feat: configurable max length for string literals (#6)

This is a way to allow short literals like:

```python
raise RuntimeError("Little msg")
```

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

README.md

@@ -57,6 +57,13 @@ applications should print nice errors, usually _without_ a traceback, unless
 something _unexpected_ occurred. An app should not print a traceback for an
 error that is known to be triggerable by a user.
 
+## Options
+
+There is one option, `--errmsg-max-string-length`, which defaults to 0 but can
+be set to a larger value. The check will ignore string literals shorter than
+this length. This option is supported in configuration mode as well. This will
+only affect string literals and not f-strings.
+
 ## Usage
 
 Just add this to your `.pre-commit-config.yaml` `flake8` check under

noxfile.py

@@ -2,7 +2,7 @@
 
 import nox
 
-nox.options.sessions = ["lint", "pylint", "tests"]
+nox.options.sessions = ["lint", "pylint", "tests", "tests_flake8"]
 
 
 @nox.session
@@ -42,3 +42,24 @@ def build(session: nox.Session) -> None:
 
     session.install("build")
     session.run("python", "-m", "build")
+
+
+@nox.session
+def tests_flake8(session: nox.Session) -> None:
+    """
+    Run the flake8 tests.
+    """
+    session.install(".", "flake8")
+    result = session.run("flake8", "tests/example1.py", silent=True, success_codes=[1])
+    if len(result.splitlines()) != 2:
+        session.error(f"Expected 2 errors from flake8\n{result}")
+
+    result = session.run(
+        "flake8",
+        "--errmsg-max-string-length=30",
+        "tests/example1.py",
+        silent=True,
+        success_codes=[1],
+    )
+    if len(result.splitlines()) != 1:
+        session.error(f"Expected 1 errors from flake8\n{result}")

src/flake8_errmsg/__init__.py

@@ -8,17 +8,17 @@
 
 from __future__ import annotations
 
+import argparse
 import ast
 import dataclasses
-import sys
 import traceback
 from collections.abc import Iterator
 from pathlib import Path
-from typing import NamedTuple
+from typing import Any, ClassVar, NamedTuple
 
 __all__ = ("__version__", "run_on_file", "main", "ErrMsgASTPlugin")
 
-__version__ = "0.2.4"
+__version__ = "0.3.0"
 
 
 class Flake8ASTErrorInfo(NamedTuple):
@@ -29,13 +29,15 @@ class Flake8ASTErrorInfo(NamedTuple):
 
 
 class Visitor(ast.NodeVisitor):
-    def __init__(self) -> None:
+    def __init__(self, max_string_len: int) -> None:
         self.errors: list[Flake8ASTErrorInfo] = []
+        self.max_string_len = max_string_len
 
     def visit_Raise(self, node: ast.Raise) -> None:
         match node.exc:
-            case ast.Call(args=[ast.Constant(value=str()), *_]):
-                self.errors.append(EM101(node))
+            case ast.Call(args=[ast.Constant(value=str(value)), *_]):
+                if len(value) >= self.max_string_len:
+                    self.errors.append(EM101(node))
             case ast.Call(args=[ast.JoinedStr(), *_]):
                 self.errors.append(EM102(node))
             case _:
@@ -52,21 +54,41 @@ def EM102(node: ast.AST) -> Flake8ASTErrorInfo:
     return Flake8ASTErrorInfo(node.lineno, node.col_offset, msg, Visitor)
 
 
+MAX_STRING_LENGTH = 0
+
+
 @dataclasses.dataclass
 class ErrMsgASTPlugin:
+    max_string_length: ClassVar[int] = 0
+
     tree: ast.AST
 
     _: dataclasses.KW_ONLY
     name: str = "flake8_errmsg"
     version: str = "0.1.0"
+    options: Any = None
 
     def run(self) -> Iterator[Flake8ASTErrorInfo]:
-        visitor = Visitor()
+        visitor = Visitor(self.max_string_length)
         visitor.visit(self.tree)
         yield from visitor.errors
 
+    @staticmethod
+    def add_options(optmanager: Any) -> None:
+        optmanager.add_option(
+            "--errmsg-max-string-length",
+            parse_from_config=True,
+            default=0,
+            type=int,
+            help="Set a maximum string length to allow inline strings. Default 0 (always disallow).",
+        )
+
+    @classmethod
+    def parse_options(cls, options: argparse.Namespace) -> None:
+        cls.max_string_length = options.errmsg_max_string_length
 
-def run_on_file(path: str) -> None:
+
+def run_on_file(path: str, max_string_length: int = 0) -> None:
     code = Path(path).read_text(encoding="utf-8")
 
     try:
@@ -78,13 +100,20 @@ def run_on_file(path: str) -> None:
         raise SystemExit(1) from None
 
     plugin = ErrMsgASTPlugin(node)
+    ErrMsgASTPlugin.max_string_length = max_string_length
+
     for err in plugin.run():
         print(f"{path}:{err.line_number}:{err.offset} {err.msg}")
 
 
 def main() -> None:
-    for item in sys.argv[1:]:
-        run_on_file(item)
+    parser = argparse.ArgumentParser()
+    parser.add_argument("--errmsg-max-string-length", type=int, default=0)
+    parser.add_argument("files", nargs="+")
+    namespace = parser.parse_args()
+
+    for item in namespace.files:
+        run_on_file(item, namespace.errmsg_max_string_length)
 
 
 if __name__ == "__main__":

tests/test_package.py

@@ -31,3 +31,17 @@ def test_err1():
         results[1].msg
         == "EM102 Exception must not use an f-string literal, assign to variable first"
     )
+
+
+def test_string_length():
+    node = ast.parse(ERR1)
+    plugin = m.ErrMsgASTPlugin(node)
+    m.ErrMsgASTPlugin.max_string_length = 10
+    results = list(plugin.run())
+    assert len(results) == 1
+    assert results[0].line_number == 2
+
+    assert (
+        results[0].msg
+        == "EM102 Exception must not use an f-string literal, assign to variable first"
+    )