pip_parse: Fix when using a python wrapper script (#505)

* pip_parse: Transmit the interpreter arguments

* Clarify --python_interpreter_target doc

python/pip_install/parse_requirements_to_bzl/__init__.py

diff --git a/python/pip_install/parse_requirements_to_bzl/__init__.py b/python/pip_install/parse_requirements_to_bzl/__init__.py
index aa0f1b6..5163b3e 100644
--- a/python/pip_install/parse_requirements_to_bzl/__init__.py
+++ b/python/pip_install/parse_requirements_to_bzl/__init__.py
@@ -136,6 +136,16 @@
         help="Path to fully resolved requirements.txt to use as the source of repos.",
     )
     parser.add_argument(
+        "--python_interpreter",
+        help="The python interpreter that will be used to download and unpack the wheels.",
+    )
+    parser.add_argument(
+        "--python_interpreter_target",
+        help="Bazel target of a python interpreter.\
+It will be used in repository rules so it must be an already built interpreter.\
+If set, it will take precedence over python_interpreter.",
+    )
+    parser.add_argument(
         "--quiet",
         type=coerce_to_bool,
         default=True,

python/pip_install/parse_requirements_to_bzl/parse_requirements_to_bzl_test.py

diff --git a/python/pip_install/parse_requirements_to_bzl/parse_requirements_to_bzl_test.py b/python/pip_install/parse_requirements_to_bzl/parse_requirements_to_bzl_test.py
index 0ac5668..65a19df 100644
--- a/python/pip_install/parse_requirements_to_bzl/parse_requirements_to_bzl_test.py
+++ b/python/pip_install/parse_requirements_to_bzl/parse_requirements_to_bzl_test.py
@@ -26,6 +26,8 @@
             pip_data_exclude = ["**.foo"]
             args.extra_pip_args = json.dumps({"arg": extra_pip_args})
             args.pip_data_exclude= json.dumps({"arg": pip_data_exclude})
+            args.python_interpreter = "/custom/python3"
+            args.python_interpreter_target = "@custom_python//:exec"
             args.environment= json.dumps({"arg": {}})
             contents = generate_parsed_requirements_contents(args)
             library_target = "@pip_parsed_deps_pypi__foo//:pkg"
@@ -38,6 +40,8 @@
             all_flags = extra_pip_args + ["--require-hashes", "True"]
             self.assertIn("'extra_pip_args': {}".format(repr(all_flags)), contents, contents)
             self.assertIn("'pip_data_exclude': {}".format(repr(pip_data_exclude)), contents, contents)
+            self.assertIn("'python_interpreter': '/custom/python3'", contents, contents)
+            self.assertIn("'python_interpreter_target': '@custom_python//:exec'", contents, contents)
             # Assert it gets set to an empty dict by default.
             self.assertIn("'environment': {}", contents, contents)
 

python/pip_install/pip_repository.bzl

diff --git a/python/pip_install/pip_repository.bzl b/python/pip_install/pip_repository.bzl
index 71d5f66..c3007e1 100644
--- a/python/pip_install/pip_repository.bzl
+++ b/python/pip_install/pip_repository.bzl
@@ -24,6 +24,24 @@
     pypath = separator.join([str(p) for p in [rules_root] + thirdparty_roots])
     return pypath
 
+def _resolve_python_interpreter(rctx):
+    """Helper function to find the python interpreter from the common attributes
+
+    Args:
+        rctx: Handle to the rule repository context.
+    Returns: Python interpreter path.
+    """
+    python_interpreter = rctx.attr.python_interpreter
+    if rctx.attr.python_interpreter_target != None:
+        target = rctx.attr.python_interpreter_target
+        python_interpreter = rctx.path(target)
+    else:
+        if "/" not in python_interpreter:
+            python_interpreter = rctx.which(python_interpreter)
+        if not python_interpreter:
+            fail("python interpreter not found")
+    return python_interpreter
+
 def _parse_optional_attrs(rctx, args):
     """Helper function to parse common attributes of pip_repository and whl_library repository rules.
 
@@ -83,15 +101,7 @@
 """
 
 def _pip_repository_impl(rctx):
-    python_interpreter = rctx.attr.python_interpreter
-    if rctx.attr.python_interpreter_target != None:
-        target = rctx.attr.python_interpreter_target
-        python_interpreter = rctx.path(target)
-    else:
-        if "/" not in python_interpreter:
-            python_interpreter = rctx.which(python_interpreter)
-        if not python_interpreter:
-            fail("python interpreter not found")
+    python_interpreter = _resolve_python_interpreter(rctx)
 
     if rctx.attr.incremental and not rctx.attr.requirements_lock:
         fail("Incremental mode requires a requirements_lock attribute be specified.")
@@ -114,6 +124,11 @@
             "--timeout",
             str(rctx.attr.timeout),
         ]
+
+        if rctx.attr.python_interpreter:
+            args += ["--python_interpreter", rctx.attr.python_interpreter]
+        if rctx.attr.python_interpreter_target:
+            args += ["--python_interpreter_target", str(rctx.attr.python_interpreter_target)]
     else:
         args = [
             python_interpreter,
@@ -266,10 +281,12 @@
 )
 
 def _impl_whl_library(rctx):
+    python_interpreter = _resolve_python_interpreter(rctx)
+
     # pointer to parent repo so these rules rerun if the definitions in requirements.bzl change.
     _parent_repo_label = Label("@{parent}//:requirements.bzl".format(parent = rctx.attr.repo))
     args = [
-        rctx.attr.python_interpreter,
+        python_interpreter,
         "-m",
         "python.pip_install.parse_requirements_to_bzl.extract_single_wheel",
         "--requirement",