Allows @AutoCodec to use factory methods.

Generalizes @AutoCodec.Constructor to @AutoCodec.Instantiator.

PiperOrigin-RevId: 183702768

24 files changed, 90 insertions, 61 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/analysis/BlazeDirectories.java b/src/main/java/com/google/devtools/build/lib/analysis/BlazeDirectories.java
index bbae6b4c20..d121a3dfe9 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/BlazeDirectories.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/BlazeDirectories.java
@@ -66,7 +66,7 @@ public final class BlazeDirectories {
   private final Path localOutputPath;
   private final String productName;
 
-  @AutoCodec.Constructor
+  @AutoCodec.Instantiator
   public BlazeDirectories(ServerDirectories serverDirectories, Path workspace, String productName) {
     this.serverDirectories = serverDirectories;
     this.workspace = workspace;
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/LanguageDependentFragment.java b/src/main/java/com/google/devtools/build/lib/analysis/LanguageDependentFragment.java
index 82bbef3af8..56c22f1f6f 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/LanguageDependentFragment.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/LanguageDependentFragment.java
@@ -52,7 +52,7 @@ public final class LanguageDependentFragment implements TransitiveInfoProvider {
 
     private final String displayName;
 
-    @AutoCodec.Constructor
+    @AutoCodec.Instantiator
     public LibraryLanguage(String displayName) {
       this.displayName = displayName;
     }
@@ -80,7 +80,7 @@ public final class LanguageDependentFragment implements TransitiveInfoProvider {
   private final Label label;
   private final ImmutableSet<LibraryLanguage> languages;
 
-  @AutoCodec.Constructor
+  @AutoCodec.Instantiator
   public LanguageDependentFragment(Label label, ImmutableSet<LibraryLanguage> languages) {
     this.label = label;
     this.languages = languages;
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/PlatformConfiguration.java b/src/main/java/com/google/devtools/build/lib/analysis/PlatformConfiguration.java
index ff12670bda..021c673010 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/PlatformConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/PlatformConfiguration.java
@@ -45,7 +45,7 @@ public class PlatformConfiguration extends BuildConfiguration.Fragment {
   private final ImmutableMap<Label, Label> toolchainResolutionOverrides;
   private final ImmutableList<Label> enabledToolchainTypes;
 
-  @AutoCodec.Constructor
+  @AutoCodec.Instantiator
   PlatformConfiguration(
       Label executionPlatform,
       ImmutableList<Label> extraExecutionPlatforms,
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/ServerDirectories.java b/src/main/java/com/google/devtools/build/lib/analysis/ServerDirectories.java
index c653c8c9ba..6797cb21a2 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/ServerDirectories.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/ServerDirectories.java
@@ -53,7 +53,7 @@ public final class ServerDirectories {
         Strings.isNullOrEmpty(installMD5) ? null : checkMD5(HashCode.fromString(installMD5)));
   }
 
-  @AutoCodec.Constructor
+  @AutoCodec.Instantiator
   ServerDirectories(Path installBase, Path outputBase, HashCode installMD5) {
     this.installBase = installBase;
     this.outputBase = outputBase;
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/config/RunUnderConverter.java b/src/main/java/com/google/devtools/build/lib/analysis/config/RunUnderConverter.java
index d367ceec6a..a09a1ce8df 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/config/RunUnderConverter.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/config/RunUnderConverter.java
@@ -65,7 +65,7 @@ public class RunUnderConverter implements Converter<RunUnder> {
     private final Label runUnderLabel;
     private final ImmutableList<String> runUnderList;
 
-    @AutoCodec.Constructor
+    @AutoCodec.Instantiator
     RunUnderLabel(String input, Label runUnderLabel, ImmutableList<String> runUnderList) {
       this.input = input;
       this.runUnderLabel = runUnderLabel;
@@ -126,7 +126,7 @@ public class RunUnderConverter implements Converter<RunUnder> {
     private final String runUnderCommand;
     private final ImmutableList<String> runUnderList;
 
