docs: generalize manpage generation script as json-to-tree.py

This should be capable of replacing every invocation of
nix eval --write-to.

Change-Id: I60387bc9b0fc54a91244eddb639beaa64d705878

1 files changed, 61 insertions, 0 deletions

diff --git a/doc/manual/json-to-tree.py b/doc/manual/json-to-tree.py
new file mode 100755
index 000000000..27c8e417c
--- /dev/null
+++ b/doc/manual/json-to-tree.py
@@ -0,0 +1,61 @@
+#!/usr/bin/env python3
+
+"""
+This script is a helper for this project's Meson buildsystem, to replace its
+usage of `nix eval --write-to`. Writing a JSON object as a nested directory
+tree is more generic, easier to maintain, and far, far less cursed. Nix
+has 'good' support for JSON output. Let's just use it.
+"""
+
+import argparse
+from pathlib import Path
+import json
+import sys
+
+name = 'json-to-tree.py'
+
+def log(*args, **kwargs):
+    kwargs['file'] = sys.stderr
+    return print(f'{name}:', *args, **kwargs)
+
+def write_dict_to_directory(current_directory: Path, data: dict, files_written=0):
+    current_directory.mkdir(parents=True, exist_ok=True)
+    for key, value in data.items():
+        nested_path = current_directory / key
+        match value:
+            case dict(nested_data):
+                files_written += write_dict_to_directory(nested_path, nested_data)
+
+            case str(content):
+                nested_path.write_text(content)
+                files_written += 1
+
+            case rest:
+                assert False, \
+                    f'should have been called on a dict or string, not {type(rest)=}\n\t{rest=}'
+
+    return files_written
+
+def main():
+    parser = argparse.ArgumentParser(name)
+    parser.add_argument('-i', '--input', type=argparse.FileType('r'), default='-',
+        help='The JSON input to operate on and output as a directory tree',
+    )
+    parser.add_argument('-o', '--output', type=Path, required=True,
+        help='The place to put the directory tree',
+    )
+    args = parser.parse_args()
+
+    json_string = args.input.read()
+
+    try:
+        data = json.loads(json_string)
+    except json.JSONDecodeError:
+        log(f'could not decode JSON from input: {json_string}')
+        raise
+
+
+    files_written = write_dict_to_directory(args.output, data)
+    log(f'wrote {files_written} files')
+
+sys.exit(main())