Allow targets to have sensible defaults for sources=.

95% of the time, a java_library() target will have
sources=globs('*.java'), and it seems unnecessary to require this
boilerplate to be repeated everywhere.

This change provides a way for target to say "if no explicit sources
are specified, use this glob".

The change is gated behind an option, because it can have unintended
consequences.  For example, in the Pants codebase itself we had a few
places where we were using a python_library() with no sources as a
dependency aggregator, when we should have been using a target().

This change fixes such quirks in our own codebase.

It also modifies a couple of our example targets to take advantage
of this functionality, as proof-of-concept.

This change required modifying quite a few tests that were creating
library targets with no sources: These tests didn't init the relevant
subsystem, and so couldn't consult the new option to see what to do
when no sources= were provided.  These tests were fixed in one of
two ways: either by initializing the subsystem, or by providing
explicit sources=[], whichever made more sense.

Note that instead of creating a new subsystem, I added this option
to the Target.UnknownArguments subsystem.  This implied an expanded
role for that subsystem, so its name was no longer applicable.
I renamed it to Target.Arguments, and deprecated its scope.

Finally, note that the defaults for library and test targets make
it easy to have tests live side-by-side with the code they test,
instead of in a separate source tree, which is a really useful
idiom IMO.

Testing Done:
CI passes: https://travis-ci.org/pantsbuild/pants/builds/168486240

Reviewed at https://rbcommons.com/s/twitter/r/4300/

contrib/findbugs/tests/java/org/pantsbuild/contrib/findbugs/BUILD

@@ -27,11 +27,21 @@ java_library(
 )
 
 java_library(
+  name='no_sources',
+  sources=[],
+  dependencies=[
+    ':low',
+    ':normal',
+    ':high',
+  ]
+)
+
+target(
   name='all',
   dependencies=[
     ':none',
     ':low',
     ':normal',
-    ':high'
+    ':high',
   ]
 )

contrib/findbugs/tests/python/pants_test/contrib/findbugs/tasks/test_findbugs_integration.py

@@ -119,7 +119,7 @@ def test_error(self):
     self.assertIn('Bugs: 1 (High: 1, Normal: 0, Low: 0)', pants_run.stdout_data)
 
   def test_transitive(self):
-    cmd = ['compile', 'contrib/findbugs/tests/java/org/pantsbuild/contrib/findbugs:all']
+    cmd = ['compile', 'contrib/findbugs/tests/java/org/pantsbuild/contrib/findbugs:no_sources']
     pants_ini_config = {'compile.findbugs': {'transitive': False}}
     pants_run = self.run_pants(cmd, config=pants_ini_config)
     self.assert_success(pants_run)

contrib/go/src/python/pants/contrib/go/targets/go_library.py

@@ -11,6 +11,8 @@
 class GoLibrary(GoLocalSource):
   """A local Go package."""
 
+  default_sources_globs = '*.go'
+
   @classmethod
   def alias(cls):
     return 'go_library'

examples/src/java/org/pantsbuild/example/hello/greet/BUILD

@@ -3,10 +3,11 @@
 
 # Note that the target has no explicit name, so it defaults to the name
 # of the directory, in this case 'greet'.
+# It also has no explicit sources, so it defaults to the sources implied
+# by the target type, in this case "globs('*.java')".
 java_library(
   dependencies = [], # A more realistic example would depend on other libs,
                      # but this "hello world" is pretty simple.
-  sources = globs('*.java'),
   provides = artifact(org='org.pantsbuild.example',
                       name='hello-greet',
                       repo=public,),

examples/src/python/example/hello/greet/BUILD

@@ -1,9 +1,13 @@
 # Copyright 2014 Pants project contributors (see CONTRIBUTORS.md).
 # Licensed under the Apache License, Version 2.0 (see LICENSE).
 