-    @AutoCodec.Constructor
+    @AutoCodec.Instantiator
     RunUnderCommand(String input, String runUnderCommand, ImmutableList<String> runUnderList) {
       this.input = input;
       this.runUnderCommand = runUnderCommand;
diff --git a/src/main/java/com/google/devtools/build/lib/bazel/rules/BazelConfiguration.java b/src/main/java/com/google/devtools/build/lib/bazel/rules/BazelConfiguration.java
index 00f2f9e4ea..a29c105d03 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/rules/BazelConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/bazel/rules/BazelConfiguration.java
@@ -123,7 +123,7 @@ public class BazelConfiguration extends Fragment {
     this(os, options.useStrictActionEnv, determineShellExecutable(os, options.shellExecutable));
   }
 
-  @AutoCodec.Constructor
+  @AutoCodec.Instantiator
   BazelConfiguration(OS os, boolean useStrictActionEnv, PathFragment shellExecutable) {
     this.os = os;
     this.useStrictActionEnv = useStrictActionEnv;
diff --git a/src/main/java/com/google/devtools/build/lib/bazel/rules/python/BazelPythonConfiguration.java b/src/main/java/com/google/devtools/build/lib/bazel/rules/python/BazelPythonConfiguration.java
index d0952b8d7d..a6ff6b086b 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/rules/python/BazelPythonConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/bazel/rules/python/BazelPythonConfiguration.java
@@ -164,7 +164,7 @@ public class BazelPythonConfiguration extends BuildConfiguration.Fragment {
 
   private final Options options;
 
-  @AutoCodec.Constructor
+  @AutoCodec.Instantiator
   BazelPythonConfiguration(Options options) {
     this.options = options;
   }
diff --git a/src/main/java/com/google/devtools/build/lib/rules/android/AndroidConfiguration.java b/src/main/java/com/google/devtools/build/lib/rules/android/AndroidConfiguration.java
index 08d4a0c611..ec656b93ef 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/android/AndroidConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/android/AndroidConfiguration.java
@@ -887,7 +887,7 @@ public class AndroidConfiguration extends BuildConfiguration.Fragment {
     }
   }
 
-  @AutoCodec.Constructor
+  @AutoCodec.Instantiator
   AndroidConfiguration(
       Label sdk,
       String cpu,
diff --git a/src/main/java/com/google/devtools/build/lib/rules/apple/AppleConfiguration.java b/src/main/java/com/google/devtools/build/lib/rules/apple/AppleConfiguration.java
index 375c6c9b7e..eaccc1eff9 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/apple/AppleConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/apple/AppleConfiguration.java
@@ -91,7 +91,7 @@ public class AppleConfiguration extends BuildConfiguration.Fragment {
   private final boolean mandatoryMinimumVersion;
   private final boolean objcProviderFromLinked;
 
-  @AutoCodec.Constructor
+  @AutoCodec.Instantiator
   AppleConfiguration(AppleCommandLineOptions options, String iosCpu) {
     this.options = options;
     this.iosCpu = iosCpu;
diff --git a/src/main/java/com/google/devtools/build/lib/rules/apple/swift/SwiftConfiguration.java b/src/main/java/com/google/devtools/build/lib/rules/apple/swift/SwiftConfiguration.java
index 09a8936000..06976f3f5b 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/apple/swift/SwiftConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/apple/swift/SwiftConfiguration.java
@@ -50,7 +50,7 @@ public class SwiftConfiguration extends BuildConfiguration.Fragment {
     this(options.enableWholeModuleOptimization, ImmutableList.copyOf(options.copts));
   }
 
