Cleanup Skylark types some more

Clarify the criterion for being a valid Skylark value;
stop claiming immutability is "the" criterion when Skylark now has mutable values;
stop relying on a reflection with a magic list (this also fixes the SkylarkShell build).
Clarify the criterion for determining immutable types when making a SkylarkNestedSet.
Clarify and use the criterion for being a valid Skylark dict key.

--
MOS_MIGRATED_REVID=103313934

1 files changed, 13 insertions, 1 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/syntax/Label.java b/src/main/java/com/google/devtools/build/lib/syntax/Label.java
index 6c712c3ead..983f7fd84d 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/Label.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/Label.java
@@ -39,7 +39,7 @@ import java.io.Serializable;
  */
 @SkylarkModule(name = "Label", doc = "A BUILD target identifier.")
 @Immutable @ThreadSafe
-public final class Label implements Comparable<Label>, Serializable {
+public final class Label implements Comparable<Label>, Serializable, SkylarkValue {
 
   /**
    * Factory for Labels from absolute string form. e.g.
@@ -406,4 +406,16 @@ public final class Label implements Comparable<Label>, Serializable {
   public static String print(Label label) {
     return label == null ? "(unknown)" : label.toString();
   }
+
+  @Override
+  public boolean isImmutable() {
+    return true;
+  }
+
+  @Override
+  public void write(Appendable buffer, char quotationMark) {
+    // TODO(bazel-team): make the representation readable Label(//foo),
+    // and isolate the legacy functions that want the unreadable variant.
+    Printer.write(buffer, toString(), quotationMark);
+  }
 }