Extract proguard rules found in imported JAR archives

In Android Studio R8 is able to use bundled proguard
rules found both in AAR archives (under /proguard.txt)
and JAR archives (under /META-INF/proguard/*)

Soong currently only handles the _easier_ AAR format
and ignores the possibility to have rules in JAR archives.

To support those rules we use the newly introduced
ExtractR8Rules cli tool in R8 to extract all the embedded
rules in the imported JAR for later propagation.

Bug: 377144587
Test: m, including okhttp-4.12.0.jar now doesn't create R8 warnings.
Change-Id: I10f9bbf76bc8daec1ec470fb493e399d1beffc8a

3 files changed, 34 insertions, 0 deletions

diff --git a/java/builder.go b/java/builder.go
index 88058e09a..72f4e145c 100644
--- a/java/builder.go
+++ b/java/builder.go
@@ -226,6 +226,12 @@ var (
 		},
 		"jarArgs")
 
+	extractR8Rules = pctx.AndroidStaticRule("extractR8Rules",
+		blueprint.RuleParams{
+			Command:     `${config.ExtractR8RulesCmd} --rules-output $out --include-origin-comments $in`,
+			CommandDeps: []string{"${config.ExtractR8RulesCmd}"},
+		})
+
 	jarjar = pctx.AndroidStaticRule("jarjar",
 		blueprint.RuleParams{
 			Command: "" +
@@ -739,6 +745,16 @@ func TransformJarsToJar(ctx android.ModuleContext, outputFile android.WritablePa
 	})
 }
 
+func TransformJarToR8Rules(ctx android.ModuleContext, outputFile android.WritablePath,
+	jar android.Path) {
+
+	ctx.Build(pctx, android.BuildParams{
+		Rule:        extractR8Rules,
+		Output:      outputFile,
+		Input:       jar,
+	})
+}
+
 func convertImplementationJarToHeaderJar(ctx android.ModuleContext, implementationJarFile android.Path,
 	headerJarFile android.WritablePath) {
 	ctx.Build(pctx, android.BuildParams{
diff --git a/java/config/config.go b/java/config/config.go
index 19d695291..2ed2953f7 100644
--- a/java/config/config.go
+++ b/java/config/config.go
@@ -174,6 +174,7 @@ func init() {
 	pctx.HostBinToolVariable("ApiCheckCmd", "apicheck")
 	pctx.HostBinToolVariable("D8Cmd", "d8")
 	pctx.HostBinToolVariable("R8Cmd", "r8")
+	pctx.HostBinToolVariable("ExtractR8RulesCmd", "extract-r8-rules")
 	pctx.HostBinToolVariable("ResourceShrinkerCmd", "resourceshrinker")
 	pctx.HostBinToolVariable("HiddenAPICmd", "hiddenapi")
 	pctx.HostBinToolVariable("ExtractApksCmd", "extract_apks")
diff --git a/java/java.go b/java/java.go
index a975ca61c..0ab344066 100644
--- a/java/java.go
+++ b/java/java.go
@@ -2827,6 +2827,23 @@ func (j *Import) GenerateAndroidBuildActions(ctx android.ModuleContext) {
 		outputFile = combinedJar
 	}
 
+	proguardFlags := android.PathForModuleOut(ctx, "proguard_flags")
+	TransformJarToR8Rules(ctx, proguardFlags, outputFile)
+
+	transitiveProguardFlags, transitiveUnconditionalExportedFlags := collectDepProguardSpecInfo(ctx)
+	android.SetProvider(ctx, ProguardSpecInfoProvider, ProguardSpecInfo{
+		ProguardFlagsFiles: depset.New[android.Path](
+			depset.POSTORDER,
+			android.Paths{proguardFlags},
+			transitiveProguardFlags,
+		),
+		UnconditionallyExportedProguardFlags: depset.New[android.Path](
+			depset.POSTORDER,
+			nil,
+			transitiveUnconditionalExportedFlags,
+		),
+	})
+
 	// Save the output file with no relative path so that it doesn't end up in a subdirectory when used as a resource.
 	// Also strip the relative path from the header output file so that the reuseImplementationJarAsHeaderJar check
 	// in a module that depends on this module considers them equal.