On Tue, Jul 29, 2025 at 03:45:29PM -0400, Patrick Palka wrote:
> On Tue, 29 Jul 2025, Nathaniel Shead wrote:
>
> > Tested on x86_64-pc-linux-gnu, OK for trunk if full bootstrap+regtest
> > passes?
> >
> > -- >8 --
> >
> > For the sake of determining if there are other errors in user code to
> > report early, many trait functions don't return error_mark_node if not
> > called in a SFINAE context (i.e., tf_error is set). This patch removes
> > some assumptions on this behaviour I'd made when improving diagnostics
> > of builtin traits.
> >
> > PR c++/121291
> >
> > gcc/cp/ChangeLog:
> >
> > * constraint.cc (diagnose_trait_expr): Remove assumption about
> > failures returning error_mark_node.
> > * method.cc (build_invoke): Adjust comment.
> > (is_nothrow_convertible): Check for errorcount changes.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * g++.dg/ext/is_invocable7.C: New test.
> > * g++.dg/ext/is_nothrow_convertible5.C: New test.
> >
> > Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
> > ---
> > gcc/cp/constraint.cc | 9 +++++---
> > gcc/cp/method.cc | 9 ++++++--
> > gcc/testsuite/g++.dg/ext/is_invocable7.C | 21 +++++++++++++++++++
> > .../g++.dg/ext/is_nothrow_convertible5.C | 15 +++++++++++++
> > 4 files changed, 49 insertions(+), 5 deletions(-)
> > create mode 100644 gcc/testsuite/g++.dg/ext/is_invocable7.C
> > create mode 100644 gcc/testsuite/g++.dg/ext/is_nothrow_convertible5.C
> >
> > diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
> > index d4a83e429e5..94238c9e8f1 100644
> > --- a/gcc/cp/constraint.cc
> > +++ b/gcc/cp/constraint.cc
> > @@ -3176,8 +3176,7 @@ diagnose_trait_expr (location_t loc, tree expr, tree
> > args)
> > inform (loc, "%qT is not invocable, because", t1);
> > else
> > inform (loc, "%qT is not invocable by %qT, because", t1, t2);
> > - tree call = build_invoke (t1, t2, tf_error);
> > - gcc_assert (call == error_mark_node);
> > + build_invoke (t1, t2, tf_error);
> > }
> > break;
> > case CPTK_IS_LAYOUT_COMPATIBLE:
> > @@ -3221,8 +3220,12 @@ diagnose_trait_expr (location_t loc, tree expr, tree
> > args)
> > inform (loc, "%qT is not nothrow invocable, because", t1);
> > else
> > inform (loc, "%qT is not nothrow invocable by %qT, because", t1, t2);
> > + /* We can't rely on build_invoke returning error_mark_node, because
> > + when passing tf_error in some cases a valid call may be returned
> > + anyway. */
> > + int errs = errorcount + sorrycount;
> > tree call = build_invoke (t1, t2, tf_error);
> > - if (call != error_mark_node)
> > + if (call != error_mark_node && errs == errorcount + sorrycount)
> > explain_not_noexcept (call);
>
> What do you think about just checking expr_noexcept_p here instead (or
> removing the assert in explain_not_noexcept)? So that if a call is not
> nothrow invocable because the selected candidate is private _and_
> because it's not noexcept, we'd report both errors. I see that
> tsubst_compound_requirement already behaves this way.
Good point, I think I like this more; it's definitely the less complex
behaviour and is also potentially useful. Here's an adjusted patch that
does this; bootstrapped and regtested on x86_64-pc-linux-gnu, OK for
trunk?
-- >8 --
For the sake of determining if there are other errors in user code to
report early, many trait functions don't always return error_mark_node
if not called in a SFINAE context (i.e., tf_error is set). This patch
removes some assumptions on this behaviour I'd made when improving
diagnostics of builtin traits.
PR c++/121291
gcc/cp/ChangeLog:
* constraint.cc (diagnose_trait_expr): Remove assumption about
failures returning error_mark_node.
* except.cc (explain_not_noexcept): Allow expr not being
noexcept.
* method.cc (build_invoke): Adjust comment.
(is_trivially_xible): Always note non-trivial components if expr
is not null or error_mark_node.
(is_nothrow_xible): Likewise for non-noexcept components.
(is_nothrow_convertible): Likewise.
gcc/testsuite/ChangeLog:
* g++.dg/ext/is_invocable7.C: New test.
* g++.dg/ext/is_nothrow_convertible5.C: New test.
Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
Reviewed-by: Patrick Palka <ppa...@redhat.com>
---
gcc/cp/constraint.cc | 3 +-
gcc/cp/except.cc | 7 ++--
gcc/cp/method.cc | 33 +++++--------------
gcc/testsuite/g++.dg/ext/is_invocable7.C | 21 ++++++++++++
.../g++.dg/ext/is_nothrow_convertible5.C | 15 +++++++++
5 files changed, 50 insertions(+), 29 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/ext/is_invocable7.C
create mode 100644 gcc/testsuite/g++.dg/ext/is_nothrow_convertible5.C
diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index d4a83e429e5..cbdfafc90c0 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -3176,8 +3176,7 @@ diagnose_trait_expr (location_t loc, tree expr, tree args)
inform (loc, "%qT is not invocable, because", t1);
else
inform (loc, "%qT is not invocable by %qT, because", t1, t2);
- tree call = build_invoke (t1, t2, tf_error);
- gcc_assert (call == error_mark_node);
+ build_invoke (t1, t2, tf_error);
}
break;
case CPTK_IS_LAYOUT_COMPATIBLE:
diff --git a/gcc/cp/except.cc b/gcc/cp/except.cc
index 2c1ef4c3af6..c0b93df9456 100644
--- a/gcc/cp/except.cc
+++ b/gcc/cp/except.cc
@@ -1218,13 +1218,14 @@ expr_noexcept_p (tree expr, tsubst_flags_t complain)
return true;
}
-/* Explain why EXPR is not noexcept. */
+/* If EXPR is not noexcept, explain why. */
void explain_not_noexcept (tree expr)
{
tree fn = cp_walk_tree_without_duplicates (&expr, check_noexcept_r, 0);
- gcc_assert (fn);
- if (DECL_P (fn))
+ if (!fn)
+ /* The call was noexcept, nothing to do. */;
+ else if (DECL_P (fn))
inform (DECL_SOURCE_LOCATION (fn), "%qD is not %<noexcept%>", fn);
else
inform (location_of (fn), "%qT is not %<noexcept%>", TREE_TYPE (fn));
diff --git a/gcc/cp/method.cc b/gcc/cp/method.cc
index 62f8d80c781..397e496ed47 100644
--- a/gcc/cp/method.cc
+++ b/gcc/cp/method.cc
@@ -1952,7 +1952,8 @@ build_trait_object (tree type, tsubst_flags_t complain)
}
/* [func.require] Build an expression of INVOKE(FN_TYPE, ARG_TYPES...). If the
- given is not invocable, returns error_mark_node. */
+ given is not invocable, returns error_mark_node, unless COMPLAIN includes
+ tf_error. */
tree
build_invoke (tree fn_type, const_tree arg_types, tsubst_flags_t complain)
@@ -2460,21 +2461,13 @@ bool
is_trivially_xible (enum tree_code code, tree to, tree from,
bool explain/*=false*/)
{
- /* In some cases, when producing errors is_xible_helper may not return
- error_mark_node, so check if it looks like we've already emitted any
- diagnostics to ensure we don't do so multiple times. */
- int errs = errorcount + sorrycount;
-
tree expr = is_xible_helper (code, to, from, explain);
if (expr == NULL_TREE || expr == error_mark_node)
return false;
tree nt = cp_walk_tree_without_duplicates (&expr, check_nontriv, NULL);
- if (explain && errs == (errorcount + sorrycount))
- {
- gcc_assert (nt);
- inform (location_of (nt), "%qE is non-trivial", nt);
- }
+ if (explain && nt)
+ inform (location_of (nt), "%qE is non-trivial", nt);
return !nt;
}
@@ -2487,9 +2480,6 @@ bool
is_nothrow_xible (enum tree_code code, tree to, tree from,
bool explain/*=false*/)
{
- /* As with is_trivially_xible. */
- int errs = errorcount + sorrycount;
-
++cp_noexcept_operand;
tree expr = is_xible_helper (code, to, from, explain);
--cp_noexcept_operand;
@@ -2497,11 +2487,8 @@ is_nothrow_xible (enum tree_code code, tree to, tree
from,
return false;
bool is_noexcept = expr_noexcept_p (expr, tf_none);
- if (explain && errs == (errorcount + sorrycount))
- {
- gcc_assert (!is_noexcept);
- explain_not_noexcept (expr);
- }
+ if (explain && !is_noexcept)
+ explain_not_noexcept (expr);
return is_noexcept;
}
@@ -2601,12 +2588,10 @@ is_nothrow_convertible (tree from, tree to, bool
explain/*=false*/)
tree expr = is_convertible_helper (from, to, explain);
if (expr == NULL_TREE || expr == error_mark_node)
return false;
+
bool is_noexcept = expr_noexcept_p (expr, tf_none);
- if (explain)
- {
- gcc_assert (!is_noexcept);
- explain_not_noexcept (expr);
- }
+ if (explain && !is_noexcept)
+ explain_not_noexcept (expr);
return is_noexcept;
}
diff --git a/gcc/testsuite/g++.dg/ext/is_invocable7.C
b/gcc/testsuite/g++.dg/ext/is_invocable7.C
new file mode 100644
index 00000000000..5c852fc8428
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/is_invocable7.C
@@ -0,0 +1,21 @@
+// PR c++/121291
+// { dg-do compile { target c++17 } }
+
+template <typename T>
+constexpr bool is_invocable = __is_invocable(T);
+
+template <typename T>
+constexpr bool is_nothrow_invocable = __is_nothrow_invocable(T);
+
+struct S {
+private:
+ int operator()() noexcept; // { dg-message "here" }
+};
+
+static_assert(is_invocable<S>); // { dg-error "assert" }
+// { dg-message "not invocable" "" { target *-*-* } .-1 }
+// { dg-error "private within this context" "" { target *-*-* } .-2 }
+
+static_assert(is_nothrow_invocable<S>); // { dg-error "assert" }
+// { dg-message "not nothrow invocable" "" { target *-*-* } .-1 }
+// { dg-error "private within this context" "" { target *-*-* } .-2 }
diff --git a/gcc/testsuite/g++.dg/ext/is_nothrow_convertible5.C
b/gcc/testsuite/g++.dg/ext/is_nothrow_convertible5.C
new file mode 100644
index 00000000000..0ce8fb82191
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/is_nothrow_convertible5.C
@@ -0,0 +1,15 @@
+// PR c++/121291
+// { dg-do compile { target c++17 } }
+
+template <typename T, typename U>
+constexpr bool is_nothrow_convertible = __is_nothrow_convertible(T, U);
+
+struct A {};
+struct B {
+private:
+ operator A() noexcept; // { dg-message "here" }
+};
+
+static_assert(is_nothrow_convertible<B, A>); // { dg-error "assert" }
+// { dg-message "not nothrow convertible" "" { target *-*-* } .-1 }
+// { dg-error "private within this context" "" { target *-*-* } .-2 }
--
2.47.0
