meson/doc: Fix doxygen config

* Doxygen had a longstanding bug [0] where it would use `dot` even if
  not configured to do so. Due to this behaviour our config magically
  worked.
  This bug is fixed in 1.9.2 therefore we need to explicitly enable
  `dot` support in order to keep existing functionality.

* Enables WARN_AS_ERROR to catch mistakes.

* Adds a version string to the header to easily identify which commit
  the docs are built from.

[0] https://github.com/doxygen/doxygen/issues/7273

doc/Doxyfile.in.in

@@ -1,4 +1,6 @@
 PROJECT_NAME            = dav1d
+PROJECT_NUMBER          = \@VCS_TAG\@
+PROJECT_BRIEF           = dav1d is an AV1 decoder
 OUTPUT_DIRECTORY        = @DOXYGEN_OUTPUT@
 STRIP_FROM_PATH         = @DOXYGEN_STRIP@
 OUTPUT_LANGUAGE         = English
@@ -7,10 +9,12 @@ EXTRACT_ALL             = YES
 OPTIMIZE_OUTPUT_FOR_C   = YES
 DOXYFILE_ENCODING       = UTF-8
 TYPEDEF_HIDES_STRUCT    = YES
+HAVE_DOT                = YES
 
 QUIET                   = YES
 WARNINGS                = YES
 WARN_IF_UNDOCUMENTED    = YES
+WARN_AS_ERROR           = FAIL_ON_WARNINGS
 
 INPUT                   = @DOXYGEN_INPUT@
 FILE_PATTERNS           = *.h

doc/meson.build

@@ -1,4 +1,4 @@
-# Copyright © 2018-2021, VideoLAN and dav1d authors
+# Copyright © 2018-2022, VideoLAN and dav1d authors
 # All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
@@ -33,12 +33,19 @@ conf_data = configuration_data()
 conf_data.set('DOXYGEN_INPUT', dav1d_src_root / 'include/dav1d')
 conf_data.set('DOXYGEN_STRIP', dav1d_src_root / 'include')
 conf_data.set('DOXYGEN_OUTPUT', meson.current_build_dir())
-doxyfile = configure_file(input: 'Doxyfile.in',
-                          output: 'Doxyfile',
+doxyfile = configure_file(input: 'Doxyfile.in.in',
+                          output: 'Doxyfile.in',
                           configuration: conf_data)
 
+doxyfile_rev_target = vcs_tag(command: [
+        'git', '--git-dir', dav1d_git_dir, 'describe', '--long', '--always'
+    ],
+    input: doxyfile,
+    output: 'Doxyfile'
+)
+
 custom_target('doc',
               build_by_default: false,
-              command: [doxygen, doxyfile],
+              command: [doxygen, doxyfile_rev_target],
               output: ['html']
 )