Allow java_system_modules_import to replace java_system_modules

Previously, there were some places where a java_system_module_import
could not be used in place of a java_system_module. That was because
the code assumed a *SystemModules type not a *systemModulesImport type.
This change introduces a SystemModulesProvider interface that is used
instead and is implemented on both types.

Bug: 142940300
Test: m nothing
      ran new tests before changes to make sure they detected the issue
	  and after to make sure the changes fixed the issue.
Change-Id: I7b16ac5708880bdf61e6f5b1e6616c986f0ed763
diff --git a/java/java_test.go b/java/java_test.go
index a2226b5..52b3bc0 100644
--- a/java/java_test.go
+++ b/java/java_test.go
@@ -982,6 +982,65 @@
 	}
 }
 
+func TestDroidstubsWithSystemModules(t *testing.T) {
+	ctx, _ := testJava(t, `
+		droidstubs {
+		    name: "stubs-source-system-modules",
+		    srcs: [
+		        "bar-doc/*.java",
+		    ],
+				sdk_version: "none",
+				system_modules: "source-system-modules",
+		}
+
+		java_library {
+				name: "source-jar",
+		    srcs: [
+		        "a.java",
+		    ],
+		}
+
+		java_system_modules {
+				name: "source-system-modules",
+				libs: ["source-jar"],
+		}
+
+		droidstubs {
+		    name: "stubs-prebuilt-system-modules",
+		    srcs: [
+		        "bar-doc/*.java",
+		    ],
+				sdk_version: "none",
+				system_modules: "prebuilt-system-modules",
+		}
+
+		java_import {
+				name: "prebuilt-jar",
+				jars: ["a.jar"],
+		}
+
+		java_system_modules_import {
+				name: "prebuilt-system-modules",
+				libs: ["prebuilt-jar"],
+		}
+		`)
+
+	checkSystemModulesUseByDroidstubs(t, ctx, "stubs-source-system-modules", "source-jar.jar")
+
+	checkSystemModulesUseByDroidstubs(t, ctx, "stubs-prebuilt-system-modules", "prebuilt-jar.jar")
+}
+
+func checkSystemModulesUseByDroidstubs(t *testing.T, ctx *android.TestContext, moduleName string, systemJar string) {
+	metalavaRule := ctx.ModuleForTests(moduleName, "android_common").Rule("metalava")
+	var systemJars []string
+	for _, i := range metalavaRule.Implicits {
+		systemJars = append(systemJars, i.Base())
+	}
+	if len(systemJars) != 1 || systemJars[0] != systemJar {
+		t.Errorf("inputs of %q must be []string{%q}, but was %#v.", moduleName, systemJar, systemJars)
+	}
+}
+
 func TestJarGenrules(t *testing.T) {
 	ctx, _ := testJava(t, `
 		java_library {
@@ -1377,3 +1436,59 @@
 		}
 	}
 }
+
+func TestJavaLibraryWithSystemModules(t *testing.T) {
+	ctx, _ := testJava(t, `
+		java_library {
+		    name: "lib-with-source-system-modules",
+		    srcs: [
+		        "a.java",
+		    ],
+				sdk_version: "none",
+				system_modules: "source-system-modules",
+		}
+
+		java_library {
+				name: "source-jar",
+		    srcs: [
+		        "a.java",
+		    ],
+		}
+
+		java_system_modules {
+				name: "source-system-modules",
+				libs: ["source-jar"],
+		}
+
+		java_library {
+		    name: "lib-with-prebuilt-system-modules",
+		    srcs: [
+		        "a.java",
+		    ],
+				sdk_version: "none",
+				system_modules: "prebuilt-system-modules",
+		}
+
+		java_import {
+				name: "prebuilt-jar",
+				jars: ["a.jar"],
+		}
+
+		java_system_modules_import {
+				name: "prebuilt-system-modules",
+				libs: ["prebuilt-jar"],
+		}
+		`)
+
+	checkBootClasspathForSystemModule(t, ctx, "lib-with-source-system-modules", "/source-jar.jar")
+
+	checkBootClasspathForSystemModule(t, ctx, "lib-with-prebuilt-system-modules", "/prebuilt-jar.jar")
+}
+
+func checkBootClasspathForSystemModule(t *testing.T, ctx *android.TestContext, moduleName string, expectedSuffix string) {
+	javacRule := ctx.ModuleForTests(moduleName, "android_common").Rule("javac")
+	bootClasspath := javacRule.Args["bootClasspath"]
+	if strings.HasPrefix(bootClasspath, "--system ") && strings.HasSuffix(bootClasspath, expectedSuffix) {
+		t.Errorf("bootclasspath of %q must start with --system and end with %q, but was %#v.", moduleName, expectedSuffix, bootClasspath)
+	}
+}