Add support for relative requirements in pip_install (#433) * Run pip within the directory containing the requirements.txt file This allows for relative requirements to be resolved in the way that standalone pip would without patching or parsing the requirements file manually * Print test errors of sub-workspaces in bazel_integration_test Prior to this, errors would be written to logs in the temp directory that would promptly be deleted on parent test teardown. This means at least the test logs will be printed on failure * Add example of relative requirement as test * Explicitly cast Path to str to support Python 3.5 * Fix multiple declarations of pip_args * Apply buildifier fix Co-authored-by: Alex Eagle <eagle@post.harvard.edu>

diff --git a/.bazelrc b/.bazelrc
index 6aee0a6..b7f29ab 100644
--- a/.bazelrc
+++ b/.bazelrc

@@ -3,7 +3,7 @@
 # This lets us glob() up all the files inside the examples to make them inputs to tests
 # (Note, we cannot use `common --deleted_packages` because the bazel version command doesn't support it)
 # To update these lines, run tools/bazel_integration_test/update_deleted_packages.sh
-build --deleted_packages=examples/legacy_pip_import/boto,examples/legacy_pip_import/extras,examples/legacy_pip_import/helloworld,examples/pip_install,examples/pip_parse,examples/py_import
-query --deleted_packages=examples/legacy_pip_import/boto,examples/legacy_pip_import/extras,examples/legacy_pip_import/helloworld,examples/pip_install,examples/pip_parse,examples/py_import
+build --deleted_packages=examples/legacy_pip_import/boto,examples/legacy_pip_import/extras,examples/legacy_pip_import/helloworld,examples/pip_install,examples/pip_parse,examples/py_import,examples/relative_requirements
+query --deleted_packages=examples/legacy_pip_import/boto,examples/legacy_pip_import/extras,examples/legacy_pip_import/helloworld,examples/pip_install,examples/pip_parse,examples/py_import,examples/relative_requirements
 
 test --test_output=errors

diff --git a/examples/BUILD b/examples/BUILD
index e263c07..826f87c 100644
--- a/examples/BUILD
+++ b/examples/BUILD

@@ -36,3 +36,8 @@
     name = "py_import_example",
     timeout = "long",
 )
+
+bazel_integration_test(
+    name = "relative_requirements_example",
+    timeout = "long",
+)

diff --git a/examples/relative_requirements/BUILD b/examples/relative_requirements/BUILD
new file mode 100644
index 0000000..d24ee5f
--- /dev/null
+++ b/examples/relative_requirements/BUILD

@@ -0,0 +1,10 @@
+load("@pip//:requirements.bzl", "requirement")
+load("@rules_python//python:defs.bzl", "py_test")
+
+py_test(
+    name = "main",
+    srcs = ["main.py"],
+    deps = [
+        requirement("relative_package_name"),
+    ],
+)

diff --git a/examples/relative_requirements/README.md b/examples/relative_requirements/README.md
new file mode 100644
index 0000000..4b9258e
--- /dev/null
+++ b/examples/relative_requirements/README.md

@@ -0,0 +1,4 @@
+# relative_requirements example
+
+This example shows how to use pip to fetch relative dependencies from a requirements.txt file,
+then use them in BUILD files as dependencies of Bazel targets.

diff --git a/examples/relative_requirements/WORKSPACE b/examples/relative_requirements/WORKSPACE
new file mode 100644
index 0000000..505fa9e
--- /dev/null
+++ b/examples/relative_requirements/WORKSPACE

@@ -0,0 +1,15 @@
+workspace(name = "example_repo")
+
+load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
+
+http_archive(
+    name = "rules_python",
+    sha256 = "b6d46438523a3ec0f3cead544190ee13223a52f6a6765a29eae7b7cc24cc83a0",
+    url = "https://github.com/bazelbuild/rules_python/releases/download/0.1.0/rules_python-0.1.0.tar.gz",
+)
+
+load("@rules_python//python:pip.bzl", "pip_install")
+
+pip_install(
+    requirements = "//:requirements.txt",
+)

diff --git a/examples/relative_requirements/main.py b/examples/relative_requirements/main.py
new file mode 100644
index 0000000..b8ac021
--- /dev/null
+++ b/examples/relative_requirements/main.py

@@ -0,0 +1,5 @@
+import relative_package_name
+
+if __name__ == "__main__":
+    # Run a function from the relative package
+    print(relative_package_name.test())

diff --git a/examples/relative_requirements/relative_package/relative_package_name/__init__.py b/examples/relative_requirements/relative_package/relative_package_name/__init__.py
new file mode 100644
index 0000000..c031192
--- /dev/null
+++ b/examples/relative_requirements/relative_package/relative_package_name/__init__.py

@@ -0,0 +1,2 @@
+def test():
+    return True

diff --git a/examples/relative_requirements/relative_package/setup.py b/examples/relative_requirements/relative_package/setup.py
new file mode 100644
index 0000000..3fd85c1
--- /dev/null
+++ b/examples/relative_requirements/relative_package/setup.py

@@ -0,0 +1,7 @@
+from setuptools import setup
+
+setup(
+    name='relative_package_name',
+    version='1.0.0',
+    packages=['relative_package_name'],
+)

diff --git a/examples/relative_requirements/requirements.txt b/examples/relative_requirements/requirements.txt
new file mode 100644
index 0000000..9a81317
--- /dev/null
+++ b/examples/relative_requirements/requirements.txt

@@ -0,0 +1 @@
+./relative_package

diff --git a/python/pip_install/extract_wheels/__init__.py b/python/pip_install/extract_wheels/__init__.py
index 214be9a..5fdf9ea 100644
--- a/python/pip_install/extract_wheels/__init__.py
+++ b/python/pip_install/extract_wheels/__init__.py

@@ -8,6 +8,7 @@
 import argparse
 import glob
 import os
+import pathlib
 import subprocess
 import sys
 import json
@@ -63,17 +64,22 @@
     deserialized_args = dict(vars(args))
     arguments.deserialize_structured_args(deserialized_args)
 
+    # Pip is run with the working directory changed to the folder containing the requirements.txt file, to allow for
+    # relative requirements to be correctly resolved. The --wheel-dir is therefore required to be repointed back to the
+    # current calling working directory (the repo root in .../external/name), where the wheel files should be written to
     pip_args = (
         [sys.executable, "-m", "pip"] + 
         (["--isolated"] if args.isolated else []) + 
         ["wheel", "-r", args.requirements] +
+        ["--wheel-dir", os.getcwd()] +
         deserialized_args["extra_pip_args"]
     )
 
     env = os.environ.copy()
     env.update(deserialized_args["environment"])
+
     # Assumes any errors are logged by pip so do nothing. This command will fail if pip fails
-    subprocess.run(pip_args, check=True, env=env)
+    subprocess.run(pip_args, check=True, env=env, cwd=str(pathlib.Path(args.requirements).parent.resolve()))
 
     extras = requirements.parse_extras(args.requirements)