[bazel] use patched python rules and build wheels cache

BUILD

@@ -6,12 +6,12 @@ load("//rules:rules.bzl", "licence_check", "yapf_check")
 
 licence_check(
     name = "licence-check",
-    licence = '''
+    exclude_patterns = [".style.yapf"],
+    licence = """
     Copyright lowRISC contributors.
     Licensed under the Apache License, Version 2.0, see LICENSE for details.
     SPDX-License-Identifier: Apache-2.0
-    ''',
-    exclude_patterns = [".style.yapf"],
+    """,
 )
 
 yapf_check(

rules/pip.bzl

@@ -7,17 +7,113 @@
 load("@rules_python//python:pip.bzl", "pip_install")
 load("@python3//:defs.bzl", "interpreter")
 
+_WHEEL_BUILD_FILE_CONTENTS = """\
+package(default_visibility = ["//visibility:public"])
+
+filegroup(
+    name = "all_wheels",
+    srcs = glob(["**/*.whl"])
+)
+"""
+
+def _pip_wheel_impl(rctx):
+    # First, check if an existing pre-built Python wheels repo exists, and if
+    # so, use it instead of building one.
+    python_wheel_repo_path = rctx.os.environ.get(
+        "BAZEL_PYTHON_WHEELS_REPO",
+        None,
+    )
+    if python_wheel_repo_path:
+        rctx.report_progress("Mounting existing Python wheels repo")
+        rctx.symlink(python_wheel_repo_path, ".")
+        return
+
+    # If a pre-built Python wheels repo does not exist, we need to build it.
+    rctx.report_progress("No Python wheels repo detected, building it instead")
+
+    # First, we install the Python wheel package so we can build other wheels.
+    args = [
+        rctx.path(rctx.attr.python_interpreter),
+        "-m",
+        "pip",
+        "install",
+        "wheel",
+    ]
+    rctx.report_progress("Installing the Python wheel package")
+    result = rctx.execute(
+        args,
+        timeout = rctx.attr.timeout,
+        quiet = rctx.attr.quiet,
+    )
+    if result.return_code:
+        fail("pip_wheel failed: {} ({})".format(result.stdout, result.stderr))
+
+    # Next, we download/build all the Python wheels for each requirement.
+    args = [
+        rctx.path(rctx.attr.python_interpreter),
+        "-m",
+        "pip",
+        "wheel",
+        "-r",
+        rctx.path(rctx.attr.requirements),
+        "-w",
+        "./",
+    ]
+    rctx.report_progress("Pre-building Python wheels")
+    result = rctx.execute(
+        args,
+        timeout = rctx.attr.timeout,
+        quiet = rctx.attr.quiet,
+    )
+    if result.return_code:
+        fail("pip_wheel failed: {} ({})".format(result.stdout, result.stderr))
+
+    # We need a BUILD file to load the downloaded Python packages.
+    rctx.file(
+        "BUILD.bazel",
+        _WHEEL_BUILD_FILE_CONTENTS,
+    )
+
+pip_wheel = repository_rule(
+    implementation = _pip_wheel_impl,
+    attrs = {
+        "python_interpreter": attr.label(
+            default = interpreter,
+            allow_single_file = True,
+            doc = "Python interpreter to use.",
+        ),
+        "requirements": attr.label(
+            default = "//:requirements.txt",
+            allow_single_file = True,
+            doc = "Python requirements file describing package dependencies.",
+        ),
+        "quiet": attr.bool(
+            default = True,
+            doc = "If True, suppress printing stdout/stderr to the terminal.",
+        ),
+        "timeout": attr.int(
+            default = 300,
+            doc = "Timeout (in seconds) on the rule's execution duration.",
+        ),
+    },
+    environ = ["BAZEL_PYTHON_WHEELS_REPO"],
+)
+
 def lowrisc_misc_linters_pip_dependencies():
-  """
-  Declares workspaces linting rules depend on.
-  Make sure to call this in your WORKSPACE file.
-
-  Make sure to call lowrisc_misc_linters_dependencies() from
-  deps.bzl first.
-  """
-
-  pip_install(
-     name = "lowrisc_misc_linters_pip",
-     python_interpreter_target = interpreter,
-     requirements = Label("//:requirements.txt"),
-  )
+    """
+    Declares workspaces linting rules depend on.
+    Make sure to call this in your WORKSPACE file.
+
+    Make sure to call lowrisc_misc_linters_dependencies() from
+    deps.bzl first.
+    """
+    pip_wheel(
+        name = "lowrisc_misc_linters_wheels",
+    )
+    pip_install(
+        name = "lowrisc_misc_linters_pip",
+        python_interpreter_target = interpreter,
+        requirements = Label("//:requirements.txt"),
+        find_links = "@lowrisc_misc_linters_wheels//:all_wheels",
+        extra_pip_args = ["--no-index"],
+    )

rules/repos.bzl

@@ -12,7 +12,7 @@ def lowrisc_misc_linters_repos():
     if not native.existing_rule("rules_python"):
         http_archive(
             name = "rules_python",
-            sha256 = "9fcf91dbcc31fde6d1edb15f117246d912c33c36f44cf681976bd886538deba6",
-            strip_prefix = "rules_python-0.8.0",
-            url = "https://github.com/bazelbuild/rules_python/archive/refs/tags/0.8.0.tar.gz",
+            sha256 = "9e9a58cff49f80afd1c9fcc7137b719531f7a7427cce4fda1d30ca27b4a46a8a",
+            strip_prefix = "rules_python-07c3f8547abbd5b97839a48af226a0fbcfaa5e7c",
+            url = "https://github.com/lowRISC/rules_python/archive/07c3f8547abbd5b97839a48af226a0fbcfaa5e7c.tar.gz",
         )