-  @AutoCodec.Constructor
+  @AutoCodec.Instantiator
   SwiftConfiguration(boolean enableWholeModuleOptimization, ImmutableList<String> copts) {
     this.enableWholeModuleOptimization = enableWholeModuleOptimization;
     this.copts = copts;
diff --git a/src/main/java/com/google/devtools/build/lib/rules/config/ConfigFeatureFlagConfiguration.java b/src/main/java/com/google/devtools/build/lib/rules/config/ConfigFeatureFlagConfiguration.java
index 287c8895c3..8ff00a46d7 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/config/ConfigFeatureFlagConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/config/ConfigFeatureFlagConfiguration.java
@@ -124,7 +124,7 @@ public final class ConfigFeatureFlagConfiguration extends BuildConfiguration.Fra
     this(options.getFlagValues());
   }
 
-  @AutoCodec.Constructor
+  @AutoCodec.Instantiator
   ConfigFeatureFlagConfiguration(ImmutableSortedMap<Label, String> flagValues) {
     this.flagValues = flagValues;
     this.flagHash = this.flagValues.isEmpty() ? null : hashFlags(this.flagValues);
diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppConfiguration.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppConfiguration.java
index bc2959f7b8..058f34db51 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppConfiguration.java
@@ -336,7 +336,7 @@ public final class CppConfiguration extends BuildConfiguration.Fragment {
         cppToolchainInfo);
   }
 
-  @AutoCodec.Constructor
+  @AutoCodec.Instantiator
   CppConfiguration(
       Label crosstoolTop,
       CrosstoolFile crosstoolFile,
diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppToolchainInfo.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppToolchainInfo.java
index 6e0c657715..135b70be3b 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppToolchainInfo.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppToolchainInfo.java
@@ -230,7 +230,7 @@ public final class CppToolchainInfo {
     }
   }
 
-  @AutoCodec.Constructor
+  @AutoCodec.Instantiator
   CppToolchainInfo(
       CToolchain toolchain,
       PathFragment crosstoolTopPathFragment,
diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CrosstoolConfigurationLoader.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CrosstoolConfigurationLoader.java
index 0753fbfba5..7244b7f3dc 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CrosstoolConfigurationLoader.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CrosstoolConfigurationLoader.java
@@ -78,7 +78,7 @@ public class CrosstoolConfigurationLoader {
     private final CrosstoolConfig.CrosstoolRelease proto;
     private final String md5;
 
-    @AutoCodec.Constructor
+    @AutoCodec.Instantiator
     CrosstoolFile(String location, CrosstoolConfig.CrosstoolRelease proto, String md5) {
       this.location = location;
       this.proto = proto;
diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/FlagList.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/FlagList.java
index 258cf630ce..ef992520b9 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/FlagList.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/FlagList.java
@@ -39,7 +39,7 @@ public class FlagList implements Serializable {
     private final String name;
     private final ImmutableList<String> flags;
 
-    @AutoCodec.Constructor
+    @AutoCodec.Instantiator
     OptionalFlag(String name, ImmutableList<String> flags) {
       this.name = name;
       this.flags = flags;
@@ -58,7 +58,7 @@ public class FlagList implements Serializable {
   private final ImmutableList<OptionalFlag> optionalFlags;
   private final ImmutableList<String> suffixFlags;
 
-  @AutoCodec.Constructor
+  @AutoCodec.Instantiator
   FlagList(
       ImmutableList<String> prefixFlags,
       ImmutableList<OptionalFlag> optionalFlags,
diff --git a/src/main/java/com/google/devtools/build/lib/rules/java/JavaConfiguration.java b/src/main/java/com/google/devtools/build/lib/rules/java/JavaConfiguration.java
index 4e8d9ceac2..e81118d36a 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/java/JavaConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/java/JavaConfiguration.java
@@ -229,7 +229,7 @@ public final class JavaConfiguration extends Fragment {
     this.pluginList = ImmutableList.copyOf(javaOptions.pluginList);
   }
 
