Validate the argument of the gql function

gql/gql.py

@@ -1,17 +1,24 @@
+from __future__ import annotations
+
 from graphql import DocumentNode, Source, parse
 
 
-def gql(request_string: str) -> DocumentNode:
-    """Given a String containing a GraphQL request, parse it into a Document.
+def gql(request_string: str | Source) -> DocumentNode:
+    """Given a string containing a GraphQL request, parse it into a Document.
 
     :param request_string: the GraphQL request as a String
-    :type request_string: str
+    :type request_string: str | Source
     :return: a Document which can be later executed or subscribed by a
         :class:`Client <gql.client.Client>`, by an
         :class:`async session <gql.client.AsyncClientSession>` or by a
         :class:`sync session <gql.client.SyncClientSession>`
 
     :raises GraphQLError: if a syntax error is encountered.
     """
-    source = Source(request_string, "GraphQL request")
+    if isinstance(request_string, Source):
+        source = request_string
+    elif isinstance(request_string, str):
+        source = Source(request_string, "GraphQL request")
+    else:
+        raise TypeError("Request must be passed as a string or Source object.")
     return parse(source)

tests/starwars/test_query.py

@@ -1,5 +1,5 @@
 import pytest
-from graphql import GraphQLError
+from graphql import GraphQLError, Source
 
 from gql import Client, gql
 from tests.starwars.schema import StarWarsSchema
@@ -323,3 +323,17 @@ def test_mutation_result(client):
     expected = {"createReview": {"stars": 5, "commentary": "This is a great movie!"}}
     result = client.execute(query, variable_values=params)
     assert result == expected
+
+
+def test_query_from_source(client):
+    source = Source("{ hero { name } }")
+    query = gql(source)
+    expected = {"hero": {"name": "R2-D2"}}
+    result = client.execute(query)
+    assert result == expected
+
+
+def test_already_parsed_query(client):
+    query = gql("{ hero { name } }")
+    with pytest.raises(TypeError, match="must be passed as a string"):
+        gql(query)