Use a single instance for all NoTransition and NoConfigTransition fac…

…tory uses.

Work towards composable starlark transitions: #22248.

PiperOrigin-RevId: 639026960
Change-Id: I46e0ebbd25a8708c944bee69da9a9582543da9b1

src/main/java/com/google/devtools/build/lib/analysis/config/transitions/NoConfigTransition.java

@@ -43,6 +43,8 @@
 public class NoConfigTransition implements PatchTransition {
 
   @SerializationConstant public static final NoConfigTransition INSTANCE = new NoConfigTransition();
+  private static final TransitionFactory<? extends TransitionFactory.Data> FACTORY_INSTANCE =
+      new AutoValue_NoConfigTransition_Factory<>();
 
   private NoConfigTransition() {}
 
@@ -57,8 +59,10 @@ public BuildOptions patch(BuildOptionsView options, EventHandler eventHandler) {
   }
 
   /** Returns a {@link TransitionFactory} instance that generates the transition. */
-  public static <T extends TransitionFactory.Data> TransitionFactory<T> createFactory() {
-    return new AutoValue_NoConfigTransition_Factory<>();
+  public static <T extends TransitionFactory.Data> TransitionFactory<T> getFactory() {
+    @SuppressWarnings("unchecked")
+    TransitionFactory<T> castFactory = (TransitionFactory<T>) FACTORY_INSTANCE;
+    return castFactory;
   }
 
   /** A {@link TransitionFactory} implementation that generates the transition. */

src/main/java/com/google/devtools/build/lib/analysis/config/transitions/NoTransition.java

@@ -24,6 +24,8 @@
 public final class NoTransition implements PatchTransition {
 
   @SerializationConstant public static final NoTransition INSTANCE = new NoTransition();
+  private static final TransitionFactory<? extends TransitionFactory.Data> FACTORY_INSTANCE =
+      new AutoValue_NoTransition_Factory<>();
 
   private NoTransition() {}
 
@@ -33,8 +35,10 @@ public BuildOptions patch(BuildOptionsView options, EventHandler eventHandler) {
   }
 
   /** Returns a {@link TransitionFactory} instance that generates the no transition. */
-  public static <T extends TransitionFactory.Data> TransitionFactory<T> createFactory() {
-    return new AutoValue_NoTransition_Factory<>();
+  public static <T extends TransitionFactory.Data> TransitionFactory<T> getFactory() {
+    @SuppressWarnings("unchecked")
+    TransitionFactory<T> castFactory = (TransitionFactory<T>) FACTORY_INSTANCE;
+    return castFactory;
   }
 
   /**

src/main/java/com/google/devtools/build/lib/analysis/constraints/EnvironmentRule.java

@@ -37,7 +37,7 @@ public class EnvironmentRule implements RuleDefinition {
   @Override
   public RuleClass build(RuleClass.Builder builder, RuleDefinitionEnvironment env) {
     return builder
-        .cfg(NoConfigTransition.createFactory())
+        .cfg(NoConfigTransition.getFactory())
         .useToolchainResolution(ToolchainResolutionMode.DISABLED)
         .override(
             attr("tags", Types.STRING_LIST)

src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkAttrModule.java

@@ -321,7 +321,7 @@ private static TransitionFactory<AttributeTransitionData> convertCfg(
       StarlarkThread thread, @Nullable Object trans) throws EvalException {
     // The most common case is no transition.
     if (trans.equals("target") || trans.equals(Starlark.NONE)) {
-      return NoTransition.createFactory();
+      return NoTransition.getFactory();
     }
     // TODO(b/203203933): remove after removing --incompatible_disable_starlark_host_transitions.
     if (trans.equals("host")) {

src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkConfig.java

@@ -63,7 +63,7 @@ public ExecutionTransitionFactory exec(Object execGroupUnchecked) {
 
   @Override
   public ConfigurationTransitionApi target() {
-    return (ConfigurationTransitionApi) NoTransition.createFactory();
+    return (ConfigurationTransitionApi) NoTransition.getFactory();
   }
 
