Re: C++ PATCH for c++/91521 - wrong error with operator->

[Marek Polacek]

On Fri, Aug 23, 2019 at 02:24:17PM -0700, Jason Merrill wrote:
> On 8/23/19 1:37 PM, Marek Polacek wrote:
> > Since r263836 we enter the "a late-specified return type" block in
> > grokdeclarator when inner_declarator is null:
> > 
> >          /* Handle a late-specified return type.  */
> >          tree late_return_type = declarator->u.function.late_return_type;
> > -       if (funcdecl_p)
> > +       if (funcdecl_p
> > +       /* This is the case e.g. for
> > +          using T = auto () -> int.  */
> > +       || inner_declarator == NULL)
> >            {
> > 
> > inner_declarator is null in this testcase too, but here we don't have
> > a real trailing return type; it's just an overloaded operator ->.  That
> > means that late_return_type is non-null, but is error_mark_node.  In
> > that case I think it's not sensible to complain about "trailing return
> > type only available" or "function with trailing return type not declared
> > with auto".  In this case that made us reject valid code.
> > 
> > Bootstrapped/regtested on x86_64-linux, ok for trunk and 9?
> > 
> > 2019-08-23  Marek Polacek  <pola...@redhat.com>
> > 
> >     PR c++/91521 - wrong error with operator->.
> >     * decl.c (grokdeclarator): Don't consider error_mark_node a valid
> >     trailing return type.
> > 
> >     * g++.dg/parse/operator8.C: New test.
> > 
> > diff --git gcc/cp/decl.c gcc/cp/decl.c
> > index 88aa69ce5de..ea5752a249e 100644
> > --- gcc/cp/decl.c
> > +++ gcc/cp/decl.c
> > @@ -11546,6 +11546,7 @@ grokdeclarator (const cp_declarator *declarator,
> >                   }
> >               }
> >             else if (late_return_type
> > +                    && late_return_type != error_mark_node
> >                      && sfk != sfk_conversion)
> >               {
> 
> What if instead of this change we check for error_mark_node inside the block
> and return without an error?

That works too.  Take your pick.

Bootstrapped/regtested on x86_64-linux, ok for trunk?

2019-08-23  Marek Polacek  <pola...@redhat.com>

        PR c++/91521 - wrong error with operator->.
        * decl.c (grokdeclarator): Return error_mark_node for an invalid
        trailing return type.

        * g++.dg/parse/operator8.C: New test.

diff --git gcc/cp/decl.c gcc/cp/decl.c
index cb5571e4f24..9f7923871db 100644
--- gcc/cp/decl.c
+++ gcc/cp/decl.c
@@ -11549,6 +11549,8 @@ grokdeclarator (const cp_declarator *declarator,
                else if (late_return_type
                         && sfk != sfk_conversion)
                  {
+                   if (late_return_type == error_mark_node)
+                     return error_mark_node;
                    if (cxx_dialect < cxx11)
                      /* Not using maybe_warn_cpp0x because this should
                         always be an error.  */
diff --git gcc/testsuite/g++.dg/parse/operator8.C 
gcc/testsuite/g++.dg/parse/operator8.C
new file mode 100644
index 00000000000..c5ee3eb934a
--- /dev/null
+++ gcc/testsuite/g++.dg/parse/operator8.C
@@ -0,0 +1,13 @@
+// PR c++/91521 - wrong error with operator->.
+// { dg-do compile }
+
+struct foo {
+       int bar() { return 0; }
+       foo* operator->() { return this; }
+};
+
+int main()
+{
+       int pt(foo()->bar());
+       return pt;
+}