On 8/28/23 19:24, Marek Polacek wrote:
On Fri, Aug 25, 2023 at 08:34:37PM -0400, Jason Merrill wrote:
On 8/25/23 19:37, Marek Polacek wrote:
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >8 --
1) When saying that a conversion is erroneous because it would use
an explicit constructor, it might be nice to show where exactly
the explicit constructor is located. For example, with this patch:
[...]
explicit.C:4:12: note: 'S::S(int)' declared here
4 | explicit S(int) { }
| ^
2) When a conversion doesn't work out merely because the conversion
function necessary to do the conversion couldn't be used because
it was marked explicit, it would be useful to the user to say so,
rather than just saying "cannot convert". For example, with this patch:
explicit.C:13:12: error: cannot convert 'S' to 'bool' in initialization
13 | bool b = S{1};
| ^~~~
| |
| S
explicit.C:5:12: note: explicit conversion function was not considered
5 | explicit operator bool() const { return true; }
| ^~~~~~~~
gcc/cp/ChangeLog:
* call.cc (convert_like_internal): Show where the conversion function
was declared.
(maybe_show_nonconverting_candidate): New.
* cp-tree.h (maybe_show_nonconverting_candidate): Declare.
* typeck.cc (convert_for_assignment): Call it.
gcc/testsuite/ChangeLog:
* g++.dg/diagnostic/explicit.C: New test.
---
gcc/cp/call.cc | 41 +++++++++++++++++++---
gcc/cp/cp-tree.h | 1 +
gcc/cp/typeck.cc | 5 +++
gcc/testsuite/g++.dg/diagnostic/explicit.C | 16 +++++++++
4 files changed, 59 insertions(+), 4 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/diagnostic/explicit.C
diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index 23e458d3252..09ebcf6a115 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -8459,12 +8459,21 @@ convert_like_internal (conversion *convs, tree expr,
tree fn, int argnum,
if (pedwarn (loc, 0, "converting to %qT from initializer list "
"would use explicit constructor %qD",
totype, convfn))
- inform (loc, "in C++11 and above a default constructor "
- "can be explicit");
+ {
+ inform (loc, "in C++11 and above a default constructor "
+ "can be explicit");
+ inform (DECL_SOURCE_LOCATION (convfn), "%qD declared here",
+ convfn);
I'd swap these two informs.
Done.
+++ b/gcc/testsuite/g++.dg/diagnostic/explicit.C
@@ -0,0 +1,16 @@
+// { dg-do compile { target c++11 } }
+
+struct S {
+ explicit S(int) { }
+ explicit operator bool() const { return true; } // { dg-message "explicit
conversion function was not considered" }
+ explicit operator int() const { return 42; } // { dg-message "explicit conversion
function was not considered" }
+};
+
+void
+g ()
+{
+ S s = {1}; // { dg-error "would use explicit constructor" }
+ bool b = S{1}; // { dg-error "cannot convert .S. to .bool. in
initialization" }
+ int i;
+ i = S{2}; // { dg-error "cannot convert .S. to .int. in assignment" }
+}
Let's also test other copy-initialization contexts: parameter passing,
return, throw, aggregate member initialization.
Done except for throw. To handle arg passing I moved the call to
maybe_show_nonconverting_candidate one line down. I guess a testcase
for throw would be
struct T {
T() { } // #1
explicit T(const T&) { } // #2
};
void
g ()
{
T t{};
throw t;
}
but #2 isn't a viable candidate so this would take more effort to handle.
True, copy-initialization is different when the types are the same.
We just say about #1 that "candidate expects 0 arguments, 1 provided".
clang++ says
e.C:3:12: note: explicit constructor is not a candidate
3 | explicit T(const T&) { }
| ^
That would be better; in add_candidates when we see an explicit
constructor we could add it to bad_fns instead of ignoring it. But that
doesn't need to be part of this patch.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >8 --
1) When saying that a conversion is erroneous because it would use
an explicit constructor, it might be nice to show where exactly
the explicit constructor is located. For example, with this patch:
[...]
explicit.C:4:12: note: 'S::S(int)' declared here
4 | explicit S(int) { }
| ^
2) When a conversion doesn't work out merely because the conversion
function necessary to do the conversion couldn't be used because
it was marked explicit, it would be useful to the user to say so,
rather than just saying "cannot convert". For example, with this patch:
explicit.C:13:12: error: cannot convert 'S' to 'bool' in initialization
13 | bool b = S{1};
| ^~~~
| |
| S
explicit.C:5:12: note: explicit conversion function was not considered
5 | explicit operator bool() const { return true; }
| ^~~~~~~~
gcc/cp/ChangeLog:
* call.cc (convert_like_internal): Show where the conversion function
was declared.
(maybe_show_nonconverting_candidate): New.
* cp-tree.h (maybe_show_nonconverting_candidate): Declare.
* typeck.cc (convert_for_assignment): Call it.
gcc/testsuite/ChangeLog:
* g++.dg/diagnostic/explicit.C: New test.
---
gcc/cp/call.cc | 41 +++++++++++++++++++---
gcc/cp/cp-tree.h | 1 +
gcc/cp/typeck.cc | 6 ++++
gcc/testsuite/g++.dg/diagnostic/explicit.C | 33 +++++++++++++++++
4 files changed, 77 insertions(+), 4 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/diagnostic/explicit.C
diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index 23e458d3252..52c9f4265a4 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -14323,4 +14332,28 @@ is_list_ctor (tree decl)
return true;
}
+/* We know that can_convert_arg_bad already said "no" when trying to convert
+ FROM to TO with ARG and FLAGS. Try to figure out if it was because
+ an explicit conversion function was skipped when looking for a way to
+ perform the conversion. At this point we've already printed an error. */
+
+void
+maybe_show_nonconverting_candidate (tree to, tree from, tree arg, int flags)
+{
+ if (!(flags & LOOKUP_ONLYCONVERTING))
+ return;
+
+ conversion_obstack_sentinel cos;
+ conversion *c = implicit_conversion (to, from, arg, /*c_cast_p=*/false,
+ flags & ~LOOKUP_ONLYCONVERTING, tf_none);
+ if (c && !c->bad_p && c->user_conv_p)
+ /* Ay, the conversion would have worked in copy-init context. */
s/copy/direct/
OK with that change.
Jason