-  @AutoCodec.Constructor
+  @AutoCodec.Instantiator
   JavaConfiguration(
       ImmutableList<String> commandLineJavacFlags,
       Label javaLauncherLabel,
diff --git a/src/main/java/com/google/devtools/build/lib/rules/objc/J2ObjcConfiguration.java b/src/main/java/com/google/devtools/build/lib/rules/objc/J2ObjcConfiguration.java
index 0d07d7393b..582453b982 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/objc/J2ObjcConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/objc/J2ObjcConfiguration.java
@@ -108,7 +108,7 @@ public class J2ObjcConfiguration extends Fragment {
         Optional.fromNullable(j2ObjcOptions.deadCodeReport));
   }
 
-  @AutoCodec.Constructor
+  @AutoCodec.Instantiator
   J2ObjcConfiguration(
       List<String> translationFlags,
       boolean removeDeadCode,
diff --git a/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcConfiguration.java b/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcConfiguration.java
index 85bfaa4a06..6139c2a541 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcConfiguration.java
@@ -117,7 +117,7 @@ public class ObjcConfiguration extends BuildConfiguration.Fragment {
     this.appleSdk = objcOptions.appleSdk;
   }
 
-  @AutoCodec.Constructor
+  @AutoCodec.Instantiator
   ObjcConfiguration(
       DottedVersion iosSimulatorVersion,
       String iosSimulatorDevice,
diff --git a/src/main/java/com/google/devtools/build/lib/rules/proto/ProtoConfiguration.java b/src/main/java/com/google/devtools/build/lib/rules/proto/ProtoConfiguration.java
index e1c1c073ff..2838f3a6c1 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/proto/ProtoConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/proto/ProtoConfiguration.java
@@ -225,7 +225,7 @@ public class ProtoConfiguration extends Fragment {
   private final ImmutableList<String> ccProtoLibrarySourceSuffixes;
   private final Options options;
 
-  @AutoCodec.Constructor
+  @AutoCodec.Instantiator
   public ProtoConfiguration(Options options) {
     this.protocOpts = ImmutableList.copyOf(options.protocOpts);
     this.ccProtoLibraryHeaderSuffixes = ImmutableList.copyOf(options.ccProtoLibraryHeaderSuffixes);
diff --git a/src/main/java/com/google/devtools/build/lib/rules/python/PythonConfiguration.java b/src/main/java/com/google/devtools/build/lib/rules/python/PythonConfiguration.java
index 83da07b243..f8ac8bc2c3 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/python/PythonConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/python/PythonConfiguration.java
@@ -41,7 +41,7 @@ public class PythonConfiguration extends BuildConfiguration.Fragment {
   private final TriState buildPythonZip;
   private final boolean buildTransitiveRunfilesTrees;
 
-  @AutoCodec.Constructor
+  @AutoCodec.Instantiator
   PythonConfiguration(
       PythonVersion defaultPythonVersion,
       boolean ignorePythonVersionAttribute,
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/serialization/autocodec/AutoCodec.java b/src/main/java/com/google/devtools/build/lib/skyframe/serialization/autocodec/AutoCodec.java
index a5bb4cd30b..a4f9fa7adb 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/serialization/autocodec/AutoCodec.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/serialization/autocodec/AutoCodec.java
@@ -40,19 +40,19 @@ public @interface AutoCodec {
    */
   enum Strategy {
     /**
-     * Uses a constructor of the class to synthesize a codec.
+     * Uses a constructor or factory method of the class to synthesize a codec.
      *
      * <p>This strategy depends on
      *
      * <ul>
-     *   <li>a designated constructor to inspect to generate the codec
+     *   <li>a designated constructor or factory method to inspect to generate the codec
      *   <li>the parameters must match member fields on name and type.
      * </ul>
      *
-     * <p>If there is a unique constructor, that is the designated constructor, otherwise one must
-     * be selected using the {@link AutoCodec.Constructor} annotation.
+     * <p>If there is a unique constructor, @AutoCodec may select that as the default instantiator,
+     * otherwise one must be selected using the {@link AutoCodec.Instantiator} annotation.
      */
-    CONSTRUCTOR,
+    INSTANTIATOR,
     /**
      * Uses the public fields to infer serialization code.
      *
@@ -70,18 +70,18 @@ public @interface AutoCodec {
   }
 
