[gnome-continuous-yocto/gnomeostree-3.28-rocko: 481/8267] image.bbclass: support duplicate compression types

[Emmanuele Bassi <ebassi src gnome org>]

commit e7b5bd2ba11118f8220b915a44bfff7c9c39ca95
Author: Patrick Ohly <patrick ohly intel com>
Date:   Wed May 18 19:24:14 2016 +0300

    image.bbclass: support duplicate compression types
    
    When a derived distro adds a certain type, say zip, to
    COMPRESSIONTYPES and later OE-core does the same, we end up with the
    type being listed twice, and that would have undesired effects
    (commands generated twice).
    
    So to support such loosely coupled extension, we de-duplicated the
    list of types first.
    
    Alternatively, such a situation could also be treated as error. But that
    seems unnecessary because typically commands for the same type will also
    do the same thing.
    
    (From OE-Core rev: 85855af359c2c3bfc1eaa942c95f1f7d7cc6698e)
    
    Signed-off-by: Patrick Ohly <patrick ohly intel com>
    Signed-off-by: Ed Bartosh <eduard bartosh intel com>
    Signed-off-by: Ed Bartosh <ed bartosh linux intel com>
    Signed-off-by: Ross Burton <ross burton intel com>
    Signed-off-by: Richard Purdie <richard purdie linuxfoundation org>

 meta/classes/image.bbclass |   10 +++++++++-
 1 files changed, 9 insertions(+), 1 deletions(-)
---
diff --git a/meta/classes/image.bbclass b/meta/classes/image.bbclass
index 6b9f979..0e81b4e 100644
--- a/meta/classes/image.bbclass
+++ b/meta/classes/image.bbclass
@@ -297,7 +297,15 @@ python setup_debugfs () {
 
 python () {
     vardeps = set()
-    ctypes = d.getVar('COMPRESSIONTYPES', True).split()
+    # We allow COMPRESSIONTYPES to have duplicates. That avoids breaking
+    # derived distros when OE-core or some other layer independently adds
+    # the same type. There is still only one command for each type, but
+    # presumably the commands will do the same when the type is the same,
+    # even when added in different places.
+    #
+    # Without de-duplication, gen_conversion_cmds() below
+    # would create the same compression command multiple times.
+    ctypes = set(d.getVar('COMPRESSIONTYPES', True).split())
     old_overrides = d.getVar('OVERRIDES', 0)
 
     def _image_base_type(type):