Build manual with Meson

doc/manual/.version

@@ -0,0 +1 @@
+../../.version

doc/manual/book.toml

@@ -7,9 +7,21 @@ additional-js = ["redirects.js"]
 edit-url-template = "https://github.com/NixOS/nix/tree/master/doc/manual/{path}"
 git-repository-url = "https://github.com/NixOS/nix"
 
+# Handles replacing @docroot@ with a path to ./src relative to that markdown file,
+# {{#include handlebars}}, and the @generated@ syntax used within these. it mostly
+# but not entirely replaces the links preprocessor (which we cannot simply use due
+# to @generated@ files living in a different directory to make meson happy). we do
+# not want to disable the links preprocessor entirely though because that requires
+# disabling *all* built-in preprocessors and selectively reenabling those we want.
+[preprocessor.substitute]
+command = "python3 ./substitute.py"
+before = ["anchors", "links"]
+
 [preprocessor.anchors]
 renderers = ["html"]
-command = "jq --from-file doc/manual/anchors.jq"
+command = "jq --from-file ./anchors.jq"
+
+[output.markdown]
 
 [output.linkcheck]
 # no Internet during the build (in the sandbox)

doc/manual/generate-deps.py

@@ -0,0 +1,22 @@
+#!/usr/bin/env python3
+
+import glob
+import sys
+
+# meson expects makefile-style dependency declarations, i.e.
+#
+#   target: dependency...
+#
+# meson seems to pass depfiles straight on to ninja even though
+# it also parses the file itself (or at least has code to do so
+# in its tree), so we must live by ninja's rules: only slashes,
+# spaces and octothorpes can be escaped, anything else is taken
+# literally. since the rules for these aren't even the same for
+# all three we will just fail when we encounter any of them (if
+# asserts are off for some reason the depfile will likely point
+# to nonexistant paths, making everything phony and thus fine.)
+for path in glob.glob(sys.argv[1] + '/**', recursive=True):
+    assert '\\' not in path
+    assert ' ' not in path
+    assert '#' not in path
+    print("ignored:", path)

doc/manual/local.mk

@@ -223,8 +223,13 @@ $(docdir)/manual/index.html: $(MANUAL_SRCS) $(d)/book.toml $(d)/anchors.jq $(d)/
 			sed -i "s,@docroot@,$$docroot,g" "$$file"; \
 		done; \
 		set -euo pipefail; \
-		RUST_LOG=warn mdbook build "$$tmp/manual" -d $(DESTDIR)$(docdir)/manual.tmp 2>&1 \
-			| { grep -Fv "because fragment resolution isn't implemented" || :; }; \
+		( \
+		    cd "$$tmp/manual"; \
+		    RUST_LOG=warn \
+		        MDBOOK_SUBSTITUTE_SEARCH=$(d)/src \
+		        mdbook build -d $(DESTDIR)$(docdir)/manual.tmp 2>&1 \
+			    | { grep -Fv "because fragment resolution isn't implemented" || :; } \
+		); \
 		rm -rf "$$tmp/manual"
 	@rm -rf $(DESTDIR)$(docdir)/manual
 	@mv $(DESTDIR)$(docdir)/manual.tmp/html $(DESTDIR)$(docdir)/manual