TypeVars in some generic functions can go unsolved, resulting in an `Any` in the evaluated type

[erictraut]

Pyright users have recently reported a couple of issues where they received an Unknown (i.e. an implicit Any) type when evaluating a call expression. These problems were both related to a case where a TypeVar was used to annotate a parameter with a default argument, but the caller didn't provide an argument for that parameter and relied on the default. This left the TypeVar unsolved.

Here's an example from the pyright issue tracker.

@JelleZijlstra suggested that pyright add a check for this condition. I've enhanced the reportInvalidTypeVarUse check to detect and report this case. See this issue for details.

The new check identifies 10 cases in the stdlib typeshed stubs and 27 cases in third-party stubs. Jelle asked that I create this issue with the full list, which I have pasted below.

<redacted>/typeshed/stdlib/argparse.pyi
  <redacted>/typeshed/stdlib/argparse.pyi:215:32 - error: Type variable "_ArgumentParserT" may go unsolved if caller supplies no argument for parameter "parser_class"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
<redacted>/typeshed/stdlib/fileinput.pyi
  <redacted>/typeshed/stdlib/fileinput.pyi:32:54 - error: Type variable "AnyStr" may go unsolved if caller supplies no argument for parameter "openhook"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
<redacted>/typeshed/stdlib/gettext.pyi
  <redacted>/typeshed/stdlib/gettext.pyi:157:22 - error: Type variable "_T" may go unsolved if caller supplies no argument for parameter "class_"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
<redacted>/typeshed/stdlib/optparse.pyi
  <redacted>/typeshed/stdlib/optparse.pyi:243:41 - error: Type variable "AnyStr" may go unsolved if caller supplies no argument for parameter "args"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
<redacted>/typeshed/stdlib/tempfile.pyi
  <redacted>/typeshed/stdlib/tempfile.pyi:387:13 - error: Type variable "AnyStr" may go unsolved if caller supplies no argument for parameter "suffix"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stdlib/tempfile.pyi:392:21 - error: Type variable "AnyStr" may go unsolved if caller supplies no argument for parameter "suffix"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stdlib/tempfile.pyi:396:20 - error: Type variable "AnyStr" may go unsolved if caller supplies no argument for parameter "suffix"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
<redacted>/typeshed/stdlib/multiprocessing/managers.pyi
  <redacted>/typeshed/stdlib/multiprocessing/managers.pyi:127:38 - error: Type variable "_KT" may go unsolved if caller supplies no argument for parameter "sequence"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stdlib/multiprocessing/managers.pyi:127:43 - error: Type variable "_VT" may go unsolved if caller supplies no argument for parameter "sequence"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stdlib/multiprocessing/managers.pyi:128:39 - error: Type variable "_T" may go unsolved if caller supplies no argument for parameter "sequence"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
<redacted>/typeshed/stubs/SQLAlchemy/sqlalchemy/orm/decl_api.pyi
  <redacted>/typeshed/stubs/SQLAlchemy/sqlalchemy/orm/decl_api.pyi:117:76 - error: Type variable "_DeclT" may go unsolved if caller supplies no argument for parameter "metaclass"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stubs/SQLAlchemy/sqlalchemy/orm/decl_api.pyi:128:37 - error: Type variable "_DeclT" may go unsolved if caller supplies no argument for parameter "metaclass"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
<redacted>/typeshed/stubs/invoke/invoke/tasks.pyi
  <redacted>/typeshed/stubs/invoke/invoke/tasks.pyi:75:17 - error: Type variable "_TaskT" may go unsolved if caller supplies no argument for parameter "klass"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
<redacted>/typeshed/stubs/mock/mock/mock.pyi
  <redacted>/typeshed/stubs/mock/mock/mock.pyi:233:14 - error: Type variable "_T" may go unsolved if caller supplies no argument for parameter "new"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
<redacted>/typeshed/stubs/mypy-extensions/mypy_extensions.pyi
  <redacted>/typeshed/stubs/mypy-extensions/mypy_extensions.pyi:24:15 - error: Type variable "_T" may go unsolved if caller supplies no argument for parameter "type"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stubs/mypy-extensions/mypy_extensions.pyi:25:22 - error: Type variable "_T" may go unsolved if caller supplies no argument for parameter "type"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stubs/mypy-extensions/mypy_extensions.pyi:26:20 - error: Type variable "_T" may go unsolved if caller supplies no argument for parameter "type"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stubs/mypy-extensions/mypy_extensions.pyi:27:27 - error: Type variable "_T" may go unsolved if caller supplies no argument for parameter "type"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stubs/mypy-extensions/mypy_extensions.pyi:28:18 - error: Type variable "_T" may go unsolved if caller supplies no argument for parameter "type"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stubs/mypy-extensions/mypy_extensions.pyi:29:17 - error: Type variable "_T" may go unsolved if caller supplies no argument for parameter "type"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
<redacted>/typeshed/stubs/psycopg2/psycopg2/_psycopg.pyi
  <redacted>/typeshed/stubs/psycopg2/psycopg2/_psycopg.pyi:409:62 - error: Type variable "_T_cur" may go unsolved if caller supplies no argument for parameter "cursor_factory"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
<redacted>/typeshed/stubs/redis/redis/commands/core.pyi
  <redacted>/typeshed/stubs/redis/redis/commands/core.pyi:644:47 - error: Type variable "_ScoreCastFuncReturn" may go unsolved if caller supplies no argument for parameter "score_cast_func"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stubs/redis/redis/commands/core.pyi:651:47 - error: Type variable "_ScoreCastFuncReturn" may go unsolved if caller supplies no argument for parameter "score_cast_func"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stubs/redis/redis/commands/core.pyi:682:47 - error: Type variable "_ScoreCastFuncReturn" may go unsolved if caller supplies no argument for parameter "score_cast_func"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stubs/redis/redis/commands/core.pyi:689:47 - error: Type variable "_ScoreCastFuncReturn" may go unsolved if caller supplies no argument for parameter "score_cast_func"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stubs/redis/redis/commands/core.pyi:859:47 - error: Type variable "_ScoreCastFuncReturn" may go unsolved if caller supplies no argument for parameter "score_cast_func"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stubs/redis/redis/commands/core.pyi:874:47 - error: Type variable "_ScoreCastFuncReturn" may go unsolved if caller supplies no argument for parameter "score_cast_func"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stubs/redis/redis/commands/core.pyi:901:47 - error: Type variable "_ScoreCastFuncReturn" may go unsolved if caller supplies no argument for parameter "score_cast_func"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stubs/redis/redis/commands/core.pyi:935:47 - error: Type variable "_ScoreCastFuncReturn" may go unsolved if caller supplies no argument for parameter "score_cast_func"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stubs/redis/redis/commands/core.pyi:958:47 - error: Type variable "_ScoreCastFuncReturn" may go unsolved if caller supplies no argument for parameter "score_cast_func"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stubs/redis/redis/commands/core.pyi:1023:47 - error: Type variable "_ScoreCastFuncReturn" may go unsolved if caller supplies no argument for parameter "score_cast_func"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stubs/redis/redis/commands/core.pyi:1038:47 - error: Type variable "_ScoreCastFuncReturn" may go unsolved if caller supplies no argument for parameter "score_cast_func"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stubs/redis/redis/commands/core.pyi:1065:47 - error: Type variable "_ScoreCastFuncReturn" may go unsolved if caller supplies no argument for parameter "score_cast_func"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stubs/redis/redis/commands/core.pyi:1099:47 - error: Type variable "_ScoreCastFuncReturn" may go unsolved if caller supplies no argument for parameter "score_cast_func"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stubs/redis/redis/commands/core.pyi:1122:47 - error: Type variable "_ScoreCastFuncReturn" may go unsolved if caller supplies no argument for parameter "score_cast_func"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
<redacted>/typeshed/stubs/setuptools/pkg_resources/__init__.pyi
  <redacted>/typeshed/stubs/setuptools/pkg_resources/__init__.pyi:63:104 - error: Type variable "_T" may go unsolved if caller supplies no argument for parameter "installer"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
  <redacted>/typeshed/stubs/setuptools/pkg_resources/__init__.pyi:67:83 - error: Type variable "_T" may go unsolved if caller supplies no argument for parameter "installer"
    Provide an overload that specifies the return type when the argument is not supplied (reportInvalidTypeVarUse)
37 errors, 0 warnings, 0 informations 

