meson: wire up support for AsciiDoctor

While our Makefile supports both Asciidoc and AsciiDoctor, our Meson
build instructions only support the former. Wire up support for the
latter, as well.

Our Makefile always favors Asciidoc, but Meson will automatically figure
out which of both to use based on whether they are installed or not. To
keep compatibility with our Makefile it favors Asciidoc over Asciidoctor
in case both are available.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 84 insertions, 28 deletions

diff --git a/Documentation/meson.build b/Documentation/meson.build
index fca3eab1f1..acd6d86ec7 100644
--- a/Documentation/meson.build
+++ b/Documentation/meson.build
@@ -204,29 +204,87 @@ manpages = {
   'gitworkflows.txt' : 7,
 }
 
-asciidoc = find_program('asciidoc')
-git = find_program('git', required: false)
-xmlto = find_program('xmlto')
+docs_backend = get_option('docs_backend')
+if docs_backend == 'auto'
+  if find_program('asciidoc', required: false).found()
+    docs_backend = 'asciidoc'
+  elif find_program('asciidoctor', required: false).found()
+    docs_backend = 'asciidoctor'
+  else
+    error('Neither asciidoc nor asciidoctor were found.')
+  endif
+endif
 
-asciidoc_conf = custom_target(
-  command: [
-    shell,
-    meson.project_source_root() / 'GIT-VERSION-GEN',
-    meson.project_source_root(),
-    '@INPUT@',
-    '@OUTPUT@',
-  ],
-  input: meson.current_source_dir() / 'asciidoc.conf.in',
-  output: 'asciidoc.conf',
-  depends: [git_version_file],
-  env: version_gen_environment,
-)
+if docs_backend == 'asciidoc'
+  asciidoc = find_program('asciidoc', required: true)
+  asciidoc_html = 'xhtml11'
+  asciidoc_docbook = 'docbook'
+  xmlto_extra = [ ]
 
-asciidoc_common_options = [
-  asciidoc,
-  '--conf-file=' + asciidoc_conf.full_path(),
-  '--attribute=build_dir=' + meson.current_build_dir(),
-]
+  asciidoc_conf = custom_target(
+    command: [
+      shell,
+      meson.project_source_root() / 'GIT-VERSION-GEN',
+      meson.project_source_root(),
+      '@INPUT@',
+      '@OUTPUT@',
+    ],
+    input: meson.current_source_dir() / 'asciidoc.conf.in',
+    output: 'asciidoc.conf',
+    depends: [git_version_file],
+    env: version_gen_environment,
+  )
+
+  asciidoc_common_options = [
+    asciidoc,
+    '--conf-file=' + asciidoc_conf.full_path(),
+    '--attribute=build_dir=' + meson.current_build_dir(),
+  ]
+
+  documentation_deps = [
+    asciidoc_conf,
+  ]
+elif docs_backend == 'asciidoctor'
+  asciidoctor = find_program('asciidoctor', required: true)
+  asciidoc_html = 'xhtml5'
+  asciidoc_docbook = 'docbook5'
+  xmlto_extra = [
+    '--skip-validation',
+    '-x', meson.current_source_dir() / 'manpage.xsl',
+  ]
+
+  asciidoctor_extensions = custom_target(
+    command: [
+      shell,
+      meson.project_source_root() / 'GIT-VERSION-GEN',
+      meson.project_source_root(),
+      '@INPUT@',
+      '@OUTPUT@',
+    ],
+    input: meson.current_source_dir() / 'asciidoctor-extensions.rb.in',
+    output: 'asciidoctor-extensions.rb',
+    depends: [git_version_file],
+    env: version_gen_environment,
+  )
+
+  asciidoc_common_options = [
+    asciidoctor,
+    '--attribute', 'compat-mode',
+    '--attribute', 'tabsize=8',
+    '--attribute', 'litdd=--',
+    '--attribute', 'docinfo=shared',
+    '--attribute', 'build_dir=' + meson.current_build_dir(),
+    '--load-path', meson.current_build_dir(),
+    '--require', 'asciidoctor-extensions',
+  ]
+
+  documentation_deps = [
+    asciidoctor_extensions,
+  ]
+endif
+
+git = find_program('git', required: false)
+xmlto = find_program('xmlto')
 
 cmd_lists = [
   'cmds-ancillaryinterrogators.txt',
@@ -243,10 +301,6 @@ cmd_lists = [
   'cmds-foreignscminterface.txt',
 ]
 
-documentation_deps = [
-  asciidoc_conf,
-]
-
 documentation_deps += custom_target(
   command: [
     perl,
@@ -278,7 +332,7 @@ foreach manpage, category : manpages
   if get_option('docs').contains('man')
     manpage_xml_target = custom_target(
       command: asciidoc_common_options + [
-        '--backend=docbook',
+        '--backend=' + asciidoc_docbook,
         '--doctype=manpage',
         '--out-file=@OUTPUT@',
         meson.current_source_dir() / manpage,
@@ -301,7 +355,7 @@ foreach manpage, category : manpages
         manpage_xml_target,
         '-o',
         meson.current_build_dir(),
-      ],
+      ] + xmlto_extra,
       output: manpage_path,
       install: true,
       install_dir: get_option('mandir') / 'man' + category.to_string(),
@@ -311,7 +365,7 @@ foreach manpage, category : manpages
   if get_option('docs').contains('html') and category == 1
     custom_target(
       command: asciidoc_common_options + [
-        '--backend=xhtml11',
+        '--backend=' + asciidoc_html,
         '--doctype=manpage',
         '--out-file=@OUTPUT@',
         meson.current_source_dir() / manpage,
diff --git a/meson_options.txt b/meson_options.txt
index 4be7eab399..f50bb40cdf 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -85,6 +85,8 @@ option('docs', type: 'array', choices: ['man', 'html'], value: [],
   description: 'Which documenattion formats to build and install.')
 option('default_help_format', type: 'combo', choices: ['man', 'html'], value: 'man',
   description: 'Default format used when executing git-help(1).')
+option('docs_backend', type: 'combo', choices: ['asciidoc', 'asciidoctor', 'auto'], value: 'auto',
+  description: 'Which backend to use to generate documentation.')
 
 # Testing.
 option('tests', type: 'boolean', value: true,