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.
+++ 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.
Jason
