## Summary
I think `division-by-zero` is a low-value diagnostic in general; most
real division-by-zero errors (especially those that are less obvious to
the human eye) will occur on values typed as `int`, in which case we
don't issue the diagnostic anyway. Mypy and pyright do not emit this
diagnostic.
Currently the diagnostic is prone to false positives because a) we do
not silence it in unreachable code, and b) we do not implement narrowing
of literals from inequality checks. We will probably fix (a) regardless,
but (b) is low priority apart from division-by-zero.
I think we have many more important things to do and should not allow
false positives on a low-value diagnostic to be a distraction. Not
opposed to re-enabling this diagnostic in future when we can prioritize
reducing its false positives.
References https://github.com/astral-sh/ty/issues/443
## Test Plan
Existing tests.
## Summary
Support direct uses of `typing.TypeAliasType`, as in:
```py
from typing import TypeAliasType
IntOrStr = TypeAliasType("IntOrStr", int | str)
def f(x: IntOrStr) -> None:
reveal_type(x) # revealed: int | str
```
closes https://github.com/astral-sh/ty/issues/392
## Ecosystem
The new false positive here:
```diff
+ error[invalid-type-form] altair/utils/core.py:49:53: The first argument to `Callable` must be either a list of types, ParamSpec, Concatenate, or `...`
```
comes from the fact that we infer the second argument as a type
expression now. We silence false positives for PEP695 `ParamSpec`s, but
not for `P = ParamSpec("P")` inside `Callable[P, ...]`.
## Test Plan
New Markdown tests
## Summary
If the user tries to use a new builtin on an old Python version, tell
them what Python version the builtin was added on, what our inferred
Python version is for their project, and what configuration settings
they can tweak to fix the error.
## Test Plan
Snapshots and screenshots:
## Summary
Updates the `--python` flag to accept Python executables in virtual
environments. Notably, we do not query the executable and it _must_ be
in a canonical location in a virtual environment. This is pretty naive,
but solves for the trivial case of `ty check --python .venv/bin/python3`
which will be a common mistake (and `ty check --python $(which python)`)
I explored this while trying to understand Python discovery in ty in
service of https://github.com/astral-sh/ty/issues/272, I'm not attached
to it, but figure it's worth sharing.
As an alternative, we can add more variants to the
`SearchPathValidationError` and just improve the _error_ message, i.e.,
by hinting that this looks like a virtual environment and suggesting the
concrete alternative path they should provide. We'll probably want to do
that for some other cases anyway (e.g., `3.13` as described in the
linked issue)
This functionality is also briefly mentioned in
https://github.com/astral-sh/ty/issues/193
Closes https://github.com/astral-sh/ty/issues/318
## Test Plan
e.g.,
```
uv run ty check --python .venv/bin/python3
```
needs test coverage still
