Add a trace_references_from dex optimization property

Introduce a new property `trace_references_from` in the optimize block.
This field allows specifying a set of downstream targets from which to
trace references when optimizing the current target.

In practice, this requires explicit breaking of any cycles that might
occur. A follow-up effort will explore doing this dynamically and
implicitly for `libs` references onto an optimized target that
enables this feature.

Bug: 212737576
Test: m nothing
Test: go test ./java
Flag: EXEMPT bugfix
Change-Id: I088bd8bf89403661a084a43b2822a6efbbc0294d

1 files changed, 43 insertions, 0 deletions

diff --git a/java/dex_test.go b/java/dex_test.go
index 66d801dcc..e94864bbc 100644
--- a/java/dex_test.go
+++ b/java/dex_test.go
@@ -866,3 +866,46 @@ func TestDebugReleaseFlags(t *testing.T) {
 		})
 	}
 }
+
+func TestTraceReferences(t *testing.T) {
+	t.Parallel()
+	bp := `
+		android_app {
+			name: "app",
+			libs: ["lib.impl"],
+			srcs: ["foo.java"],
+			platform_apis: true,
+		}
+
+		java_library {
+			name: "lib",
+			optimize: {
+				enabled: true,
+				trace_references_from: ["app"],
+			},
+			srcs: ["bar.java"],
+			static_libs: ["lib.impl"],
+			installable: true,
+		}
+
+		java_library {
+			name: "lib.impl",
+			srcs: ["baz.java"],
+		}
+	`
+	result := android.GroupFixturePreparers(
+		PrepareForTestWithJavaDefaultModules,
+	).RunTestWithBp(t, bp)
+
+	appJar := result.ModuleForTests(t, "app", "android_common").Output("combined/app.jar").Output
+	libJar := result.ModuleForTests(t, "lib", "android_common").Output("combined/lib.jar").Output
+	libTraceRefs := result.ModuleForTests(t, "lib", "android_common").Rule("traceReferences")
+	libR8 := result.ModuleForTests(t, "lib", "android_common").Rule("r8")
+
+	android.AssertStringDoesContain(t, "expected trace reference source from app jar",
+		libTraceRefs.Args["sources"], "--source "+appJar.String())
+	android.AssertStringEquals(t, "expected trace reference target into lib jar",
+		libJar.String(), libTraceRefs.Input.String())
+	android.AssertStringDoesContain(t, "expected trace reference proguard flags in lib r8 flags",
+		libR8.Args["r8Flags"], "trace_references.flags")
+}