Skylark no longer crashes when the default value of an attribute is a label string that points to a remote repository.

Fixes #1442.

--
MOS_MIGRATED_REVID=132320130

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

diff --git a/src/main/java/com/google/devtools/build/lib/packages/Attribute.java b/src/main/java/com/google/devtools/build/lib/packages/Attribute.java
index fed7bd4..80bba9b 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/Attribute.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/Attribute.java
@@ -620,14 +620,24 @@
 
     /**
      * See value(TYPE) above. This method is only meant for Skylark usage.
+     *
+     * <p>The parameter {@code context} is relevant iff the default value is a Label string.
+     * In this case, {@code context} must point to the parent Label in order to be able to convert
+     * the default value string to a proper Label.
      */
-    public Builder<TYPE> defaultValue(Object defaultValue) throws ConversionException {
+    public Builder<TYPE> defaultValue(Object defaultValue, Object context)
+        throws ConversionException {
       Preconditions.checkState(!valueSet, "the default value is already set");
-      value = type.convert(defaultValue, "attribute " + name);
+      value = type.convert(defaultValue, "attribute " + name, context);
       valueSet = true;
       return this;
     }
 
+    /** See value(TYPE) above. This method is only meant for Skylark usage. */
+    public Builder<TYPE> defaultValue(Object defaultValue) throws ConversionException {
+      return defaultValue(defaultValue, null);
+    }
+
     public boolean isValueSet() {
       return valueSet;
     }

src/main/java/com/google/devtools/build/lib/rules/SkylarkAttr.java

diff --git a/src/main/java/com/google/devtools/build/lib/rules/SkylarkAttr.java b/src/main/java/com/google/devtools/build/lib/rules/SkylarkAttr.java
index ea52e11..2e4bbb6 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/SkylarkAttr.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/SkylarkAttr.java
@@ -172,7 +172,7 @@
             new SkylarkComputedDefaultTemplate(
                 type, callback.getParameterNames(), callback, ast.getLocation()));
       } else {
-        builder.defaultValue(defaultValue);
+        builder.defaultValue(defaultValue, env.getGlobals().label());
       }
     }
 

src/test/java/com/google/devtools/build/lib/skylark/SkylarkIntegrationTest.java

diff --git a/src/test/java/com/google/devtools/build/lib/skylark/SkylarkIntegrationTest.java b/src/test/java/com/google/devtools/build/lib/skylark/SkylarkIntegrationTest.java
index 6d156f2..3387941 100644
--- a/src/test/java/com/google/devtools/build/lib/skylark/SkylarkIntegrationTest.java
+++ b/src/test/java/com/google/devtools/build/lib/skylark/SkylarkIntegrationTest.java
@@ -64,6 +64,28 @@
   }
 
   @Test
+  public void testRemoteLabelAsDefaultAttributeValue() throws Exception {
+    scratch.file(
+        "test/skylark/extension.bzl",
+        "def _impl(ctx):",
+        "  pass",
+        "my_rule = rule(implementation = _impl,",
+        "    attrs = { 'dep' : attr.label_list(default=[\"@r//:t\"]) })");
+
+    // We are only interested in whether the label string in the default value can be converted
+    // to a proper Label without an exception (see GitHub issue #1442).
+    // Consequently, we expect getTarget() to fail later since the repository does not exist.
+    checkError(
+        "test/skylark",
+        "the_rule",
+        "no such package '@r//': error loading package 'external': "
+            + "The repository named 'r' could not be resolved",
+        "load('/test/skylark/extension', 'my_rule')",
+        "",
+        "my_rule(name='the_rule')");
+  }
+
+  @Test
   public void testSameMethodNames() throws Exception {
     // The alias feature of load() may hide the fact that two methods in the stack trace have the
     // same name. This is perfectly legal as long as these two methods are actually distinct.