Better error message

Author: Pierre-Sassoulas

pylint/checkers/exceptions.py

@@ -15,6 +15,7 @@
 
 from pylint import checkers
 from pylint.checkers import utils
+from pylint.interfaces import HIGH
 from pylint.typing import MessageDefinitionTuple
 
 if TYPE_CHECKING:
@@ -131,7 +132,7 @@ def _is_raising(body: list) -> bool:
         "try-except-raise block!",
     ),
     "W0707": (
-        "Consider explicitly re-raising using 'raise NewError(...) from old_error'",
+        "Consider explicitly re-raising using %s'%s from %s'",
         "raise-missing-from",
         "Python 3's exception chaining means it shows the traceback of the "
         "current exception, but also the original exception. Not using `raise "
@@ -333,19 +334,39 @@ def _check_raise_missing_from(self, node: nodes.Raise) -> None:
         # like `exc.with_traceback(whatever)`. We won't analyze these, we'll just assume
         # there's a violation on two simple cases: `raise SomeException(whatever)` and `raise
         # SomeException`.
+
+        need_to_raise = False
+        except_as_exc = ""
+        exception_name = "exc"
         if containing_except_node.name is None:
             # The `except` doesn't have an `as exception:` part, meaning there's no way that
             # the `raise` is raising the same exception.
-            self.add_message("raise-missing-from", node=node)
-        elif isinstance(node.exc, nodes.Call) and isinstance(node.exc.func, nodes.Name):
-            # We have a `raise SomeException(whatever)`.
-            self.add_message("raise-missing-from", node=node)
+            if isinstance(containing_except_node.type, nodes.Name):
+                class_of_old_error = containing_except_node.type.name
+            elif isinstance(containing_except_node.type, nodes.Tuple):
+                class_of_old_error = ", ".join(
+                    n.name for n in containing_except_node.type.elts
+                )
+            except_as_exc = f"'except {class_of_old_error} as {exception_name}' and "
+            need_to_raise = True
         elif (
-            isinstance(node.exc, nodes.Name)
-            and node.exc.name != containing_except_node.name.name
+            isinstance(node.exc, nodes.Call)
+            and isinstance(node.exc.func, nodes.Name)
+            or (
+                isinstance(node.exc, nodes.Name)
+                and node.exc.name != containing_except_node.name.name
+            )
         ):
-            # We have a `raise SomeException`.
-            self.add_message("raise-missing-from", node=node)
+            # We have a `raise SomeException(whatever)` or a `raise SomeException`
+            exception_name = containing_except_node.name.name
+            need_to_raise = True
+        if need_to_raise:
+            self.add_message(
+                "raise-missing-from",
+                node=node,
+                args=(except_as_exc, node.as_string(), exception_name),
+                confidence=HIGH,
+            )
 
     def _check_catching_non_exception(self, handler, exc, part):
         if isinstance(exc, nodes.Tuple):

tests/functional/r/raise_missing_from.txt

@@ -1,7 +1,7 @@
-raise-missing-from:11:4:11:18::Consider explicitly re-raising using 'raise NewError(...) from old_error':UNDEFINED
-raise-missing-from:19:4:19:25::Consider explicitly re-raising using 'raise NewError(...) from old_error':UNDEFINED
-raise-missing-from:25:4:25:18::Consider explicitly re-raising using 'raise NewError(...) from old_error':UNDEFINED
-raise-missing-from:31:4:31:18::Consider explicitly re-raising using 'raise NewError(...) from old_error':UNDEFINED
-raise-missing-from:45:20:45:34::Consider explicitly re-raising using 'raise NewError(...) from old_error':UNDEFINED
-raise-missing-from:53:4:53:20::Consider explicitly re-raising using 'raise NewError(...) from old_error':UNDEFINED
-raise-missing-from:59:4:59:47::Consider explicitly re-raising using 'raise NewError(...) from old_error':UNDEFINED
+raise-missing-from:11:4:11:18::Consider explicitly re-raising using 'except ZeroDivisionError as exc' and 'raise KeyError from exc':HIGH
+raise-missing-from:19:4:19:25::Consider explicitly re-raising using 'except ZeroDivisionError as exc' and 'raise (foo + bar).baz from exc':HIGH
+raise-missing-from:25:4:25:18::Consider explicitly re-raising using 'raise KeyError from e':HIGH
+raise-missing-from:31:4:31:18::Consider explicitly re-raising using 'raise KeyError from e':HIGH
+raise-missing-from:45:20:45:34::Consider explicitly re-raising using 'raise KeyError from e':HIGH
+raise-missing-from:53:4:53:20::Consider explicitly re-raising using 'raise KeyError() from e':HIGH
+raise-missing-from:59:4:59:47::Consider explicitly re-raising using 'raise KeyError(whatever, whatever=whatever) from e':HIGH