meson: include pre-generated man pages & HTML docs in dist tarballs

iputils is a core utility (hard to avoid on e.g. servers or small images, even)
so it's handy to have a minimal set of build dependencies. Pre-generate
the man pages and HTML docs and include them in the dist tarball so they can
be used without installing libxslt, docbook, and friends.

This is a followup to 83f011a and
72a3687.

Bug: iputils#479
Bug: https://bugs.gentoo.org/908817
Bug: https://bugs.gentoo.org/920901
Signed-off-by: Sam James <sam@gentoo.org>

doc/meson.build

@@ -20,6 +20,30 @@ if build_tracepath == true
 	manpages += ['tracepath']
 endif
 
+if meson.version().version_compare('>=0.58.0')
+	# Use the docs included in a dist tarball if available
+	fs = import('fs')
+	out_man_pages = []
+	out_html_pages = []
+	generated_docs_exist = true
+	foreach page : manpages
+		man_page_name = page.replace('.xml', '.8')
+		html_page_name = page.replace('.xml', '.html')
+		out_man_pages += man_page_name
+		out_html_pages += html_page_name
+		if not fs.exists(man_page_name) or not fs.exists(html_page_name)
+			generated_docs_exist = false
+		endif
+	endforeach
+	if generated_docs_exist
+		install_man(out_man_pages)
+	        install_data(out_html_pages, install_dir : join_paths(get_option('datadir'), meson.project_name()))
+		subdir_done()
+	endif
+else
+	warning('Will not attempt to use pre-generated man pages with <0.58.0')
+endif
+
 xsltproc = find_program('xsltproc', required : build_mans or build_html_mans)
 xsltproc_args = [
 	'--nonet',

meson.build

@@ -220,6 +220,10 @@ endif
 
 if build_mans == true or build_html_mans == true
 	subdir ('doc')
+
+	if meson.version().version_compare('>=0.48.0')
+		meson.add_dist_script('tools/meson-build-dist-man.sh')
+	endif
 endif
 
 if run_tests

tools/meson-build-dist-man.sh

@@ -0,0 +1,12 @@
+#!/bin/sh
+# This script should be invoked by meson itself (via 'meson dist')
+# See https://github.com/mesonbuild/meson/issues/2166 and more specifically,
+# https://github.com/mesonbuild/meson/issues/2166#issuecomment-629696911.
+set -eu
+
+cd "$MESON_DIST_ROOT"
+DIR=$(mktemp -d)
+meson setup "$DIR" -DBUILD_MANS=true -DBUILD_HTML_MANS=true
+meson compile -C "$DIR"
+cp "$DIR"/doc/* doc/
+rm -rf "$DIR"