nixos-render-docs: improve error messages for multi-title manual chapters

pkgs/tools/nix/nixos-render-docs/src/nixos_render_docs/__init__.py

@@ -1,12 +1,38 @@
 import argparse
 import os
 import sys
+import textwrap
+import traceback
+from io import StringIO
+from pprint import pprint
 from typing import Any, Dict
 
 from .md import Converter
 from . import manual
 from . import options
 
+def pretty_print_exc(e: BaseException, *, _desc_text: str = "error") -> None:
+    print(f"\x1b[1;31m{_desc_text}:\x1b[0m", file=sys.stderr)
+    # destructure Exception and RuntimeError specifically so we can show nice
+    # messages for errors that weren't given their own exception type with
+    # a good pretty-printer.
+    if type(e) is Exception or type(e) is RuntimeError:
+        args = e.args
+        if len(args) and isinstance(args[0], str):
+            print("\t", args[0], file=sys.stderr, sep="")
+            args = args[1:]
+        buf = StringIO()
+        for arg in args:
+            pprint(arg, stream=buf)
+        if extra_info := buf.getvalue():
+            print(f"\x1b[1;34mextra info:\x1b[0m", file=sys.stderr)
+            print(textwrap.indent(extra_info, "\t"), file=sys.stderr, end="")
+    else:
+        print(e)
+    if e.__context__ is not None:
+        print("", file=sys.stderr)
+        pretty_print_exc(e.__context__, _desc_text="caused by")
+
 def main() -> None:
     parser = argparse.ArgumentParser(description='render nixos manual bits')
 
@@ -16,9 +42,14 @@ def main() -> None:
     manual.build_cli(commands.add_parser('manual'))
 
     args = parser.parse_args()
-    if args.command == 'options':
-        options.run_cli(args)
-    elif args.command == 'manual':
-        manual.run_cli(args)
-    else:
-        raise RuntimeError('command not hooked up', args)
+    try:
+        if args.command == 'options':
+            options.run_cli(args)
+        elif args.command == 'manual':
+            manual.run_cli(args)
+        else:
+            raise RuntimeError('command not hooked up', args)
+    except Exception as e:
+        traceback.print_exc()
+        pretty_print_exc(e)
+        sys.exit(1)

pkgs/tools/nix/nixos-render-docs/src/nixos_render_docs/manual.py

@@ -3,6 +3,7 @@ import json
 
 from abc import abstractmethod
 from collections.abc import MutableMapping, Sequence
+from pathlib import Path
 from typing import Any, cast, NamedTuple, Optional, Union
 from xml.sax.saxutils import escape, quoteattr
 from markdown_it.token import Token
@@ -26,11 +27,15 @@ class BaseConverter(Converter):
         super().__init__(manpage_urls)
         self._sections = []
 
-    def add_section(self, id: Optional[str], chapters: list[str]) -> None:
+    def add_section(self, id: Optional[str], chapters: list[Path]) -> None:
         self._sections.append(RenderedSection(id))
-        for content in chapters:
-            self._md.renderer._title_seen = False # type: ignore[attr-defined]
-            self._sections[-1].chapters.append(self._render(content))
+        for chpath in chapters:
+            try:
+                with open(chpath, 'r') as f:
+                    self._md.renderer._title_seen = False # type: ignore[attr-defined]
+                    self._sections[-1].chapters.append(self._render(f.read()))
+            except Exception as e:
+                raise RuntimeError(f"failed to render manual chapter {chpath}") from e
 
     @abstractmethod
     def finalize(self) -> str: raise NotImplementedError()
@@ -45,7 +50,13 @@ class ManualDocBookRenderer(DocBookRenderer):
         (tag, attrs) = super()._heading_tag(token, tokens, i, options, env)
         if self._title_seen:
             if token.tag == 'h1':
-                raise RuntimeError("only one title heading allowed", token)
+                assert token.map is not None
+                raise RuntimeError(
+                    "only one title heading (# [text...]) allowed per manual chapter "
+                    f"but found a second in lines [{token.map[0]}..{token.map[1]}]. "
+                    "please remove all such headings except the first, split your "
+                    "chapters, or demote the subsequent headings to (##) or lower.",
+                    token)
             return (tag, attrs)
         self._title_seen = True
         return ("chapter", attrs | {
@@ -111,7 +122,7 @@ class ChaptersAction(argparse.Action):
                  values: Union[str, Sequence[Any], None], opt_str: Optional[str] = None) -> None:
         sections = getattr(ns, self.dest)
         if sections is None: raise argparse.ArgumentError(self, "no active section")
-        sections[-1].chapters.extend(cast(Sequence[str], values))
+        sections[-1].chapters.extend(map(Path, cast(Sequence[str], values)))
 
 def _build_cli_db(p: argparse.ArgumentParser) -> None:
     p.add_argument('--manpage-urls', required=True)
@@ -124,11 +135,7 @@ def _run_cli_db(args: argparse.Namespace) -> None:
     with open(args.manpage_urls, 'r') as manpage_urls:
         md = DocBookConverter(json.load(manpage_urls))
         for section in args.contents:
-            chapters = []
-            for p in section.chapters:
-                with open(p, 'r') as f:
-                    chapters.append(f.read())
-            md.add_section(section.id, chapters)
+            md.add_section(section.id, section.chapters)
         with open(args.outfile, 'w') as f:
             f.write(md.finalize())