:10:13: note: 'constexpr Jam::Jam()' is not usable as a 'constexpr' function because:
10 | constexpr Jam() { ft(); }
| ^~~
z.C:10:23: error: call to non-'constexpr' function 'int Jam::ft()'
10 | constexpr Jam() { ft(); }
| ~~^~
z.C:8:7: note: 'int Jam::ft()' declared here
8 | int ft() { return 42; }
| ^~
Like maybe_save_constexpr_fundef, explain_invalid_constexpr_fn should
also check the body of a constructor, not just the mem-initializer.
PR c++/111272
gcc/cp/ChangeLog:
* constexpr.cc (explain_invalid_constexpr_fn): Also check the body of
a constructor in C++14 and up.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1y/constexpr-diag1.C: New test.
---
gcc/cp/constexpr.cc | 10 +++++++++-
gcc/testsuite/g++.dg/cpp1y/constexpr-diag1.C | 21 ++++++++++++++++++++
2 files changed, 30 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp1y/constexpr-diag1.C
base-commit: d78fef5371759849944966dec65d9e987efba509
Comments
On 10/13/23 18:15, Marek Polacek wrote:
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
OK.
> -- >8 --
> In C++23, since P2448, a constexpr function F that calls a non-constexpr
> function N is OK as long as we don't actually call F in a constexpr
> context. So instead of giving an error in maybe_save_constexpr_fundef,
> we only give an error when evaluating the call. Unfortunately, as shown
> in this PR, the diagnostic can be truncated:
>
> z.C:10:13: note: 'constexpr Jam::Jam()' is not usable as a 'constexpr' function because:
> 10 | constexpr Jam() { ft(); }
> | ^~~
>
> ...because what? With this patch, we say:
>
> z.C:10:13: note: 'constexpr Jam::Jam()' is not usable as a 'constexpr' function because:
> 10 | constexpr Jam() { ft(); }
> | ^~~
> z.C:10:23: error: call to non-'constexpr' function 'int Jam::ft()'
> 10 | constexpr Jam() { ft(); }
> | ~~^~
> z.C:8:7: note: 'int Jam::ft()' declared here
> 8 | int ft() { return 42; }
> | ^~
>
> Like maybe_save_constexpr_fundef, explain_invalid_constexpr_fn should
> also check the body of a constructor, not just the mem-initializer.
>
> PR c++/111272
>
> gcc/cp/ChangeLog:
>
> * constexpr.cc (explain_invalid_constexpr_fn): Also check the body of
> a constructor in C++14 and up.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp1y/constexpr-diag1.C: New test.
> ---
> gcc/cp/constexpr.cc | 10 +++++++++-
> gcc/testsuite/g++.dg/cpp1y/constexpr-diag1.C | 21 ++++++++++++++++++++
> 2 files changed, 30 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/g++.dg/cpp1y/constexpr-diag1.C
>
> diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
> index 0f948db7c2d..dde4fec4a44 100644
> --- a/gcc/cp/constexpr.cc
> +++ b/gcc/cp/constexpr.cc
> @@ -1098,7 +1098,15 @@ explain_invalid_constexpr_fn (tree fun)
> body = massage_constexpr_body (fun, body);
> require_potential_rvalue_constant_expression (body);
> if (DECL_CONSTRUCTOR_P (fun))
> - cx_check_missing_mem_inits (DECL_CONTEXT (fun), body, true);
> + {
> + cx_check_missing_mem_inits (DECL_CONTEXT (fun), body, true);
> + if (cxx_dialect > cxx11)
> + {
> + /* Also check the body, not just the ctor-initializer. */
> + body = DECL_SAVED_TREE (fun);
> + require_potential_rvalue_constant_expression (body);
> + }
> + }
> }
> }
> }
> diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-diag1.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-diag1.C
> new file mode 100644
> index 00000000000..0e2909e83ef
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-diag1.C
> @@ -0,0 +1,21 @@
> +// PR c++/111272
> +// { dg-do compile { target c++14 } }
> +// { dg-options "-Werror=invalid-constexpr" }
> +// { dg-prune-output "some warnings being treated as errors" }
> +
> +struct Jam
> +{
> + // constexpr // n.b.
> + int ft() { return 42; } // { dg-message "declared here" }
> +
> + constexpr Jam() { ft(); } // { dg-error "call to non-.constexpr. function" }
> +// { dg-message "declared here" "" { target c++20_down } .-1 }
> +};
> +
> +constexpr bool test()
> +{
> + Jam j; // { dg-error "called in a constant expression" }
> + return true;
> +}
> +
> +static_assert(test(), ""); // { dg-error "non-constant condition" }
>
> base-commit: d78fef5371759849944966dec65d9e987efba509
@@ -1098,7 +1098,15 @@ explain_invalid_constexpr_fn (tree fun)
body = massage_constexpr_body (fun, body);
require_potential_rvalue_constant_expression (body);
if (DECL_CONSTRUCTOR_P (fun))
- cx_check_missing_mem_inits (DECL_CONTEXT (fun), body, true);
+ {
+ cx_check_missing_mem_inits (DECL_CONTEXT (fun), body, true);
+ if (cxx_dialect > cxx11)
+ {
+ /* Also check the body, not just the ctor-initializer. */
+ body = DECL_SAVED_TREE (fun);
+ require_potential_rvalue_constant_expression (body);
+ }
+ }
}
}
}
new file mode 100644
@@ -0,0 +1,21 @@
+// PR c++/111272
+// { dg-do compile { target c++14 } }
+// { dg-options "-Werror=invalid-constexpr" }
+// { dg-prune-output "some warnings being treated as errors" }
+
+struct Jam
+{
+ // constexpr // n.b.
+ int ft() { return 42; } // { dg-message "declared here" }
+
+ constexpr Jam() { ft(); } // { dg-error "call to non-.constexpr. function" }
+// { dg-message "declared here" "" { target c++20_down } .-1 }
+};
+
+constexpr bool test()
+{
+ Jam j; // { dg-error "called in a constant expression" }
+ return true;
+}
+
+static_assert(test(), ""); // { dg-error "non-constant condition" }