Make callback in python patch more readable.

Summary:
Currently callback uses lambda. We can create an actual function to make it more readable.

{F1973681999}

Reviewed By: thedavekwon

Differential Revision: D66996590

fbshipit-source-id: f0d22c4107e62c536d57b957abaf31ae66ac9698

third-party/thrift/src/thrift/compiler/generate/templates/patch/thrift_patch.py.mustache

@@ -43,6 +43,7 @@ from common.thrift.patch.detail.py_bindings.DynamicPatch import (
     BinaryPatch,
     StructPatch as DynamicStructPatch,
     UnionPatch as DynamicUnionPatch,
+    DynamicPatch
 )
 
 import thrift.python.types as _fbthrift_python_types
@@ -73,8 +74,14 @@ class {{struct:py_name}}Patch(
             {{#field:type}}{{> ../python/types/unadapted_pep484_type}}{{/field:type}},
             {{#field:type}}{{> ../python/types/unadapted_pep484_patch_type}}{{/field:type}}]:
 
+        {{#field:type}}
+        {{! e.g., if field is an i32, this function convert DynamicPatch --> I32Patch }}
+        def cast_dynamic_patch_to_typed_field_patch(patch: DynamicPatch, type_info) -> {{#field:type}}{{> ../python/types/unadapted_pep484_patch_type}}{{/field:type}}:
+            {{> ../python/common/thrift_patch_callback}}
+        {{/field:type}}
+
         return {{> types/field_patch_type}}(
-            {{#field:type}}{{> ../python/common/thrift_patch_callback}}{{/field:type}},
+            cast_dynamic_patch_to_typed_field_patch,
             self._patch,
             {{field:key}},
             {{#field:type}}{{> ../python/types/typeinfo }}{{/field:type}})

third-party/thrift/src/thrift/compiler/generate/templates/python/common/thrift_patch_callback.mustache

@@ -14,24 +14,51 @@
   See the License for the specific language governing permissions and
   limitations under the License.
 
-}}{{!
-  Lambda is not type checked by pyre, though here we only used lambda internally, it won't affect UX.
-}}lambda patch, type_info: {{!
-}}{{#type:bool?}}patch.as_bool_patch(){{/type:bool?}}{{!
-}}{{#type:byte?}}patch.as_byte_patch(){{/type:byte?}}{{!
-}}{{#type:i16?}}patch.as_i16_patch(){{/type:i16?}}{{!
-}}{{#type:i32?}}patch.as_i32_patch(){{/type:i32?}}{{!
-}}{{#type:i64?}}patch.as_i64_patch(){{/type:i64?}}{{!
-}}{{#type:double?}}patch.as_double_patch(){{/type:double?}}{{!
-}}{{#type:float?}}patch.as_float_patch(){{/type:float?}}{{!
-}}{{#type:string?}}patch.as_string_patch(){{/type:string?}}{{!
-}}{{#type:binary?}}patch.as_binary_patch(){{/type:binary?}}{{!
-}}{{#type:enum}}patch.as_enum_patch(){{/type:enum}}{{!
-}}{{#type:list?}}ListPatch(patch.as_list_patch(), type_info){{/type:list?}}{{!
-}}{{#type:set?}}SetPatch(patch.as_set_patch(), type_info){{/type:set?}}{{!
-}}{{#type:map?}}{{#type:value_type}}{{!
-}}MapPatch({{> common/thrift_patch_callback}}, patch.as_map_patch(), type_info){{!
-}}{{/type:value_type}}{{/type:map?}}{{!
-}}{{#type:struct}}{{!
-    }}{{#type:need_patch_module_path?}}{{type:patch_module_path}}.{{/type:need_patch_module_path?}}{{struct:py_name}}Patch(patch){{!
-}}{{/type:struct}}
+}}
+{{#type:bool?}}
+return patch.as_bool_patch()
+{{/type:bool?}}
+{{#type:byte?}}
+return patch.as_byte_patch()
+{{/type:byte?}}
+{{#type:i16?}}
+return patch.as_i16_patch()
+{{/type:i16?}}
+{{#type:i32?}}
+return patch.as_i32_patch()
+{{/type:i32?}}
+{{#type:i64?}}
+return patch.as_i64_patch()
+{{/type:i64?}}
+{{#type:float?}}
+return patch.as_float_patch()
+{{/type:float?}}
+{{#type:double?}}
+return patch.as_double_patch()
+{{/type:double?}}
+{{#type:string?}}
+return patch.as_string_patch()
+{{/type:string?}}
+{{#type:binary?}}
+return patch.as_binary_patch()
+{{/type:binary?}}
+{{#type:enum?}}
+return patch.as_enum_patch()
+{{/type:enum?}}
+{{#type:list?}}
+return ListPatch(patch.as_list_patch(), type_info)
+{{/type:list?}}
+{{#type:set?}}
+return SetPatch(patch.as_set_patch(), type_info)
+{{/type:set?}}
+{{#type:map?}}
+{{! e.g., if map value is an i32, this function convert DynamicPatch --> I32Patch }}
+{{#type:value_type}}
+def cast_dynamic_patch_to_typed_map_value_patch(patch: DynamicPatch, type_info) -> {{> types/unadapted_pep484_patch_type}}:
+    {{> common/thrift_patch_callback}}
+{{/type:value_type}}
+return MapPatch(cast_dynamic_patch_to_typed_map_value_patch, patch.as_map_patch(), type_info)
+{{/type:map?}}
+{{#type:struct}}
+return {{#type:need_patch_module_path?}}{{type:patch_module_path}}.{{/type:need_patch_module_path?}}{{struct:py_name}}Patch(patch)
+{{/type:struct}}