Make ConfiguredJarList immutable

By making the Append and RemoveList methods return a new list instead
of modifying the existing list it makes the ConfiguredJarList usages
easier to reason about and safer to use, especially considering that
they are primarily used in global configuration.

Bug: 171479578
Test: m nothing
Change-Id: I102c4fb42f0c54e4ed299d2921fbf5efeb6e99b9

android/config.go

@@ -1362,13 +1362,22 @@ func (l *ConfiguredJarList) IndexOfJar(jar string) int {
 }
 
 // Append an (apex, jar) pair to the list.
-func (l *ConfiguredJarList) Append(apex string, jar string) {
-	l.apexes = append(l.apexes, apex)
-	l.jars = append(l.jars, jar)
+func (l *ConfiguredJarList) Append(apex string, jar string) ConfiguredJarList {
+	// Create a copy of the backing arrays before appending to avoid sharing backing
+	// arrays that are mutated across instances.
+	apexes := make([]string, 0, len(l.apexes)+1)
+	copy(apexes, l.apexes)
+	apexes = append(apexes, apex)
+
+	jars := make([]string, 0, len(l.jars)+1)
+	copy(jars, l.jars)
+	jars = append(l.jars, jar)
+
+	return ConfiguredJarList{apexes, jars}
 }
 
 // Filter out sublist.
-func (l *ConfiguredJarList) RemoveList(list ConfiguredJarList) {
+func (l *ConfiguredJarList) RemoveList(list ConfiguredJarList) ConfiguredJarList {
 	apexes := make([]string, 0, l.Len())
 	jars := make([]string, 0, l.Len())
 
@@ -1380,13 +1389,7 @@ func (l *ConfiguredJarList) RemoveList(list ConfiguredJarList) {
 		}
 	}
 
-	l.apexes = apexes
-	l.jars = jars
-}
-
-// A copy of itself.
-func (l *ConfiguredJarList) CopyOf() ConfiguredJarList {
-	return ConfiguredJarList{CopyOf(l.apexes), CopyOf(l.jars)}
+	return ConfiguredJarList{apexes, jars}
 }
 
 // A copy of the list of strings containing jar components.
@@ -1461,17 +1464,16 @@ func splitConfiguredJarPair(ctx PathContext, str string) (string, string) {
 }
 
 func CreateConfiguredJarList(ctx PathContext, list []string) ConfiguredJarList {
-	apexes := make([]string, 0, len(list))
-	jars := make([]string, 0, len(list))
+	apexes := make([]string, len(list))
+	jars := make([]string, len(list))
 
-	l := ConfiguredJarList{apexes, jars}
-
-	for _, apexjar := range list {
+	for i, apexjar := range list {
 		apex, jar := splitConfiguredJarPair(ctx, apexjar)
-		l.Append(apex, jar)
+		apexes[i] = apex
+		jars[i] = jar
 	}
 
-	return l
+	return ConfiguredJarList{apexes, jars}
 }
 
 func EmptyConfiguredJarList() ConfiguredJarList {

java/dexpreopt_config.go

@@ -81,13 +81,12 @@ func genBootImageConfigs(ctx android.PathContext) map[string]*bootImageConfig {
 		targets := dexpreoptTargets(ctx)
 		deviceDir := android.PathForOutput(ctx, ctx.Config().DeviceName())
 
-		artModules := global.ArtApexJars.CopyOf()
+		artModules := global.ArtApexJars
 		// With EMMA_INSTRUMENT_FRAMEWORK=true the Core libraries depend on jacoco.
 		if ctx.Config().IsEnvTrue("EMMA_INSTRUMENT_FRAMEWORK") {
-			artModules.Append("com.android.art", "jacocoagent")
+			artModules = artModules.Append("com.android.art", "jacocoagent")
 		}
-		frameworkModules := global.BootJars.CopyOf()
-		frameworkModules.RemoveList(artModules)
+		frameworkModules := global.BootJars.RemoveList(artModules)
 
 		artSubdir := "apex/art_boot_images/javalib"
 		frameworkSubdir := "system/framework"