Handle puncuation-only search options.

src/parser/plain_link.rs

@@ -140,7 +140,14 @@ fn file_path_plain<'b, 'g, 'r, 's>(
         tag(":"),
         parser_with_context!(path_plain)(&parser_context),
         opt(map(
-            tuple((tag("::"), is_not(" \t\r\n"))),
+            tuple((
+                tag("::"),
+                verify(is_not(" \t\r\n"), |search_option| {
+                    Into::<&str>::into(search_option)
+                        .chars()
+                        .any(char::is_alphanumeric)
+                }),
+            )),
             |(_, search_option)| search_option,
         )),
     )))(input)?;

src/parser/regular_link.rs

@@ -262,7 +262,7 @@ fn file_path_reg<'s>(input: OrgSource<'s>) -> Res<OrgSource<'s>, PathReg<'s>> {
             search_option: search_option
                 .map(Into::<&str>::into)
                 .map(Into::<Cow<str>>::into),
-            application: todo!(),
+            application: None, // TODO
         },
     ))
 }