• argparse (argparse: remove incorrect default in overload #7929)
• fileinput (fileinput: Fix TypeVar usage #7934, issue Wrong stub for fileinput.input() #7922)
• gettext (gettext: fix unconstrained TypeVar #7935)
• optparse (optparse: fix unconstrained TypeVar #7936)
• tempfile (tempfile: Fix TypeVar usage #7939)
• multiprocessing.managers (multiprocessing.managers: fix TypeVar usage #7938)
• sqlalchemy.orm.decl_api, beautifulsoup (Fix TypeVars in beautifulsoup and SQLAlchemy #8087)
• invoke.tasks (invoke: Fix unconstrained TypeVar #7943)
• mock.mock (mock: Fix unconstrained TypeVar #7945)
• mypy_extensions (mypy_extensions: fix TypeVar usage #7937)
• psycopg2._psycopg (psycopg2: stub improvements #7964)
• redis.commands.core:
  • redis: Fix unconstrained TypeVars in a few redis commands #7942
  • redis: fix more unconstrained TypeVars #8084
• pkg_resources (pkg_resources: Fix unconstrained TypeVars #7941)
• cachetools constructor methods (cachetools: Fix invalid TypeVar usage #8073)
• builtins/collections constructor methods (builtins: Fix unconstrained overloads in set() and frozenset() #7944)
• Misc (Fix miscellaneous invalid TypeVar usages #8074)

[srittau]

Thanks, that's very helpful! We should enable that check when it's available and we've fixed the issues.

[JelleZijlstra]

Thanks Eric! I added a checklist to your comment so we can track the remaining work.