From 8514b5c26d7e99ef68fc6354649cbaa31ae473e7 Mon Sep 17 00:00:00 2001
From: Colin Cross <ccross@android.com>
Date: Thu, 14 Dec 2023 13:59:50 -0800
Subject: [PATCH] Optimize returning the zero value from provider APIs

Now that nothing calls *Context.*Provider directly, make the blueprint
methods return a nil any interface instead of the zero value that was
constructed via reflection.  The type-safe wrappers will return a
zero value that can be constructed without any reflection or copying.

Bug: 316410648
Test: provider_test.go
Change-Id: I0abde5bacab9964a83f03c1644b51295a6c34d0b
---
 context.go    | 14 ++++----------
 module_ctx.go | 25 +++++--------------------
 provider.go   |  3 ---
 3 files changed, 9 insertions(+), 33 deletions(-)

diff --git a/context.go b/context.go
index ca30874..1592154 100644
--- a/context.go
+++ b/context.go
@@ -4036,18 +4036,12 @@ func (c *Context) ModuleType(logicModule Module) string {
 }
 
 // ModuleProvider returns the value, if any, for the provider for a module.  If the value for the
-// provider was not set it returns the zero value of the type of the provider, which means the
-// return value can always be type-asserted to the type of the provider.  The return value should
-// always be considered read-only.  It panics if called before the appropriate mutator or
-// GenerateBuildActions pass for the provider on the module.  The value returned may be a deep
-// copy of the value originally passed to SetProvider.
+// provider was not set it returns nil and false.  The return value should always be considered read-only.
+// It panics if called before the appropriate mutator or GenerateBuildActions pass for the provider on the
+// module.  The value returned may be a deep copy of the value originally passed to SetProvider.
 func (c *Context) ModuleProvider(logicModule Module, provider AnyProviderKey) (any, bool) {
 	module := c.moduleInfo[logicModule]
-	value, ok := c.provider(module, provider.provider())
-	if value == nil {
-		value = provider.provider().zero
-	}
-	return value, ok
+	return c.provider(module, provider.provider())
 }
 
 func (c *Context) BlueprintFile(logicModule Module) string {
diff --git a/module_ctx.go b/module_ctx.go
index fb65755..cb86f43 100644
--- a/module_ctx.go
+++ b/module_ctx.go
@@ -334,16 +334,14 @@ type BaseModuleContext interface {
 	OtherModuleReverseDependencyVariantExists(name string) bool
 
 	// OtherModuleProvider returns the value for a provider for the given module.  If the value is
-	// not set it returns the zero value of the type of the provider, so the return value can always
-	// be type asserted to the type of the provider.  The value returned may be a deep copy of the
-	// value originally passed to SetProvider.
+	// not set it returns nil and false.  The value returned may be a deep copy of the value originally
+	// passed to SetProvider.
 	//
 	// This method shouldn't be used directly, prefer the type-safe android.OtherModuleProvider instead.
 	OtherModuleProvider(m Module, provider AnyProviderKey) (any, bool)
 
 	// Provider returns the value for a provider for the current module.  If the value is
-	// not set it returns the zero value of the type of the provider, so the return value can always
-	// be type asserted to the type of the provider.  It panics if called before the appropriate
+	// not set it returns nil and false.  It panics if called before the appropriate
 	// mutator or GenerateBuildActions pass for the provider.  The value returned may be a deep
 	// copy of the value originally passed to SetProvider.
 	//
@@ -611,24 +609,11 @@ func (m *baseModuleContext) OtherModuleReverseDependencyVariantExists(name strin
 
 func (m *baseModuleContext) OtherModuleProvider(logicModule Module, provider AnyProviderKey) (any, bool) {
 	module := m.context.moduleInfo[logicModule]
-	value, ok := m.context.provider(module, provider.provider())
-	if value == nil {
-		value = provider.provider().zero
-	}
-	return value, ok
+	return m.context.provider(module, provider.provider())
 }
 
 func (m *baseModuleContext) Provider(provider AnyProviderKey) (any, bool) {
-	value, ok := m.context.provider(m.module, provider.provider())
-	if value == nil {
-		value = provider.provider().zero
-	}
-	return value, ok
-}
-
-func (m *baseModuleContext) HasProvider(provider AnyProviderKey) bool {
-	_, ok := m.context.provider(m.module, provider.provider())
-	return ok
+	return m.context.provider(m.module, provider.provider())
 }
 
 func (m *baseModuleContext) SetProvider(provider AnyProviderKey, value interface{}) {
diff --git a/provider.go b/provider.go
index 36411d8..48527b1 100644
--- a/provider.go
+++ b/provider.go
@@ -48,7 +48,6 @@ type typedProviderKey[K any] struct {
 type providerKey struct {
 	id      int
 	typ     string
-	zero    any
 	mutator string
 }
 
@@ -84,7 +83,6 @@ func NewProvider[K any]() ProviderKey[K] {
 func NewMutatorProvider[K any](mutator string) ProviderKey[K] {
 	checkCalledFromInit()
 
-	zero := *new(K)
 	typ := fmt.Sprintf("%T", *new(K))
 
 	provider := ProviderKey[K]{
@@ -92,7 +90,6 @@ func NewMutatorProvider[K any](mutator string) ProviderKey[K] {
 			providerKey: providerKey{
 				id:      len(providerRegistry),
 				typ:     typ,
-				zero:    zero,
 				mutator: mutator,
 			},
 		},