   @Override

src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkRuleClassFunctions.java

@@ -862,7 +862,7 @@ public static StarlarkRuleFunction createRule(
   private static TransitionFactory<RuleTransitionData> convertConfig(@Nullable Object cfg)
       throws EvalException {
     if (cfg.equals(Starlark.NONE)) {
-      return NoTransition.createFactory();
+      return NoTransition.getFactory();
     }
     if (cfg instanceof StarlarkDefinedConfigTransition starlarkDefinedConfigTransition) {
       // defined in Starlark via, cfg = transition

src/main/java/com/google/devtools/build/lib/packages/Attribute.java

@@ -395,7 +395,7 @@ public static class Builder<TYPE> {
     private final String name;
     private final Type<TYPE> type;
     private TransitionFactory<AttributeTransitionData> transitionFactory =
-        NoTransition.createFactory();
+        NoTransition.getFactory();
     private RuleClassNamePredicate allowedRuleClassesForLabels = ANY_RULE;
     private RuleClassNamePredicate allowedRuleClassesForLabelsWarning = NO_RULE;
     private FileTypeSet allowedFileTypesForLabels;

src/main/java/com/google/devtools/build/lib/rules/platform/ConstraintSettingRule.java

@@ -36,7 +36,7 @@ public class ConstraintSettingRule implements RuleDefinition {
   public RuleClass build(RuleClass.Builder builder, RuleDefinitionEnvironment env) {
     return builder
         .advertiseStarlarkProvider(ConstraintSettingInfo.PROVIDER.id())
-        .cfg(NoConfigTransition.createFactory())
+        .cfg(NoConfigTransition.getFactory())
         .exemptFromConstraintChecking("this rule helps *define* a constraint")
         .useToolchainResolution(ToolchainResolutionMode.DISABLED)
         .removeAttribute(":action_listener")

src/main/java/com/google/devtools/build/lib/rules/platform/ConstraintValueRule.java

@@ -38,7 +38,7 @@ public class ConstraintValueRule implements RuleDefinition {
   public RuleClass build(RuleClass.Builder builder, RuleDefinitionEnvironment env) {
     return builder
         .advertiseStarlarkProvider(ConstraintValueInfo.PROVIDER.id())
-        .cfg(NoConfigTransition.createFactory())
+        .cfg(NoConfigTransition.getFactory())
         .exemptFromConstraintChecking("this rule helps *define* a constraint")
         .useToolchainResolution(ToolchainResolutionMode.DISABLED)
         .removeAttribute(":action_listener")

src/main/java/com/google/devtools/build/lib/rules/platform/PlatformRule.java

@@ -46,7 +46,7 @@ public RuleClass build(RuleClass.Builder builder, RuleDefinitionEnvironment env)
     <!-- #END_BLAZE_RULE.NAME --> */
     return builder
         .advertiseStarlarkProvider(PlatformInfo.PROVIDER.id())
-        .cfg(NoConfigTransition.createFactory())
+        .cfg(NoConfigTransition.getFactory())
         .exemptFromConstraintChecking("this rule helps *define* a constraint")
         .useToolchainResolution(ToolchainResolutionMode.DISABLED)
         .removeAttribute(":action_listener")

src/test/java/com/google/devtools/build/lib/analysis/config/transitions/ComposingTransitionFactoryTest.java

@@ -137,7 +137,7 @@ public void compose_split_split() {
   public void compose_noTrans_first() {
     TransitionFactory<StubData> patch = new StubPatchFactory(FLAG_1, "value");
     TransitionFactory<StubData> composed =
-        ComposingTransitionFactory.of(NoTransition.createFactory(), patch);
+        ComposingTransitionFactory.of(NoTransition.getFactory(), patch);
 
     assertThat(composed).isNotNull();
     assertThat(composed).isEqualTo(patch);
@@ -147,7 +147,7 @@ public void compose_noTrans_first() {
   public void compose_noTrans_second() {
     TransitionFactory<StubData> patch = new StubPatchFactory(FLAG_1, "value");
     TransitionFactory<StubData> composed =
-        ComposingTransitionFactory.of(patch, NoTransition.createFactory());
+        ComposingTransitionFactory.of(patch, NoTransition.getFactory());
 
     assertThat(composed).isNotNull();
     assertThat(composed).isEqualTo(patch);

src/test/java/com/google/devtools/build/lib/analysis/config/transitions/NoConfigTransitionTest.java

@@ -32,7 +32,7 @@ public class NoConfigTransitionTest extends BuildViewTestCase {
   private static final MockRule NO_CONFIG_RULE =
       () ->
           MockRule.define(
-              "no_config_rule", (builder, env) -> builder.cfg(NoConfigTransition.createFactory()));
+              "no_config_rule", (builder, env) -> builder.cfg(NoConfigTransition.getFactory()));
 
   @Override
   protected ConfiguredRuleClassProvider createRuleClassProvider() {