mypyc failed to compile list comprehensions

[hauntsaninja]

from typing import List

def list_comp(self) -> List[int]:
    if True:
        return [i for i in [5]]
    return [i for i in [5]]

Traceback (most recent call last):
  File "/Users/shantanu/dev/mypy/build/setup.py", line 5, in <module>
    ext_modules=mypycify(['rep.py'], opt_level="3", debug_level="1"),
  File "/Users/shantanu/dev/mypy/mypyc/build.py", line 494, in mypycify
    groups, group_cfilenames = mypyc_build(
  File "/Users/shantanu/dev/mypy/mypyc/build.py", line 405, in mypyc_build
    group_cfiles, ops_text = generate_c(all_sources, options, groups, fscache,
  File "/Users/shantanu/dev/mypy/mypyc/build.py", line 207, in generate_c
    modules, ctext = emitmodule.compile_modules_to_c(
  File "/Users/shantanu/dev/mypy/mypyc/codegen/emitmodule.py", line 414, in compile_modules_to_c
    modules = compile_modules_to_ir(result, mapper, compiler_options, errors)
  File "/Users/shantanu/dev/mypy/mypyc/codegen/emitmodule.py", line 258, in compile_modules_to_ir
    scc_ir = compile_scc_to_ir(trees, result, mapper, compiler_options, errors)
  File "/Users/shantanu/dev/mypy/mypyc/codegen/emitmodule.py", line 209, in compile_scc_to_ir
    modules = build_ir(
  File "/opt/homebrew/Cellar/python@3.9/3.9.13_1/Frameworks/Python.framework/Versions/3.9/lib/python3.9/contextlib.py", line 79, in inner
    return func(*args, **kwds)
  File "/Users/shantanu/dev/mypy/mypyc/irbuild/main.py", line 83, in build_ir
    transform_mypy_file(builder, module)
  File "/Users/shantanu/dev/mypy/mypyc/irbuild/main.py", line 128, in transform_mypy_file
    builder.accept(node)
  File "/Users/shantanu/dev/mypy/mypyc/irbuild/builder.py", line 194, in accept
    node.accept(self.visitor)
  File "/Users/shantanu/dev/mypy/mypy/nodes.py", line 758, in accept
    return visitor.visit_func_def(self)
  File "/Users/shantanu/dev/mypy/mypyc/irbuild/visitor.py", line 117, in visit_func_def
    transform_func_def(self.builder, fdef)
  File "/Users/shantanu/dev/mypy/mypyc/irbuild/function.py", line 69, in transform_func_def
    func_ir, func_reg = gen_func_item(builder, fdef, fdef.name, builder.mapper.fdef_to_sig(fdef))
  File "/Users/shantanu/dev/mypy/mypyc/irbuild/function.py", line 296, in gen_func_item
    builder.accept(fitem.body)
  File "/Users/shantanu/dev/mypy/mypyc/irbuild/builder.py", line 194, in accept
    node.accept(self.visitor)
  File "/Users/shantanu/dev/mypy/mypy/nodes.py", line 1110, in accept
    return visitor.visit_block(self)
  File "/Users/shantanu/dev/mypy/mypyc/irbuild/visitor.py", line 126, in visit_block
    transform_block(self.builder, block)
  File "/Users/shantanu/dev/mypy/mypyc/irbuild/statement.py", line 47, in transform_block
    builder.accept(stmt)
  File "/Users/shantanu/dev/mypy/mypyc/irbuild/builder.py", line 194, in accept
    node.accept(self.visitor)
  File "/Users/shantanu/dev/mypy/mypy/nodes.py", line 1267, in accept
    return visitor.visit_return_stmt(self)
  File "/Users/shantanu/dev/mypy/mypyc/irbuild/visitor.py", line 134, in visit_return_stmt
    transform_return_stmt(self.builder, stmt)
  File "/Users/shantanu/dev/mypy/mypyc/irbuild/statement.py", line 70, in transform_return_stmt
    retval = builder.accept(stmt.expr)
  File "/Users/shantanu/dev/mypy/mypyc/irbuild/builder.py", line 180, in accept
    res = node.accept(self.visitor)
  File "/Users/shantanu/dev/mypy/mypy/nodes.py", line 2136, in accept
    return visitor.visit_list_comprehension(self)
  File "/Users/shantanu/dev/mypy/mypyc/irbuild/visitor.py", line 246, in visit_list_comprehension
    return transform_list_comprehension(self.builder, expr)
  File "/Users/shantanu/dev/mypy/mypyc/irbuild/expression.py", line 810, in transform_list_comprehension
    return translate_list_comprehension(builder, o.generator)
  File "/Users/shantanu/dev/mypy/mypyc/irbuild/for_helpers.py", line 200, in translate_list_comprehension
    comprehension_helper(builder, loop_params, gen_inner_stmts, gen.line)
  File "/Users/shantanu/dev/mypy/mypyc/irbuild/for_helpers.py", line 271, in comprehension_helper
    handle_loop(loop_params)
  File "/Users/shantanu/dev/mypy/mypyc/irbuild/for_helpers.py", line 237, in handle_loop
    for_loop_helper(builder, index, expr,
  File "/Users/shantanu/dev/mypy/mypyc/irbuild/for_helpers.py", line 60, in for_loop_helper
    for_gen = make_for_loop_generator(builder, index, expr, body_block, normal_loop_exit, line)
  File "/Users/shantanu/dev/mypy/mypyc/irbuild/for_helpers.py", line 398, in make_for_loop_generator
    item_type = builder._analyze_iterable_item_type(expr)
  File "/Users/shantanu/dev/mypy/mypyc/irbuild/builder.py", line 795, in _analyze_iterable_item_type
    iterable = get_proper_type(self.types[expr])
rep.py:6: KeyError: <mypy.nodes.ListExpr object at 0x1045257c0>

[JukkaL]

Mypy considers the second list comprehension unreachable, and it doesn't export type information for it. The simplest fix here would probably be to fall back to Any (or object) types whenever mypy failed to generate type information. The code would still be compiled even though it's not needed, but at least it shouldn't fail to compile.