1 files changed, 84 insertions, 0 deletions
diff --git a/doc/manual/docroot.py b/doc/manual/docroot.py
new file mode 100755
index 000000000..e95f8abbf
--- /dev/null
+++ b/doc/manual/docroot.py
@@ -0,0 +1,84 @@
+#!/usr/bin/env python3
+
+from pathlib import Path
+import json
+import os, os.path
+import sys
+
+name = 'process-docroot.py'
+
+def log(*args, **kwargs):
+    kwargs['file'] = sys.stderr
+    return print(f'{name}:', *args, **kwargs)
+
+def replace_docroot(relative_md_path: Path, content: str, book_root: Path):
+    assert not relative_md_path.is_absolute(), f'{relative_md_path=} from mdbook should be relative'
+
+    md_path_abs = book_root / relative_md_path
+    docroot_abs = md_path_abs.parent
+    assert docroot_abs.is_dir(), f'supposed docroot {docroot_abs} is not a directory (cwd={os.getcwd()})'
+
+    # The paths mdbook gives us are relative to the directory with book.toml.
+    # @docroot@ wants to be replaced with the path relative to `src/`.
+    docroot_rel = os.path.relpath(book_root / 'src', start=docroot_abs)
+
+    return content.replace('@docroot@', docroot_rel)
+
+def recursive_replace(data, book_root):
+    match data:
+        case {'sections': sections}:
+            return data | dict(
+                sections = [recursive_replace(section, book_root) for section in sections],
+            )
+        case {'Chapter': chapter}:
+            # Path to the .md file for this chapter, relative to book_root.
+            path_to_chapter = Path('src') / chapter['path']
+            chapter_content = chapter['content']
+
+            return data | dict(
+                Chapter = chapter | dict(
+                    content = replace_docroot(path_to_chapter, chapter_content, book_root),
+                    sub_items = [recursive_replace(sub_item, book_root) for sub_item in chapter['sub_items']],
+                ),
+            )
+
+        case rest:
+            assert False, f'should have been called on a dict, not {type(rest)=}\n\t{rest=}'
+
+def main():
+
+    if len(sys.argv) > 1 and sys.argv[1] == 'supports':
+        log('confirming to mdbook that we support their stuff')
+        return 0
+
+    # mdbook communicates with us over stdin and stdout.
+    # It splorks us a JSON array, the first element describing the context,
+    # the second element describing the book itself,
+    # and then expects us to send it the modified book JSON over stdout.
+
+    context, book = json.load(sys.stdin)
+
+    # book_root is *not* @docroot@. @docroot@ gets replaced with a relative path to `./src/`.
+    # book_root is the directory where book.toml, aka `src`'s parent.
+    book_root = Path(context['root'])
+    assert book_root.exists(), f'{book_root=} does not exist'
+    assert book_root.joinpath('book.toml').is_file(), f'{book_root / "book.toml"} is not a file'
+
+    log('replacing all occurrences of @docroot@ with a relative path')
+
+    # Find @docroot@ in all parts of our recursive book structure.
+    replaced_content = recursive_replace(book, book_root)
+
+    replaced_content_str = json.dumps(replaced_content)
+
+    # Give mdbook our changes.
+    print(replaced_content_str)
+
+    log('done!')
+
+try:
+    sys.exit(main())
+except AssertionError as e:
+    print(f'{name}: INTERNAL ERROR in mdbook preprocessor', file=sys.stderr)
+    print(f'this is a bug in {name}')
+    raise