Avoid raising bare Exception

libcst/__init__.py

@@ -4,6 +4,7 @@
 # LICENSE file in the root directory of this source tree.
 
 from libcst._batched_visitor import BatchableCSTVisitor, visit_batched
+from libcst._excep import CSTLogicError
 from libcst._exceptions import MetadataException, ParserSyntaxError
 from libcst._flatten_sentinel import FlattenSentinel
 from libcst._maybe_sentinel import MaybeSentinel
@@ -238,6 +239,7 @@
     "CSTNodeT",
     "CSTTransformer",
     "CSTValidationError",
+    "CSTLogicError",
     "CSTVisitor",
     "CSTVisitorT",
     "FlattenSentinel",

libcst/_excep.py

@@ -0,0 +1,8 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+
+class CSTLogicError(Exception):
+    pass

libcst/_nodes/base.py

@@ -8,6 +8,7 @@
 from dataclasses import dataclass, field, fields, replace
 from typing import Any, cast, ClassVar, Dict, List, Mapping, Sequence, TypeVar, Union
 
+from libcst._excep import CSTLogicError
 from libcst._flatten_sentinel import FlattenSentinel
 from libcst._nodes.internal import CodegenState
 from libcst._removal_sentinel import RemovalSentinel
@@ -237,7 +238,7 @@ def visit(
 
         # validate return type of the user-defined `visitor.on_leave` method
         if not isinstance(leave_result, (CSTNode, RemovalSentinel, FlattenSentinel)):
-            raise Exception(
+            raise CSTValidationError(
                 "Expected a node of type CSTNode or a RemovalSentinel, "
                 + f"but got a return value of {type(leave_result).__name__}"
             )
@@ -383,7 +384,7 @@ def deep_replace(
         new_tree = self.visit(_ChildReplacementTransformer(old_node, new_node))
         if isinstance(new_tree, (FlattenSentinel, RemovalSentinel)):
             # The above transform never returns *Sentinel, so this isn't possible
-            raise Exception("Logic error, cannot get a *Sentinel here!")
+            raise CSTLogicError("Logic error, cannot get a *Sentinel here!")
         return new_tree
 
     def deep_remove(
@@ -400,7 +401,7 @@ def deep_remove(
 
         if isinstance(new_tree, FlattenSentinel):
             # The above transform never returns FlattenSentinel, so this isn't possible
-            raise Exception("Logic error, cannot get a FlattenSentinel here!")
+            raise CSTLogicError("Logic error, cannot get a FlattenSentinel here!")
 
         return new_tree
 
@@ -422,7 +423,7 @@ def with_deep_changes(
         new_tree = self.visit(_ChildWithChangesTransformer(old_node, changes))
         if isinstance(new_tree, (FlattenSentinel, RemovalSentinel)):
             # This is impossible with the above transform.
-            raise Exception("Logic error, cannot get a *Sentinel here!")
+            raise CSTLogicError("Logic error, cannot get a *Sentinel here!")
         return new_tree
 
     def __eq__(self: _CSTNodeSelfT, other: object) -> bool:

libcst/_nodes/expression.py

@@ -18,6 +18,7 @@
 from typing import Callable, Generator, Literal, Optional, Sequence, Union
 
 from libcst._add_slots import add_slots
+from libcst._excep import CSTLogicError
 from libcst._maybe_sentinel import MaybeSentinel
 from libcst._nodes.base import CSTCodegenError, CSTNode, CSTValidationError
 from libcst._nodes.internal import (
@@ -666,7 +667,7 @@ def quote(self) -> StringQuoteLiteral:
         if len(quote) not in {1, 3}:
             # We shouldn't get here due to construction validation logic,
             # but handle the case anyway.
-            raise Exception(f"Invalid string {self.value}")
+            raise CSTLogicError(f"Invalid string {self.value}")
 
         # pyre-ignore We know via the above validation that we will only
         # ever return one of the four string literals.
@@ -1010,7 +1011,7 @@ def _validate(self) -> None:
         elif isinstance(right, FormattedString):
             rightbytes = "b" in right.prefix
         else:
-            raise Exception("Logic error!")
+            raise CSTLogicError("Logic error!")
         if leftbytes != rightbytes:
             raise CSTValidationError("Cannot concatenate string and bytes.")
 
@@ -1688,7 +1689,7 @@ def _codegen_impl(
             if default_indicator == "->":
                 state.add_token(" ")
         else:
-            raise Exception("Logic error!")
+            raise CSTLogicError("Logic error!")
 
