From 36b059748d06e39fb3e588463bbc4ddcd2255f27 Mon Sep 17 00:00:00 2001
From: Alexander Bantyev <balsoft@balsoft.ru>
Date: Thu, 23 Mar 2023 19:27:41 +0400
Subject: Split nix-env and nix-store documentation per-subcommand

Documentation on "classic" commands with many sub-commands are
notoriously hard to discover due to lack of overview and anchor links.
Additionally the information on common options and environment variables
is not accessible offline in man pages, and therefore often overlooked
by readers.

With this change, each sub-command of nix-store and nix-env gets its
own page in the manual (listed in the table of contents), and each own
man page.

Also, man pages for each subcommand now (again) list common options
and environment variables. While this makes each page quite long and
some common parameters don't apply, this should still make it easier
to navigate as that additional information was not accessible on the
command line at all.

It is now possible to run 'nix-store --<subcommand> --help` to display
help pages for the given subcommand.

Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>
---
 doc/manual/local.mk | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

(limited to 'doc/manual/local.mk')

diff --git a/doc/manual/local.mk b/doc/manual/local.mk
index 284a85ab5..a38046701 100644
--- a/doc/manual/local.mk
+++ b/doc/manual/local.mk
@@ -13,6 +13,13 @@ man-pages := $(foreach n, \
 	nix.conf.5 nix-daemon.8 \
 , $(d)/$(n))
 
+# man pages for subcommands
+# convert from `$(d)/src/command-ref/nix-{1}/{2}.md` to `$(d)/nix-{1}-{2}.1`
+# FIXME: unify with how nix3-cli man pages are generated
+man-pages += $(foreach subcommand, \
+	$(filter-out %opt-common.md %env-common.md, $(wildcard $(d)/src/command-ref/nix-*/*.md)), \
+	$(d)/$(subst /,-,$(subst $(d)/src/command-ref/,,$(subst .md,.1,$(subcommand)))))
+
 clean-files += $(d)/*.1 $(d)/*.5 $(d)/*.8
 
 # Provide a dummy environment for nix, so that it will not access files outside the macOS sandbox.
@@ -38,6 +45,26 @@ define process-includes
 	done < <(grep '{{#include' $(1))
 endef
 
+$(d)/nix-env-%.1: $(d)/src/command-ref/nix-env/%.md
+	@printf "Title: %s\n\n" "$(subst nix-env-,nix-env --,$$(basename "$@" .1))" > $^.tmp
+	$(render-subcommand)
+
+$(d)/nix-store-%.1: $(d)/src/command-ref/nix-store/%.md
+	@printf -- 'Title: %s\n\n' "$(subst nix-store-,nix-store --,$$(basename "$@" .1))" > $^.tmp
+	$(render-subcommand)
+
+# FIXME: there surely is some more deduplication to be achieved here with even darker Make magic
+define render-subcommand
+  @cat $^ >> $^.tmp
+	@$(call process-includes,$^,$^.tmp)
+	$(trace-gen) lowdown -sT man --nroff-nolinks -M section=1 $^.tmp -o $@
+	@# fix up `lowdown`'s automatic escaping of `--`
+	@# https://github.com/kristapsdz/lowdown/blob/edca6ce6d5336efb147321a43c47a698de41bb7c/entity.c#L202
+	@sed -i 's/\e\[u2013\]/--/' $@
+	@rm $^.tmp
+endef
+
+
 $(d)/%.1: $(d)/src/command-ref/%.md
 	@printf "Title: %s\n\n" "$$(basename $@ .1)" > $^.tmp
 	@cat $^ >> $^.tmp
-- 
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