Allow reading diagrams from file

content/nested/diagram.mmd

@@ -0,0 +1,11 @@
+sequenceDiagram
+    participant Alice
+    participant Bob
+    Alice->John: Hello John, how are you?
+    loop Healthcheck
+        John->John: Fight against hypochondria
+    end
+    Note right of John: Rational thoughts prevail...
+    John-->Alice: Great!
+    John->Bob: How about you?
+    Bob-->John: Jolly good!

content/nested/index.md

@@ -4,3 +4,7 @@ tags:
     - tag2
 ---
 # Nested
+
+```mermaid
+{% include_file "./diagram.mmd" %}
+```

hooks/include-file.py

@@ -0,0 +1,19 @@
+from jinja2_simple_tags import StandaloneTag
+import os
+
+def on_env(env, config, files):
+    env.add_extension(IncludeFileTag)
+
+    return env
+
+class IncludeFileTag(StandaloneTag):
+    tags = {"include_file"}
+
+    def render(self, path):
+        if path.startswith("/"):
+            file_path = os.path.join(self.context["config"]["site_dir"], path.removeprefix("/"))
+        else:
+            file_path = os.path.join(os.path.dirname(self.context["page"].file.abs_src_path), path)
+
+        with open(file_path) as f:
+            return f.read()

hooks/kroki.py

@@ -47,11 +47,18 @@ def on_config(config):
     opener.addheaders = [('User-Agent','mkdocs')]
     install_opener(opener)
 
-    custom_fences = [{
-        "name": "blockdiag",
-        "class": "blockdiag",
-        "format": partial(fence_div_format, config["site_dir"])
-    }]
+    custom_fences = [
+        {
+            "name": "blockdiag",
+            "class": "blockdiag",
+            "format": partial(fence_div_format, config["site_dir"])
+        },
+        {
+            "name": "mermaid",
+            "class": "mermaid",
+            "format": partial(fence_div_format, config["site_dir"])
+        }
+    ]
 
     config.mdx_configs["pymdownx.superfences"] = {
         "custom_fences": custom_fences

mkdocs.yml

@@ -18,6 +18,7 @@ hooks:
   - hooks/globals.py
   - hooks/pygments-styles.py
   - hooks/kroki.py
+  - hooks/include-file.py
 
 markdown_extensions:
   - attr_list