         # Now, output the indicator and the rest of the annotation
         state.add_token(default_indicator)

libcst/_nodes/statement.py

@@ -10,6 +10,7 @@
 from typing import Literal, Optional, Pattern, Sequence, Union
 
 from libcst._add_slots import add_slots
+from libcst._excep import CSTLogicError
 from libcst._maybe_sentinel import MaybeSentinel
 from libcst._nodes.base import CSTNode, CSTValidationError
 from libcst._nodes.expression import (
@@ -1161,12 +1162,10 @@ def _validate(self) -> None:
                 )
         try:
             self.evaluated_name
-        except Exception as e:
-            if str(e) == "Logic error!":
-                raise CSTValidationError(
-                    "The imported name must be a valid qualified name."
-                )
-            raise e
+        except CSTLogicError as e:
+            raise CSTValidationError(
+                "The imported name must be a valid qualified name."
+            ) from e
 
     def _visit_and_replace_children(self, visitor: CSTVisitorT) -> "ImportAlias":
         return ImportAlias(
@@ -1195,7 +1194,7 @@ def _name(self, node: CSTNode) -> str:
         elif isinstance(node, Attribute):
             return f"{self._name(node.value)}.{node.attr.value}"
         else:
-            raise Exception("Logic error!")
+            raise CSTLogicError("Logic error!")
 
     @property
     def evaluated_name(self) -> str:

libcst/_nodes/tests/test_funcdef.py

@@ -1052,7 +1052,9 @@ def _parse_statement_force_38(code: str) -> cst.BaseCompoundStatement:
         code, config=cst.PartialParserConfig(python_version="3.8")
     )
     if not isinstance(statement, cst.BaseCompoundStatement):
-        raise Exception("This function is expecting to parse compound statements only!")
+        raise ValueError(
+            "This function is expecting to parse compound statements only!"
+        )
     return statement
 
 

libcst/_nodes/tests/test_namedexpr.py

@@ -22,7 +22,9 @@ def _parse_statement_force_38(code: str) -> cst.BaseCompoundStatement:
         code, config=cst.PartialParserConfig(python_version="3.8")
     )
     if not isinstance(statement, cst.BaseCompoundStatement):
-        raise Exception("This function is expecting to parse compound statements only!")
+        raise ValueError(
+            "This function is expecting to parse compound statements only!"
+        )
     return statement
 
 

libcst/_nodes/tests/test_removal_behavior.py

@@ -95,7 +95,7 @@ def test_removal_pass_behavior(
         self, before: str, after: str, visitor: Type[CSTTransformer]
     ) -> None:
         if before.endswith("\n") or after.endswith("\n"):
-            raise Exception("Test cases should not be newline-terminated!")
+            raise ValueError("Test cases should not be newline-terminated!")
 
         # Test doesn't have newline termination case
         before_module = parse_module(before)

libcst/_parser/base_parser.py

@@ -103,7 +103,7 @@ def __init__(
     def parse(self) -> _NodeT:
         # Ensure that we don't re-use parsers.
         if self.__was_parse_called:
-            raise Exception("Each parser object may only be used to parse once.")
+            raise ValueError("Each parser object may only be used to parse once.")
         self.__was_parse_called = True
 
         for token in self.tokens:

libcst/_parser/conversions/expression.py

@@ -12,7 +12,8 @@
     Intnumber as INTNUMBER_RE,
 )
 
-from libcst._exceptions import PartialParserSyntaxError
+from libcst._excep import CSTLogicError
+from libcst._exceptions import ParserSyntaxError, PartialParserSyntaxError
 from libcst._maybe_sentinel import MaybeSentinel
 from libcst._nodes.expression import (
     Arg,
@@ -327,7 +328,12 @@ def convert_boolop(
     # Convert all of the operations that have no precedence in a loop
     for op, rightexpr in grouper(rightexprs, 2):
         if op.string not in BOOLOP_TOKEN_LUT:
-            raise Exception(f"Unexpected token '{op.string}'!")
+            raise ParserSyntaxError(
+                f"Unexpected token '{op.string}'!",
+                lines=config.lines,
+                raw_line=0,
+                raw_column=0,
+            )
         leftexpr = BooleanOperation(
             left=leftexpr,
             # pyre-ignore Pyre thinks that the type of the LUT is CSTNode.
@@ -420,7 +426,12 @@ def convert_comp_op(
             )
         else:
             # this should be unreachable
-            raise Exception(f"Unexpected token '{op.string}'!")
+            raise ParserSyntaxError(
+                f"Unexpected token '{op.string}'!",
+                lines=config.lines,
+                raw_line=0,
+                raw_column=0,
+            )
     else:
         # A two-token comparison
         leftcomp, rightcomp = children
@@ -451,7 +462,12 @@ def convert_comp_op(
             )
         else:
             # this should be unreachable
-            raise Exception(f"Unexpected token '{leftcomp.string} {rightcomp.string}'!")
+            raise ParserSyntaxError(
+                f"Unexpected token '{leftcomp.string} {rightcomp.string}'!",
+                lines=config.lines,
+                raw_line=0,
+                raw_column=0,
+            )
 
