Re: [PATCH] make rich_location safe to copy

[David Malcolm <dmalcolm@redhat.com>]

On Wed, 2021-06-16 at 11:21 -0600, Martin Sebor wrote:
> On 6/16/21 10:35 AM, Jason Merrill wrote:
> > On 6/16/21 12:11 PM, Martin Sebor wrote:
> > > On 6/16/21 9:06 AM, David Malcolm wrote:
> > > > On Wed, 2021-06-16 at 08:52 -0600, Martin Sebor wrote:
> > > > > On 6/16/21 6:38 AM, David Malcolm wrote:
> > > > > > On Tue, 2021-06-15 at 19:48 -0600, Martin Sebor wrote:
> > > > > > 
> > > > > > Thanks for writing the patch.
> > > > > > 
> > > > > > > While debugging locations I noticed the semi_embedded_vec
> > > > > > > template
> > > > > > > in line-map.h doesn't declare a copy ctor or copy
> > > > > > > assignment, but
> > > > > > > is being copied in a couple of places in the C++ parser
> > > > > > > (via
> > > > > > > gcc_rich_location).  It gets away with it most likely
> > > > > > > because it
> > > > > > > never grows beyond the embedded buffer.
> > > > > > 
> > > > > > Where are these places?  I wasn't aware of this.
> > > > > 
> > > > > They're in the attached file along with the diff to reproduce
> > > > > the errors.
> > > > 
> > > > Thanks.
> > > > 
> > > > Looks like:
> > > > 
> > > >     gcc_rich_location richloc = tok->location;
> > > > 
> > > > is implicitly constructing a gcc_rich_location, then copying it
> > > > to
> > > > richloc.  This should instead be simply:
> > > > 
> > > >     gcc_rich_location richloc (tok->location);
> > > > 
> > > > which directly constructs the richloc in place, as I understand
> > > > it.
> > > 
> > > I see, tok->location is location_t here, and the
> > > gcc_rich_location
> > > ctor that takes it is not declared explicit (that would prevent
> > > the implicit conversion).
> > > 
> > > The attached patch solves the rich_location problem by a) making
> > > the ctor explicit, b) disabling the rich_location copy ctor, c)
> > > changing the parser to use direct initialization.  (I CC Jason
> > > as a heads up on the C++ FE bits.)
> > 
> > The C++ bits are fine.
> > 
> > > The semi_embedded_vec should be fixed as well, regardless of this
> > > particular use and patch.  Let me know if it's okay to commit
> > > (I'm
> > > not open to disabling its copy ctor).
> > 
> > > +  /* Not copyable or assignable.  */
> > 
> > This comment needs a rationale.
> 
> Done in the attached patch.

LGTM; thanks

Dave

> 
> Providing a rationale in each instance sounds like a good addition
> to the coding conventions.  Let me propose a patch for that.
> 
> Martin