Use Mutability for Args class.

Make sure we do not keep reference to SkylarkRuleContext in Args object.

RELNOTES: None.
PiperOrigin-RevId: 170346094

src/main/java/com/google/devtools/build/lib/analysis/skylark/SkylarkActionFactory.java

@@ -50,12 +50,15 @@
 import com.google.devtools.build.lib.skylarkinterface.SkylarkValue;
 import com.google.devtools.build.lib.syntax.BaseFunction;
 import com.google.devtools.build.lib.syntax.BuiltinFunction;
+import com.google.devtools.build.lib.syntax.Environment;
 import com.google.devtools.build.lib.syntax.EvalException;
 import com.google.devtools.build.lib.syntax.EvalUtils;
+import com.google.devtools.build.lib.syntax.Mutability;
 import com.google.devtools.build.lib.syntax.Runtime;
 import com.google.devtools.build.lib.syntax.Runtime.NoneType;
 import com.google.devtools.build.lib.syntax.SkylarkDict;
 import com.google.devtools.build.lib.syntax.SkylarkList;
+import com.google.devtools.build.lib.syntax.SkylarkMutable;
 import com.google.devtools.build.lib.syntax.SkylarkNestedSet;
 import com.google.devtools.build.lib.syntax.SkylarkSemanticsOptions;
 import com.google.devtools.build.lib.syntax.SkylarkSignatureProcessor;
@@ -65,6 +68,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.UUID;
+import javax.annotation.Nullable;
 
 /**
  * Provides a Skylark interface for all action creation needs.
@@ -869,9 +873,8 @@ private static String convertLatin1ToUtf8(String latin1) {
             + "# ]"
             + "</pre>"
   )
-  static class Args implements SkylarkValue {
-
-    private final SkylarkRuleContext context;
+  static class Args extends SkylarkMutable {
+    private final Mutability mutability;
     private final SkylarkCustomCommandLine.Builder commandLine;
     private ParameterFileType parameterFileType = ParameterFileType.SHELL_QUOTED;
     private String flagFormatString;
@@ -1101,11 +1104,11 @@ public void setParamFileFormat(String format) throws EvalException {
       this.parameterFileType = parameterFileType;
     }
 
-    public Args(
-        SkylarkRuleContext context,
+    private Args(
+        @Nullable Mutability mutability,
         SkylarkSemanticsOptions skylarkSemantics,
         EventHandler eventHandler) {
-      this.context = context;
+      this.mutability = mutability != null ? mutability : Mutability.IMMUTABLE;
       this.commandLine = new SkylarkCustomCommandLine.Builder(skylarkSemantics, eventHandler);
     }
 
@@ -1114,8 +1117,8 @@ public SkylarkCustomCommandLine build() {
     }
 
     @Override
-    public boolean isImmutable() {
-      return context.isImmutable();
+    public Mutability mutability() {
+      return mutability;
     }
 
     @Override
@@ -1128,14 +1131,28 @@ public void repr(SkylarkPrinter printer) {
     }
   }
 
-  @SkylarkCallable(
+  @SkylarkSignature(
     name = "args",
-    doc = "returns an Args object that can be used to build memory-efficient command lines."
+    doc = "returns an Args object that can be used to build memory-efficient command lines.",
+    objectType = SkylarkActionFactory.class,
+    returnType = Args.class,
+    parameters = {
+        @Param(
+            name = "self",
+            type = SkylarkActionFactory.class,
+            doc = "This 'actions' object."
+        )
+    },
+    useEnvironment = true
   )
-  public Args args() {
-    return new Args(
-        context, skylarkSemanticsOptions, ruleContext.getAnalysisEnvironment().getEventHandler());
-  }
+  public static final BuiltinFunction args =
+      new BuiltinFunction("args") {
+        public Args invoke(SkylarkActionFactory self, Environment env) {
+          return new Args(env.mutability(),
+              env.getSemantics(),
+              self.ruleContext.getAnalysisEnvironment().getEventHandler());
+        }
+      };
 
   @Override
   public boolean isImmutable() {
@@ -1151,4 +1168,8 @@ public void repr(SkylarkPrinter printer) {
   void nullify() {
     ruleContext = null;
   }
+
+  static {
+    SkylarkSignatureProcessor.configureSkylarkFunctions(SkylarkActionFactory.class);
+  }
 }