feat: add checks for built-in exceptions (#23)

Closes #13. This can only be done for built-in exceptions, since there's
no way to tell if a variable is a class or an object.

Signed-off-by: Henry Schreiner <[email protected]>

Author: henryiii

README.md

@@ -12,6 +12,8 @@ A checker for Flake8 that helps format nice error messages. The checks are:
 - **EM102**: Check for raw usage of an f-string literal in Exception raising.
 - **EM103**: Check for raw usage of `.format` on a string literal in Exception
   raising.
+- **EM104**: Check for missing parentheses for built-in exceptions.
+- **EM105**: Check for missing message for built-in exceptions.
 
 The issue is that Python includes the line with the raise in the default
 traceback (and most other formatters, like Rich and IPython to too). That means
@@ -78,7 +80,8 @@ script entry-point (`pipx run flake8-errmsg <files>`) or module entry-point
 Q: Why Python 3.10+ only? <br/> A: This is a static checker and for developers.
 Developers and static checks should be on 3.10 already. And I was lazy and match
 statements are fantastic for this sort of thing. And the AST module changed in
-3.8 anyway.
+3.8 anyway. Use [Ruff][] (which contains the checks from this plugin) if you
+need to run on older versions.
 
 Q: What other sorts of checks are acceptable? <br/> A: Things that help with
 nice errors. For example, maybe requiring `raise SystemExit(n)` over `sys.exit`,
@@ -91,4 +94,5 @@ nice errors. For example, maybe requiring `raise SystemExit(n)` over `sys.exit`,
 [pypi-link]:                https://pypi.org/project/flake8-errmsg/
 [pypi-platforms]:           https://img.shields.io/pypi/pyversions/flake8-errmsg
 [pypi-version]:             https://img.shields.io/pypi/v/flake8-errmsg
+[ruff]:                      https://github.com/astral-sh/ruff
 <!-- prettier-ignore-end -->

src/flake8_errmsg/__init__.py

@@ -8,15 +8,24 @@
 
 import argparse
 import ast
+import builtins
 import dataclasses
+import inspect
 import traceback
 from collections.abc import Iterator
 from pathlib import Path
 from typing import Any, ClassVar, NamedTuple
 
 __all__ = ("__version__", "run_on_file", "main", "ErrMsgASTPlugin")
 
-__version__ = "0.4.0"
+__version__ = "0.5.0"
+
+BUILTIN_EXCEPTION_LIST = {
+    name
+    for name in dir(builtins)
+    if inspect.isclass(_cls := getattr(builtins, name))
+    and issubclass(_cls, BaseException)
+}
 
 
 class Flake8ASTErrorInfo(NamedTuple):
@@ -46,6 +55,12 @@ def visit_Raise(self, node: ast.Raise) -> None:
                 ]
             ):
                 self.errors.append(EM103(node))
+            case ast.Name(id=name) if name in BUILTIN_EXCEPTION_LIST:
+                self.errors.append(EM104(node))
+            case ast.Call(
+                func=ast.Name(id=name), args=[]
+            ) if name in BUILTIN_EXCEPTION_LIST:
+                self.errors.append(EM105(node))
             case _:
                 pass
 
@@ -65,6 +80,16 @@ def EM103(node: ast.AST) -> Flake8ASTErrorInfo:
     return Flake8ASTErrorInfo(node.lineno, node.col_offset, msg, Visitor)
 
 
+def EM104(node: ast.AST) -> Flake8ASTErrorInfo:
+    msg = "EM104 Built-in Exceptions must not be thrown without being called"
+    return Flake8ASTErrorInfo(node.lineno, node.col_offset, msg, Visitor)
+
+
+def EM105(node: ast.AST) -> Flake8ASTErrorInfo:
+    msg = "EM105 Built-in Exceptions must have a useful message"
+    return Flake8ASTErrorInfo(node.lineno, node.col_offset, msg, Visitor)
+
+
 MAX_STRING_LENGTH = 0
 
 

tests/test_package.py

@@ -61,3 +61,32 @@ def test_err2():
         results[0].msg
         == "EM103 Exception must not use a .format() string directly, assign to variable first"
     )
+
+
+ERR3 = """\
+raise RuntimeError
+"""
+
+
+def test_err3():
+    node = ast.parse(ERR3)
+    results = list(m.ErrMsgASTPlugin(node).run())
+    assert len(results) == 1
+    assert results[0].line_number == 1
+    assert (
+        results[0].msg
+        == "EM104 Built-in Exceptions must not be thrown without being called"
+    )
+
+
+ERR4 = """\
+raise RuntimeError()
+"""
+
+
+def test_err4():
+    node = ast.parse(ERR4)
+    results = list(m.ErrMsgASTPlugin(node).run())
+    assert len(results) == 1
+    assert results[0].line_number == 1
+    assert results[0].msg == "EM105 Built-in Exceptions must have a useful message"