Re: [OE-Core][PATCH 2/3] cargo: Move CARGO_MANIFEST_PATH/CARGO_SRC_DIR to cargo_common

[Richard Purdie <richard.purdie@linuxfoundation.org>]

On Fri, 2023-12-08 at 08:23 +0000, Alex Kiernan wrote:
> On Fri, Dec 8, 2023 at 8:15 AM Alex Kiernan via lists.openembedded.org
> <alex.kiernan=gmail.com@lists.openembedded.org> wrote:
> > 
> > On Thu, Dec 7, 2023 at 10:40 PM Richard Purdie
> > <richard.purdie@linuxfoundation.org> wrote:
> > > 
> > > On Thu, 2023-12-07 at 13:39 +0000, Alex Kiernan wrote:
> > > > cargo_common_do_configure uses CARGO_MANIFEST_PATH (which depends on
> > > > CARGO_SRC_DIR), but their definition was in cargo.bbclass.
> > > > 
> > > > Match the other variables here and change to default values, rather
> > > > than weak defaults.
> > > 
> > > FWIW "single value" class variables tend to work much better as ??=
> > > (which I'd call default value) since than it doesn't matter if the
> > > recipe setting comes before or after the inherit and the inherit
> > > position in the recipe doesn't matter.
> > > 
> > 
> > Ah, I guess that makes sense - for "single value" :append/:remove
> > aren't really useful, so leaving the actual assignment as late as
> > possible works?
> > 
> 
> And I've just read the bitbake docs and I clearly still don't really
> understand... its += / -= rather than append/remove which are the
> things which are important here.
> 
> > TBH I've never really been very clear what the "right" thing to use is
> > between ?= and ??=

For something which isn't a single value, you'd need to use += or
append and that gets much more unclear. My comments were only for
single value variables as we don't have a good answer for the rest,
much as I wish we had.

Cheers,

Richard