Fix tags field for myst_parser (#119)

ablog/post.py

@@ -173,6 +173,16 @@ def apply(self):
 
         # Pull the metadata for the page to check if it is a blog post
         metadata = {fn.children[0].astext(): fn.children[1].astext() for fn in docinfo.traverse(nodes.field)}
+        tags = metadata.get("tags")
+        if isinstance(tags, str):
+            # myst_parser store front-matter field to TextNode in dict_to_fm_field_list.
+            # like ["a", "b", "c"]
+            # remove [] and quote
+            try:
+                tags = eval(tags)
+                metadata["tags"] = ",".join(tags)
+            except Exception:
+                logging.warning(f"fail to eval tags: {tags}")
         if docinfo.traverse(nodes.author):
             metadata["author"] = list(docinfo.traverse(nodes.author))[0].astext()
         # These two fields are special-cased in docutils