Revert "Convert overrides to a TransitionMutator"

This reverts commit 49be24b833934d2675395c09594bb2d39b828944.

Reason for revert: b/338643193
Bug: 319288033
Bug: 338643193

Change-Id: I7106e779e52ffc943bdcf7ee3b7c7b65fe34122e
diff --git a/android/override_module.go b/android/override_module.go
index 163f7b7..1341f53 100644
--- a/android/override_module.go
+++ b/android/override_module.go
@@ -28,7 +28,6 @@
 // module based on it.
 
 import (
-	"fmt"
 	"sort"
 	"sync"
 
@@ -121,7 +120,7 @@
 	addOverride(o OverrideModule)
 	getOverrides() []OverrideModule
 
-	override(ctx BaseModuleContext, bm OverridableModule, o OverrideModule)
+	override(ctx BaseModuleContext, m Module, o OverrideModule)
 	GetOverriddenBy() string
 	GetOverriddenByModuleDir() string
 
@@ -192,14 +191,15 @@
 }
 
 // Overrides a base module with the given OverrideModule.
-func (b *OverridableModuleBase) override(ctx BaseModuleContext, bm OverridableModule, o OverrideModule) {
+func (b *OverridableModuleBase) override(ctx BaseModuleContext, m Module, o OverrideModule) {
+
 	for _, p := range b.overridableProperties {
 		for _, op := range o.getOverridingProperties() {
 			if proptools.TypeEqual(p, op) {
 				err := proptools.ExtendProperties(p, op, nil, proptools.OrderReplace)
 				if err != nil {
 					if propertyErr, ok := err.(*proptools.ExtendPropertyError); ok {
-						ctx.OtherModulePropertyErrorf(bm, propertyErr.Property, "%s", propertyErr.Err.Error())
+						ctx.PropertyErrorf(propertyErr.Property, "%s", propertyErr.Err.Error())
 					} else {
 						panic(err)
 					}
@@ -210,7 +210,7 @@
 	// Adds the base module to the overrides property, if exists, of the overriding module. See the
 	// comment on OverridableModuleBase.overridesProperty for details.
 	if b.overridesProperty != nil {
-		*b.overridesProperty = append(*b.overridesProperty, ctx.OtherModuleName(bm))
+		*b.overridesProperty = append(*b.overridesProperty, ctx.ModuleName())
 	}
 	b.overridableModuleProperties.OverriddenBy = o.Name()
 	b.overridableModuleProperties.OverriddenByModuleDir = o.ModuleDir()
@@ -235,7 +235,7 @@
 // to keep them in this order and not put any order mutators between them.
 func RegisterOverridePostDepsMutators(ctx RegisterMutatorsContext) {
 	ctx.BottomUp("override_deps", overrideModuleDepsMutator).Parallel()
-	ctx.Transition("override", &overrideTransitionMutator{})
+	ctx.BottomUp("perform_override", performOverrideMutator).Parallel()
 	// overridableModuleDepsMutator calls OverridablePropertiesDepsMutator so that overridable modules can
 	// add deps from overridable properties.
 	ctx.BottomUp("overridable_deps", overridableModuleDepsMutator).Parallel()
@@ -262,6 +262,18 @@
 			ctx.PropertyErrorf("base", "%q is not a valid module name", base)
 			return
 		}
+		// See if there's a prebuilt module that overrides this override module with prefer flag,
+		// in which case we call HideFromMake on the corresponding variant later.
+		ctx.VisitDirectDepsWithTag(PrebuiltDepTag, func(dep Module) {
+			prebuilt := GetEmbeddedPrebuilt(dep)
+			if prebuilt == nil {
+				panic("PrebuiltDepTag leads to a non-prebuilt module " + dep.Name())
+			}
+			if prebuilt.UsePrebuilt() {
+				module.setOverriddenByPrebuilt(dep)
+				return
+			}
+		})
 		baseModule := ctx.AddDependency(ctx.Module(), overrideBaseDepTag, *module.getOverrideModuleProperties().Base)[0]
 		if o, ok := baseModule.(OverridableModule); ok {
 			overrideModule := ctx.Module().(OverrideModule)
@@ -273,13 +285,11 @@
 
