Binding a name that is used before but now out of scope in a pattern match breaks mypy #16793
Description
If you already used a name like value to define something in a branch of a match, like a function def value()... and by some reason you use the same name as a binding in another branch of the match case Some(value), then I guess that value is lookup for it's previous value (a function) instead of making a new fresh variable for it, this broke an assertion.
some.py:10: error: INTERNAL ERROR -- Please try using mypy master on GitHub:
https://mypy.readthedocs.io/en/stable/common_issues.html#using-a-development-mypy-build
Please report a bug at https://github.com/python/mypy/issues
version: 1.9.0+dev.75b68fa2c0d32bd08b98b00aece20c22d82b1b15
Traceback (most recent call last):
File "projects/mal/impls/python.3/.env/bin/mypy", line 8, in <module>
sys.exit(console_entry())
File "projects/mypy/mypy/__main__.py", line 15, in console_entry
main()
File "projects/mypy/mypy/main.py", line 100, in main
res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
File "projects/mypy/mypy/main.py", line 182, in run_build
res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
File "projects/mypy/mypy/build.py", line 191, in build
result = _build(
File "projects/mypy/mypy/build.py", line 265, in _build
graph = dispatch(sources, manager, stdout)
File "projects/mypy/mypy/build.py", line 2941, in dispatch
process_graph(graph, manager)
File "projects/mypy/mypy/build.py", line 3339, in process_graph
process_stale_scc(graph, scc, manager)
File "projects/mypy/mypy/build.py", line 3440, in process_stale_scc
graph[id].type_check_first_pass()
File "projects/mypy/mypy/build.py", line 2309, in type_check_first_pass
self.type_checker().check_first_pass()
File "projects/mypy/mypy/checker.py", line 481, in check_first_pass
self.accept(d)
File "projects/mypy/mypy/checker.py", line 591, in accept
stmt.accept(self)
File "projects/mypy/mypy/nodes.py", line 787, in accept
return visitor.visit_func_def(self)
File "projects/mypy/mypy/checker.py", line 1001, in visit_func_def
self._visit_func_def(defn)
File "projects/mypy/mypy/checker.py", line 1005, in _visit_func_def
self.check_func_item(defn, name=defn.name)
File "projects/mypy/mypy/checker.py", line 1078, in check_func_item
self.check_func_def(defn, typ, name, allow_empty)
File "projects/mypy/mypy/checker.py", line 1294, in check_func_def
self.accept(item.body)
File "projects/mypy/mypy/checker.py", line 591, in accept
stmt.accept(self)
File "projects/mypy/mypy/nodes.py", line 1223, in accept
return visitor.visit_block(self)
File "projects/mypy/mypy/checker.py", line 2771, in visit_block
self.accept(s)
File "projects/mypy/mypy/checker.py", line 591, in accept
stmt.accept(self)
File "projects/mypy/mypy/nodes.py", line 1607, in accept
return visitor.visit_match_stmt(self)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "projects/mypy/mypy/checker.py", line 5063, in visit_match_stmt
inferred_types = self.infer_variable_types_from_type_maps(type_maps)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "projects/mypy/mypy/checker.py", line 5127, in infer_variable_types_from_type_maps
assert isinstance(node, Var)
AssertionError:
some.py:10: : note: use --pdb to drop into pdb
I was able to reduce the crash to this file:
from dataclasses import dataclass
@dataclass
class Some:
value: int | "Some"
def some(x: Some):
match x:
case int():
def value():
return 1
case Some(value):
pass
I put a print in the function handling the match and got:
NameExpr(x [l])
Pattern(
ClassPattern:11(
NameExpr(int [builtins.int])))
Body(
FuncDef:13(
value
Block:14(
ReturnStmt:14(
IntExpr(1)))))
Pattern(
ClassPattern:16(
NameExpr(Some [some.Some])
Positionals(
AsPattern:16(
NameExpr(value [l])))))
Body(
PassStmt:17()))
The particular source of the crash is the
AsPattern:16(
NameExpr(value [l])))))
A print of the value that breaks the assert just before breaking:
FuncDef:13(
value
Block:14(
ReturnStmt:14(
IntExpr(1))))
FuncDef:13(
value
Block:14(
ReturnStmt:14(
IntExpr(1))))
- Mypy version used: both 1.7.something and 1.9.0+dev.75b68fa2c0d32bd08b98b00aece20c22d82b1b15
- Mypy command-line flags: None
- Mypy configuration options from
mypy.ini(and other config files): None - Python version used: 3.11.6
- Operating system and version: Archlinux