On Tue, Sep 18, 2018 at 11:47 PM, Marek Polacek <pola...@redhat.com> wrote:
> As I mentioned in the PR, [class.conv.fct] says "A conversion function is
> never
> used to convert a (possibly cv-qualified) object to the (possibly
> cv-qualified)
> same object type (or a reference to it), to a (possibly cv-qualified) base
> class
> of that type (or a reference to it), or to (possibly cv-qualified) void." but
> I
> noticed we weren't warning about
>
> struct X {
> operator X();
> };
>
> (and there are no tests for this case) because comparing types directly only
> works for TYPE_CANONICAL, otherwise we have to use same_type_*.
>
> I'm also changing the warning about 'void' since we can't form a reference to
> void.
>
> I'll also note that I think we should warn about this by default, not only
> when -Wconversion is in effect.
Agreed, this should get a new flag that is on by default.
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
OK.
> 2018-09-18 Marek Polacek <pola...@redhat.com>
>
> PR c++/87357 - missing -Wconversion warning
> * decl.c (grok_op_properties): Remove diagnostic parts mentioning
> a conversion to a reference to void. Use
> same_type_ignoring_top_level_qualifiers_p rather than comparing types
> directly.
>
> * g++.dg/warn/Wconversion5.C: New test.
>
> diff --git gcc/cp/decl.c gcc/cp/decl.c
> index 827c1720335..503b433cbd1 100644
> --- gcc/cp/decl.c
> +++ gcc/cp/decl.c
> @@ -13553,15 +13553,11 @@ grok_op_properties (tree decl, bool complain)
> t = TYPE_MAIN_VARIANT (TREE_TYPE (t));
>
> if (VOID_TYPE_P (t))
> - warning_at (loc, OPT_Wconversion,
> - ref
> - ? G_("conversion to a reference to void "
> - "will never use a type conversion operator")
> - : G_("conversion to void "
> - "will never use a type conversion operator"));
> + warning_at (loc, OPT_Wconversion, "conversion to void "
> + "will never use a type conversion operator");
> else if (class_type)
> {
> - if (t == class_type)
> + if (same_type_ignoring_top_level_qualifiers_p (t, class_type))
> warning_at (loc, OPT_Wconversion,
> ref
> ? G_("conversion to a reference to the same type "
> diff --git gcc/testsuite/g++.dg/warn/Wconversion5.C
> gcc/testsuite/g++.dg/warn/Wconversion5.C
> index e69de29bb2d..00b1ddab188 100644
> --- gcc/testsuite/g++.dg/warn/Wconversion5.C
> +++ gcc/testsuite/g++.dg/warn/Wconversion5.C
> @@ -0,0 +1,20 @@
> +// PR c++/87357
> +// { dg-do compile }
> +// { dg-options "-Wconversion" }
> +
> +struct B { };
> +
> +struct X : public B {
> + operator X(); // { dg-warning "3:conversion to the same type will never
> use a type conversion operator" }
> + operator X&(); // { dg-warning "3:conversion to a reference to the same
> type will never use a type conversion operator" }
> + operator X() const; // { dg-warning "3:conversion to the same type will
> never use a type conversion operator" }
> + operator const X(); // { dg-warning "3:conversion to the same type will
> never use a type conversion operator" }
> +
> + operator B(); // { dg-warning "3:conversion to a base class will never use
> a type conversion operator" }
> + operator B&(); // { dg-warning "3:conversion to a reference to a base
> class will never use a type conversion operator" }
> + operator B() const; // { dg-warning "3:conversion to a base class will
> never use a type conversion operator" }
> + operator const B(); // { dg-warning "3:conversion to a base class will
> never use a type conversion operator" }
> +
> + operator void(); // { dg-warning "3:conversion to void will never use a
> type conversion operator" }
> + operator void() const; // { dg-warning "3:conversion to void will never
> use a type conversion operator" }
> +};
