Fix native tasks.

Running a `./pants lint` across the whole repo revealed an issue
accessing a non-existant `self.linker.platform` attribute in
`LinkSharedLibraries`. Add basic unit tests to exercise task execution
with a full cache miss and then a full hit.

src/python/pants/backend/native/tasks/link_shared_libraries.py

@@ -63,6 +63,10 @@ def _toolchain(self):
   def linker(self):
     return self._request_single(Linker, self._toolchain)
 
+  @memoized_property
+  def platform(self):
+    return Platform.create()
+
   def _retrieve_single_product_at_target_base(self, product_mapping, target):
     self.context.log.debug("product_mapping: {}".format(product_mapping))
     self.context.log.debug("target: {}".format(target))
@@ -105,7 +109,7 @@ def execute(self):
   def _retrieve_shared_lib_from_cache(self, vt):
     native_artifact = vt.target.ctypes_native_library
     path_to_cached_lib = os.path.join(
-      vt.results_dir, native_artifact.as_shared_lib(self.linker.platform))
+      vt.results_dir, native_artifact.as_shared_lib(self.platform))
     if not os.path.isfile(path_to_cached_lib):
       raise self.LinkSharedLibrariesError("The shared library at {} does not exist!"
                                           .format(path_to_cached_lib))
@@ -137,8 +141,8 @@ def _make_link_request(self, vt, compiled_objects_product, native_target_deps_pr
     'linux': lambda: ['-shared'],
   }
 
-  def _get_shared_lib_cmdline_args(self, platform):
-    return platform.resolve_platform_specific(self._SHARED_CMDLINE_ARGS)
+  def _get_shared_lib_cmdline_args(self):
+    return self.platform.resolve_platform_specific(self._SHARED_CMDLINE_ARGS)
 
   def _execute_link_request(self, link_request):
     object_files = link_request.object_files
@@ -147,14 +151,14 @@ def _execute_link_request(self, link_request):
       raise self.LinkSharedLibrariesError("No object files were provided in request {}!"
                                           .format(link_request))
 
-    platform = Platform.create()
     linker = link_request.linker
     native_artifact = link_request.native_artifact
     output_dir = link_request.output_dir
-    resulting_shared_lib_path = os.path.join(output_dir, native_artifact.as_shared_lib(platform))
+    resulting_shared_lib_path = os.path.join(output_dir,
+                                             native_artifact.as_shared_lib(self.platform))
     # We are executing in the results_dir, so get absolute paths for everything.
     cmd = ([linker.exe_filename] +
-           self._get_shared_lib_cmdline_args(platform) +
+           self._get_shared_lib_cmdline_args() +
            ['-o', os.path.abspath(resulting_shared_lib_path)] +
            [os.path.abspath(obj) for obj in object_files])
 
@@ -166,7 +170,7 @@ def _execute_link_request(self, link_request):
           cwd=output_dir,
           stdout=workunit.output('stdout'),
           stderr=workunit.output('stderr'),
-          env=linker.get_invocation_environment_dict(platform))
+          env=linker.get_invocation_environment_dict(self.platform))
       except OSError as e:
         workunit.set_outcome(WorkUnit.FAILURE)
         raise self.LinkSharedLibrariesError(

src/python/pants/backend/native/tasks/native_compile.py

@@ -12,6 +12,7 @@
 from pants.backend.native.config.environment import Executable, Platform
 from pants.backend.native.targets.native_library import NativeLibrary
 from pants.backend.native.tasks.native_task import NativeTask
+from pants.base.build_environment import get_buildroot
 from pants.base.exceptions import TaskError
 from pants.base.workunit import WorkUnit, WorkUnitLabel
 from pants.build_graph.dependency_context import DependencyContext
@@ -134,7 +135,7 @@ def execute(self):
   # This may be calculated many times for a target, so we memoize it.
   @memoized_method
   def _include_dirs_for_target(self, target):
-    return target.sources_relative_to_target_base().rel_root
+    return os.path.join(get_buildroot(), target.target_base)
 
   class NativeSourcesByType(datatype(['rel_root', 'headers', 'sources'])): pass
 
@@ -168,7 +169,7 @@ def get_sources_headers_for_target(self, target):
         "Conflicting filenames:\n{}"
         .format(target.address.spec, target.alias(), '\n'.join(duplicate_filename_err_msgs)))
 
-    return [os.path.join(rel_root, src) for src in target_relative_sources]
+    return [os.path.join(get_buildroot(), rel_root, src) for src in target_relative_sources]
 
   # FIXME(#5951): expand `Executable` to cover argv generation (where an `Executable` is subclassed
   # to modify or extend the argument list, as declaratively as possible) to remove
@@ -266,7 +267,7 @@ def _compile(self, compile_request):
         workunit.set_outcome(WorkUnit.FAILURE)
         raise self.NativeCompileError(
           "Error in '{section_name}' with command {cmd} for request {req}. Exit code was: {rc}."
-          .format(section_name=self.workunit_name, cmd=argv, req=compile_request, rc=rc))
+          .format(section_name=self.workunit_label, cmd=argv, req=compile_request, rc=rc))
 
   def collect_cached_objects(self, versioned_target):
     """Scan `versioned_target`'s results directory and return the output files from that directory.