 
 @with_production("star_expr", "'*' expr")
@@ -493,7 +509,12 @@ def convert_binop(
     # Convert all of the operations that have no precedence in a loop
     for op, rightexpr in grouper(rightexprs, 2):
         if op.string not in BINOP_TOKEN_LUT:
-            raise Exception(f"Unexpected token '{op.string}'!")
+            raise ParserSyntaxError(
+                f"Unexpected token '{op.string}'!",
+                lines=config.lines,
+                raw_line=0,
+                raw_column=0,
+            )
         leftexpr = BinaryOperation(
             left=leftexpr,
             # pyre-ignore Pyre thinks that the type of the LUT is CSTNode.
@@ -540,7 +561,12 @@ def convert_factor(
             )
         )
     else:
-        raise Exception(f"Unexpected token '{op.string}'!")
+        raise ParserSyntaxError(
+            f"Unexpected token '{op.string}'!",
+            lines=config.lines,
+            raw_line=0,
+            raw_column=0,
+        )
 
     return WithLeadingWhitespace(
         UnaryOperation(operator=opnode, expression=factor.value), op.whitespace_before
@@ -651,7 +677,7 @@ def convert_atom_expr_trailer(
             )
         else:
             # This is an invalid trailer, so lets give up
-            raise Exception("Logic error!")
+            raise CSTLogicError()
     return WithLeadingWhitespace(atom, whitespace_before)
 
 
@@ -870,9 +896,19 @@ def convert_atom_basic(
                 Imaginary(child.string), child.whitespace_before
             )
         else:
-            raise Exception(f"Unparseable number {child.string}")
+            raise ParserSyntaxError(
+                f"Unparseable number {child.string}",
+                lines=config.lines,
+                raw_line=0,
+                raw_column=0,
+            )
     else:
-        raise Exception(f"Logic error, unexpected token {child.type.name}")
+        raise ParserSyntaxError(
+            f"Logic error, unexpected token {child.type.name}",
+            lines=config.lines,
+            raw_line=0,
+            raw_column=0,
+        )
 
 
 @with_production("atom_squarebrackets", "'[' [testlist_comp_list] ']'")
@@ -1447,7 +1483,7 @@ def convert_arg_assign_comp_for(
         if equal.string == ":=":
             val = convert_namedexpr_test(config, children)
             if not isinstance(val, WithLeadingWhitespace):
-                raise Exception(
+                raise TypeError(
                     f"convert_namedexpr_test returned {val!r}, not WithLeadingWhitespace"
                 )
             return Arg(value=val.value)

libcst/_parser/conversions/params.py

@@ -6,6 +6,7 @@
 
 from typing import Any, List, Optional, Sequence, Union
 
+from libcst._excep import CSTLogicError
 from libcst._exceptions import PartialParserSyntaxError
 from libcst._maybe_sentinel import MaybeSentinel
 from libcst._nodes.expression import (
@@ -121,7 +122,7 @@ def add_param(
                 # Example code:
                 #     def fn(*abc, *): ...
                 # This should be unreachable, the grammar already disallows it.
-                raise Exception(
+                raise ValueError(
                     "Cannot have multiple star ('*') markers in a single argument "
                     + "list."
                 )
@@ -136,7 +137,7 @@ def add_param(
                 # Example code:
                 # def fn(foo, /, *, /, bar): ...
                 # This should be unreachable, the grammar already disallows it.
-                raise Exception(
+                raise ValueError(
                     "Cannot have multiple slash ('/') markers in a single argument "
                     + "list."
                 )
@@ -168,7 +169,7 @@ def add_param(
                 # Example code:
                 #     def fn(**kwargs, trailing=None)
                 # This should be unreachable, the grammar already disallows it.
-                raise Exception("Cannot have any arguments after a kwargs expansion.")
+                raise ValueError("Cannot have any arguments after a kwargs expansion.")
         elif (
             isinstance(param.star, str) and param.star == "*" and param.default is None
         ):
@@ -181,7 +182,7 @@ def add_param(
                 # Example code:
                 #     def fn(*first, *second): ...
                 # This should be unreachable, the grammar already disallows it.
-                raise Exception(
+                raise ValueError(
                     "Expected a keyword argument but found a starred positional "
                     + "argument expansion."
                 )
@@ -197,13 +198,13 @@ def add_param(
                 # Example code:
                 #     def fn(**first, **second)
                 # This should be unreachable, the grammar already disallows it.
-                raise Exception(
+                raise ValueError(
                     "Multiple starred keyword argument expansions are not allowed in a "
                     + "single argument list"
                 )
         else:
             # The state machine should never end up here.
-            raise Exception("Logic error!")
+            raise CSTLogicError("Logic error!")
 
         return current_param