Integrate black formatter with Bazel for local development

BUILD

@@ -12,7 +12,42 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+load("@pip//:requirements.bzl", "entry_point")
+
 exports_files([
     "build_defs.bzl",
     "LICENSE",
+    "requirements.txt",
 ])
+
+# Black formatter binary. Use with:
+#   bazel run //:black -- [args]
+# Example to format all Python files:
+#   bazel run //:black -- .
+alias(
+    name = "black",
+    actual = entry_point("black"),
+)
+
+# Target to fix Python formatting issues.
+# Usage: bazel run //:black_fix -- .
+sh_binary(
+    name = "black_fix",
+    srcs = ["scripts/black_fix.sh"],
+    data = [
+        ":black",
+        "scripts/black_common.sh",
+    ],
+)
+
+# Target to check Python formatting.
+# Usage: bazel run //:black_check
+# This runs black --check --diff . on the workspace.
+sh_binary(
+    name = "black_check",
+    srcs = ["scripts/black_check.sh"],
+    data = [
+        ":black",
+        "scripts/black_common.sh",
+    ],
+)

MODULE.bazel

@@ -15,3 +15,11 @@ bazel_dep(
     repo_name = "com_google_googletest",
 )
 bazel_dep(name = "rules_python", version = "0.31.0")
+
+pip = use_extension("@rules_python//python/extensions:pip.bzl", "pip")
+pip.parse(
+    hub_name = "pip",
+    python_version = "3.11",
+    requirements_lock = "//:requirements.txt",
+)
+use_repo(pip, "pip")

requirements.txt

@@ -0,0 +1 @@
+black==24.8.0

scripts/black_check.sh

@@ -0,0 +1,36 @@
+#!/bin/bash
+# Copyright 2019 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Script to check Python formatting with black.
+# Usage: bazel run //:black_check
+#
+# This will pass if all files are correctly formatted and fail otherwise,
+# printing a diff of the required changes.
+
+set -e
+
+SCRIPT_DIR="$(dirname "$0")"
+source "$SCRIPT_DIR/black_common.sh"
+
+# Find the black binary
+find_black "$SCRIPT_DIR" || exit 1
+
+# Change to the workspace directory (BUILD_WORKSPACE_DIRECTORY is set by bazel run)
+if [[ -n "$BUILD_WORKSPACE_DIRECTORY" ]]; then
+    cd "$BUILD_WORKSPACE_DIRECTORY"
+fi
+
+# Run black in check mode
+exec "$BLACK_BIN" --check --diff .

scripts/black_common.sh

@@ -0,0 +1,51 @@
+#!/bin/bash
+# Copyright 2019 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Shared functions for black formatter scripts.
+# Source this file to use the find_black function.
+
+# Find the black binary in the Bazel runfiles.
+# Sets BLACK_BIN to the path of the black binary.
+# Returns 0 on success, 1 on failure.
+find_black() {
+    local script_dir="$1"
+
+    # Try to find black in different possible locations
+    BLACK_BIN="$script_dir/black/black"
+    if [[ -x "$BLACK_BIN" ]]; then
+        return 0
+    fi
+
+    BLACK_BIN="$script_dir/../pip/bin/black/black"
+    if [[ -x "$BLACK_BIN" ]]; then
+        return 0
+    fi
+
+    # Search for black in runfiles
+    if [[ -n "$RUNFILES_DIR" ]]; then
+        BLACK_BIN="$(find "$RUNFILES_DIR" -name "black" -type f -executable 2>/dev/null | head -1)"
+        if [[ -n "$BLACK_BIN" ]] && [[ -x "$BLACK_BIN" ]]; then
+            return 0
+        fi
+    fi
+
+    # Could not find black
+    echo "Error: Could not find black binary" >&2
+    echo "Searched in:" >&2
+    echo "  - $script_dir/black/black" >&2
+    echo "  - $script_dir/../pip/bin/black/black" >&2
+    echo "  - RUNFILES_DIR=$RUNFILES_DIR" >&2
+    return 1
+}

scripts/black_fix.sh

@@ -0,0 +1,35 @@
+#!/bin/bash
+# Copyright 2019 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Script to run black formatter to fix Python files.
+# Usage: bazel run //:black_fix -- [args]
+#
+# Example: bazel run //:black_fix -- .
+
+set -e
+
+SCRIPT_DIR="$(dirname "$0")"
+source "$SCRIPT_DIR/black_common.sh"
+
+# Find the black binary
+find_black "$SCRIPT_DIR" || exit 1
+
+# Change to the workspace directory (BUILD_WORKSPACE_DIRECTORY is set by bazel run)
+if [[ -n "$BUILD_WORKSPACE_DIRECTORY" ]]; then
+    cd "$BUILD_WORKSPACE_DIRECTORY"
+fi
+
+# Run black with the provided arguments
+exec "$BLACK_BIN" "$@"