meson: wire up the git-subtree(1) command

Wire up the git-subtree(1) command, which is part of "contrib/". Note
that we have to move around the exact location where we include the
"contrib/" subdirectory so that it comes after building the docs so that
we have access to some of the common functionality.

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

contrib/subtree/meson.build

@@ -0,0 +1,71 @@
+git_subtree = custom_target(
+  input: 'git-subtree.sh',
+  output: 'git-subtree',
+  command: [
+    shell,
+    meson.project_source_root() / 'generate-script.sh',
+    '@INPUT@',
+    '@OUTPUT@',
+    meson.project_build_root() / 'GIT-BUILD-OPTIONS',
+  ],
+  install: true,
+  install_dir: get_option('libexecdir') / 'git-core',
+)
+
+subtree_test_environment = test_environment
+subtree_test_environment.prepend('PATH', meson.current_build_dir())
+
+test('t7900-subtree', shell,
+  args: [ 't7900-subtree.sh' ],
+  env: subtree_test_environment,
+  workdir: meson.current_source_dir() / 't',
+  depends: test_dependencies + bin_wrappers + [ git_subtree ],
+  timeout: 0,
+)
+
+if get_option('docs').contains('man')
+  subtree_xml = custom_target(
+    command: asciidoc_common_options + [
+      '--backend=' + asciidoc_docbook,
+      '--doctype=manpage',
+      '--out-file=@OUTPUT@',
+      '@INPUT@',
+    ],
+    depends: documentation_deps,
+    input: 'git-subtree.txt',
+    output: 'git-subtree.xml',
+  )
+
+  custom_target(
+    command: [
+      xmlto,
+      '-m', '@INPUT@',
+      'man',
+      subtree_xml,
+      '-o',
+      meson.current_build_dir(),
+    ] + xmlto_extra,
+    input: [
+      '../../Documentation/manpage-normal.xsl',
+    ],
+    output: 'git-subtree.1',
+    install: true,
+    install_dir: get_option('mandir') / 'man1',
+  )
+endif
+
+if get_option('docs').contains('html')
+  custom_target(
+    command: asciidoc_common_options + [
+      '--backend=' + asciidoc_html,
+      '--doctype=manpage',
+      '--out-file=@OUTPUT@',
+      '@INPUT@',
+    ],
+    depends: documentation_deps,
+    input: 'git-subtree.txt',
+    output: 'git-subtree.html',
+    install: true,
+    install_dir: get_option('datadir') / 'doc/git-doc',
+  )
+endif

meson.build

@@ -1857,7 +1857,6 @@ endforeach
 if intl.found()
   subdir('po')
 endif
-subdir('contrib')
 
 # Gitweb requires Perl, so we disable the auto-feature if Perl was not found.
 # We make sure further up that Perl is required in case the gitweb option is
@@ -1884,6 +1883,8 @@ if get_option('docs') != []
   subdir('Documentation')
 endif
 
+subdir('contrib')
+
 foreach key, value : {
   'DIFF': diff.full_path(),
   'GIT_TEST_CMP': diff.full_path() + ' -u',