[ty] Reachability analysis for isinstance(…) branches by sharkdp · Pull Request #19503 · astral-sh/ruff (original) (raw)

sharkdp changed the title[ty] Type inference for isinstance(…) calls [ty] Reachability analysis for isinstance(…) branches

Jul 23, 2025

sharkdp marked this pull request as ready for review

July 23, 2025 09:19

sharkdp deleted the david/isinstance-inference branch

July 23, 2025 11:06

UnboundVariable pushed a commit to UnboundVariable/ruff that referenced this pull request

Jul 23, 2025

• main: (28 commits) [ty] highlight the argument in static_assert error messages (astral-sh#19426) [ty] Infer single-valuedness for enums based on int/str (astral-sh#19510) [ty] Restructure submodule query around File dependency [ty] Make Module a Salsa ingredient [ty] Reachability analysis for isinstance(…) branches (astral-sh#19503) [ty] Normalize single-member enums to their instance type (astral-sh#19502) [ty] Invert ty_ide and ty_project dependency (astral-sh#19501) [ty] Implement mock language server for testing (astral-sh#19391) [ty] Detect enums if metaclass is a subtype of EnumType/EnumMeta (astral-sh#19481) [ty] perform type narrowing for places marked global too (astral-sh#19381) [ty] Use ThinVec for sub segments in PlaceExpr (astral-sh#19470) [ty] Splat variadic arguments into parameter list (astral-sh#18996) [flake8-pyi] Skip fix if all Union members are None (PYI016) (astral-sh#19416) Skip notebook with errors in ecosystem check (astral-sh#19491) [ty] Consistent use of American english (in rules) (astral-sh#19488) [ty] Support iterating over enums (astral-sh#19486) Fix panic for illegal Literal[…] annotations with inner subscript expressions (astral-sh#19489) Move fix suggestion to subdiagnostic (astral-sh#19464) [ty] Implement non-stdlib stub mapping for classes and functions (astral-sh#19471) [ty] Disallow illegal uses of ClassVar (astral-sh#19483) ...

Conflicts:

crates/ty_ide/src/goto.rs

dcreager added a commit that referenced this pull request

Jul 23, 2025

• main: [ty] Fix narrowing and reachability of class patterns with arguments (#19512) [ty] Implemented partial support for "find references" language server feature. (#19475) [flake8-use-pathlib] Add autofix for PTH101, PTH104, PTH105, PTH121 (#19404) [perflint] Parenthesize generator expressions (PERF401) (#19325) [pep8-naming] Fix N802 false positives for CGIHTTPRequestHandler and SimpleHTTPRequestHandler (#19432) [pylint] Handle empty comments after line continuation (PLR2044) (#19405) Move concise diagnostic rendering to ruff_db (#19398) [ty] highlight the argument in static_assert error messages (#19426) [ty] Infer single-valuedness for enums based on int/str (#19510) [ty] Restructure submodule query around File dependency [ty] Make Module a Salsa ingredient [ty] Reachability analysis for isinstance(…) branches (#19503) [ty] Normalize single-member enums to their instance type (#19502) [ty] Invert ty_ide and ty_project dependency (#19501) [ty] Implement mock language server for testing (#19391) [ty] Detect enums if metaclass is a subtype of EnumType/EnumMeta (#19481) [ty] perform type narrowing for places marked global too (#19381)

AlexWaygood pushed a commit that referenced this pull request

Jul 25, 2025

Summary

Add more precise type inference for a limited set of isinstance(…) calls, i.e. return Literal[True] if we can be sure that this is the correct result. This improves exhaustiveness checking / reachability analysis for if-elif-else chains with isinstance checks. For example:

def is_number(x: int | str) -> bool:  # no "can implicitly return `None` error here anymore
    if isinstance(x, int):
        return True
    elif isinstance(x, str):
        return False

    # code here is now detected as being unreachable

This PR also adds a new test suite for exhaustiveness checking.

Test Plan

New Markdown tests

Ecosystem analysis

The removed diagnostics look good. There's one case where a "true positive" is removed in unreachable code. src is annotated as being of type str, but there is an elif isinstance(src, bytes) branch, which we now detect as unreachable. And so the diagnostic inside that branch is silenced. I don't think this is a problem, especially once we have a "graying out" feature, or a lint that warns about unreachable code.

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