feat: add snapshot diffing support

src/syrupy/assertion.py

@@ -26,6 +26,7 @@
         PropertyMatcher,
         SerializableData,
         SerializedData,
+        SnapshotIndex,
     )
 
 
@@ -169,10 +170,11 @@ def __with_prop(self, prop_name: str, prop_value: Any) -> None:
     def __call__(
         self,
         *,
+        diff: Optional["SnapshotIndex"] = None,
         exclude: Optional["PropertyFilter"] = None,
         extension_class: Optional[Type["AbstractSyrupyExtension"]] = None,
         matcher: Optional["PropertyMatcher"] = None,
-        name: Optional[str] = None,
+        name: Optional["SnapshotIndex"] = None,
     ) -> "SnapshotAssertion":
         """
         Modifies assertion instance options
@@ -185,6 +187,8 @@ def __call__(
             self.__with_prop("_matcher", matcher)
         if name:
             self.__with_prop("_custom_index", name)
+        if diff is not None:
+            self.__with_prop("_snapshot_diff", diff)
         return self
 
     def __dir__(self) -> List[str]:
@@ -202,8 +206,17 @@ def _assert(self, data: "SerializableData") -> bool:
         assertion_success = False
         assertion_exception = None
         try:
-            snapshot_data = self._recall_data()
+            snapshot_data = self._recall_data(index=self.index)
             serialized_data = self._serialize(data)
+            snapshot_diff = getattr(self, "_snapshot_diff", None)
+            if snapshot_diff is not None:
+                snapshot_data_diff = self._recall_data(index=snapshot_diff)
+                if snapshot_data_diff is None:
+                    raise SnapshotDoesNotExist()
+                serialized_data = self.extension.diff_snapshots(
+                    serialized_data=serialized_data,
+                    snapshot_data=snapshot_data_diff,
+                )
             matches = snapshot_data is not None and self.extension.matches(
                 serialized_data=serialized_data, snapshot_data=snapshot_data
             )
@@ -241,8 +254,8 @@ def _post_assert(self) -> None:
         while self._post_assert_actions:
             self._post_assert_actions.pop()()
 
-    def _recall_data(self) -> Optional["SerializableData"]:
+    def _recall_data(self, index: "SnapshotIndex") -> Optional["SerializableData"]:
         try:
-            return self.extension.read_snapshot(index=self.index)
+            return self.extension.read_snapshot(index=index)
         except SnapshotDoesNotExist:
             return None

src/syrupy/extensions/amber/serializer.py

@@ -1,6 +1,9 @@
 import functools
 import os
-from types import GeneratorType
+from types import (
+    GeneratorType,
+    MappingProxyType,
+)
 from typing import (
     TYPE_CHECKING,
     Any,
@@ -163,7 +166,7 @@ def _serialize(
             serialize_method = cls.serialize_number
         elif isinstance(data, (set, frozenset)):
             serialize_method = cls.serialize_set
-        elif isinstance(data, dict):
+        elif isinstance(data, (dict, MappingProxyType)):
             serialize_method = cls.serialize_dict
         elif cls.__is_namedtuple(data):
             serialize_method = cls.serialize_namedtuple

src/syrupy/extensions/base.py

@@ -15,10 +15,10 @@
     List,
     Optional,
     Set,
-    Union,
 )
 
 from syrupy.constants import (
+    DISABLE_COLOR_ENV_VAR,
     SNAPSHOT_DIRNAME,
     SYMBOL_CARRIAGE,
     SYMBOL_ELLIPSIS,
@@ -40,7 +40,11 @@
     snapshot_diff_style,
     snapshot_style,
 )
-from syrupy.utils import walk_snapshot_dir
+from syrupy.utils import (
+    env_context,
+    obj_attrs,
+    walk_snapshot_dir,
+)
 
 if TYPE_CHECKING:
     from syrupy.location import PyTestLocation
@@ -49,6 +53,7 @@
         PropertyMatcher,
         SerializableData,
         SerializedData,
+        SnapshotIndex,
     )
 
 
@@ -74,7 +79,7 @@ class SnapshotFossilizer(ABC):
     def test_location(self) -> "PyTestLocation":
         raise NotImplementedError
 
-    def get_snapshot_name(self, *, index: Union[str, int] = 0) -> str:
+    def get_snapshot_name(self, *, index: "SnapshotIndex" = 0) -> str:
         """Get the snapshot name for the assertion index in a test location"""
         index_suffix = ""
         if isinstance(index, (str,)):
@@ -83,7 +88,7 @@ def get_snapshot_name(self, *, index: Union[str, int] = 0) -> str:
             index_suffix = f".{index}"
         return f"{self.test_location.snapshot_name}{index_suffix}"
 
-    def get_location(self, *, index: Union[str, int]) -> str:
+    def get_location(self, *, index: "SnapshotIndex") -> str:
         """Returns full location where snapshot data is stored."""
         basename = self._get_file_basename(index=index)
         fileext = f".{self._file_extension}" if self._file_extension else ""
@@ -110,7 +115,7 @@ def discover_snapshots(self) -> "SnapshotFossils":
 
         return discovered
 
-    def read_snapshot(self, *, index: Union[str, int]) -> "SerializedData":
+    def read_snapshot(self, *, index: "SnapshotIndex") -> "SerializedData":
         """
         Utility method for reading the contents of a snapshot assertion.
         Will call `_pre_read`, then perform `read` and finally `post_read`,
@@ -132,7 +137,7 @@ def read_snapshot(self, *, index: Union[str, int]) -> "SerializedData":
         finally:
             self._post_read(index=index)
 
-    def write_snapshot(self, *, data: "SerializedData", index: Union[str, int]) -> None:
+    def write_snapshot(self, *, data: "SerializedData", index: "SnapshotIndex") -> None:
         """
         Utility method for writing the contents of a snapshot assertion.
         Will call `_pre_write`, then perform `write` and finally `_post_write`.
@@ -178,17 +183,17 @@ def delete_snapshots(
         """
         raise NotImplementedError
 
-    def _pre_read(self, *, index: Union[str, int] = 0) -> None:
+    def _pre_read(self, *, index: "SnapshotIndex" = 0) -> None:
         pass
 
-    def _post_read(self, *, index: Union[str, int] = 0) -> None:
+    def _post_read(self, *, index: "SnapshotIndex" = 0) -> None:
         pass
 
-    def _pre_write(self, *, data: "SerializedData", index: Union[str, int] = 0) -> None:
+    def _pre_write(self, *, data: "SerializedData", index: "SnapshotIndex" = 0) -> None:
         self.__ensure_snapshot_dir(index=index)
 
     def _post_write(
-        self, *, data: "SerializedData", index: Union[str, int] = 0
+        self, *, data: "SerializedData", index: "SnapshotIndex" = 0
     ) -> None:
         pass
 
@@ -225,11 +230,11 @@ def _dirname(self) -> str:
     def _file_extension(self) -> str:
         raise NotImplementedError
 
-    def _get_file_basename(self, *, index: Union[str, int]) -> str:
+    def _get_file_basename(self, *, index: "SnapshotIndex") -> str:
         """Returns file basename without extension. Used to create full filepath."""
         return self.test_location.filename
 
-    def __ensure_snapshot_dir(self, *, index: Union[str, int]) -> None:
+    def __ensure_snapshot_dir(self, *, index: "SnapshotIndex") -> None:
         """
         Ensures the folder path for the snapshot file exists.
         """
@@ -240,6 +245,16 @@ def __ensure_snapshot_dir(self, *, index: Union[str, int]) -> None:
 
 
 class SnapshotReporter(ABC):
+    _context_line_count = 1
+
+    def diff_snapshots(
+        self, serialized_data: "SerializedData", snapshot_data: "SerializedData"
+    ) -> "SerializedData":
+        env = {DISABLE_COLOR_ENV_VAR: "true"}
+        attrs = {"_context_line_count": 0}
+        with env_context(**env), obj_attrs(self, attrs):
+            return "\n".join(self.diff_lines(serialized_data, snapshot_data))
+
     def diff_lines(
         self, serialized_data: "SerializedData", snapshot_data: "SerializedData"
     ) -> Iterator[str]:
@@ -250,10 +265,6 @@ def diff_lines(
     def _ends(self) -> Dict[str, str]:
         return {"\n": self._marker_new_line, "\r": self._marker_carriage}
 
-    @property
-    def _context_line_count(self) -> int:
-        return 1
-
     @property
     def _context_line_max(self) -> int:
         return self._context_line_count * 2

src/syrupy/extensions/single_file.py

@@ -4,7 +4,6 @@
     TYPE_CHECKING,
     Optional,
     Set,
-    Union,
 )
 from unicodedata import category
 
