[ADD] extension: allow to build graphs using graphviz

Part-of: odoo/documentation#1956

conf.py

@@ -1,10 +1,12 @@
 import re
 import os
+import shutil
 import sys
 from pathlib import Path
 
 import docutils
 from pygments.lexers import JsonLexer, XmlLexer
+from sphinx.ext import graphviz
 from sphinx.util import logging
 import sphinx
 
@@ -156,6 +158,7 @@ else:
     extensions += [
         'autodoc_placeholder',
     ]
+extensions.append('sphinx.ext.graphviz' if shutil.which('dot') else 'graphviz_placeholder')
 
 todo_include_todos = False
 

extensions/graphviz_placeholder/__init__.py

@@ -0,0 +1,25 @@
+from docutils.parsers.rst import Directive, directives
+from docutils import nodes
+
+
+class PlaceHolder(Directive):
+    """ Placeholder class for directives that must be skipped. """
+
+    has_content = True
+
+    def run(self):
+        node = nodes.literal_block('graphviz', '')
+        node += nodes.Text(
+            f'{self.content[0]}\n'
+            '> Graph not rendered because `dot` is not installed'
+        )
+        return [node]
+
+
+def setup(app):
+    directives.register_directive('graphviz', PlaceHolder)
+
+    return {
+        'parallel_read_safe': True,
+        'parallel_write_safe': True
+    }

extensions/odoo_theme/static/style.scss

@@ -971,6 +971,13 @@ header.o_main_header {
                 }
             }
         }
+        .graphviz {
+            overflow-x: auto;
+            white-space: nowrap;
+            img {
+                max-width: unset;
+            }
+        }
     }
 }
 //------------------------------------------------------------------------------