Export dex implementation jars from prebuilt_apex

Dexpreopt and boot jars package check all require access to dex
implementation jars created for java_library and java_sdk_library. They
were available when building from source but not when building from
prebuilts, even though they are embedded within the .apex files that
are referenced from prebuilt_apex.

This changes adds support to prebuilt_apex to export the dex
implementation jars and updates java_import to use those exported dex
implementation jars.

In a source build dexpreopt/boot jars package check access the apex (or
platform) specific variant of a java_library, e.g. core-oj, from which
it retrieves the dex implementation jar path.

After this change in a prebuilt build dexpreopt/boot jars package check
behave in the same way except in this case they retrieve the dex
implementation jar path from the apex (or platform) specific variant of
the java_import, e.g. core-oj.

The work to export files from a `.apex` file for use by other modules
is performed by a new `deapexer` module type. It is not used directly
in an `Android.bp` file but instead is created implicitly by
`prebuilt_apex`,

In order to do that this contains the following changes:
* Adds a new `dexapexer` module type to handle the exporting of files
  from the `.apex` file.
* Adds an exported_java_libs property to prebuilt_apex to specify the
  set of libraries whose dex implementation jars need exporting.
* Creates apex specific variants of the libraries listed in the
  exported_java_libs property.
* Adds the set of exported files to the ApexInfo to make them available
  to the apex specific variants.
* Prevents the prebuilt_apex variants from being merged together as
  they will not be compatible.
* Modifies java_import to use the exported file for variants of a
  prebuilt_apex.
* Adds a ninja rule to unpack (using deapexer) the contents of the
  prebuilt_apex's apex file, verify that the required files are present
  and make them available as outputs for other rules to use.
* Some minor refactorings to support these changes.
* Adds tests to cover prebuilt only, prebuilt with source preferred,
  and prebuilt preferred with source.

Test: m nothing
Bug: 171061220
Change-Id: Ic9bed81fb65b92f0d59f64c0bce168a9ed44cfac

1 files changed, 83 insertions, 0 deletions

diff --git a/android/deapexer.go b/android/deapexer.go
new file mode 100644
index 000000000..63508d78b
--- /dev/null
+++ b/android/deapexer.go
@@ -0,0 +1,83 @@
+// Copyright (C) 2021 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package android
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/google/blueprint"
+)
+
+// Provides support for interacting with the `deapexer` module to which a `prebuilt_apex` module
+// will delegate the work to export files from a prebuilt '.apex` file.
+
+// The information exported by the `deapexer` module, access it using `DeapxerInfoProvider`.
+type DeapexerInfo struct {
+	// map from the name of an exported file from a prebuilt_apex to the path to that file. The
+	// exported file name is of the form <module>{<tag>} where <tag> is currently only allowed to be
+	// ".dexjar".
+	//
+	// See Prebuilt.ApexInfoMutator for more information.
+	exports map[string]Path
+}
+
+// The set of supported prebuilt export tags. Used to verify the tag parameter for
+// `PrebuiltExportPath`.
+var supportedPrebuiltExportTags = map[string]struct{}{
+	".dexjar": {},
+}
+
+// PrebuiltExportPath provides the path, or nil if not available, of a file exported from the
+// prebuilt_apex that created this ApexInfo.
+//
+// The exported file is identified by the module name and the tag:
+// * The module name is the name of the module that contributed the file when the .apex file
+//   referenced by the prebuilt_apex was built. It must be specified in one of the exported_...
+//   properties on the prebuilt_apex module.
+// * The tag identifies the type of file and is dependent on the module type.
+//
+// See apex/deapexer.go for more information.
+func (i DeapexerInfo) PrebuiltExportPath(name, tag string) Path {
+
+	if _, ok := supportedPrebuiltExportTags[tag]; !ok {
+		panic(fmt.Errorf("unsupported prebuilt export tag %q, expected one of %s",
+			tag, strings.Join(SortedStringKeys(supportedPrebuiltExportTags), ", ")))
+	}
+
+	path := i.exports[name+"{"+tag+"}"]
+	return path
+}
+
+// Provider that can be used from within the `GenerateAndroidBuildActions` of a module that depends
+// on a `deapexer` module to retrieve its `DeapexerInfo`.
+var DeapexerProvider = blueprint.NewProvider(DeapexerInfo{})
+
+// NewDeapexerInfo creates and initializes a DeapexerInfo that is suitable
+// for use with a prebuilt_apex module.
+//
+// See apex/deapexer.go for more information.
+func NewDeapexerInfo(exports map[string]Path) DeapexerInfo {
+	return DeapexerInfo{
+		exports: exports,
+	}
+}
+
+type deapexerTagStruct struct {
+	blueprint.BaseDependencyTag
+}
+
+// A tag that is used for dependencies on the `deapexer` module.
+var DeapexerTag = deapexerTagStruct{}