Add ability to shallow-freeze individual objects

Clarify that the IMMUTABLE Mutability should only be used for deeply immutable things, not tuples. Created a new SHALLOW_IMMUTABLE Mutability for them.

Note that the new shallow-freezing functionality marks things as deeply IMMUTABLE without traversing its contents. I.e., it lies, and it is up to the caller to ensure this doesn't cause problems.

RELNOTES: NONE
PiperOrigin-RevId: 189767422

1 files changed, 8 insertions, 1 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/syntax/SkylarkDict.java b/src/main/java/com/google/devtools/build/lib/syntax/SkylarkDict.java
index 8c951cbb44..db656328fd 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/SkylarkDict.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/SkylarkDict.java
@@ -62,7 +62,8 @@ public final class SkylarkDict<K, V> extends MutableMap<K, V>
 
   private final LinkedHashMap<K, V> contents = new LinkedHashMap<>();
 
-  private final Mutability mutability;
+  /** Final except for {@link #unsafeShallowFreeze}; must not be modified any other way. */
+  private Mutability mutability;
 
   private SkylarkDict(@Nullable Mutability mutability) {
     this.mutability = mutability == null ? Mutability.IMMUTABLE : mutability;
@@ -154,6 +155,12 @@ public final class SkylarkDict<K, V> extends MutableMap<K, V>
   }
 
   @Override
+  public void unsafeShallowFreeze() {
+    Mutability.Freezable.checkUnsafeShallowFreezePrecondition(this);
+    this.mutability = Mutability.IMMUTABLE;
+  }
+
+  @Override
   protected Map<K, V> getContentsUnsafe() {
     return contents;
   }