@@ -21,6 +20,7 @@
         PropertyMatcher,
         SerializableData,
         SerializedData,
+        SnapshotIndex,
     )
 
 
@@ -34,7 +34,7 @@ def serialize(
     ) -> "SerializedData":
         return bytes(data)
 
-    def get_snapshot_name(self, *, index: Union[str, int] = 0) -> str:
+    def get_snapshot_name(self, *, index: "SnapshotIndex" = 0) -> str:
         return self.__clean_filename(
             super(SingleFileSnapshotExtension, self).get_snapshot_name(index=index)
         )
@@ -48,7 +48,7 @@ def delete_snapshots(
     def _file_extension(self) -> str:
         return "raw"
 
-    def _get_file_basename(self, *, index: Union[str, int]) -> str:
+    def _get_file_basename(self, *, index: "SnapshotIndex") -> str:
         return self.get_snapshot_name(index=index)
 
     @property

src/syrupy/types.py

@@ -8,6 +8,7 @@
     Union,
 )
 
+SnapshotIndex = Union[int, str]
 SerializableData = Any
 SerializedData = Union[str, bytes]
 PropertyName = Hashable

src/syrupy/utils.py

@@ -6,6 +6,7 @@
 from pathlib import Path
 from typing import (
     Any,
+    Dict,
     Iterator,
 )
 
@@ -66,3 +67,17 @@ def env_context(**kwargs: str) -> Iterator[None]:
     finally:
         os.environ.clear()
         os.environ.update(prev_env)
+
+
+def set_attrs(obj: Any, attrs: Dict[str, Any]) -> Any:
+    for k in attrs:
+        setattr(obj, k, attrs[k])
+
+
+@contextmanager
+def obj_attrs(obj: Any, attrs: Dict[str, Any]) -> Iterator[None]:
+    prev_attrs = {k: getattr(obj, k, None) for k in attrs}
+    try:
+        yield set_attrs(obj, attrs)
+    finally:
+        set_attrs(obj, prev_attrs)

tests/syrupy/extensions/amber/__snapshots__/test_amber_snapshot_diff.ambr

@@ -0,0 +1,108 @@
+# name: test_snapshot_diff
+  dict({
+    'field_0': True,
+    'field_1': 'no_value',
+    'nested': dict({
+      'field_0': 1,
+    }),
+  })
+# ---
+# name: test_snapshot_diff.1
+      ...
+  -   'field_1': 'no_value',
+  +   'field_1': 'yes_value',
+      ...
+# ---
+# name: test_snapshot_diff.2
+      ...
+  -   'field_1': 'no_value',
+  +   'field_1': 'yes_value',
+      ...
+  -     'field_0': 1,
+  +     'field_0': 2,
+    ...
+# ---
+# name: test_snapshot_diff_id.1
+      ...
+  -   'field_1': 'no_value',
+  +   'field_1': 'yes_value',
+      ...
+  -     True,
+        ...
+  -     None,
+  +     False,
+      ...
+  -     'no',
+  +     'yes',
+  -     False,
+  +     0,
+      ...
+# ---
+# name: test_snapshot_diff_id[case3]
+        ...
+  -     'field_0': True,
+  +     'field_0': 2,
+          ...
+  -     'field_0': True,
+  +     'field_0': 2,
+          ...
+# ---
+# name: test_snapshot_diff_id[large snapshot]
+  dict({
+    'field_0': True,
+    'field_1': 'no_value',
+    'field_2': 0,
+    'field_3': None,
+    'field_4': 1,
+    'field_5': False,
+    'field_6': tuple(
+      True,
+      'hey',
+      2,
+      None,
+    ),
+    'field_7': set({
+      'no',
+      False,
+      None,
+    }),
+    'nested_0': dict({
+      'field_0': True,
+      'field_1': 'no_value',
+      'field_2': 0,
+      'field_3': None,
+      'field_4': 1,
+      'field_5': False,
+      'field_6': tuple(
+        True,
+        'hey',
+        2,
+        None,
+      ),
+      'field_7': set({
+        'no',
+        False,
+        None,
+      }),
+    }),
+    'nested_1': dict({
+      'field_0': True,
+      'field_1': 'no_value',
+      'field_2': 0,
+      'field_3': None,
+      'field_4': 1,
+      'field_5': False,
+      'field_6': tuple(
+        True,
+        'hey',
+        2,
+        None,
+      ),
+      'field_7': set({
+        'no',
+        False,
+        None,
+      }),
+    }),
+  })
+# ---