first implement v1 of robot impl (pantsbuild#8793)

See pex-tool/pex#789 for a description of the issue, and https://docs.google.com/document/d/1B_g0Ofs8aQsJtrePPR1PCtSAKgBG1o59AhS_NwfFnbI/edit for a google doc with pros and cons of different approaches.

@jsirois was extremely helpful throughout the development of this feature, and pex-tool/pex#819 and pex-tool/pex#821 in pex `2.0.3` will help to optimize several other aspects of this process when we can unrevert pantsbuild#8787.

**Note:** `src/python/pants/backend/python/subsystems/pex_build_util.py` was removed in this PR, along with all floating references to it.

With `--binary-py-generate-ipex`, a `.ipex` file will be created when `./pants binary` is run against a `python_binary()` target. This `.ipex` archive will create a `.pex` file and run it when first executed. The `.ipex` archive contains:
- in `IPEX-INFO`: the source files to inject into the resulting `.pex`, and pypi indices to resolve requirements from.
- in `BOOSTRAP-PEX-INFO`: the `PEX-INFO` of the pex file that *would* have been generated if `--generate-ipex` was False.
- in `ipex.py`: A bootstrap script which will generate a `.pex` file when the `.ipex` file is first executed.

For a `.ipex` file which hydrates the `tensorflow==1.14.0` dependency when it is first run, this translates to a >100x decrease in file size:
```bash
X> ls dist
total 145M
-rwxr-xr-x 1 dmcclanahan staff 267k Dec 10 21:11 dehydrated.ipex*
-rwxr-xr-x 1 dmcclanahan staff 134M Dec 10 21:11 dehydrated.pex*
```

contrib/python/src/python/pants/contrib/python/checks/tasks/checkstyle/checkstyle.py

@@ -7,7 +7,7 @@
 from packaging import version
 from pants.backend.python.interpreter_cache import PythonInterpreterCache
 from pants.backend.python.python_requirement import PythonRequirement
-from pants.backend.python.subsystems.pex_build_util import PexBuilderWrapper
+from pants.python.pex_build_util import PexBuilderWrapper
 from pants.backend.python.subsystems.python_setup import PythonSetup
 from pants.backend.python.targets.python_requirement_library import PythonRequirementLibrary
 from pants.backend.python.targets.python_target import PythonTarget

contrib/python/src/python/pants/contrib/python/checks/tasks/python_eval.py

@@ -6,9 +6,6 @@
 import pkgutil
 
 from pants.backend.python.interpreter_cache import PythonInterpreterCache
-from pants.backend.python.subsystems.pex_build_util import (PexBuilderWrapper,
-                                                            has_python_requirements,
-                                                            has_python_sources)
 from pants.backend.python.targets.python_binary import PythonBinary
 from pants.backend.python.targets.python_library import PythonLibrary
 from pants.backend.python.targets.python_target import PythonTarget
@@ -17,6 +14,11 @@
 from pants.base.exceptions import TaskError
 from pants.base.generator import Generator, TemplateData
 from pants.base.workunit import WorkUnit, WorkUnitLabel
+from pants.python.pex_build_util import (
+    PexBuilderWrapper,
+    has_python_requirements,
+    has_python_sources,
+)
 from pants.task.lint_task_mixin import LintTaskMixin
 from pants.util.dirutil import safe_concurrent_creation, safe_mkdir
 from pants.util.memo import memoized_property

contrib/python/tests/python/pants_test/contrib/python/checks/tasks/checkstyle/test_checkstyle.py

@@ -12,7 +12,7 @@
 from pants.backend.python.targets.python_library import PythonLibrary
 from pants.base.build_environment import get_buildroot
 from pants.base.exceptions import TaskError
-from pants.python.python_repos import PythonRepos
+from pants.backend.python.subsystems.python_repos import PythonRepos
 from pants.util.contextutil import environment_as
 from pants.util.dirutil import safe_mkdtemp, safe_rmtree
 from pants_test.backend.python.tasks.python_task_test_base import PythonTaskTestBase

contrib/python/tests/python/pants_test/contrib/python/checks/tasks/test_python_eval.py

@@ -4,7 +4,7 @@
 from textwrap import dedent
 
 from pants.backend.python.subsystems.python_setup import PythonSetup
-from pants.python.python_repos import PythonRepos
+from pants.backend.python.subsystems.python_repos import PythonRepos
 from pants_test.backend.python.tasks.python_task_test_base import PythonTaskTestBase
 
 from pants.contrib.python.checks.tasks.python_eval import PythonEval

examples/3rdparty/python/BUILD

@@ -33,3 +33,8 @@ unpacked_whls(
   ],
   within_data_subdir='purelib/tensorflow',
 )
+
+files(
+  name='examples_python_3rdparty',
+  sources=['**/*'],
+)

