[F403, F405, F821] Warn on undefined names

src/fixit/rules/pyflakes/no_undefined_name.py

@@ -0,0 +1,143 @@
+# 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.
+
+import libcst as cst
+
+from fixit import CstLintRule, InvalidTestCase as Invalid, ValidTestCase as Valid
+
+
+class NoUndefinedNameRule(CstLintRule):
+    """
+    The variable name is either undefined, or it's imported implicitly
+    through a `from ... import *` statement.
+
+    Autofix: N/A
+    """
+
+    METADATA_DEPENDENCIES = (cst.metadata.ScopeProvider,)
+
+    def __init__(self) -> None:
+        super().__init__()
+        self.has_import_star = False
+
+    def message(self, name: str) -> str:
+        if not self.has_import_star:
+            return f"{name} must be defined before use"
+        else:
+            return (f"{name} is either undefined or it has been defined "
+                   "implicitly through a `from ... import *` statement. "
+                   f"Define {name}, changing any import-star statements "
+                    "to explicit imports as necessary.")
+
+    def visit_ImportFrom(self, node: cst.ImportFrom) -> None:
+        if isinstance(node.names, cst.ImportStar):
+            self.has_import_star = True
+
+    def visit_Name(self, node: cst.Name) -> None:
+        try:
+            metadata = self.get_metadata(cst.metadata.ScopeProvider, node)
+            assert metadata is not None
+            accesses = metadata.accesses
+        except KeyError:
+            # Not all Names have ExpressionContext
+            return
+        for access in accesses:
+            if access.node is node and len(access.referents) == 0:
+                assert isinstance(access.node, cst.Name)
+                name = access.node.value
+                self.report(node, self.message(name))
+
+    VALID = [
+        Valid(
+            """
+            y = 1 + 2
+            """
+        ),
+        Valid(
+            """
+            def b(l):
+                return sum(l)
+
+            x = b([1, 3, 5, 6, 8])
+            """
+        ),
+        Valid(
+            """
+            from a import *
+            import c
+
+            x = c.d([1, 3, 5, 6, 8])
+            """
+        ),
+        Valid(
+            """
+            from a import b
+
+            def fn():
+                return b([1, 3, 5, 6, 8])
+            """
+        ),
+        Valid(
+            """
+            from a import b
+
+            x = [1, 3, 5, 6, 8]
+            y = [2, 4, 6, 7, 9]
+
+            z = [b(l) for l in [x, y]]
+            """
+        ),
+        Valid(
+            """
+            for i in [1, 3, 5, 6, 8]:
+                print(i)
+            """
+        ),
+        Valid(
+            """
+            def fn():
+                global b
+                b = 3
+
+            x = b + 2
+            """
+        ),
+    ]
+
+    INVALID = [
+        Invalid(
+            """
+            def b(l: List[int]):
+                return sum(l)
+
+            x = b([1, 3, 5, 6, 8])
+            """
+        ),
+        Invalid(
+            """
+            x = b([1, 3, 5, 6, 8])
+
+            def b(l):
+                return sum(l)
+            """
+        ),
+        Invalid(
+            """
+            from a import *
+
+            x = b([1, 3, 5, 6, 8])
+            """
+        ),
+        Invalid(
+            """
+            from a import b
+
+            def fn():
+                x = b([1, 3, 5, 6, 8])
+
+            y = x + 2
+            """
+        ),
+    ]