we now wrap 412's

Author: l0lawrence

sdk/storage/azure-storage-file-datalake/azure/storage/filedatalake/_deserialize.py

@@ -157,10 +157,16 @@ def process_storage_error(storage_error) -> NoReturn:  # type: ignore [misc] # p
     serialized = False
     if not storage_error.response:
         raise storage_error
-    # Preserve generated exceptions for cases where remapping is not needed.
-    # ResourceExistsError is intentionally excluded so ConditionNotMet can be remapped
-    # to ResourceModifiedError based on x-ms-error-code.
-    if isinstance(storage_error, (ResourceNotFoundError, ClientAuthenticationError)):
+    # The generated layer now pre-maps 412 (Precondition Failed) responses to typed
+    # exceptions based on the request's match condition (e.g. ResourceExistsError for
+    # IfMissing, ResourceNotFoundError for IfPresent). Historically 412 was not
+    # pre-mapped and always flowed through the error-code mapping below, surfacing as
+    # ResourceModifiedError. Skip the "already serialized" shortcut for 412 so it is
+    # re-mapped from x-ms-error-code (ConditionNotMet -> ResourceModifiedError) and the
+    # public exception type is preserved for users.
+    if storage_error.response.status_code != 412 and isinstance(
+        storage_error, (ResourceNotFoundError, ClientAuthenticationError, ResourceExistsError)
+    ):
         serialized = True
     error_code = storage_error.response.headers.get("x-ms-error-code")
     error_message = storage_error.message

sdk/storage/azure-storage-file-datalake/azure/storage/filedatalake/_shared/response_handlers.py

@@ -93,12 +93,16 @@ def process_storage_error(storage_error) -> NoReturn:  # type: ignore [misc] # p
         )
     if not storage_error.response or storage_error.response.status_code in [200, 204]:
         raise storage_error
-    # Preserve generated exceptions for cases where remapping is not needed.
-    # ResourceExistsError is intentionally excluded so ConditionNotMet can be remapped
-    # to ResourceModifiedError based on x-ms-error-code.
-    if isinstance(
+    # The generated layer now pre-maps 412 (Precondition Failed) responses to typed
+    # exceptions based on the request's match condition (e.g. ResourceExistsError for
+    # IfMissing, ResourceNotFoundError for IfPresent). Historically 412 was not
+    # pre-mapped and always flowed through the error-code mapping below, surfacing as
+    # ResourceModifiedError. Skip the "already serialized" shortcut for 412 so it is
+    # re-mapped from x-ms-error-code (ConditionNotMet -> ResourceModifiedError) and the
+    # public exception type is preserved for users.
+    if storage_error.response.status_code != 412 and isinstance(
         storage_error,
-        (PartialBatchErrorException, ClientAuthenticationError, ResourceNotFoundError),
+        (PartialBatchErrorException, ClientAuthenticationError, ResourceNotFoundError, ResourceExistsError),
     ):
         serialized = True
     error_code = storage_error.response.headers.get("x-ms-error-code")