pycross: Add patching support to py_wheel_library

This patch adds a few arguments to `py_wheel_library` to simulate how
`http_archive` accepts patch-related arguments.

I also amended the existing test to validate the behaviour at a very
high level.

References: bazelbuild#1360

tests/pycross/0001-Add-new-file-for-testing-patch-support.patch

@@ -0,0 +1,17 @@
+From b2ebe6fe67ff48edaf2ae937d24b1f0b67c16f81 Mon Sep 17 00:00:00 2001
+From: Philipp Schrader <[email protected]>
+Date: Thu, 28 Sep 2023 09:02:44 -0700
+Subject: [PATCH] Add new file for testing patch support
+
+---
+ site-packages/numpy/file_added_via_patch.txt | 1 +
+ 1 file changed, 1 insertion(+)
+ create mode 100644 site-packages/numpy/file_added_via_patch.txt
+
+diff --git a/site-packages/numpy/file_added_via_patch.txt b/site-packages/numpy/file_added_via_patch.txt
+new file mode 100644
+index 0000000..9d947a4
+--- /dev/null
++++ b/site-packages/numpy/file_added_via_patch.txt
+@@ -0,0 +1 @@
++Hello from a patch!

tests/pycross/BUILD.bazel

@@ -17,6 +17,12 @@ load("//third_party/rules_pycross/pycross/private:wheel_library.bzl", "py_wheel_
 
 py_wheel_library(
     name = "extracted_wheel_for_testing",
+    patch_args = [
+        "-p1",
+    ],
+    patches = [
+        "0001-Add-new-file-for-testing-patch-support.patch",
+    ],
     wheel = "@wheel_for_testing//file",
 )
 

tests/pycross/py_wheel_library_test.py

@@ -23,9 +23,7 @@
 class TestPyWheelLibrary(unittest.TestCase):
     def setUp(self):
         self.extraction_dir = Path(
-            RUNFILES.Rlocation(
-                "rules_python/tests/pycross/extracted_wheel_for_testing"
-            )
+            RUNFILES.Rlocation("rules_python/tests/pycross/extracted_wheel_for_testing")
         )
         self.assertTrue(self.extraction_dir.exists(), self.extraction_dir)
         self.assertTrue(self.extraction_dir.is_dir(), self.extraction_dir)
@@ -43,6 +41,11 @@ def test_file_presence(self):
                 (self.extraction_dir / path).exists(), f"{path} does not exist"
             )
 
+    def test_patched_file_contents(self):
+        """Validate that the patch got applied correctly."""
+        file = self.extraction_dir / "site-packages/numpy/file_added_via_patch.txt"
+        self.assertEqual(file.read_text(), "Hello from a patch!\n")
+
 
 if __name__ == "__main__":
     unittest.main()

third_party/rules_pycross/pycross/private/tools/wheel_installer.py

@@ -20,6 +20,7 @@
 import argparse
 import os
 import shutil
+import subprocess
 import sys
 import tempfile
 from pathlib import Path
@@ -97,6 +98,24 @@ def main(args: Any) -> None:
 
     setup_namespace_pkg_compatibility(lib_dir)
 
+    patch_args = [args.patch_tool] + args.patch_arg
+    patch_dir = args.patch_dir or "."
+    for patch in args.patch or []:
+        with patch.open("r") as stdin:
+            try:
+                subprocess.run(
+                    patch_args,
+                    stdin=stdin,
+                    check=True,
+                    stdout=subprocess.PIPE,
+                    stderr=subprocess.STDOUT,
+                    cwd=args.directory / patch_dir,
+                )
+            except subprocess.CalledProcessError as error:
+                print(f"Patch {patch} failed to apply:")
+                print(error.stdout.decode("utf-8"))
+                raise
+
 
 def parse_flags(argv) -> Any:
     parser = argparse.ArgumentParser(description="Extract a Python wheel.")
@@ -127,6 +146,33 @@ def parse_flags(argv) -> Any:
         help="The output path.",
     )
 
+    parser.add_argument(
+        "--patch",
+        type=Path,
+        action="append",
+        help="A patch file to apply.",
+    )
+
+    parser.add_argument(
+        "--patch-arg",
+        type=Path,
+        default=[],
+        action="append",
+        help="An argument for the patch_tool when applying the patches.",
+    )
+
+    parser.add_argument(
+        "--patch-tool",
+        type=str,
+        help="The tool to invoke when applying patches.",
+    )
+
+    parser.add_argument(
+        "--patch-dir",
+        type=str,
+        help="The directory from which to invoke patch_tool.",
+    )
+
     return parser.parse_args(argv[1:])
 
 

third_party/rules_pycross/pycross/private/wheel_library.bzl

@@ -33,8 +33,12 @@ def _py_wheel_library_impl(ctx):
     args = ctx.actions.args().use_param_file("--flagfile=%s")
     args.add("--wheel", wheel_file)
     args.add("--directory", out.path)
+    args.add_all(ctx.files.patches, format_each = "--patch=%s")
+    args.add_all(ctx.attr.patch_args, format_each = "--patch-arg=%s")
+    args.add("--patch-tool", ctx.attr.patch_tool)
+    args.add("--patch-dir", ctx.attr.patch_dir)
 
-    inputs = [wheel_file]
+    inputs = [wheel_file] + ctx.files.patches
     if name_file:
         inputs.append(name_file)
         args.add("--wheel-name-file", name_file)
@@ -119,6 +123,28 @@ and py_test targets must specify either `legacy_create_init=False` or the global
 This option is required to support some packages which cannot handle the conversion to pkg-util style.
             """,
         ),
+        "patch_args": attr.string_list(
+            default = ["-p0"],
+            doc =
+                "The arguments given to the patch tool. Defaults to -p0, " +
+                "however -p1 will usually be needed for patches generated by " +
+                "git. If multiple -p arguments are specified, the last one will take effect.",
+        ),
+        "patch_dir": attr.string(
+            default = "",
+            doc = "The directory from which to invoke the patch_tool.",
+        ),
+        "patch_tool": attr.string(
+            default = "patch",
+            doc = "The patch(1) utility to use.",
+        ),
+        "patches": attr.label_list(
+            allow_files = True,
+            default = [],
+            doc =
+                "A list of files that are to be applied as patches after " +
+                "extracting the archive. This will use the patch command line tool.",
+        ),
         "python_version": attr.string(
             doc = "The python version required for this wheel ('PY2' or 'PY3')",
             values = ["PY2", "PY3", ""],