Bug 1502457 - Derive the default update channel from the application display version. r=nalexander

Depends on D11986

Differential Revision: https://phabricator.services.mozilla.com/D11987

--HG--
extra : moz-landing-system : lando

build/moz.configure/init.configure

@@ -1151,19 +1151,35 @@ set_config('MOZ_APP_VERSION', milestone.app_version)
 set_config('MOZ_APP_VERSION_DISPLAY', milestone.app_version_display)
 add_old_configure_assignment('MOZ_APP_VERSION', milestone.app_version)
 
-# The app update channel is 'default' when not supplied. The value is used in
-# the application's confvars.sh (and is made available to a project specific
-# moz.configure).
+
+# The app update channel is 'default' when not supplied, and MOZILLA_OFFICIAL
+# is not set. When MOZILLA_OFFICIAL is set, the default is derived from
+# the application display version.
+@depends(milestone, mozilla_official)
+def default_update_channel(milestone, mozilla_official):
+    if not mozilla_official:
+        return 'default'
+    if milestone.is_release_or_beta:
+        if 'esr' in milestone.app_version_display:
+            return 'esr'
+        if 'b' in milestone.app_version_display:
+            return 'beta'
+        return 'release'
+    if milestone.is_nightly:
+        return 'nightly'
+    return 'default'
+
+
 option('--enable-update-channel',
        nargs=1,
        help='Select application update channel',
-       default='default')
+       default=default_update_channel)
 
 
-@depends('--enable-update-channel')
-def update_channel(channel):
+@depends('--enable-update-channel', default_update_channel)
+def update_channel(channel, default_update_channel):
     if channel[0] == '':
-        return 'default'
+        return default_update_channel
     return channel[0].lower()