[bitbake-devel] wanting clarification on overrides, _append, += and combinations of those

[Paul Eggleton]

On Saturday 24 November 2012 09:23:20 Robert P. J. Day wrote:
>   preparing my own write-up on how bitbake processes combinations of
> overrides, _append and += and ran across an example in oe-core that is
> unnecessarily whitespacey, just wanted to make sure i was
> understanding this properly.
> 
>   in the current bitbake user manual, there's this example of mixing
> overrides, _append and +=:
> 
>   OVERRIDES = "foo"
>   A_foo_append = "X"
>   A_foo_append += "Y"
> 
>   This behaves as per the first case above, but the value of A would
>   be "X Y" instead of just "X".
> 
>   that, of course, makes sense as the "+=" operator automatically adds
> a leading space to what is being appended.  so for fun, i scanned all
> of oe-core looking for examples of "_append.*+=" for classroom demo
> purposes, and the *only* examples i found were in
> meta/recipes-devtools/python/python-smartpm_1.4.1.bb:
> 
> RDEPENDS_python-smartpm_append = " python-smartpm-backend-rpm python-codecs
> python-textutils python-xml" RDEPENDS_python-smartpm_append += "
> python-fcntl python-pickle python-crypt python-compression python-shell"
> RDEPENDS_python-smartpm_append += " python-resource python-netclient
> python-threading python-unixadmin"
> 
>   i can see that that first line *does* need an explicit leading space
> in the value being assigned, but the next two "+=" lines don't, do
> they?  it won't hurt, of course, you'll just *two* spaces inserted
> instead of one.  but i just want to make sure i understand what's
> happening there since it has the potential to be confusing for someone
> trying to follow along.

I would strongly discourage the use of += in conjunction with _append because 
the intent is unclear - I think we've discussed this before; this is just a 
case where it slipped through. Ideally this would just be done as a += split 
onto multiple lines and I will make sure it gets changed to that if someone 
else doesn't get to it first.

Cheers,
Paul

-- 

Paul Eggleton
Intel Open Source Technology Centre