+
+# Note that the target has no explicit name, so it defaults to the name
+# of the directory, in this case 'greet'.
+# It also has no explicit sources, so it defaults to the sources implied
+# by the target type, in this case "globs('*.py')".
 python_library(
   dependencies=[
     '3rdparty/python:ansicolors',
   ],
-  sources=globs('*.py'),
 )

migrations/options/src/python/migrate_config.py

@@ -18,6 +18,8 @@
   # E.g.:
   #('backends', 'packages'): ('DEFAULT', 'backend_packages'),
   #('unknown-arguments', 'ignored'): None,
+
+  ('unknown-arguments', 'ignored'): ('target-arguments', 'ignored'),
 }
 
 

pants.ini

@@ -58,9 +58,14 @@ pants_ignore: +[
   ]
 
 
+[target-arguments]
+implicit_sources: True
+
+
 [jvm]
 options: ["-Xmx1g", "-XX:MaxPermSize=256m"]
 
+
 [cache]
 # Caching is on globally by default, but we disable it here for development purposes.
 # It is explicitly re-enabled below for [cache.bootstrap] only.
@@ -262,14 +267,17 @@ resolver_cache_dir: %(pants_bootstrapdir)s/python_cache/requirements
 # You can change this to point to a config.ini holding the definition of your keys.
 keystore_config_location: %(pants_configdir)s/android/keystore/default_config.ini
 
+
 [test.pytest]
 timeouts: true
 timeout_default: 60
 
+
 [test.junit]
 timeouts: true
 timeout_default: 60
 
+
 [buildgen.go]
 materialize: True
 remote: True

src/docs/first_tutorial.md

@@ -272,10 +272,12 @@ Here, `java_library` is the target's *type*. Different target types
 support different arguments. The following arguments are pretty common:
 
 **name**<br>
-We use a target's name to refer to the target. This argument isn't just
-"pretty common," it's required. You use names on the command line to
-specify which targets to operate on. You also use names in `BUILD` files
-when one target refers to another, e.g. in `dependencies`:
+We use a target's name to refer to the target. If you omit the name,
+it defaults to the name of the directory the `BUILD` file is in.
+
+You use names on the command line to specify which targets to operate on.
+You also use names in `BUILD` files when one target refers to another,
+e.g. in `dependencies`:
 
 **dependencies**<br>
 List of things this target depends upon. If this target's code imports
@@ -284,7 +286,21 @@ target imports code that "lives" in `.jar`s/`.egg`s from elsewhere,
 refer to them here.
 
 **sources**<br>
-List of source files. The `globs` function is handy here.
+List of source files, which must be under the directory tree rooted
+at the BUILD file's directory.
+
+You can provide an explicit list, e.g.,
+`sources=['Foo.java', 'Bar.java']`, or use the `globs` function
+to glob over files, e.g., `sources=globs('*.java')`. Similarly,
+`rglobs` will apply the glob pattern recursively in all subdirectories
+of the BUILD file's directory.
+
+If you omit `sources` in a target, Pants will attempt to apply a
+sensible default that depends on the target type.
+E.g., `junit_tests` will default to globbing over `*Test.java`,
+`java_library` will default to globbing over `*.java`, minus the
+test files, and so on.
+
 
 The Usual Commands
 ------------------

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

@@ -1,7 +1,7 @@
 # Copyright 2014 Pants project contributors (see CONTRIBUTORS.md).
 # Licensed under the Apache License, Version 2.0 (see LICENSE).
 
-python_library(
+target(
   name = 'all',
   dependencies = [
     ':antlr_gen',

src/python/pants/backend/jvm/targets/BUILD

@@ -1,5 +1,5 @@
 
-python_library(
+target(
   name = 'all',
   dependencies = [
     ':jvm',
@@ -77,6 +77,7 @@ python_library(
   ],
   dependencies = [
     '3rdparty/python/twitter/commons:twitter.common.collections',
+    ':java',  # For a dep on java_tests.py, which we might want to move to a separate target.
     ':jvm',
     'src/python/pants/backend/jvm/subsystems:scala_platform',
     'src/python/pants/base:exceptions',

src/python/pants/backend/jvm/targets/java_library.py

@@ -6,6 +6,7 @@
                         unicode_literals, with_statement)
 
 from pants.backend.jvm.targets.exportable_jvm_library import ExportableJvmLibrary
+from pants.backend.jvm.targets.java_tests import JavaTests
 
 
 class JavaLibrary(ExportableJvmLibrary):
@@ -20,6 +21,9 @@ class JavaLibrary(ExportableJvmLibrary):
   :API: public
   """
 