tests/python/pants_test/backend/native/tasks/BUILD

@@ -0,0 +1,18 @@
+python_tests(
+  dependencies=[
+    ':native_task_test_base',
+    'src/python/pants/backend/native/targets',
+    'src/python/pants/backend/native/tasks',
+  ],
+  tags={'platform_specific_behavior'},
+)
+
+python_library(
+  name='native_task_test_base',
+  sources=['native_task_test_base.py'],
+  dependencies=[
+    'src/python/pants/backend/native',
+    'src/python/pants/backend/native/targets',
+    'tests/python/pants_test:task_test_base',
+  ],
+)

tests/python/pants_test/backend/native/tasks/native_task_test_base.py

@@ -0,0 +1,45 @@
+# coding=utf-8
+# Copyright 2018 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+from __future__ import absolute_import, division, print_function, unicode_literals
+
+from textwrap import dedent
+
+from pants.backend.native import register
+from pants.backend.native.targets.native_library import CppLibrary
+from pants_test.task_test_base import TaskTestBase
+
+
+class NativeTaskTestBase(TaskTestBase):
+
+  @classmethod
+  def rules(cls):
+    return super(NativeTaskTestBase, cls).rules() + register.rules()
+
+  def create_simple_cpp_library(self, **kwargs):
+    self.create_file('src/cpp/test/test.hpp', contents=dedent("""
+      #ifndef __TEST_HPP__
+      #define __TEST_HPP__
+      
+      int test(int);
+      
+      extern "C" int test_exported(int);
+      
+      #endif
+    """))
+    self.create_file('src/cpp/test/test.cpp', contents=dedent("""
+      #include "test.hpp"
+      
+      int test(int x) {
+        return x / 137;
+      }
+      
+      extern "C" int test_exported(int x) {
+        return test(x * 42);
+      }
+    """))
+    return self.make_target(spec='src/cpp/test',
+                            target_type=CppLibrary,
+                            sources=['test.hpp', 'test.cpp'],
+                            **kwargs)

tests/python/pants_test/backend/native/tasks/test_cpp_compile.py

@@ -0,0 +1,22 @@
+# coding=utf-8
+# Copyright 2018 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+from __future__ import absolute_import, division, print_function, unicode_literals
+
+from pants.backend.native.tasks.cpp_compile import CppCompile
+from pants_test.backend.native.tasks.native_task_test_base import NativeTaskTestBase
+
+
+class CppCompileTest(NativeTaskTestBase):
+  @classmethod
+  def task_type(cls):
+    return CppCompile
+
+  def test_caching(self):
+    cpp = self.create_simple_cpp_library()
+    context = self.context(target_roots=[cpp])
+
+    cpp_compile = self.create_task(context)
+    cpp_compile.execute()
+    cpp_compile.execute()

tests/python/pants_test/backend/native/tasks/test_link_shared_libraries.py

@@ -0,0 +1,31 @@
+# coding=utf-8
+# Copyright 2018 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+from __future__ import absolute_import, division, print_function, unicode_literals
+
+import os
+
+from pants.backend.native.targets.native_artifact import NativeArtifact
+from pants.backend.native.tasks.cpp_compile import CppCompile
+from pants.backend.native.tasks.link_shared_libraries import LinkSharedLibraries
+from pants_test.backend.native.tasks.native_task_test_base import NativeTaskTestBase
+
+
+class LinkSharedLibrariesTest(NativeTaskTestBase):
+  @classmethod
+  def task_type(cls):
+    return LinkSharedLibraries
+
+  def test_caching(self):
+    cpp = self. create_simple_cpp_library(ctypes_native_library=NativeArtifact(lib_name='test'),)
+
+    cpp_compile_task_type = self.synthesize_task_subtype(CppCompile, 'cpp_compile_scope')
+    context = self.context(target_roots=[cpp], for_task_types=[cpp_compile_task_type])
+
+    cpp_compile = cpp_compile_task_type(context, os.path.join(self.pants_workdir, 'cpp_compile'))
+    cpp_compile.execute()
+
+    link_shared_libraries = self.create_task(context)
+    link_shared_libraries.execute()
+    link_shared_libraries.execute()

tests/python/pants_test/test_base.py

@@ -268,10 +268,16 @@ def alias_groups(cls):
     """
     return BuildFileAliases(targets={'target': Target})
 
+  @classmethod
+  def rules(cls):
+    # Required for sources_for:
+    return [RootRule(SourcesField)]
+
   @classmethod
   def build_config(cls):
     build_config = BuildConfiguration()
     build_config.register_aliases(cls.alias_groups())
+    build_config.register_rules(cls.rules())
     return build_config
 
   def setUp(self):
@@ -368,8 +374,7 @@ def _init_engine(cls):
       native=init_native(),
       build_configuration=cls.build_config(),
       build_ignore_patterns=None,
-      # Required for sources_for:
-      rules=[RootRule(SourcesField)],
+      rules=cls.build_config().rules(),
     ).new_session()
     cls._scheduler = graph_session.scheduler_session
     cls._build_graph, cls._address_mapper = graph_session.create_build_graph(