[OE-core] what is the value of 'BBPATH ?= ""' in layer.conf?

[Robert Yang]

On 11/22/2015 05:10 PM, Robert P. J. Day wrote:
>
>    perusing some wind river layers, and in the layer.conf file here:
>
> https://github.com/WindRiver-OpenSourceLabs/wr-kernel/blob/LB21_7.0_RCPL0002/conf/layer.conf
>
> i see the opening snippet:
>
>    BBPATH ?= ""
>    # We have a conf and classes directory, add to BBPATH
>    BBPATH := "${LAYERDIR}:${BBPATH}"
>
> what is the purpose of that initial assignment
>
>    BBPATH ?= ""

There would be a warning when BBPATH is null, but that had been fixed,
so we don't need it nowadays.

// Robert

>
> if that variable has no value, won't it just expand to the empty
> string so that the eventual effect is the same? or is there something
> more subtle happening here?
>
> rday
>