Add exported_plugins to java.Library.

The behaviour is similar to go/be#java_library.exported_plugins. Plugins added to exported_plugins of library X are not applied to the library itself, but rather to libraries that directly depend on the library X.

Test: m checkbuild
Bug: 139740873
Change-Id: I4042bd482ad9cb12d6fbaac51f039d38b1b7a428
diff --git a/java/java_test.go b/java/java_test.go
index efef7c1..dc498a4 100644
--- a/java/java_test.go
+++ b/java/java_test.go
@@ -332,6 +332,89 @@
 	}
 }
 
+func TestExportedPlugins(t *testing.T) {
+	type Result struct {
+		library    string
+		processors string
+	}
+	var tests = []struct {
+		name    string
+		extra   string
+		results []Result
+	}{
+		{
+			name:    "Exported plugin is not a direct plugin",
+			extra:   `java_library { name: "exports", srcs: ["a.java"], exported_plugins: ["plugin"] }`,
+			results: []Result{{library: "exports", processors: "-proc:none"}},
+		},
+		{
+			name: "Exports plugin to dependee",
+			extra: `
+				java_library{name: "exports", exported_plugins: ["plugin"]}
+				java_library{name: "foo", srcs: ["a.java"], libs: ["exports"]}
+				java_library{name: "bar", srcs: ["a.java"], static_libs: ["exports"]}
+			`,
+			results: []Result{
+				{library: "foo", processors: "-processor com.android.TestPlugin"},
+				{library: "bar", processors: "-processor com.android.TestPlugin"},
+			},
+		},
+		{
+			name: "Exports plugin to android_library",
+			extra: `
+				java_library{name: "exports", exported_plugins: ["plugin"]}
+				android_library{name: "foo", srcs: ["a.java"],  libs: ["exports"]}
+				android_library{name: "bar", srcs: ["a.java"], static_libs: ["exports"]}
+			`,
+			results: []Result{
+				{library: "foo", processors: "-processor com.android.TestPlugin"},
+				{library: "bar", processors: "-processor com.android.TestPlugin"},
+			},
+		},
+		{
+			name: "Exports plugin is not propagated via transitive deps",
+			extra: `
+				java_library{name: "exports", exported_plugins: ["plugin"]}
+				java_library{name: "foo", srcs: ["a.java"], libs: ["exports"]}
+				java_library{name: "bar", srcs: ["a.java"], static_libs: ["foo"]}
+			`,
+			results: []Result{
+				{library: "foo", processors: "-processor com.android.TestPlugin"},
+				{library: "bar", processors: "-proc:none"},
+			},
+		},
+		{
+			name: "Exports plugin appends to plugins",
+			extra: `
+                java_plugin{name: "plugin2", processor_class: "com.android.TestPlugin2"}
+				java_library{name: "exports", exported_plugins: ["plugin"]}
+				java_library{name: "foo", srcs: ["a.java"], libs: ["exports"], plugins: ["plugin2"]}
+			`,
+			results: []Result{
+				{library: "foo", processors: "-processor com.android.TestPlugin,com.android.TestPlugin2"},
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			ctx, _ := testJava(t, `
+				java_plugin {
+					name: "plugin",
+					processor_class: "com.android.TestPlugin",
+				}
+			`+test.extra)
+
+			for _, want := range test.results {
+				javac := ctx.ModuleForTests(want.library, "android_common").Rule("javac")
+				if javac.Args["processor"] != want.processors {
+					t.Errorf("For library %v, expected %v, found %v", want.library, want.processors, javac.Args["processor"])
+				}
+			}
+		})
+	}
+}
+
 func TestSdkVersionByPartition(t *testing.T) {
 	testJavaError(t, "sdk_version must have a value when the module is located at vendor or product", `
 		java_library {