added fuzzy matching for name not defined errors

Author: KevinRK29

mypy/semanal.py

@@ -7475,6 +7475,12 @@ def name_not_defined(self, name: str, ctx: Context, namespace: str | None = None
             self.record_incomplete_ref()
             return
         message = f'Name "{name}" is not defined'
+        # Collect all names in scope to suggest similar alternatives
+        alternatives = self._get_names_in_scope()
+        alternatives.discard(name)
+        matches = best_matches(name, alternatives, n=3)
+        if matches:
+            message += f"; did you mean {pretty_seq(matches, 'or')}?"
         self.fail(message, ctx, code=codes.NAME_DEFINED)
 
         if f"builtins.{name}" in SUGGESTED_TEST_FIXTURES:
@@ -7499,6 +7505,36 @@ def name_not_defined(self, name: str, ctx: Context, namespace: str | None = None
             ).format(module=module, name=lowercased[fullname].rsplit(".", 1)[-1])
             self.note(hint, ctx, code=codes.NAME_DEFINED)
 
+    def _get_names_in_scope(self) -> set[str]:
+        """Collect all names visible in the current scope for fuzzy matching suggestions.
+
+        This includes:
+        - Local variables (from function scopes)
+        - Class attributes (if it's inside a class)
+        - Global/module-level names
+        - Builtins
+        """
+        names: set[str] = set()
+
+        for table in self.locals:
+            if table is not None:
+                names.update(table.keys())
+
+        if self.type is not None:
+            names.update(self.type.names.keys())
+
+        names.update(self.globals.keys())
+
+        b = self.globals.get("__builtins__", None)
+        if b and isinstance(b.node, MypyFile):
+            # Only include public builtins (not _private ones)
+            for builtin_name in b.node.names.keys():
+                if not (len(builtin_name) > 1 and builtin_name[0] == "_" and builtin_name[1] != "_"):
+                    names.add(builtin_name)
+
+        # Filter out internal/dunder names that aren't useful for suggestions and might introduce noise
+        return {n for n in names if not n.startswith("__") or n.endswith("__")}
+
     def already_defined(
         self, name: str, ctx: Context, original_ctx: SymbolTableNode | SymbolNode | None, noun: str
     ) -> None: