disallow quoted annotations, __future__ imports, and runtime-only nodes

tests/test_transformers.py

@@ -31,7 +31,6 @@ def test_comments(source: str) -> None:
         "__version__: str = '3.14'\n",
         "def concat(*args: str) -> str: ...\n",
         "class C:\n    def f(self, /) -> None: ...\n",
-        "raise NotImplementedError\n",
     ],
 )
 def test_already_compatible(source: str) -> None:

tests/test_visitors.py

@@ -2,6 +2,7 @@
 
 import libcst as cst
 import pytest
+from unpy.exceptions import StubError
 from unpy.visitors import StubVisitor
 
 
@@ -11,6 +12,37 @@ def _visit(*lines: str) -> StubVisitor:
     return visitor
 
 
+# stub errors
+
+
+def test_illegal_future_import():
+    # https://github.com/jorenham/unpy/issues/43
+    with pytest.raises(StubError):
+        _visit("from __future__ import annotations")
+
+
+@pytest.mark.parametrize(
+    "source",
+    [
+        "Const: 'str' = ...",
+        "type Alias = 'str'",
+        "from typing import TypeAlias\nAlias: TypeAlias = 'str'",
+        "from typing import TypeAliasType\nAlias = TypeAliasType('Alias', 'str')",
+        "from typing import TypeVar\nT = TypeVar('T', bound='str')",
+        "from typing import TypeVar\nT = TypeVar('T', default='str')",
+        "def f(x: 'str') -> str: ...",
+        "def f(x: str) -> 'str': ...",
+        "def f[T: 'str'](x: T) -> T: ...",
+        "def f[T: str = 'str'](x: T) -> T: ...",
+        "class C[T: 'str']: ...",
+        "class C[T: str = 'str']: ...",
+    ],
+)
+def test_stringified_annotations(source: str):
+    with pytest.raises(StubError):
+        _visit(source)
+
+
 # imports
 
 
@@ -271,9 +303,7 @@ def test_import_access_package_attr_attr() -> None:
     }
 
 
-# baseclass
-# TODO: more tests
-
+# baseclasses
 
 def test_baseclasses_single() -> None:
     visitor = _visit(

unpy/exceptions.py

@@ -0,0 +1,5 @@
+__all__ = ("StubError",)
+
+
+class StubError(TypeError):
+    pass

unpy/visitors.py

@@ -1,29 +1,29 @@
 import collections
-import functools
 from typing import Final, override
 
 import libcst as cst
-from libcst.metadata import Scope, ScopeProvider
+import libcst.metadata as cst_meta
 
 import unpy._cst as uncst
+from unpy.exceptions import StubError
 
 __all__ = ("StubVisitor",)
 
 _MODULE_BUILTINS: Final = "builtins"
-_MODULE_PATHLIB: Final = "pathlib"
 _MODULE_TP: Final = "typing"
 _MODULE_TPX: Final = "typing_extensions"
 
-_ILLEGAL_BASES: Final = (
-    (_MODULE_BUILTINS, "BaseExceptionGroup"),
-    (_MODULE_BUILTINS, "ExceptionGroup"),
-    (_MODULE_BUILTINS, "_IncompleteInputError"),
-    (_MODULE_BUILTINS, "PythonFinalizationError"),
-    (_MODULE_BUILTINS, "EncodingWarning"),
-    (_MODULE_PATHLIB, "Path"),
-    (_MODULE_TP, "Any"),
-    (_MODULE_TPX, "Any"),
-)
+
+def _check_annotation_expr(
+    node: cst.BaseExpression,
+    /,
+    name: str | None = None,
+) -> None:
+    if isinstance(node, cst.BaseString):
+        error = StubError("quoted annotations should not be included in stubs")
+        if name:
+            error.add_note(f"in {name!r}")
+        raise error
 
 
 class StubVisitor(cst.CSTVisitor):  # noqa: PLR0904
@@ -32,9 +32,9 @@ class StubVisitor(cst.CSTVisitor):  # noqa: PLR0904
     classes, and type-aliases.
     """
 
-    METADATA_DEPENDENCIES = (ScopeProvider,)
+    METADATA_DEPENDENCIES = (cst_meta.ScopeProvider,)
 
