feat(runfiles): Added type hints to @rules_python//python/runfiles (#1654)

This change adds mypy types directly to the
`rules_python.python.runfiles` library as well as regression testing to
CI.

---------

Co-authored-by: Ignas Anikevicius <[email protected]>

Author: UebelAndre

.github/workflows/mypy.yaml

@@ -0,0 +1,32 @@
+name: mypy
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    types:
+      - opened
+      - synchronize
+
+defaults:
+  run:
+    shell: bash
+
+jobs:
+  ci:
+    runs-on: ubuntu-20.04
+    steps:
+      # Checkout the code
+      - uses: actions/checkout@v2
+      - uses: jpetrucciani/mypy-check@master
+        with:
+          requirements: 1.6.0
+          python_version: 3.8
+          path: 'python/runfiles'
+      - uses: jpetrucciani/mypy-check@master
+        with:
+          requirements: 1.6.0
+          python_version: 3.8
+          path: 'tests/runfiles'
+      

CHANGELOG.md

@@ -21,6 +21,9 @@ A brief description of the categories of changes:
 
 ### Changed
 
+* (runfiles) `rules_python.python.runfiles` now directly implements type hints
+  and drops support for python2 as a result.
+
 * (toolchains) `py_runtime`, `py_runtime_pair`, and `PyRuntimeInfo` now use the
   rules_python Starlark implementation, not the one built into Bazel. NOTE: This
   only applies to Bazel 6+; Bazel 5 still uses the builtin implementation.

python/runfiles/BUILD.bazel

@@ -27,6 +27,7 @@ py_library(
         "__init__.py",
         "runfiles.py",
     ],
+    data = ["py.typed"],
     imports = [
         # Add the repo root so `import python.runfiles.runfiles` works. This makes it agnostic
         # to the --experimental_python_import_all_repositories setting.
@@ -49,6 +50,7 @@ py_wheel(
     dist_folder = "dist",
     distribution = "bazel_runfiles",
     homepage = "https://github.com/bazelbuild/rules_python",
+    python_requires = ">=3.7",
     strip_path_prefixes = ["python"],
     twine = "@publish_deps_twine//:pkg",
     # this can be replaced by building with --stamp --embed_label=1.2.3