   /**
-   * Marks a specific constructor when using the CONSTRUCTOR strategy.
+   * Marks a specific method when using the INSTANTIATOR strategy.
    *
-   * <p>Indicates a constructor for codec generation. A compile-time error will result if multiple
-   * constructors are thus tagged.
+   * <p>Indicates an instantiator, either a constructor or factory method, for codec generation. A
+   * compile-time error will result if multiple methods are thus tagged.
    */
-  @Target(ElementType.CONSTRUCTOR)
-  @interface Constructor {}
+  @Target({ElementType.CONSTRUCTOR, ElementType.METHOD})
+  @interface Instantiator {}
 
   /**
    * Marks a specific constructor parameter as a dependency.
    *
-   * <p>When a constructor selected for the {@code CONSTRUCTOR} strategy has one of its parameters
+   * <p>When a constructor selected for the {@code INSTANTIATOR} strategy has one of its parameters
    * tagged {@code @Dependency}, {@code @AutoCodec} generates an {@link
    * com.google.devtools.build.lib.skyframe.serialization.InjectingObjectCodec} instead of the usual
    * {@link com.google.devtools.build.lib.skyframe.serialization.ObjectCodec} with the dependency
@@ -97,7 +97,7 @@ public @interface AutoCodec {
   @Target(ElementType.PARAMETER)
   @interface Dependency {}
 
-  Strategy strategy() default Strategy.CONSTRUCTOR;
+  Strategy strategy() default Strategy.INSTANTIATOR;
   /**
    * Specifies a deserialization dependency.
    *
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/serialization/autocodec/AutoCodecProcessor.java b/src/main/java/com/google/devtools/build/lib/skyframe/serialization/autocodec/AutoCodecProcessor.java
index 052aa242b2..52f060f8cb 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/serialization/autocodec/AutoCodecProcessor.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/serialization/autocodec/AutoCodecProcessor.java
@@ -33,6 +33,7 @@ import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
 import java.util.stream.Collectors;
+import java.util.stream.Stream;
 import javax.annotation.Nullable;
 import javax.annotation.processing.AbstractProcessor;
 import javax.annotation.processing.ProcessingEnvironment;
@@ -40,6 +41,7 @@ import javax.annotation.processing.Processor;
 import javax.annotation.processing.RoundEnvironment;
 import javax.lang.model.SourceVersion;
 import javax.lang.model.element.Element;
+import javax.lang.model.element.ElementKind;
 import javax.lang.model.element.ExecutableElement;
 import javax.lang.model.element.Modifier;
 import javax.lang.model.element.TypeElement;
@@ -97,8 +99,8 @@ public class AutoCodecProcessor extends AbstractProcessor {
       @Nullable TypeElement dependencyType = getDependencyType(annotation);
       TypeSpec.Builder codecClassBuilder = null;
       switch (annotation.strategy()) {
-        case CONSTRUCTOR:
-          codecClassBuilder = buildClassWithConstructorStrategy(encodedType, dependencyType);
+        case INSTANTIATOR:
+          codecClassBuilder = buildClassWithInstantiatorStrategy(encodedType, dependencyType);
           break;
         case PUBLIC_FIELDS:
           codecClassBuilder = buildClassWithPublicFieldsStrategy(encodedType, dependencyType);
@@ -145,9 +147,9 @@ public class AutoCodecProcessor extends AbstractProcessor {
     }
   }
 
