On 3/13/20 1:42 PM, Daniel P. Berrangé wrote:
We need the "$(space)" variable to contain a single whitespace
character. We do this by assigning and then appending an empty
string to the variable. Variable appends get separated by a
single whitespace historically, but GNU make 4.3 introduced a
behaviour regression.
https://lists.gnu.org/archive/html/bug-make/2020-01/msg00057.html
[quote]
* WARNING: Backward-incompatibility!
Previously appending using '+=' to an empty variable would
result in a value starting with a space. Now the initial
space is only added if the variable already contains some
value. Similarly, appending an empty string does not
add a trailing space.
[/quote]
This patch tries a new trick to get a single whitespace by
getting make to expand two non-existant variables separated
by a space.
Reviewed-by: Eric Blake <eblake@xxxxxxxxxx>
https://blog.jgc.org/2007/06/escaping-comma-and-space-in-gnu-make.html
needs to be updated to cover this change in GNU make, but it also points
out that GNU make permits:
$(space) = $(null) $(null)
as a way to then write [$( )] or [$ ] instead of [$(space)] (all three
producing "[ ]"), if you really want to go crazy with odd macro names.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
