Add is_target_root in export

To reconstruct the build graph for import/indexing optimization, intellij pants plugin would need to know where roots start in the graph.

Testing Done:
https://travis-ci.org/pantsbuild/pants/builds/140961443

Bugs closed: 3610

Reviewed at https://rbcommons.com/s/twitter/r/4030/

src/docs/export.md

@@ -168,6 +168,10 @@ The following is an abbreviated export file from a command in the pants repo:
 
 # Export Format Changes
 
+## 1.0.9
+
+Added 'is_target_root' field to target
+
 ## 1.0.8
 
 Conditionally added 'transitive' and 'scope' fields to target

src/python/pants/backend/project_info/tasks/export.py

@@ -56,7 +56,7 @@ class ExportTask(IvyTaskMixin, PythonTask):
   #
   # Note format changes in src/docs/export.md and update the Changelog section.
   #
-  DEFAULT_EXPORT_VERSION = '1.0.8'
+  DEFAULT_EXPORT_VERSION = '1.0.9'
 
   @classmethod
   def subsystem_dependencies(cls):
@@ -173,6 +173,8 @@ def generate_targets_map(self, targets, classpath_products=None):
     else:
       classpath_products = None
 
+    target_roots_set = set(self.context.target_roots)
+
     def process_target(current_target):
       """
       :type current_target:pants.build_graph.target.Target
@@ -209,6 +211,7 @@ def get_target_type(target):
 
       info['transitive'] = current_target.transitive
       info['scope'] = str(current_target.scope)
+      info['is_target_root'] = current_target in target_roots_set
 
       if isinstance(current_target, PythonRequirementLibrary):
         reqs = current_target.payload.get_field_value('requirements', set())

tests/python/pants_test/backend/project_info/tasks/test_export.py

@@ -218,7 +218,7 @@ def test_without_dependencies(self):
   def test_version(self):
     result = self.execute_export_json('project_info:first')
     # If you have to update this test, make sure export.md is updated with changelog notes
-    self.assertEqual('1.0.8', result['version'])
+    self.assertEqual('1.0.9', result['version'])
 
   def test_sources(self):
     self.set_options(sources=True)
@@ -272,6 +272,7 @@ def test_jvm_target(self):
       'is_code_gen': False,
       'targets': ['project_info:jar_lib', '//:scala-library'],
       'is_synthetic': False,
+      'is_target_root': True,
       'roots': [
          {
            'source_root': '{root}/project_info/this/is/a/source'.format(root=self.build_root),

tests/python/pants_test/backend/project_info/tasks/test_export_integration.py

@@ -262,3 +262,14 @@ def test_intransitive_and_scope(self):
       synthetic_target = '{}:shadow-unstable-intransitive-1'.format(test_path)
       self.assertEquals(False, json_data['targets'][synthetic_target]['transitive'])
       self.assertEquals('compile test', json_data['targets'][synthetic_target]['scope'])
+
+  def test_export_is_target_roots(self):
+    with self.temporary_workdir() as workdir:
+      test_target = 'examples/tests/java/org/pantsbuild/example/::'
+      json_data = self.run_export(test_target, workdir, load_libs=False)
+      for target_address, attributes in json_data['targets'].items():
+        # Make sure all targets under `test_target`'s directory are target roots.
+        self.assertEqual(
+          attributes['is_target_root'],
+          target_address.startswith("examples/tests/java/org/pantsbuild/example")
+        )