-  private TypeSpec.Builder buildClassWithConstructorStrategy(
+  private TypeSpec.Builder buildClassWithInstantiatorStrategy(
       TypeElement encodedType, @Nullable TypeElement dependency) {
-    ExecutableElement constructor = selectConstructorForConstructorStrategy(encodedType);
+    ExecutableElement constructor = selectInstantiator(encodedType);
     PartitionedParameters parameters = isolateDependency(constructor);
     if (dependency != null) {
       if (parameters.dependency != null) {
@@ -165,7 +167,7 @@ public class AutoCodecProcessor extends AbstractProcessor {
 
     initializeUnsafeOffsets(codecClassBuilder, encodedType, parameters.fields);
 
-    codecClassBuilder.addMethod(buildSerializeMethodWithConstructor(encodedType, parameters));
+    codecClassBuilder.addMethod(buildSerializeMethodWithInstantiator(encodedType, parameters));
 
     MethodSpec.Builder deserializeBuilder =
         AutoCodecUtil.initializeDeserializeMethodBuilder(encodedType, parameters.dependency);
@@ -206,33 +208,52 @@ public class AutoCodecProcessor extends AbstractProcessor {
     return result;
   }
 
-  private static ExecutableElement selectConstructorForConstructorStrategy(
-      TypeElement encodedType) {
+  private ExecutableElement selectInstantiator(TypeElement encodedType) {
     List<ExecutableElement> constructors =
         ElementFilter.constructorsIn(encodedType.getEnclosedElements());
-    ImmutableList<ExecutableElement> markedConstructors =
-        constructors
+    Stream<ExecutableElement> factoryMethods =
+        ElementFilter.methodsIn(encodedType.getEnclosedElements())
             .stream()
-            .filter(c -> c.getAnnotation(AutoCodec.Constructor.class) != null)
+            .filter(AutoCodecProcessor::hasInstantiatorAnnotation)
+            .peek(m -> verifyFactoryMethod(encodedType, m));
+    ImmutableList<ExecutableElement> markedInstantiators =
+        Stream.concat(
+                constructors.stream().filter(AutoCodecProcessor::hasInstantiatorAnnotation),
+                factoryMethods)
             .collect(toImmutableList());
-    if (markedConstructors.isEmpty()) {
+    if (markedInstantiators.isEmpty()) {
       // If nothing is marked, see if there is a unique constructor.
       if (constructors.size() > 1) {
         throw new IllegalArgumentException(
             encodedType.getQualifiedName()
-                + " has multiple constructors but no Constructor annotation.");
+                + " has multiple constructors but no Instantiator annotation.");
       }
       // In Java, every class has at least one constructor, so this never fails.
       return constructors.get(0);
     }
-    if (markedConstructors.size() == 1) {
-      return markedConstructors.get(0);
+    if (markedInstantiators.size() == 1) {
+      return markedInstantiators.get(0);
     }
     throw new IllegalArgumentException(
-        encodedType.getQualifiedName() + " has multiple Constructor annotations.");
+        encodedType.getQualifiedName() + " has multiple Instantiator annotations.");
   }
 
-  private MethodSpec buildSerializeMethodWithConstructor(
+  private static boolean hasInstantiatorAnnotation(Element elt) {
+    return elt.getAnnotation(AutoCodec.Instantiator.class) != null;
+  }
+
+  private void verifyFactoryMethod(TypeElement encodedType, ExecutableElement elt) {
+    if (!elt.getModifiers().contains(Modifier.STATIC)
+        || !env.getTypeUtils().isSubtype(elt.getReturnType(), encodedType.asType())) {
+      throw new IllegalArgumentException(
+          encodedType.getQualifiedName()
+              + " tags "
+              + elt.getSimpleName()
+              + " as an Instantiator, but it's not a valid factory method.");
+    }
+  }
+
+  private MethodSpec buildSerializeMethodWithInstantiator(
       TypeElement encodedType, PartitionedParameters parameters) {
     MethodSpec.Builder serializeBuilder =
         AutoCodecUtil.initializeSerializeMethodBuilder(encodedType, parameters.dependency);
@@ -379,28 +400,36 @@ public class AutoCodecProcessor extends AbstractProcessor {
   }
 
