Fix version number in generated gtk-doc (#3259)

* Fix version number in generated gtk-doc

By using a separate XML file for the version number.

Resolves: #3255.

* Avoid newline in `version.xml.in`

doc/libvips-docs.xml

@@ -4,12 +4,13 @@
                "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd"
 [
   <!ENTITY % local.common.attrib "xmlns:xi  CDATA  #FIXED 'http://www.w3.org/2003/XInclude'">
+  <!ENTITY version SYSTEM "version.xml">
 ]>
 <book id="index" xmlns:xlink="http://www.w3.org/1999/xlink">
   <bookinfo>
     <title>libvips Reference Manual</title>
     <releaseinfo>
-      For libvips @VIPS_VERSION@. The latest version of this documentation
+      For libvips &version;. The latest version of this documentation
       can be found on the <ulink role="online-location" url="/">libvips
       website</ulink>.
     </releaseinfo>

doc/meson.build

@@ -126,8 +126,12 @@ images = files(
 )
 
 version_conf = configuration_data()
-version_conf.set('VIPS_VERSION', meson.project_version ())
-vips_docs = configure_file(input: 'libvips-docs.xml.in', output: 'libvips-docs.xml', configuration: version_conf)
+version_conf.set('VIPS_VERSION', meson.project_version())
+version_xml = configure_file(
+    input: 'version.xml.in',
+    output: '@BASENAME@',
+    configuration: version_conf
+)
 
 glib_prefix = glib_dep.get_variable(pkgconfig: 'prefix')
 glib_docpath = glib_prefix / 'share' / 'gtk-doc' / 'html'
@@ -135,16 +139,14 @@ docpath = get_option('prefix') / get_option('datadir') / 'gtk-doc' / 'html'
 
 gnome.gtkdoc('libvips',
     mode: 'none',
-    main_xml: 'libvips-docs.xml.in',
+    main_xml: 'libvips-docs.xml',
     src_dir: [
         join_paths(project_source_root, 'libvips'),
         join_paths(project_build_root, 'libvips'),
     ],
     dependencies: libvips_dep,
-    scan_args: [
-        '--ignore-headers=' + ' '.join(private_headers),
-        '--rebuild-types',
-    ],
+    ignore_headers: private_headers,
+    scan_args: '--rebuild-types',
     mkdb_args: [ '--default-includes=vips/vips.h' ],
     fixxref_args: [
         '--html-dir=@0@'.format(docpath),
@@ -152,7 +154,7 @@ gnome.gtkdoc('libvips',
         '--extra-dir=@0@'.format(join_paths(glib_docpath, 'gobject')),
         '--extra-dir=@0@'.format(join_paths(glib_docpath, 'gio')),
     ],
-    content_files: [ content_files, markdown_content_files_docbook ],
+    content_files: [ content_files, markdown_content_files_docbook, version_xml ],
     expand_content_files: [ content_files ],
     html_assets: images,
     install: true

doc/version.xml.in

@@ -0,0 +1 @@
+@VIPS_VERSION@