[Buildroot] [PATCH 2/7] pkg-infra: assign BR_NO_CHECK_HASH_FOR so it is recursively-expanded

[Yann E. MORIN <yann.morin.1998@free.fr>]

arnout, All,

On 2015-05-01 15:07 +0200, Arnout Vandecappelle spake thusly:
> On 29/04/15 00:39, Yann E. MORIN wrote:
> > Currently, assigning to BR_NO_CHECK_HASH_FOR in conditionals, but
> > referencing vairaible assigned to later, fails. Here's a failing
>               variable
> 
> > test-case, which is the reduced test-case of how we handle
> > BR_NO_CHECK_HASH_FOR for now:
> > 
> >     export FOO
> > 
> >     ifeq ($(BAR_V),)
> >     BAR_V=1
> >     else
> >     FOO += $(BAR_S)
> >     endif
> 
>  I think the test case is too complicated - in fact the conditional construct
> has nothing to do with it.

Yup, right, I know. However, I wanted a reduced test-case that still
ressembled our current code base.

> The culprit is appending to it, which means we never
> explicitly set it to recursively expanded. Exported variables that are not
> defined explicitly for some reason default to be immediately expanded rather
> than recursively.

Exactly. However, there's nothing like so explained in the make manual.

> export FOO
> FOO += $(BAR)
> $(warning FOO='$(FOO)' BAR='$(BAR)')
> BAR = BAR
> $(warning FOO='$(FOO)' BAR='$(BAR)')
> default:
> 
> Will give
> 
> /tmp/Makefile:3: FOO=' ' BAR=''
> /tmp/Makefile:5: FOO=' ' BAR='BAR'
> 
> while explicitly setting FOO to be recursively expanded:
> 
> export FOO =
> 
> will give
> 
> /tmp/Makefile:3: FOO=' ' BAR=''
> /tmp/Makefile:5: FOO=' BAR' BAR='BAR'

Do you prefere I use your even-more-simplified test-case, or may I keep
the reduced test-case I provided that ressemble our current code-path?

> > 
> >     BAR_S = bar-$(BAR_V).tar
> > 
> >     all:
> >         @echo "BAR_S=\"$(BAR_S)\""
> >         @$(SHELL) -c 'echo "FOO=\"$${FOO}\""'
> > 
> > Run it with:
> > 
> >     $ make
> >     BAR_S="bar-1.tar"
> >     FOO=""
> >     $ make BAR_V=2
> >     BAR_S="bar-2.tar"
> >     FOO=" "
> > 
> > Now, change the firstline to read:
> > 
> >     export FOO =
> > 
> > And we now get:
> > 
> >     $ make
> >     BAR_S="bar-1.tar"
> >     FOO=""
> >     $ make BAR_V=2
> >     BAR_S="bar-2.tar"
> >     FOO=" bar-2.tar"
> > 
> > This new behaviour will be needed later for Xenomai, which handles the
> > version string in an unusual way.
> > 
> > (Note how there's a leading space in both cases? In Buildroot, we do not
> > care that extra space, it is simply ignored).
> 
>  The leading space is there because += always inserts a space, even if the
> variable was empty before.

Yes, I know. I'll ditch that comment.

> > Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
> > Cc: Arnout Vandecappelle <arnout@mind.be>
> > Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
> > ---
> >  package/pkg-download.mk | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/package/pkg-download.mk b/package/pkg-download.mk
> > index a38062e..f0651db 100644
> > --- a/package/pkg-download.mk
> > +++ b/package/pkg-download.mk
> > @@ -56,7 +56,9 @@ domainseparator = $(if $(1),$(1),/)
> >  github = https://github.com/$(1)/$(2)/archive/$(3)
> >  
> >  # Expressly do not check hashes for those files
> > -export BR_NO_CHECK_HASH_FOR
> > +# It needs to be assigned so as to be a recursively-expanded variable, and
> > +# so that it can be assigned inside conditionals.
> 
> # Exported variables default to immediately expanded,

I would avoid stating that. That's the behaviour we observed, but
nothing is said about that in the make manual. If a future version of
make changes that behaviour, the comment would be wrong.

However, I'll ditch the comment about conditionals.

> # but we need it to be
> # recursively-epxanded, so explicitly define it.
> 
> 
>  With all that,
> 
>   Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

Regards,
Yann E. MORIN.

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