Validate attrs init aliases before code generation

Author: uwezkhan

src/attr/_make.py

@@ -8,6 +8,7 @@
 import enum
 import inspect
 import itertools
+import keyword
 import linecache
 import sys
 import types
@@ -496,6 +497,8 @@ def _transform_attrs(
             _OBJ_SETATTR.__get__(a)("alias", _default_init_alias_for(a.name))
             _OBJ_SETATTR.__get__(a)("alias_is_default", True)
 
+    _validate_init_aliases(attrs)
+
     # Create AttrsClass *after* applying the field_transformer since it may
     # add or remove attributes!
     attr_names = [a.name for a in attrs]
@@ -2426,6 +2429,27 @@ def _default_init_alias_for(name: str) -> str:
     return name.lstrip("_")
 
 
+def _validate_init_aliases(attrs: tuple["Attribute", ...]) -> None:
+    """
+    Ensure init aliases are valid Python parameter names.
+    """
+    for a in attrs:
+        if a.init is False:
+            continue
+
+        alias = a.alias
+        if (
+            not isinstance(alias, str)
+            or not alias.isidentifier()
+            or keyword.iskeyword(alias)
+        ):
+            msg = (
+                f"Invalid initialization alias {alias!r} for attribute "
+                f"{a.name!r}. Aliases must be valid Python identifiers."
+            )
+            raise TypeError(msg)
+
+
 class Attribute:
     """
     *Read-only* representation of an attribute.
@@ -3423,4 +3447,4 @@ def pipe_converter(val):
 
     if return_instance:
         return Converter(pipe_converter, takes_self=True, takes_field=True)
-    return pipe_converter
+    return pipe_converter

tests/test_make.py

@@ -2448,6 +2448,46 @@ class EvolveCase:
             dunder__=5,
         ) == EvolveCase(1, 4, 5)
 
+    @pytest.mark.parametrize("alias", ["x=1", "class", "not valid", 1])
+    def test_invalid_alias(self, alias):
+        """
+        Invalid aliases are rejected before they can be used in generated
+        __init__ source code.
+        """
+
+        with pytest.raises(
+            TypeError, match="Invalid initialization alias"
+        ):
+            @attrs.define
+            class C:
+                x: int = attrs.field(alias=alias)
+
+    def test_invalid_alias_not_executed(self, monkeypatch):
+        """
+        Aliases are parameter names, not Python source code.
+        """
+
+        marker = "_attrs_alias_executed"
+        monkeypatch.delattr("builtins." + marker, raising=False)
+
+        with pytest.raises(
+            TypeError, match="Invalid initialization alias"
+        ):
+            attr.make_class(
+                "C",
+                {
+                    "x": attr.ib(
+                        alias=(
+                            "x=__import__('builtins').setattr("
+                            "__import__('builtins'), "
+                            f"{marker!r}, True)"
+                        )
+                    )
+                },
+            )
+
+        assert getattr(__import__("builtins"), marker, False) is False
+
     def test_alias_is_default(self):
         """
         alias_is_default is True for auto-generated aliases and False for
@@ -3211,4 +3251,4 @@ def test_make_class(self):
         assert () == C1.__match_args__
 
         C1 = make_class("C1", {"a": attr.ib(kw_only=True), "b": attr.ib()})
-        assert ("b",) == C1.__match_args__
+        assert ("b",) == C1.__match_args__