Change https://r.android.com/1335521 added tag property to the Dist
struct so that it could be used to select one of a number of different
output files to copy to the dist instead of the single file that the
module type made available for dist. The output files were selected
by passing the tag to OutputFiles(tag).
Module types that wanted to support this new approach had to explicitly
set AndroidMkEntries.DistFiles = GenerateTaggedDistFiles(module).
Unfortunately, doing that had a side effect of changing the behavior of
dist entries without a tag.
That was because the change treated a tag that was not specified, as
being the same as "". So, prior to the change no tag meant use the
default dist file but after it meant use the paths returned by
OutputFiles(""). That changed the behavior of the java.Library type
which affected the behavior of the android_app module type.
Prior to the change the java_library would make the
Library.outputFile available for dist when no tag was specified. After
that change it would make Library.outputFile plus
Library.extraOutputFiles. The latter is usually empty except for
android_app which adds some extra files into there which will now be
copied to the dist. That change may have been intentional but there
was no mention of it in the change or the bug. Even if it wasn't
intentional it may still be beneficial.
Any module type that wants to add support for tags in dist runs the
risk of introducing similar changes in behavior. This change
differentiates between the tag not being set and the tag being set to
"" to avoid that possibility and to make the default behavior
explicit for those module types that have switched.
It does so as follows:
* Adds a DefaultDistTag constant that is used when the tag is not set.
It is a string that is unlikely to be used as an actual tag as it
does not start with a . and uses some special characters.
* The DefaultDistTag is used in MakeDefaultDistFiles(paths) to indicate
that the supplied paths are the default ones and and also in
GenerateTaggedDistFiles() for Dist structures that have no tag
property set.
* The DefaultDistTag is passed to OutputFiles(tag) just in case the
module type has explicitly defined the paths to associate with that
tag in there. If it has then it overrides the legacy behavior. If it
has not then it is just ignored and falls back to using the previous
behavior.
* The java.Library.OutputFiles(tag) method explicitly handles the
DefaultDistTag and returns Library.outputFile for it which restores
the behavior from before the change that added dist.tag support.
* Similar change was made to apexBundle.OutputFiles(tag) in order to
preserve its previous behaviour.
* The customModule used by TestGetDistContributions has been modified
to also preserve its previous behavior after this change.
Test: m nothing
m dist sdk - before and after this change, compare result to
make sure that there are no significant differences.
Test the effect on the apex by following instructions in
http://b/172951145
Bug: 174226317
Change-Id: Ib8f0d9307751cc2ed34e3d9a5538d3c144666f6d
74f05598eb