+  default_sources_globs = '*.java'
+  default_sources_exclude_globs = JavaTests.java_test_globs
+
   @classmethod
   def subsystems(cls):
     return super(JavaLibrary, cls).subsystems()

src/python/pants/backend/jvm/targets/java_tests.py

@@ -13,12 +13,18 @@
 from pants.base.payload_field import PrimitiveField
 
 
+# TODO: Rename this to JUnitTests.  It isn't just for Java language tests.
 class JavaTests(JvmTarget):
   """JUnit tests.
 
   :API: public
   """
 
+  java_test_globs = ('*Test.java',)
+  scala_test_globs = ('*Test.scala', '*Spec.scala')
+
+  default_sources_globs = java_test_globs + scala_test_globs
+
   CONCURRENCY_SERIAL = 'SERIAL'
   CONCURRENCY_PARALLEL_CLASSES = 'PARALLEL_CLASSES'
   CONCURRENCY_PARALLEL_METHODS = 'PARALLEL_METHODS'

src/python/pants/backend/jvm/targets/scala_library.py

@@ -7,6 +7,7 @@
 
 from pants.backend.jvm.subsystems.scala_platform import ScalaPlatform
 from pants.backend.jvm.targets.exportable_jvm_library import ExportableJvmLibrary
+from pants.backend.jvm.targets.java_tests import JavaTests
 from pants.base.exceptions import TargetDefinitionException
 from pants.build_graph.address import Address
 
@@ -23,6 +24,9 @@ class ScalaLibrary(ExportableJvmLibrary):
   :API: public
   """
 
+  default_sources_globs = '*.scala'
+  default_sources_exclude_globs = JavaTests.scala_test_globs
+
   @classmethod
   def subsystems(cls):
     return super(ScalaLibrary, cls).subsystems() + (ScalaPlatform, )

src/python/pants/backend/jvm/tasks/BUILD

@@ -1,7 +1,7 @@
 # Copyright 2016 Pants project contributors (see CONTRIBUTORS.md).
 # Licensed under the Apache License, Version 2.0 (see LICENSE).
 
-python_library(
+target(
   name = 'all',
   dependencies = [
     ':benchmark_run',

src/python/pants/backend/project_info/tasks/BUILD

@@ -1,7 +1,7 @@
 # Copyright 2015 Pants project contributors (see CONTRIBUTORS.md).
 # Licensed under the Apache License, Version 2.0 (see LICENSE).
 
-python_library(
+target(
   name = 'all',
   dependencies = [
     ':dependencies',

src/python/pants/backend/python/targets/python_library.py

@@ -6,11 +6,14 @@
                         unicode_literals, with_statement)
 
 from pants.backend.python.targets.python_target import PythonTarget
+from pants.backend.python.targets.python_tests import PythonTests
 
 
 class PythonLibrary(PythonTarget):
   """A Python library.
 
   :API: public
   """
-  pass
+
+  default_sources_globs = '*.py'
+  default_sources_exclude_globs = PythonTests.default_sources_globs

src/python/pants/backend/python/targets/python_tests.py

@@ -16,6 +16,9 @@ class PythonTests(PythonTarget):
   :API: public
   """
 
+  # These are the patterns matched by pytest's test discovery.
+  default_sources_globs = ('test_*.py', '*_test.py')
+
   def __init__(self, coverage=None, timeout=None, **kwargs):
     """
     :param coverage: the module(s) whose coverage should be generated, e.g.