Add a way for BaseCodecs to register association with subtypes

Also add accessor to SkylarkInfo for the custom error message, and expose its concrete implementation classes for the benefit of reflection.

PiperOrigin-RevId: 182443146

2 files changed, 48 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/packages/SkylarkInfo.java b/src/main/java/com/google/devtools/build/lib/packages/SkylarkInfo.java
index 5445f80f64..a2da054efa 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/SkylarkInfo.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/SkylarkInfo.java
@@ -17,6 +17,7 @@ package com.google.devtools.build.lib.packages;
 import com.google.common.base.Joiner;
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableCollection;
+import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Sets;
@@ -27,6 +28,7 @@ import com.google.devtools.build.lib.syntax.Concatable;
 import com.google.devtools.build.lib.syntax.EvalException;
 import com.google.devtools.build.lib.syntax.EvalUtils;
 import java.util.Arrays;
+import java.util.List;
 import java.util.Map;
 import javax.annotation.Nullable;
 
@@ -71,6 +73,13 @@ public abstract class SkylarkInfo extends Info implements Concatable {
    */
   protected abstract Iterable<Object> getValues();
 
+  /**
+   * Returns the custom (i.e. per-instance, as opposed to per-provider-type) error message string
+   * format used by this provider instance, or null if not set.
+   */
+  @Nullable
+  public abstract String getCustomErrorMessageFormatForUnknownField();
+
   /** Returns the layout for this provider if it is schemaful, null otherwise. */
   @Nullable
   public abstract Layout getLayout();
@@ -136,6 +145,15 @@ public abstract class SkylarkInfo extends Info implements Concatable {
   }
 
   /**
+   * Returns the concrete implementation classes of this abstract class.
+   *
+   * <p>This is useful for code that depends on reflection.
+   */
+  public static List<Class<? extends SkylarkInfo>> getImplementationClasses() {
+    return ImmutableList.of(MapBackedSkylarkInfo.class, CompactSkylarkInfo.class);
+  }
+
+  /**
    * A specification of what fields a provider instance has, and how they are ordered in an
    * array-backed implementation.
    *
@@ -261,6 +279,11 @@ public abstract class SkylarkInfo extends Info implements Concatable {
     }
 
     @Override
+    public String getCustomErrorMessageFormatForUnknownField() {
+      return errorMessageFormatForUnknownField;
+    }
+
+    @Override
     public Layout getLayout() {
       return null;
     }
@@ -318,6 +341,11 @@ public abstract class SkylarkInfo extends Info implements Concatable {
     }
 
     @Override
+    public String getCustomErrorMessageFormatForUnknownField() {
+      return null;
+    }
+
+    @Override
     public Layout getLayout() {
       return layout;
     }
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/serialization/BaseCodec.java b/src/main/java/com/google/devtools/build/lib/skyframe/serialization/BaseCodec.java
index dd286fc7eb..abec3f1007 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/serialization/BaseCodec.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/serialization/BaseCodec.java
@@ -14,8 +14,10 @@
 
 package com.google.devtools.build.lib.skyframe.serialization;
 
+import com.google.common.collect.ImmutableList;
 import com.google.devtools.build.skyframe.SkyKey;
 import com.google.devtools.build.skyframe.SkyValue;
+import java.util.List;
 
 /** An opaque interface for codecs that just reveals the {@link Class} of its objects. */
 interface BaseCodec<T> {
@@ -28,4 +30,22 @@ interface BaseCodec<T> {
    * (b/26186886).
    */
   Class<T> getEncodedClass();
+
+  /**
+   * Returns additional subtypes of {@code T} that may be serialized/deserialized using this codec
+   * without loss of information.
+   *
+   * <p>This method is intended for when {@code T} has multiple concrete implementations whose
+   * details are known to the codec but not to the codec dispatching mechanism. It signals that the
+   * dispatcher may choose to use this codec for the subtype, rather than raise {@link
+   * SerializationException.NoCodecException}.
+   *
+   * <p>This method should not be used if the codec's serialization and deserialization methods
+   * perform their own dispatching to other codecs for subtypes of {@code T}.
+   *
+   * <p>{@code T} itself should not be included in the returned list.
+   */
+  default List<Class<? extends T>> additionalEncodedSubclasses() {
+    return ImmutableList.of();
+  }
 }