readme: make local file links work relative to out/

Thanks to awesome help at:
https://github.com/asciidoctor/asciidoctor/issues/3324

Gemfile

@@ -0,0 +1,3 @@
+source 'https://rubygems.org'
+
+gem 'asciidoctor', '2.0.10'

Gemfile.lock

@@ -0,0 +1,13 @@
+GEM
+  remote: https://rubygems.org/
+  specs:
+    asciidoctor (2.0.10)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  asciidoctor (= 2.0.10)
+
+BUNDLED WITH
+   2.0.1

README.adoc

@@ -14880,20 +14880,21 @@ Source: link:build-doc[]
 When running link:build-doc[], we do the following checks:
 
 * `<<>>` inner links are not broken
-* `+link:somefile[]+` links point to paths that exist via <<asciidoctor-extract-links>>. Upstream wontfix at: https://github.com/asciidoctor/asciidoctor/issues/3210
+* `+link:somefile[]+` links point to paths that exist via <<asciidoctor-extract-link-targets>>. Upstream wontfix at: https://github.com/asciidoctor/asciidoctor/issues/3210
 
 The scripts prints what you have to fix and exits with an error status if there are any errors.
 
-===== asciidoctor-extract-links
+[[asciidoctor-extract-link-targets]]
+===== asciidoctor/extract-link-targets
 
-Documentation for link:asciidoctor-extract-links[]
+Documentation for link:asciidoctor/extract-link-targets[]
 
 Extract link targets from Asciidoctor document.
 
 Usage:
 
 ....
-./asciidoctor-extract-links README.adoc
+./asciidoctor/extract-link-targets README.adoc
 ....
 
 Output: one link target per line.
@@ -14930,7 +14931,7 @@ ls "$(./getvar buildroot_build_dir)"
 
 Note that host tools like QEMU and gem5 store all archs in a single directory to factor out build objects, so cleaning one arch will clean all of them.
 
-To only nuke only one Buildroot package, we can use the link:https://buildroot.org/downloads/manual/manual.html#pkg-build-steps[]`-dirclean`] Buildroot target:
+To only nuke only one Buildroot package, we can use the link:https://buildroot.org/downloads/manual/manual.html#pkg-build-steps[`-dirclean`] Buildroot target:
 
 ....
 ./build-buildroot --no-all -- <package-name>-dirclean

asciidoctor/link-target-up.rb

@@ -0,0 +1,31 @@
+#!/usr/bin/env ruby
+
+=begin
+README.html links break because we place that output file in out/
+This extension hacks local link targets to the right path.
+=end
+
+require 'asciidoctor'
+require 'asciidoctor/extensions'
+
+class Main < Asciidoctor::Extensions::InlineMacroProcessor
+  use_dsl
+  named :link
+  ExternalLinkRegex = /^https?:\/\//
+  def process parent, target, attrs
+    text = attrs[1]
+    if text.nil? || text.empty?
+      text = target
+    end
+    if !ExternalLinkRegex.match?(target)
+      target = File.join('..', target)
+    end
+    create_anchor parent, text, type: :link, target: target
+  end
+end
+
+Asciidoctor::Extensions.register do
+  inline_macro Main
+end
+
+#(Asciidoctor.load_file(ARGV[0])).convert

build-doc

@@ -19,25 +19,22 @@ https://github.com/cirosantilli/linux-kernel-module-cheat#build-the-documentatio
         )
 
     def timed_main(self):
-        self.sh.run_cmd(
+        asciidoctor_dir = os.path.join(self.env['root_dir'], 'asciidoctor')
+        exit_status = self.sh.run_cmd(
             [
                 'asciidoctor', LF,
-                '-o', self.env['readme_out'], LF,
+                '--failure-level', 'info', LF,
-                '-v', self.env['readme'], LF,
+                '--require', os.path.join(asciidoctor_dir, 'link-target-up.rb'), LF,
+                '--out-file', self.env['readme_out'], LF,
+                '--trace', LF,
+                '--verbose', LF,
+                self.env['readme'], LF,
             ],
             out_file=self.env['build_doc_log'],
         )
-        error_re = re.compile('^asciidoctor: WARNING: ')
-        exit_status = 0
-        if not self.env['dry_run']:
-            with open(self.env['build_doc_log']) as f:
-                for line in f:
-                    if error_re.search(line):
-                        exit_status = 1
-                        break
         external_link_re = re.compile('^https?://')
         for link in subprocess.check_output([
-            os.path.join(self.env['root_dir'], 'asciidoctor-extract-links'),
+            os.path.join(asciidoctor_dir, 'extract-link-targets'),
             self.env['readme']
         ]).decode().splitlines():
             if not external_link_re.match(link):