[OE-core] subtle weirdness when you combine "_append" with "+="?

[Robert P. J. Day]

On Tue, 16 Aug 2016, Ulf Magnusson wrote:

> On Tue, Aug 16, 2016 at 4:02 PM, Robert P. J. Day <rpjday at crashcourse.ca> wrote:
> >
> >   was about to submit a small number of patches to clean up redundancy
> > when people combine "_append" with "+=" (because it offends my
> > delicate sensibilities), and ran across this in oe-core,
> > unfs3_0.9.22.r497.bb:
> >
> >   DEPENDS_append_class-nativesdk += "flex-nativesdk"
> >
> > uh, what?
> >
> >   most of the time, i assume the above doesn't hurt, it's just ...
> > silly. but normally, with "_append", you *need* to add the leading
> > space explicitly, and that's not being done above. so does that mean
> > that combining "_append" with "+=" *does* generate a leading space?
> > that just makes my head hurt -- the possibility that "_append" is
> > being used in a way that normally makes it fail, only to have "+="
> > step in and save the day. at which point "_append" saves processing
> > that until the end of parsing? yeesh.
> >
> >   thoughts?
>
> By the point the += is handled, the override won't have been interpreted
> yet. My guess is that += fetches the value of the variable
> "DEPENDS_append_class-nativesdk", gets back the empty string, and
> adds a space followed by "flex-nativesdk" to that.
>
> The resulting " flex-nativesdk" is then interpreted as usual when the
> overrides are handled.
>
> You might like the note I added to
> https://www.yoctoproject.org/docs/2.2/bitbake-user-manual/bitbake-user-manual.html#override-style-operation-advantages
> by the way. :)

  that note is pretty much what i've been whining about for a long
time. :-) in any event, when one sees something like the above:

  DEPENDS_append_class-nativesdk += "flex-nativesdk"

what is the *proper* cleanup?

rday

-- 

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Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

Twitter:                                       http://twitter.com/rpjday
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