Re: [PATCH OSSTEST] ap-fetch-version-old: Fix qemu branch handling after mergin of qemu trees

[Ian Jackson <Ian.Jackson@eu.citrix.com>]

Ian Campbell writes ("[PATCH OSSTEST] ap-fetch-version-old: Fix qemu branch handling after mergin of qemu trees"):
> ap-fetch-version-old should always reference the output gate, but
> 99e92a6b3991 "Switch to merged qemu-xen{,-traditional}.git trees"
> switched it to use TREE_QEMU_UPSTREAM directly, which can be
> overridden by cr-daily-branch. This broke at least when
> OSSTEST_BASELINES_ONLY=y since "cr-daily-branch qemu-mainline" ends up looking
> for an "upstream-tested" branch in the qemu.org git tree, when it should be
> looking at our output tree on xenbits.
> 
> Follow pattern of TREE_LINUX and set BASE_TREE_QEMU_UPSTREAM to the
> output gate and then conditionally set TREE_QEMU_UPSTREAM to the
> BASE_TREE if it is not already set. Switch ap-fetch-version-old to use
> BASE_TREE.
...
> +if [ "x${TREE_QEMU_UPSTREAM}" ]; then
> +	: ${TREE_QEMU_UPSTREAM:=${BASE_TREE_QEMU_UPSTREAM}}
> +fi

${FOO:=BAR} sets FOO iff FOO is unset or empty, so there is no need
for the if.  The place you cribbed this from also has to set a
variable for the refname.

Everthing else about this is fine.  Thanks for the in-person explanation.

Ian.