examples/src/python/example/tensorflow_custom_op/BUILD

@@ -37,3 +37,21 @@ ctypes_compatible_cpp_library(
   ],
   ctypes_native_library=native_artifact(lib_name='tensorflow-zero-out-operator'),
 )
+
+
+python_binary(
+  name='show-tf-version',
+  source='show_tf_version.py',
+  dependencies=[
+    'examples/3rdparty/python:tensorflow',
+  ],
+  compatibility=['CPython>=3.6,<4'],
+)
+
+files(
+  name='show-tf-version-files',
+  sources=['**/*'],
+  dependencies=[
+    'examples/3rdparty/python:examples_python_3rdparty',
+  ],
+)

examples/src/python/example/tensorflow_custom_op/show_tf_version.py

@@ -0,0 +1,6 @@
+# Copyright 2019 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+import tensorflow as tf
+
+print(f"tf version: {tf.__version__}")

src/python/pants/backend/codegen/grpcio/python/grpcio_run.py

@@ -7,7 +7,7 @@
 
 from pants.backend.codegen.grpcio.python.grpcio_prep import GrpcioPrep
 from pants.backend.codegen.grpcio.python.python_grpcio_library import PythonGrpcioLibrary
-from pants.backend.python.subsystems.pex_build_util import identify_missing_init_files
+from pants.python.pex_build_util import identify_missing_init_files
 from pants.backend.python.targets.python_library import PythonLibrary
 from pants.base.build_environment import get_buildroot
 from pants.base.exceptions import TaskError

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

@@ -20,7 +20,6 @@
 from pants.backend.jvm.tasks.ivy_task_mixin import IvyTaskMixin
 from pants.backend.project_info.tasks.export_version import DEFAULT_EXPORT_VERSION
 from pants.backend.python.interpreter_cache import PythonInterpreterCache
-from pants.backend.python.subsystems.pex_build_util import has_python_requirements
 from pants.backend.python.targets.python_requirement_library import PythonRequirementLibrary
 from pants.backend.python.targets.python_target import PythonTarget
 from pants.backend.python.targets.python_tests import PythonTests
@@ -34,6 +33,7 @@
 from pants.java.distribution.distribution import DistributionLocator
 from pants.java.executor import SubprocessExecutor
 from pants.java.jar.jar_dependency_utils import M2Coordinate
+from pants.python.pex_build_util import has_python_requirements
 from pants.task.console_task import ConsoleTask
 from pants.util.memo import memoized_property
 

src/python/pants/backend/python/register.py

@@ -45,10 +45,15 @@
 from pants.build_graph.build_file_aliases import BuildFileAliases
 from pants.build_graph.resources import Resources
 from pants.goal.task_registrar import TaskRegistrar as task
+from pants.python.pex_build_util import PexBuilderWrapper
 
 
 def global_subsystems():
-  return python_native_code.PythonNativeCode, subprocess_environment.SubprocessEnvironment
+  return {
+    python_native_code.PythonNativeCode,
+    subprocess_environment.SubprocessEnvironment,
+    PexBuilderWrapper.Factory,
+  }
 
 
 def build_file_aliases():

src/python/pants/backend/python/rules/BUILD

@@ -6,6 +6,7 @@ python_library(
     '3rdparty/python:dataclasses',
     '3rdparty/python:setuptools',
     'src/python/pants/backend/python/subsystems',
+    'src/python/pants/backend/python/subsystems/ipex',
     'src/python/pants/build_graph',
     'src/python/pants/engine/legacy:graph',
     'src/python/pants/engine:build_files',

src/python/pants/backend/python/rules/inject_init.py

@@ -3,7 +3,7 @@
 
 from dataclasses import dataclass
 
-from pants.backend.python.subsystems.pex_build_util import identify_missing_init_files
+from pants.python.pex_build_util import identify_missing_init_files
 from pants.engine.fs import EMPTY_DIRECTORY_DIGEST, Digest, Snapshot
 from pants.engine.isolated_process import ExecuteProcessRequest, ExecuteProcessResult
 from pants.engine.rules import rule

src/python/pants/backend/python/subsystems/executable_pex_tool.py

@@ -7,7 +7,7 @@
 from pex.pex_builder import PEXBuilder
 from pex.pex_info import PexInfo
 
-from pants.backend.python.subsystems.pex_build_util import PexBuilderWrapper
+from pants.python.pex_build_util import PexBuilderWrapper
 from pants.subsystem.subsystem import Subsystem
 from pants.util.dirutil import is_executable, safe_concurrent_creation
 

src/python/pants/backend/python/subsystems/ipex/BUILD

@@ -0,0 +1,7 @@
+# Copyright 2019 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+# NB: This target is written into an .ipex file as the main script, and should not have any
+# dependencies on another python code! .ipex files should always contain pex and setuptools
+# requirements in order to run the main script!
+python_library()

