Fix and test prep script.

.vscode/BUILD.bazel

@@ -19,7 +19,7 @@ alias(
 
 alias(
     name = "install_sapling_hooks",
-    actual = "//.vscode/prep:prep_bin",
+    actual = "//py/devtools/prep:prep_bin",
 )
 
 bazel_lint(

BUILD.bazel

@@ -1,3 +1,5 @@
+load("//py:rules.bzl", "py_library")
+
 # Add rules here to build your software
 # See https://docs.bazel.build/versions/master/build-ref.html#BUILD_files
 
@@ -239,11 +241,14 @@ bazel_lint(
 py_venv(
     name = "venv",
     deps = [
-        "//.vscode/prep:prep_bin",
         "//bzl/versioning",
         "//ini/git/merge_drivers/bazel_lockfile",
         "//project/cultist/gen/testing",
+        "//py",
         "//py/ci/postUpgrade:postUpgrade_bin",
+        "//py/devtools",
+        "//py/devtools/prep",
+        "//py/devtools/prep:prep_bin",
         "//py/hello_world:hello_world_bin",
         "//py/ibazel:ibazel_bin",
         "//py/ipynb",
@@ -259,3 +264,11 @@ alias(
     name = "go",
     actual = "//sh/bin:go",
 )
+
+# gazelle:python_root
+
+py_library(
+    name = "monorepo",
+    srcs = ["__init__.py"],
+    visibility = ["//:__subpackages__"],
+)

__init__.py

@@ -0,0 +1,5 @@
+"""
+The monorepo!
+
+Apparently this file is mandatory in a lot of Python versions.
+"""

py/BUILD.bazel

@@ -1,4 +1,5 @@
 load("//bzl:rules.bzl", "bazel_lint")
+load("//py:rules.bzl", "py_library")
 
 "Root for pure python projects."
 
@@ -9,3 +10,9 @@ bazel_lint(
         "rules.bzl",
     ],
 )
+
+py_library(
+    name = "py",
+    srcs = ["__init__.py"],
+    visibility = ["//:__subpackages__"],
+)

py/__init__.py

@@ -0,0 +1,2 @@
+
+#

.vscode/prep/BUILD.bazel → py/devtools/BUILD.bazel

@@ -1,14 +1,13 @@
 load("//bzl:rules.bzl", "bazel_lint")
-load("//py:rules.bzl", "py_binary")
+load("//py:rules.bzl", "py_library")
+
+py_library(
+    name = "devtools",
+    srcs = ["__init__.py"],
+    visibility = ["//:__subpackages__"],
+)
 
 bazel_lint(
     name = "bazel_lint",
     srcs = ["BUILD.bazel"],
 )
-
-py_binary(
-    name = "prep_bin",
-    srcs = ["__main__.py"],
-    main = "__main__.py",
-    visibility = ["//:__subpackages__"],
-)

py/devtools/__init__.py

@@ -0,0 +1 @@
+#

py/devtools/prep/BUILD.bazel

@@ -0,0 +1,31 @@
+load("//bzl:rules.bzl", "bazel_lint")
+load("//py:rules.bzl", "py_binary", "py_library", "py_test")
+
+bazel_lint(
+    name = "bazel_lint",
+    srcs = ["BUILD.bazel"],
+)
+
+py_binary(
+    name = "prep_bin",
+    srcs = ["__main__.py"],
+    main = "__main__.py",
+    visibility = ["//:__subpackages__"],
+    deps = [":prep"],
+)
+
+py_test(
+    name = "prep_test",
+    srcs = ["__test__.py"],
+    main = "__test__.py",
+    deps = [":prep"],
+)
+
+py_library(
+    name = "prep",
+    srcs = [
+        "__init__.py",
+        "lib.py",
+    ],
+    visibility = ["//:__subpackages__"],
+)

py/devtools/prep/__init__.py

@@ -0,0 +1 @@
+#

py/devtools/prep/__main__.py

@@ -0,0 +1,3 @@
+from py.devtools.prep.lib import main
+if __name__ == "__main__":
+    main()

