Follow-up options/documentation changes after scala removed from BUIL…

…D.tools

* Allow users to specify the runtime spec if they are specifying a custom scala version.
* Add deprecation warning for runtime option

Testing Done:
travis is green https://travis-ci.org/pantsbuild/pants/builds/100450093

http://ec2-54-146-169-50.compute-1.amazonaws.com:8080/job/pants_ci_trigger/52/
http://ec2-54-146-169-50.compute-1.amazonaws.com:8080/job/pants_ci_trigger/60/console

Bugs closed: 2773

Reviewed at https://rbcommons.com/s/twitter/r/3302/

migrations/options/src/python/migrate_config.py

@@ -318,6 +318,7 @@
   ('resolve.ivy', 'nailgun-server'): None,
   ('resolve.ivy', 'xalan'): None,
   ('scala-platform', 'scalac'): None,
+  ('scala-platform', 'runtime'): None,
   ('test.junit', 'cobertura-instrument'): None,
   ('test.junit', 'cobertura-report'): None,
   ('test.junit', 'cobertura-run'): None,
@@ -395,6 +396,11 @@
                    'limit the number of overrides by inverting the default with a DEFAULT section '
                    'value of False.')
 
+scala_buildtools_defaults = ('Scala runtime is now determined based on the version specified. '
+                             'Pants will use a default minor version based on the major version '
+                             'specified eg: 2.10.  If custom is specified then the full version '
+                             'may be defined in the spec provided in option --runtime-spec ')
+
 scrooge_gen_deps_note = ('The scrooge-gen per-language config fields have been refactored into '
                          'two options: one for service deps, and one for structs deps.')
 compile_jar_note = ('The isolated jvm compile `jar` option is critical to performant operation '
@@ -557,6 +563,7 @@
   ('resolve.ivy', 'nailgun-server'): jvm_tool_spec_override,
   ('resolve.ivy', 'xalan'): jvm_tool_spec_override,
   ('scala-platform', 'scalac'): jvm_tool_spec_override,
+  ('scala-platform', 'runtime'): scala_buildtools_defaults,
   ('test.junit', 'cobertura-instrument'): jvm_tool_spec_override,
   ('test.junit', 'cobertura-report'): jvm_tool_spec_override,
   ('test.junit', 'cobertura-run'): jvm_tool_spec_override,

src/python/pants/backend/jvm/subsystems/scala_platform.py

@@ -12,6 +12,7 @@
 from pants.backend.jvm.targets.jar_dependency import JarDependency
 from pants.backend.jvm.targets.jar_library import JarLibrary
 from pants.build_graph.address import Address
+from pants.option.custom_types import list_option
 from pants.subsystem.subsystem import Subsystem
 
 
@@ -47,13 +48,26 @@ class ScalaPlatform(JvmToolMixin, ZincLanguageMixin, Subsystem):
   @classmethod
   def register_options(cls, register):
     super(ScalaPlatform, cls).register_options(register)
-    # Version specified will allow the user provide some sane defaults for common
-    # versions of scala. If version is something other than one of the common
-    # versions the user will be able to override the defaults by specifying
-    # custom build targets for //:scalac and //:scala-library
     register('--version', advanced=True, default='2.10', choices=['2.10', '2.11', 'custom'],
              help='The scala "platform version", which is suffixed onto all published '
-                  'libraries. This should match the declared compiler/library versions.')
+                  'libraries. This should match the declared compiler/library versions. '
+                  'Version specified will allow the user provide some sane defaults for common '
+                  'versions of scala. If version is something other than one of the common '
+                  'versions the user will be able to override the defaults by specifying '
+                  '"custom" as the --version, custom build targets can be specified in the targets '
+                  'for //:scalac and //:scala-library ')
+
+    register('--runtime', advanced=True, type=list_option, default=['//:scala-library'],
+             help='Target specs pointing to the scala runtime libraries.',
+             deprecated_version='0.0.75',
+             deprecated_hint='Option is no longer used, --version is used to specify the major '
+                             'version. The runtime is created based on major version. '
+                             'The runtime target will be defined at the address //:scala-library '
+                             'unless it is overriden by the option --runtime-spec and a --version '
+                             'is set to custom.')
+
+    register('--runtime-spec', advanced=True, default='//:scala-library',
+             help='Address to be used for custom scala runtime.')
 
     # Scala 2.10
     cls.register_jvm_tool(register,
@@ -150,8 +164,12 @@ def runtime(self):
     """Return the proper runtime based on scala version.
     :return iterator: list with single runtime.
     """
-    runtime_name = scala_build_info.get(self._get_label()).runtime_name
-    return [getattr(self, runtime_name)]
+    # If the version is custom allow the user the option to set the spec.
+    if self._get_label() == 'custom':
+      return self.get_options().runtime_spec
+    else:
+      runtime_name = scala_build_info.get(self._get_label()).runtime_name
+      return [getattr(self, runtime_name)]
 
   @classmethod
   def _synthetic_runtime_target(cls, buildgraph):