panic calling `collect_schema` on lazy group_by + map_batches

[wence-]

panic calling `collect_schema` on lazy group_by + map_batches

[wence-]

One could support this on the python side with something like:

diff --git a/py-polars/polars/datatypes/_parse.py b/py-polars/polars/datatypes/_parse.py
index 55345909c..fcbdd9376 100644
--- a/py-polars/polars/datatypes/_parse.py
+++ b/py-polars/polars/datatypes/_parse.py
@@ -37,7 +37,7 @@ else:  # pragma: no cover
     UnionType = UnionTypeOld
 
 
-def parse_into_dtype(input: Any) -> PolarsDataType:
+def parse_into_dtype(input: Any, *, include_unknown: bool = False) -> PolarsDataType:
     """
     Parse an input into a Polars data type.
 
@@ -46,7 +46,7 @@ def parse_into_dtype(input: Any) -> PolarsDataType:
     TypeError
         If the input cannot be parsed into a Polars data type.
     """
-    if is_polars_dtype(input):
+    if is_polars_dtype(input, include_unknown=include_unknown):
         return input
     elif isinstance(input, ForwardRef):
         return _parse_forward_ref_into_dtype(input)
diff --git a/py-polars/polars/datatypes/classes.py b/py-polars/polars/datatypes/classes.py
index 08aeb53c5..68cc7be18 100644
--- a/py-polars/polars/datatypes/classes.py
+++ b/py-polars/polars/datatypes/classes.py
@@ -604,7 +604,7 @@ class List(NestedType):
     inner: PolarsDataType
 
     def __init__(self, inner: PolarsDataType | PythonDataType):
-        self.inner = polars.datatypes.parse_into_dtype(inner)
+        self.inner = polars.datatypes.parse_into_dtype(inner, include_unknown=True)
 
     def __eq__(self, other: PolarsDataType) -> bool:  # type: ignore[override]
         # This equality check allows comparison of type classes and type instances.
@@ -675,7 +675,7 @@ class Array(NestedType):
             msg = "Array constructor is missing the required argument `shape`"
             raise TypeError(msg)
 
-        inner_parsed = polars.datatypes.parse_into_dtype(inner)
+        inner_parsed = polars.datatypes.parse_into_dtype(inner, include_unknown=True)
         inner_shape = inner_parsed.shape if isinstance(inner_parsed, Array) else ()
 
         if isinstance(shape, int):
@@ -754,7 +754,7 @@ class Field:
 
     def __init__(self, name: str, dtype: PolarsDataType):
         self.name = name
-        self.dtype = polars.datatypes.parse_into_dtype(dtype)
+        self.dtype = polars.datatypes.parse_into_dtype(dtype, include_unknown=True)
 
     def __eq__(self, other: Field) -> bool:  # type: ignore[override]
         return (self.name == other.name) & (self.dtype == other.dtype)