Only allow literals on top-level

which avoids potentially confusing constructs like
`dict of {{"a", "b"}: int}`

Co-authored-by: Oriol Abril-Pla <oriol.abril.pla@gmail.com>

Author: lagru

src/docstub/_docstrings.py

@@ -173,20 +173,20 @@ def transform(self, tree):
         finally:
             self._collected_imports = None
 
-    def doctype(self, tree):
+    def annotation(self, tree):
         out = " | ".join(tree.children)
         return out
 
-    def type_or(self, tree):
+    def types_or(self, tree):
         out = " | ".join(tree.children)
         return out
 
     def optional(self, tree):
         out = "None"
         literal = [child for child in tree.children if child.type == "LITERAL"]
         assert len(literal) <= 1
-        if len(literal) == 1:
-            out = lark.Discard  # Should be covered by doctype
+        if literal:
+            out = lark.Discard  # Type should cover the default
         return out
 
     def extra_info(self, tree):

src/docstub/doctype.lark

@@ -1,12 +1,13 @@
-?start : doctype
+?start : annotation
 
-doctype : type_or ("," optional)? ("," extra_info)?
+annotation : (literals | types_or) ("," optional)? ("," extra_info)?
 
-type_or : type (("or" | "|") type)*
+literals : "{" literal ("," literal)* "}"
+
+types_or : type (("or" | "|") type)*
 
 ?type : qualname
       | sphinx_ref
-      | "{" literal ("," literal)* "}" -> literals
       | shape_n_dtype
 
 optional : "optional"
@@ -19,11 +20,11 @@ sphinx_ref : ":" (NAME ":")? NAME ":`" qualname "`"
 // Name with leading dot separated path
 qualname : (/~/ ".")? (NAME ".")* NAME contains?
 
-contains: "[" type_or ("," type_or)* "]"
-        | "[" type_or "," PY_ELLIPSES "]"
+contains: "[" types_or ("," types_or)* "]"
+        | "[" types_or "," PY_ELLIPSES "]"
         | "of" type
-        | "of" "(" type_or ("," type_or)* ")"
-        | "of" "{" type_or ":" type_or "}"
+        | "of" "(" types_or ("," types_or)* ")"
+        | "of" "{" types_or ":" types_or "}"
 
 // Array-like form with dtype or shape information
 shape_n_dtype : shape? ARRAY_NAME ("of" dtype)?