Refactor Skylark Environment-s

Make Environment-s freezable: Introduce a class Mutability
as a revokable capability to mutate objects in an Environment.
For now, only Environment-s carry this capability.
Make sure that every Mutability is revoked in the same function that create...

This reinstates a change that previously rolled-back because it broke the
serializability of SkylarkLookupValue. Bad news: serializing it succeeds for the
wrong reason, because a SkylarkEnvironment was stored as a result (now an
Environment.Extension) that was Serializable but inherited its bindings from an Environment (now an Environment.BaseExtension) which wasn't Serializable.
Apparently, Java doesn't try to serialize the bindings then (or at least doesn't
error out when it fails), because these bindings map variable names to pretty
arbitrary objects, and a lot of those we find in practice aren't Serializable.
Thus the current code passes the same tests as the previous code, but obviously
the serialization is just as ineffective as it used to be.

--
MOS_MIGRATED_REVID=102776694

1 files changed, 12 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/events/Location.java b/src/main/java/com/google/devtools/build/lib/events/Location.java
index 74b04a913a..1b9110d664 100644
--- a/src/main/java/com/google/devtools/build/lib/events/Location.java
+++ b/src/main/java/com/google/devtools/build/lib/events/Location.java
@@ -149,6 +149,18 @@ public abstract class Location implements Serializable {
   }
 
   /**
+   * Returns a line corresponding to the position denoted by getStartOffset.
+   * Returns null if this information is not available.
+   */
+  public Integer getStartLine() {
+    LineAndColumn lac = getStartLineAndColumn();
+    if (lac == null) {
+      return null;
+    }
+    return lac.getLine();
+  }
+
+  /**
    * Returns a (line, column) pair corresponding to the position denoted by
    * getEndOffset.  Returns null if this information is not available.
    */