-    _global_scope: Scope
+    _global_scope: cst_meta.Scope
 
     _stack_scope: Final[collections.deque[str]]
     _stack_attr: Final[collections.deque[cst.Attribute]]
@@ -199,7 +199,12 @@ def _register_import(
         module: str | None = None,
         alias: str | None = None,
     ) -> str:
+        # this `str.removesuffix` avoids a double `.` in case of `from . import name`
         fqn = f"{module.removesuffix(".")}.{name}" if module else name
+
+        if fqn.startswith("__future__"):
+            raise StubError("__future__ imports are useless in stubs")
+
         alias = alias or name
 
         if self.imports.setdefault(fqn, alias) != alias:
@@ -249,8 +254,8 @@ def _build_type_param(  # noqa: C901
         name = param.name.value
         default = tpar.default
 
-        if isinstance(default, cst.BaseString):
-            raise NotImplementedError("stringified type parameter defaults")
+        if default:
+            _check_annotation_expr(default)
 
         name_any = self.imported_from_typing_as("Any")
         name_object = self.imported_as(_MODULE_BUILTINS, "object")
@@ -279,8 +284,6 @@ def _build_type_param(  # noqa: C901
         constraints: tuple[cst.BaseExpression, ...] = ()
         if not (bound := param.bound):
             pass
-        elif isinstance(bound, cst.BaseString):
-            raise NotImplementedError("stringified type parameter bounds")
         elif (
             name_any
             and isinstance(bound, cst.Name | cst.Attribute)
@@ -308,6 +311,8 @@ def _build_type_param(  # noqa: C901
 
             constraints = tuple(cons)
             bound = None
+        else:
+            _check_annotation_expr(bound)
 
         if _default_any and bound is not None:
             # if `default=Any`, replace it the value of `bound` (`Any` is horrible)
@@ -370,8 +375,8 @@ def __after_import(self, /) -> None:
 
     @override
     def visit_Module(self, /, node: cst.Module) -> None:
-        scope = self.get_metadata(ScopeProvider, node)
-        assert isinstance(scope, Scope)
+        scope = self.get_metadata(cst_meta.ScopeProvider, node)
+        assert isinstance(scope, cst_meta.Scope)
         self._global_scope = scope
 
     @override
@@ -431,6 +436,10 @@ def leave_Attribute(self, /, original_node: cst.Attribute) -> None:
         node = self._stack_attr.pop()
         assert node is original_node
 
+    @override
+    def visit_Annotation(self, /, node: cst.Annotation) -> None:
+        _check_annotation_expr(node.annotation)
+
     def __check_assign_imported(self, node: cst.Assign | cst.AnnAssign, /) -> None:
         if not isinstance(node.value, cst.Name | cst.Attribute):
             return
@@ -446,10 +455,44 @@ def __check_assign_imported(self, node: cst.Assign | cst.AnnAssign, /) -> None:
     def visit_Assign(self, node: cst.Assign) -> None:
         self.__check_assign_imported(node)
 
+        # TODO(jorenham): enforce len(node.targets) == 1
+
+        if (
+            len(node.targets) == 1
+            and isinstance(target := node.targets[0].target, cst.Name)
+            and isinstance(node.value, cst.Call)
+            # typevar-likes can only "contain" annotations if they have >1 [kw]args
+            and len(node.value.args) > 1
+            and isinstance(node.value.func, cst.Name | cst.Attribute)
+            and isinstance(strname := node.value.args[0].value, cst.SimpleString)
+            and strname.raw_value == target.value
+        ):
+            # this is (probably) a legacy typevar-like (or a manual `TypeAliasType`)
+            # TODO(jorenham): either warn user & register, or just disallow this
+
+            fname = ""  # set later if needed
+            for arg in node.value.args[1:]:
+                # annotations can only occur in the positional args and the
+                # `bound` or `default` kwargs
+                if arg.keyword is None or arg.keyword.value in {"bound", "default"}:
+                    fname = fname or uncst.get_name_strict(node.value.func)
+                    _check_annotation_expr(arg.value, f"{target.value} = {fname}(...)")
+
     @override
     def visit_AnnAssign(self, node: cst.AnnAssign) -> None:
         self.__check_assign_imported(node)
 