py/devtools/prep/__test__.py

@@ -0,0 +1,54 @@
+import os
+import unittest
+import tempfile
+import shutil
+
+from py.devtools.prep.lib import (
+    get_sapling_config_dir,
+    ensure_sapling_include,
+    configure_sapling,
+)
+
+class TestSaplingConfig(unittest.TestCase):
+    def setUp(self):
+        """
+        Create a fresh temporary directory before each test,
+        mimicking Pytest's `tmp_path` fixture.
+        """
+        self.tmp_dir = tempfile.mkdtemp()
+
+    def tearDown(self):
+        """
+        Remove the temporary directory after each test.
+        """
+        shutil.rmtree(self.tmp_dir)
+
+    def test_get_sapling_config_dir(self):
+        git_path = os.path.join(self.tmp_dir, ".git")
+        os.mkdir(git_path)
+        expected_dir = os.path.join(git_path, "sl")
+        actual_dir = get_sapling_config_dir(self.tmp_dir)
+        self.assertEqual(actual_dir, expected_dir)
+
+    def test_ensure_sapling_include(self):
+        config_file = os.path.join(self.tmp_dir, "config")
+
+        # File doesn’t exist initially
+        changed = ensure_sapling_include(config_file)
+        self.assertTrue(changed, "Should create file and prepend line.")
+
+        # Calling again detects it's already included
+        changed_again = ensure_sapling_include(config_file)
+        self.assertFalse(changed_again, "No change after second include.")
+
+    def test_configure_sapling(self):
+        configure_sapling(self.tmp_dir)
+        config_dir = os.path.join(self.tmp_dir, ".sl")
+        self.assertTrue(
+            os.path.isfile(os.path.join(config_dir, "config")),
+            "Config file should exist in .sl directory."
+        )
+
+
+if __name__ == "__main__":
+    unittest.main()

py/devtools/prep/lib.py

@@ -0,0 +1,81 @@
+#!/usr/bin/env python3
+
+import os
+import re
+from argparse import ArgumentParser
+from tempfile import TemporaryFile
+from shutil import copyfileobj
+
+def get_sapling_config_dir(working_directory: str) -> str:
+    """
+    Determine the appropriate config directory for Sapling:
+    - If .git exists in working_directory, use .git/sl/
+    - Otherwise, use .sl/
+    """
+    git_dir = os.path.join(working_directory, ".git")
+    if os.path.isdir(git_dir):
+        return os.path.join(git_dir, "sl")
+    return os.path.join(working_directory, ".sl")
+
+def ensure_sapling_include(config_file_path: str) -> bool:
+    """
+    Ensure the Sapling config file includes:
+        %include ../ini/sl/config.ini
+    If the include is missing, it is prepended, and the file is updated.
+    Returns True if the file was changed; False if it was already correct.
+    """
+    # Create the directory for config_file_path if needed
+    os.makedirs(os.path.dirname(config_file_path), exist_ok=True)
+
+    # Open in "a+" mode so that the file is created if it does not exist
+    with open(config_file_path, "a+") as config_file:
+        # Move pointer to start for reading
+        config_file.seek(0)
+        lines = config_file.readlines()
+
+        # Regex to match line exactly: %%include ../ini/sl/config.ini
+        pattern = re.compile(r"^%include\s+\.\./ini/sl/config\.ini\s*$")
+
+        # If any line matches, there's nothing to fix
+        if any(pattern.match(line.strip()) for line in lines):
+            return False
+
+        print("It seems you're not importing the standard Sapling config. I'll fix this.")
+
+        # We need to prepend the missing line
+        config_file.seek(0)
+
+        # Clear the file using truncate, then rebuild
+        config_file.truncate()
+
+        # Prepend the missing line, then original lines
+        with TemporaryFile(mode="w+") as temp:
+            temp.write("%include ../ini/sl/config.ini" + os.linesep)
+            for line in lines:
+                temp.write(line)
+
+            # Copy temporary contents back into the original file
+            temp.seek(0)
+            copyfileobj(temp, config_file)
+
+    return True
+
+def configure_sapling(working_directory: str) -> None:
+    """
+    High-level function that locates the config directory and ensures the standard Sapling include.
+    """
+    config_dir = get_sapling_config_dir(working_directory)
+    config_file_path = os.path.join(config_dir, "config")
+    ensure_sapling_include(config_file_path)
+
+def main():
+    parser = ArgumentParser(
+        prog="scm-conf.py",
+        description="Configure local SCM to use repo config."
+    )
+    parser.add_argument(
+        "working_directory",
+        help="Directory to run in (exists due to Bazel stubbornness)."
+    )
+    args = parser.parse_args()
+    configure_sapling(args.working_directory)