Invalidate tasks based on BinaryUtil.version.

The assumption is that binaries are uniquely identified by their version
and name. This is at least true of pants-supported bintray binaries for
protoc and ragel.

Additionally invalidation is arranged for protoc plugins based on name.
This is not ideal - it allows for changing a plugin without chaging its
name - but its strictly better than not invalidating at all for changing
plugin lists.

Testing Done:
CI went green here:
  https://travis-ci.org/pantsbuild/pants/builds/72238973

Bugs closed: 1855

Reviewed at https://rbcommons.com/s/twitter/r/2516/

src/python/pants/backend/codegen/tasks/BUILD

@@ -109,6 +109,7 @@ python_library(
     'src/python/pants/base:source_root',
     'src/python/pants:binary_util',
     'src/python/pants/util:dirutil',
+    'src/python/pants/util:memo',
   ],
 )
 

src/python/pants/backend/codegen/tasks/protobuf_gen.py

@@ -25,6 +25,7 @@
 from pants.binary_util import BinaryUtil
 from pants.fs.archive import ZIP
 from pants.util.dirutil import safe_mkdir
+from pants.util.memo import memoized_property
 
 
 class ProtobufGen(SimpleCodegenTask):
@@ -36,17 +37,23 @@ def global_subsystems(cls):
   @classmethod
   def register_options(cls, register):
     super(ProtobufGen, cls).register_options(register)
-    register('--version', advanced=True,
+
+    # The protoc version and the plugin names are used as proxies for the identity of the protoc
+    # executable environment here.  Although version is an obvious proxy for the protoc binary
+    # itself, plugin names are less so and plugin authors must include a version in the name for
+    # proper invalidation of protobuf products in the face of plugin modification that affects
+    # plugin outputs.
+    register('--version', advanced=True, fingerprint=True,
              help='Version of protoc.  Used to create the default --javadeps and as part of '
                   'the path to lookup the tool with --pants-support-baseurls and '
                   '--pants-bootstrapdir.  When changing this parameter you may also need to '
                   'update --javadeps.',
              default='2.4.1')
-    # TODO(Eric Ayers) Mix the value of this option into the fingerprint
-    register('--plugins', advanced=True, action='append',
+    register('--plugins', advanced=True, fingerprint=True, action='append',
              help='Names of protobuf plugins to invoke.  Protoc will look for an executable '
                   'named protoc-gen-$NAME on PATH.',
              default=[])
+
     register('--extra_path', advanced=True, action='append',
              help='Prepend this path onto PATH in the environment before executing protoc. '
                   'Intended to help protoc find its plugins.',
@@ -74,13 +81,12 @@ def __init__(self, *args, **kwargs):
     self.plugins = self.get_options().plugins
     self._extra_paths = self.get_options().extra_path
 
+  @memoized_property
+  def protobuf_binary(self):
     binary_util = BinaryUtil.Factory.create()
-    self.protobuf_binary = binary_util.select_binary(self.get_options().supportdir,
-                                                     self.get_options().version,
-                                                     'protoc')
-
-  def invalidate_for_files(self):
-    return [self.protobuf_binary]
+    return binary_util.select_binary(self.get_options().supportdir,
+                                     self.get_options().version,
+                                     'protoc')
 
   @property
   def javadeps(self):

src/python/pants/backend/codegen/tasks/ragel_gen.py

@@ -32,7 +32,10 @@ def register_options(cls, register):
     register('--supportdir', default='bin/ragel', advanced=True,
              help='The path to find the ragel binary.  Used as part of the path to lookup the'
                   'tool with --pants-support-baseurls and --pants_bootstrapdir.')
-    register('--version', default='6.9', advanced=True,
+
+    # We take the cautious approach here and assume a version bump will always correspond to
+    # changes in ragel codegen products.
+    register('--version', default='6.9', advanced=True, fingerprint=True,
              help='The version of ragel to use.  Used as part of the path to lookup the'
                   'tool with --pants-support-baseurls and --pants-bootstrapdir')
 
@@ -51,9 +54,6 @@ def ragel_binary(self):
   def javadeps(self):
     return OrderedSet()
 
-  def invalidate_for_files(self):
-    return [self.ragel_binary]
-
   def is_gentarget(self, target):
     return isinstance(target, JavaRagelLibrary)
 

tests/python/pants_test/backend/codegen/tasks/test_ragel_gen.py

@@ -94,7 +94,6 @@ def test_ragel_gen(self):
     task = self.create_task(self.context(target_roots=[target]))
 
     task._ragel_binary = 'ragel'
-    task.invalidate_for_files = lambda: []
     task._java_out = self.task_outdir
 
     sources = [os.path.join(self.task_outdir, 'com/example/atoi/Parser.java')]