src/python/pants/backend/python/subsystems/ipex/ipex_launcher.py

@@ -0,0 +1,131 @@
+# Copyright 2019 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+"""Entrypoint script for a "dehydrated" .ipex file generated with --generate-ipex.
+
+This script will "hydrate" a normal .pex file in the same directory, then execute it.
+"""
+
+import json
+import os
+import sys
+import tempfile
+
+from pex import resolver
+from pex.common import open_zip
+from pex.fetcher import Fetcher, PyPIFetcher
+from pex.interpreter import PythonInterpreter
+from pex.pex_builder import PEXBuilder
+from pex.pex_info import PexInfo
+from pkg_resources import Requirement
+
+
+APP_CODE_PREFIX = 'user_files/'
+
+
+def _strip_app_code_prefix(path):
+  if not path.startswith(APP_CODE_PREFIX):
+    raise ValueError("Path {path} in IPEX-INFO did not begin with '{APP_CODE_PREFIX}'."
+                     .format(path=path, APP_CODE_PREFIX=APP_CODE_PREFIX))
+  return path[len(APP_CODE_PREFIX):]
+
+
+def _log(message):
+  sys.stderr.write(message + '\n')
+
+
+def _sanitize_requirements(requirements):
+  """
+  Remove duplicate keys such as setuptools or pex which may be injected multiple times into the
+  resulting ipex when first executed.
+  """
+  project_names = []
+  new_requirements = {}
+
+  for r in requirements:
+    r = Requirement(r)
+    if r.marker and not r.marker.evaluate():
+      continue
+    if r.name not in new_requirements:
+      project_names.append(r.name)
+      new_requirements[r.name] = str(r)
+  sanitized_requirements = [new_requirements[n] for n in project_names]
+
+  return sanitized_requirements
+
+
+def modify_pex_info(pex_info, **kwargs):
+  new_info = json.loads(pex_info.dump())
+  new_info.update(kwargs)
+  return PexInfo.from_json(json.dumps(new_info))
+
+
+def _hydrate_pex_file(self, hydrated_pex_file):
+  # We extract source files into a temporary directory before creating the pex.
+  td = tempfile.mkdtemp()
+
+  with open_zip(self) as zf:
+    # Populate the pex with the pinned requirements and distribution names & hashes.
+    bootstrap_info = PexInfo.from_json(zf.read('BOOTSTRAP-PEX-INFO'))
+    bootstrap_builder = PEXBuilder(pex_info=bootstrap_info, interpreter=PythonInterpreter.get())
+
+    # Populate the pex with the needed code.
+    try:
+      ipex_info = json.loads(zf.read('IPEX-INFO').decode('utf-8'))
+      for path in ipex_info['code']:
+        unzipped_source = zf.extract(path, td)
+        bootstrap_builder.add_source(unzipped_source, env_filename=_strip_app_code_prefix(path))
+    except Exception as e:
+      raise ValueError("Error: {e}. The IPEX-INFO for this .ipex file was:\n{info}"
+                       .format(e=e, info=json.dumps(ipex_info, indent=4)))
+
+  # Perform a fully pinned intransitive resolve to hydrate the install cache.
+  resolver_settings = ipex_info['resolver_settings']
+  # TODO: Here we convert .indexes and .find_links into the old .fetchers until pants upgrades to
+  # pex 2.0. At that time, we can remove anything relating to fetchers from `resolver_settings`, and
+  # avoid removing the 'indexes' and 'find_links' keys, which are correct for pex 2.0.
+  fetchers = [PyPIFetcher(url) for url in resolver_settings.pop('indexes')]
+  fetchers.extend(Fetcher([url]) for url in resolver_settings.pop('find_links'))
+  resolver_settings['fetchers'] = fetchers
+
+  sanitized_requirements = _sanitize_requirements(bootstrap_info.requirements)
+  bootstrap_info = modify_pex_info(bootstrap_info, requirements=sanitized_requirements)
+  bootstrap_builder.info = bootstrap_info
+
+  resolved_distributions = resolver.resolve(
+    requirements=bootstrap_info.requirements,
+    cache=bootstrap_info.pex_root,
+    platform='current',
+    transitive=False,
+    interpreter=bootstrap_builder.interpreter,
+    **resolver_settings
+  )
+  # TODO: this shouldn't be necessary, as we should be able to use the same 'distributions' from
+  # BOOTSTRAP-PEX-INFO. When the .ipex is executed, the normal pex bootstrap fails to see these
+  # requirements or recognize that they should be pulled from the cache for some reason.
+  for resolved_dist in resolved_distributions:
+    bootstrap_builder.add_distribution(resolved_dist.distribution)
+
+  bootstrap_builder.build(hydrated_pex_file, bytecode_compile=False)
+
+
+def main(self):
+  filename_base, ext = os.path.splitext(self)
+
+  # If the ipex (this pex) is already named '.pex', ensure the output filename doesn't collide by
+  # inserting an intermediate '.ipex'!
+  if ext == '.pex':
+    hydrated_pex_file = '{filename_base}.ipex.pex'.format(filename_base=filename_base)
+  else:
+    hydrated_pex_file = '{filename_base}.pex'.format(filename_base=filename_base)
+
+  if not os.path.exists(hydrated_pex_file):
+    _log('Hydrating {} to {}...'.format(self, hydrated_pex_file))
+    _hydrate_pex_file(self, hydrated_pex_file)
+
+  os.execv(sys.executable, [sys.executable, hydrated_pex_file] + sys.argv[1:])
+
+
+if __name__ == '__main__':
+  self = sys.argv[0]
+  main(self)