   /**
-   * Invokes the constructor and returns the value.
+   * Invokes the instantiator and returns the value.
    *
-   * <p>Used by the {@link AutoCodec.Strategy.CONSTRUCTOR} strategy.
+   * <p>Used by the {@link AutoCodec.Strategy.INSTANTIATOR} strategy.
    */
   private static void addReturnNew(
-      MethodSpec.Builder builder, TypeElement type, ExecutableElement constructor) {
-    List<? extends TypeMirror> allThrown = constructor.getThrownTypes();
+      MethodSpec.Builder builder, TypeElement type, ExecutableElement instantiator) {
+    List<? extends TypeMirror> allThrown = instantiator.getThrownTypes();
     if (!allThrown.isEmpty()) {
       builder.beginControlFlow("try");
     }
     String parameters =
-        constructor
+        instantiator
             .getParameters()
             .stream()
             .map(AutoCodecProcessor::handleFromParameter)
             .collect(Collectors.joining(", "));
-    builder.addStatement("return new $T($L)", TypeName.get(type.asType()), parameters);
+    if (instantiator.getKind().equals(ElementKind.CONSTRUCTOR)) {
+      builder.addStatement("return new $T($L)", TypeName.get(type.asType()), parameters);
+    } else { // Otherwise, it's a factory method.
+      builder.addStatement(
+          "return $T.$L($L)",
+          TypeName.get(type.asType()),
+          instantiator.getSimpleName(),
+          parameters);
+    }
     if (!allThrown.isEmpty()) {
       for (TypeMirror thrown : allThrown) {
         builder.nextControlFlow("catch ($T e)", TypeName.get(thrown));
         builder.addStatement(
-            "throw new $T(\"$L constructor threw an exception\", e)",
+            "throw new $T(\"$L instantiator threw an exception\", e)",
             SerializationException.class,
             type.getQualifiedName());
       }
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/LineNumberTable.java b/src/main/java/com/google/devtools/build/lib/syntax/LineNumberTable.java
index 4706fa2f3b..9edf92777e 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/LineNumberTable.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/LineNumberTable.java
@@ -87,7 +87,7 @@ public abstract class LineNumberTable implements Serializable {
       this(computeLinestart(buffer), path, buffer.length);
     }
 
-    @AutoCodec.Constructor
+    @AutoCodec.Instantiator
     Regular(int[] linestart, PathFragment path, int bufferLength) {
       this.linestart = linestart;
       this.path = path;
@@ -262,7 +262,7 @@ public abstract class LineNumberTable implements Serializable {
           buffer.length);
     }
 
-    @AutoCodec.Constructor
+    @AutoCodec.Instantiator
     HashLine(ImmutableList<SingleHashLine> table, PathFragment defaultPath, int bufferLength) {
       this.table = table;
       this.defaultPath = defaultPath;
diff --git a/src/main/java/com/google/devtools/build/lib/util/RegexFilter.java b/src/main/java/com/google/devtools/build/lib/util/RegexFilter.java
index 4d3b7ef670..c64ea5157e 100644
--- a/src/main/java/com/google/devtools/build/lib/util/RegexFilter.java
+++ b/src/main/java/com/google/devtools/build/lib/util/RegexFilter.java
@@ -91,7 +91,7 @@ public final class RegexFilter {
    * <p>Null {@code inclusionPattern} or {@code exclusionPattern} means that inclusion or exclusion
    * matching will not be applied, respectively.
    */
-  @AutoCodec.Constructor
+  @AutoCodec.Instantiator
   RegexFilter(@Nullable Pattern inclusionPattern, @Nullable Pattern exclusionPattern) {
     this.inclusionPattern = inclusionPattern;
     this.exclusionPattern = exclusionPattern;