api-marcro: throw compiler error if description for enums is empty

A description is required for the API schema types and we fallback to
the rust doc-comment when no explicit one is set.
But a empty string was returned if no doc-comment existed, so check
for the comment to be non-empty and throw a compile-time error
otherwise.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

proxmox-api-macro/src/api/enums.rs

@@ -74,6 +74,12 @@ fn handle_string_enum(
 
         if schema.description.is_none() {
             let (comment, span) = util::get_doc_comments(&enum_ty.attrs)?;
+            if comment.is_empty() {
+                error!(
+                    Span::call_site(),
+                    "missing doc comment on enum for api-schema description"
+                );
+            }
             schema.description = Maybe::Derived(syn::LitStr::new(comment.trim(), span));
         }