Add apex_files output group to apex_aab to forward all base APEX files

for each architecture.

The Mainline CI build target produces both .aab files and .apex files
for each module, in the following layout:

x.aab
y.aab
mainline_modules_arm/x.apex
mainline_modules_arm/y.apex
mainline_modules_arm64/x.apex
mainline_modules_arm64/y.apex
..

Currently, we're only producing the .aab files by building the apex_aab
targets. To dist the .apex files, we either build the apex targets
separately within a --config={android_arm, android_arm64, ..} loop, or
we could just forward the 1:4 split transition'd multi-arch apex files
from the apex_aab target, which are already built.

This is a output group because it can be controlled from a filegroup or
the command line --output_groups flag, which makes it easy to extend the
mainline build script.

For example:

```
apex_aab(
   name = "module",
   mainline_module = "//path/to:apex",
)

filegroup(
   name = "apex_files",
   srcs = [":module"],
   output_group = "apex_files",
)
```

Or: b build //path/to/module --output_groups=apex_files

produces the following:

bazel-bin/path/to/mainline_modules_arm/module.apex
bazel-bin/path/to/mainline_modules_arm64/module.apex
bazel-bin/path/to/mainline_modules_x86/module.apex
bazel-bin/path/to/mainline_modules_x86_64/module.apex

Test: new analysis test
Bug: 238723069
Change-Id: I3f4efa4eff1adeba8c315d9f97729a3a529b32c0

1 files changed, 27 insertions, 6 deletions

diff --git a/rules/apex/apex_aab.bzl b/rules/apex/apex_aab.bzl
index a814b705..6fee25b1 100644
--- a/rules/apex/apex_aab.bzl
+++ b/rules/apex/apex_aab.bzl
@@ -198,12 +198,29 @@ def _apex_bundle(ctx, module_name, merged_base_file, bundle_config_file):
 def _apex_aab_impl(ctx):
     """Implementation of apex_aab rule, which drives the process of creating aab
     file from apex files created for each arch."""
+    prefixed_signed_apex_files = []
     apex_base_files = []
     bundle_config_file = None
     module_name = ctx.attr.mainline_module[0].label.name
     for arch in ctx.split_attr.mainline_module:
-        apex_file = ctx.split_attr.mainline_module[arch].files.to_list()[0]
-        proto_convert_file = _apex_proto_convert(ctx, arch, module_name, apex_file)
+        signed_apex = ctx.split_attr.mainline_module[arch][ApexInfo].signed_output
+
+        # Forward the individual files for all variants in an additional output group,
+        # so dependents can easily access the multi-arch base APEX files by building
+        # this target with --output_groups=apex_files.
+        #
+        # Copy them into an arch-specific directory, since they have the same basename.
+        prefixed_signed_apex_file = ctx.actions.declare_file(
+            "mainline_modules_" + arch + "/" + signed_apex.basename,
+        )
+        ctx.actions.run_shell(
+            inputs = [signed_apex],
+            outputs = [prefixed_signed_apex_file],
+            command = " ".join(["cp", signed_apex.path, prefixed_signed_apex_file.path]),
+        )
+        prefixed_signed_apex_files.append(prefixed_signed_apex_file)
+
+        proto_convert_file = _apex_proto_convert(ctx, arch, module_name, signed_apex)
         base_file = _apex_base_file(ctx, arch, module_name, proto_convert_file)
         apex_base_files.append(base_file)
 
@@ -214,11 +231,15 @@ def _apex_aab_impl(ctx):
     merged_base_file = _merge_base_files(ctx, module_name, apex_base_files)
     bundle_file = _apex_bundle(ctx, module_name, merged_base_file, bundle_config_file)
 
-    return [DefaultInfo(files = depset([bundle_file]))]
+    return [
+        DefaultInfo(files = depset([bundle_file])),
+        OutputGroupInfo(apex_files = depset(prefixed_signed_apex_files)),
+    ]
 
-# apex_aab rule creates Android Apk Bundle (.aab) file of the APEX specified in mainline_module.
-# There is no equivalent Soong module, and it is currently done in shell script by
-# invoking Soong multiple times.
+# apex_aab rule creates multi-arch outputs of a Mainline module, such as the
+# Android Apk Bundle (.aab) file of the APEX specified in mainline_module.
+# There is no equivalent Soong module, and it is currently done in shell script
+# by invoking Soong multiple times.
 apex_aab = rule(
     implementation = _apex_aab_impl,
     attrs = {