 // Now, goes through all overridable modules, finds all modules overriding them, creates a local
 // variant for each of them, and performs the actual overriding operation by calling override().
-type overrideTransitionMutator struct{}
-
-func (overrideTransitionMutator) Split(ctx BaseModuleContext) []string {
+func performOverrideMutator(ctx BottomUpMutatorContext) {
 	if b, ok := ctx.Module().(OverridableModule); ok {
 		overrides := b.getOverrides()
 		if len(overrides) == 0 {
-			return []string{""}
+			return
 		}
 		variants := make([]string, len(overrides)+1)
 		// The first variant is for the original, non-overridden, base module.
@@ -287,69 +297,27 @@
 		for i, o := range overrides {
 			variants[i+1] = o.(Module).Name()
 		}
-		return variants
+		mods := ctx.CreateLocalVariations(variants...)
+		// Make the original variation the default one to depend on if no other override module variant
+		// is specified.
+		ctx.AliasVariation(variants[0])
+		for i, o := range overrides {
+			mods[i+1].(OverridableModule).override(ctx, mods[i+1], o)
+			if prebuilt := o.getOverriddenByPrebuilt(); prebuilt != nil {
+				// The overriding module itself, too, is overridden by a prebuilt.
+				// Perform the same check for replacement
+				checkInvariantsForSourceAndPrebuilt(ctx, mods[i+1], prebuilt)
+				// Copy the flag and hide it in make
+				mods[i+1].ReplacedByPrebuilt()
+			}
+		}
 	} else if o, ok := ctx.Module().(OverrideModule); ok {
 		// Create a variant of the overriding module with its own name. This matches the above local
 		// variant name rule for overridden modules, and thus allows ReplaceDependencies to match the
 		// two.
-		return []string{o.Name()}
-	}
-
-	return []string{""}
-}
-
-func (overrideTransitionMutator) OutgoingTransition(ctx OutgoingTransitionContext, sourceVariation string) string {
-	if o, ok := ctx.Module().(OverrideModule); ok {
-		if ctx.DepTag() == overrideBaseDepTag {
-			return o.Name()
-		}
-	}
-
-	// Variations are always local and shouldn't affect the variant used for dependencies
-	return ""
-}
-
-func (overrideTransitionMutator) IncomingTransition(ctx IncomingTransitionContext, incomingVariation string) string {
-	if _, ok := ctx.Module().(OverridableModule); ok {
-		return incomingVariation
-	} else if o, ok := ctx.Module().(OverrideModule); ok {
-		// To allow dependencies to be added without having to know the variation.
-		return o.Name()
-	}
-
-	return ""
-}
-
-func (overrideTransitionMutator) Mutate(ctx BottomUpMutatorContext, variation string) {
-	if o, ok := ctx.Module().(OverrideModule); ok {
-		overridableDeps := ctx.GetDirectDepsWithTag(overrideBaseDepTag)
-		if len(overridableDeps) > 1 {
-			panic(fmt.Errorf("expected a single dependency with overrideBaseDepTag, found %q", overridableDeps))
-		} else if len(overridableDeps) == 1 {
-			b := overridableDeps[0].(OverridableModule)
-			b.override(ctx, b, o)
-
-			checkPrebuiltReplacesOverride(ctx, b)
-		}
-	}
-}
-
-func checkPrebuiltReplacesOverride(ctx BottomUpMutatorContext, b OverridableModule) {
-	// See if there's a prebuilt module that overrides this override module with prefer flag,
-	// in which case we call HideFromMake on the corresponding variant later.
-	prebuiltDeps := ctx.GetDirectDepsWithTag(PrebuiltDepTag)
-	for _, prebuiltDep := range prebuiltDeps {
-		prebuilt := GetEmbeddedPrebuilt(prebuiltDep)
-		if prebuilt == nil {
-			panic("PrebuiltDepTag leads to a non-prebuilt module " + prebuiltDep.Name())
-		}
-		if prebuilt.UsePrebuilt() {
-			// The overriding module itself, too, is overridden by a prebuilt.
-			// Perform the same check for replacement
-			checkInvariantsForSourceAndPrebuilt(ctx, b, prebuiltDep)
-			// Copy the flag and hide it in make
-			b.ReplacedByPrebuilt()
-		}
+		ctx.CreateLocalVariations(o.Name())
+		// To allow dependencies to be added without having to know the above variation.
+		ctx.AliasVariation(o.Name())
 	}
 }