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

src/main/java/com/google/devtools/build/lib/analysis/ConfiguredRuleClassProvider.java

@@ -38,10 +38,11 @@
 import com.google.devtools.build.lib.packages.RuleClassProvider;
 import com.google.devtools.build.lib.rules.RuleConfiguredTargetFactory;
 import com.google.devtools.build.lib.rules.SkylarkModules;
+import com.google.devtools.build.lib.syntax.Environment;
+import com.google.devtools.build.lib.syntax.Environment.Extension;
 import com.google.devtools.build.lib.syntax.Label;
-import com.google.devtools.build.lib.syntax.SkylarkEnvironment;
+import com.google.devtools.build.lib.syntax.Mutability;
 import com.google.devtools.build.lib.syntax.SkylarkType;
-import com.google.devtools.build.lib.syntax.ValidationEnvironment;
 import com.google.devtools.build.lib.vfs.PathFragment;
 import com.google.devtools.common.options.OptionsClassProvider;
 
@@ -310,9 +311,7 @@ public Label load(String from) {
 
   private final PrerequisiteValidator prerequisiteValidator;
 
-  private final ImmutableMap<String, SkylarkType> skylarkAccessibleJavaClasses;
-
-  private final ValidationEnvironment skylarkValidationEnvironment;
+  private final Environment.Frame globals;
 
   public ConfiguredRuleClassProvider(
       PathFragment preludePath,
@@ -338,10 +337,7 @@ public ConfiguredRuleClassProvider(
     this.configurationFragments = configurationFragments;
     this.configurationCollectionFactory = configurationCollectionFactory;
     this.prerequisiteValidator = prerequisiteValidator;
-    this.skylarkAccessibleJavaClasses = skylarkAccessibleJavaClasses;
-    this.skylarkValidationEnvironment = new ValidationEnvironment(
-        // TODO(bazel-team): refactor constructors so we don't have those null-s
-        createSkylarkRuleClassEnvironment(null, null));
+    this.globals = createGlobals(skylarkAccessibleJavaClasses);
   }
 
   public PrerequisiteValidator getPrerequisiteValidator() {
@@ -425,22 +421,46 @@ public BuildOptions createBuildOptions(OptionsClassProvider optionsProvider) {
     return BuildOptions.of(configurationOptions, optionsProvider);
   }
 
-  @Override
-  public SkylarkEnvironment createSkylarkRuleClassEnvironment(
-      EventHandler eventHandler, String astFileContentHashCode) {
-    SkylarkEnvironment env = SkylarkModules.getNewEnvironment(eventHandler, astFileContentHashCode);
-    for (Map.Entry<String, SkylarkType> entry : skylarkAccessibleJavaClasses.entrySet()) {
-      env.update(entry.getKey(), entry.getValue().getType());
+  private Environment.Frame createGlobals(
+      ImmutableMap<String, SkylarkType> skylarkAccessibleJavaClasses) {
+    try (Mutability mutability = Mutability.create("ConfiguredRuleClassProvider globals")) {
+      Environment env = createSkylarkRuleClassEnvironment(
+          mutability, SkylarkModules.GLOBALS, null, null, null);
+      for (Map.Entry<String, SkylarkType> entry : skylarkAccessibleJavaClasses.entrySet()) {
+        env.setup(entry.getKey(), entry.getValue().getType());
+      }
+      return env.getGlobals();
     }
-    env.setLoadingPhase();
+  }
+
+  private Environment createSkylarkRuleClassEnvironment(
+      Mutability mutability,
+      Environment.Frame globals,
+      EventHandler eventHandler,
+      String astFileContentHashCode,
+      Map<PathFragment, Extension> importMap) {
+    Environment env = Environment.builder(mutability)
+        .setSkylark()
+        .setGlobals(globals)
+        .setEventHandler(eventHandler)
+        .setFileContentHashCode(astFileContentHashCode)
+        .setImportedExtensions(importMap)
+        .setLoadingPhase()
+        .build();
     return env;
   }
 
   @Override
-  public ValidationEnvironment getSkylarkValidationEnvironment() {
-    return skylarkValidationEnvironment;
+  public Environment createSkylarkRuleClassEnvironment(
+      Mutability mutability,
+      EventHandler eventHandler,
+      String astFileContentHashCode,
+      Map<PathFragment, Extension> importMap) {
+    return createSkylarkRuleClassEnvironment(
+        mutability, globals, eventHandler, astFileContentHashCode, importMap);
   }
 
+
   @Override
   public String getDefaultWorkspaceFile() {
     return defaultWorkspaceFile;

src/main/java/com/google/devtools/build/lib/events/Location.java

@@ -148,6 +148,18 @@ public LineAndColumn getStartLineAndColumn() {
     return null;
   }
 
+  /**
+   * 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.

src/main/java/com/google/devtools/build/lib/packages/ExternalPackage.java

@@ -24,6 +24,7 @@
 import com.google.devtools.build.lib.events.Location;
 import com.google.devtools.build.lib.events.StoredEventHandler;
 import com.google.devtools.build.lib.packages.RuleFactory.InvalidRuleException;
+import com.google.devtools.build.lib.syntax.Environment;
 import com.google.devtools.build.lib.syntax.FuncallExpression;
 import com.google.devtools.build.lib.syntax.Label;
 import com.google.devtools.build.lib.syntax.Label.SyntaxException;
@@ -120,7 +121,8 @@ public void addBindRule(
         attributes.put("actual", actual);
       }
       StoredEventHandler handler = new StoredEventHandler();
-      Rule rule = RuleFactory.createRule(this, bindRuleClass, attributes, handler, null, location);
+      Rule rule = RuleFactory.createRule(
+          this, bindRuleClass, attributes, handler, null, location, null);
       overwriteRule(rule);
       rule.setVisibility(ConstantRuleVisibility.PUBLIC);
     }
@@ -130,11 +132,11 @@ public void addBindRule(
      * WORKSPACE files to overwrite "earlier" ones.
      */
     public Builder createAndAddRepositoryRule(RuleClass ruleClass, RuleClass bindRuleClass,
-        Map<String, Object> kwargs, FuncallExpression ast)
+        Map<String, Object> kwargs, FuncallExpression ast, Environment env)
         throws InvalidRuleException, NameConflictException, SyntaxException {
       StoredEventHandler eventHandler = new StoredEventHandler();
-      Rule tempRule = RuleFactory.createRule(this, ruleClass, kwargs, eventHandler, ast,
-          ast.getLocation());
+      Rule tempRule = RuleFactory.createRule(
+          this, ruleClass, kwargs, eventHandler, ast, ast.getLocation(), env);
       addEvents(eventHandler.getEvents());
       try {
         repositoryMap.put(RepositoryName.create("@" + tempRule.getName()), tempRule);