doc: separate manpage URLs from the Pandoc filter

Move the manpage-to-URL mapping to `doc/manpage-urls.json` so that we can
reuse that file elsewhere, and generate the `link-manpages.lua` filter from
that file.

Also modify the Pandoc filter so that it doesn't wrap manpages that are
already inside a link.

Keeping a Lua filter is essential for speed: a Python filter would
increase the runtime `md-to-db.sh` from ~20s to ~30s (but Python is not
to blame; marshalling Pandoc types to and from JSON is a costly operation).
Parsing in Lua seems tedious, so I went with the Nix way.

1 files changed, 1 insertions, 1 deletions

diff --git a/doc/contributing/contributing-to-documentation.chapter.md b/doc/contributing/contributing-to-documentation.chapter.md
index 81482523cd0e..889b4114acca 100644
--- a/doc/contributing/contributing-to-documentation.chapter.md
+++ b/doc/contributing/contributing-to-documentation.chapter.md
@@ -53,7 +53,7 @@ Additional syntax extensions are available, though not all extensions can be use
   This syntax is taken from [MyST](https://myst-parser.readthedocs.io/en/latest/using/syntax.html#targets-and-cross-referencing).
 
 - []{#ssec-contributing-markup-inline-roles}
-  If you want to link to a man page, you can use `` {manpage}`nix.conf(5)` ``, which will turn into {manpage}`nix.conf(5)`. The references will turn into links when a mapping exists in {file}`doc/build-aux/pandoc-filters/link-unix-man-references.lua`.
+  If you want to link to a man page, you can use `` {manpage}`nix.conf(5)` ``, which will turn into {manpage}`nix.conf(5)`. The references will turn into links when a mapping exists in {file}`doc/manpage-urls.json`.
 
   A few markups for other kinds of literals are also available: