https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53281
--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
A further improvement might be to stop talking about "passing '...' as 'this'
argument" since that's a leaky abstraction: although member functions are
implemented with a hidden 'this' parameter, that's not how most C++ programmers
think of it, or how the abstract machine is described. Also, 'this' is a
pointer, and 'const Foo' is not a pointer type (Clang loses points there too).
So maybe this would be better:
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -7796,8 +7796,15 @@ build_over_call (struct z_candidate *cand, int flags,
tsubst_flags_t complain)
{
if (complain & tf_error)
{
- if (permerror (input_location, "passing %qT as %<this%> "
- "argument discards qualifiers",
+ int argquals = cp_type_quals (TREE_TYPE (argtype));
+ int fnquals = cp_type_quals (TREE_TYPE (fn));
+ int discarded = argquals & ~fnquals;
+ bool non_const = discarded & TYPE_QUAL_CONST;
+ bool non_volatile = discarded & TYPE_QUAL_VOLATILE;
+ if (permerror (input_location, "cannot call %s%s member "
+ "function on object of type %qT",
+ non_const ? "non-const" : "",
+ non_volatile ? "non-volatile" : "",
TREE_TYPE (argtype)))
inform (DECL_SOURCE_LOCATION (fn), " in call to %qD", fn);
}
cv.cc: In member function 'void Foo::bar2(const Foo&)':
cv.cc:4:26: error: cannot call non-const member function on object of type
'const Foo' [-fpermissive]
foo.bar1();
^
cv.cc:2:14: note: in call to 'void Foo::bar1()'
void bar1() {}
^~~~