+        if (
+            node.value
+            and isinstance(node.target, cst.Name)
+            and isinstance(ann := node.annotation.annotation, cst.Name | cst.Attribute)
+            and (type_alias_name := self.imported_from_typing_as("TypeAlias"))
+            and uncst.get_name_strict(ann) == type_alias_name
+        ):
+            # this is a legacy `typing[_extensions].TypeAlias`
+            # TODO(jorenham): either warn user & register, or just disallow this
+            _check_annotation_expr(node.value, f"{node.target.value}")
+
     @override
     def visit_AssignTarget(self, node: cst.AssignTarget) -> None:
         assert not self._stack_attr
@@ -470,6 +513,8 @@ def visit_TypeAlias(self, /, node: cst.TypeAlias) -> None:
         name = node.name.value
         assert name not in self.type_aliases
 
+        _check_annotation_expr(node.value, f"type {name}")
+
         if tpars := node.type_parameters:
             self.type_aliases[name] = self._register_type_params(name, tpars)
         else:
@@ -482,6 +527,12 @@ def visit_TypeAlias(self, /, node: cst.TypeAlias) -> None:
     def visit_FunctionDef(self, /, node: cst.FunctionDef) -> None:
         self._stack_scope.append(node.name.value)
 
+        assert isinstance(node.body, cst.SimpleStatementSuite | cst.IndentedBlock)
+        if len(node.body.body) != 1 or not isinstance(node.body.body[0], cst.Ellipsis):
+            error = StubError("function body must contain only `...`")
+            qualname = ".".join(self._stack_scope)
+            error.add_note(qualname)
+
         if tpars := node.type_parameters:
             self._register_type_params(self._stack_scope[0], tpars)
 
@@ -492,14 +543,6 @@ def leave_FunctionDef(self, /, original_node: cst.FunctionDef) -> None:
 
         _ = self._stack_scope.pop()
 
-    @functools.cached_property
-    def _illegal_bases(self, /) -> frozenset[str]:
-        return frozenset({
-            base_name
-            for module, name in _ILLEGAL_BASES
-            if (base_name := self.imported_as(module, name))
-        })
-
     @override
     def visit_ClassDef(self, /, node: cst.ClassDef) -> None:
         name = node.name.value
@@ -537,15 +580,6 @@ def visit_ClassDef(self, /, node: cst.ClassDef) -> None:
             # TODO: figure out the FQN if not a global name (i.e. locally scoped)
             bases.append(basename)
 
-        base_set = set(bases)
-        if base_set and (illegal := base_set & self._illegal_bases):
-            if len(illegal) == 1:
-                raise NotImplementedError(f"{illegal.pop()!r} as base class")
-            raise ExceptionGroup(
-                "unsupported base classes",
-                [NotImplementedError(f"{base!r} as base class") for base in illegal],
-            )
-
         if tpars := node.type_parameters:
             self._register_type_params(stack[0], tpars, infer_variance=True)
 
@@ -555,3 +589,38 @@ def leave_ClassDef(self, /, original_node: cst.ClassDef) -> None:
         # https://github.com/jorenham/unpy/issues/46
 
         _ = self._stack_scope.pop()
+
+    @override
+    def on_visit(self, /, node: cst.CSTNode) -> bool:
+        if isinstance(node, cst.BaseSmallStatement):
+            if isinstance(
+                node,
+                cst.Del
+                | cst.Pass
+                | cst.Break
+                | cst.Continue
+                | cst.Return
+                | cst.Raise
+                | cst.Assert
+                | cst.Global
+                | cst.Nonlocal,
+            ):
+                keyword = type(node).__name__.lower()
+                raise StubError(f"{keyword!r} statements are useless in stubs")
+        elif isinstance(node, cst.BaseCompoundStatement):
+            if isinstance(
+                node,
+                cst.Try | cst.TryStar | cst.With | cst.For | cst.While | cst.Match,
+            ):
+                keyword = type(node).__name__.lower()
+                raise StubError(f"{keyword!r} statements are useless in stubs")
+        elif isinstance(node, cst.BaseExpression):
+            if isinstance(node, cst.BooleanOperation):
+                raise StubError("boolean operations are useless in stubs")
+            if isinstance(node, cst.FormattedString):
+                raise StubError("f-strings are useless in stubs")
+            if isinstance(node, cst.Lambda | cst.Await | cst.Yield):
+                keyword = type(node).__name__.lower()
+                raise StubError(f"{keyword!r} is an invalid expression")
+
+        return super().on_visit(node)