## Summary
Related to #13773
This PR adds support for unpacking `for` statement targets.
This involves updating the `value` field in the `Unpack` target to use
an enum which specifies the "where did the value expression came from?".
This is because for an iterable expression, we need to unpack the
iterator type while for assignment statement we need to unpack the value
type itself. And, this needs to be done in the unpack query.
### Question
One of the ways unpacking works in `for` statement is by looking at the
union of the types because if the iterable expression is a tuple then
the iterator type will be union of all the types in the tuple. This
means that the test cases that will test the unpacking in `for`
statement will also implicitly test the unpacking union logic. I was
wondering if it makes sense to merge these cases and only add the ones
that are specific to the union unpacking or for statement unpacking
logic.
## Test Plan
Add test cases involving iterating over a tuple type. I've intentionally
left out certain cases for now and I'm curious to know any thoughts on
the above query.
## Summary
Refer:
https://github.com/astral-sh/ruff/issues/13773#issuecomment-2548020368
This PR adds support for unpacking union types.
Unpacking a union type requires us to first distribute the types for all
the targets that are involved in an unpacking. For example, if there are
two targets and a union type that needs to be unpacked, each target will
get a type from each element in the union type.
For example, if the type is `tuple[int, int] | tuple[int, str]` and the
target has two elements `(a, b)`, then
* The type of `a` will be a union of `int` and `int` which are at index
0 in the first and second tuple respectively which resolves to an `int`.
* Similarly, the type of `b` will be a union of `int` and `str` which
are at index 1 in the first and second tuple respectively which will be
`int | str`.
### Refactors
There are couple of refactors that are added in this PR:
* Add a `debug_assertion` to validate that the unpack target is a list
or a tuple
* Add a separate method to handle starred expression
## Test Plan
Update `unpacking.md` with additional test cases that uses union types.
This is done using parameter type hints style.
## Summary
Adds meta information to `Type::Todo`, allowing developers to easily
trace back the origin of a particular `@Todo` type they encounter.
Instead of `Type::Todo`, we now write either `type_todo!()` which
creates a `@Todo[path/to/source.rs:123]` type with file and line
information, or using `type_todo!("PEP 604 unions not supported")`,
which creates a variant with a custom message.
`Type::Todo` now contains a `TodoType` field. In release mode, this is
just a zero-sized struct, in order not to create any overhead. In debug
mode, this is an `enum` that contains the meta information.
`Type` implements `Copy`, which means that `TodoType` also needs to be
copyable. This limits the design space. We could intern `TodoType`, but
I discarded this option, as it would require us to have access to the
salsa DB everywhere we want to use `Type::Todo`. And it would have made
the macro invocations less ergonomic (requiring us to pass `db`).
So for now, the meta information is simply a `&'static str` / `u32` for
the file/line variant, or a `&'static str` for the custom message.
Anything involving a chain/backtrace of several `@Todo`s or similar is
therefore currently not implemented. Also because we currently don't see
any direct use cases for this, and because all of this will eventually
go away.
Note that the size of `Type` increases from 16 to 24 bytes, but only in
debug mode.
## Test Plan
- Observed the changes in Markdown tests.
- Added custom messages for all `Type::Todo`s that were revealed in the
tests
- Ran red knot in release and debug mode on the following Python file:
```py
def f(x: int) -> int:
reveal_type(x)
```
Prints `@Todo` in release mode and `@Todo(function parameter type)` in
debug mode.
## Summary
This PR fixes a panic which can occur in an unpack assignment when:
* (number of target expressions) - (number of tuple types) > 2
* There's a starred expression
The reason being that the `insert` panics because the index is greater
than the length.
This is an error case and so practically it should occur very rarely.
The solution is to resize the types vector to match the number of
expressions and then insert the starred expression type.
## Test Plan
Add a new test case.
## Summary
This PR adds support for unpacking tuple expression in an assignment
statement where the target expression can be a tuple or a list (the
allowed sequence targets).
The implementation introduces a new `infer_assignment_target` which can
then be used for other targets like the ones in for loops as well. This
delegates it to the `infer_definition`. The final implementation uses a
recursive function that visits the target expression in source order and
compares the variable node that corresponds to the definition. At the
same time, it keeps track of where it is on the assignment value type.
The logic also accounts for the number of elements on both sides such
that it matches even if there's a gap in between. For example, if
there's a starred expression like `(a, *b, c) = (1, 2, 3)`, then the
type of `a` will be `Literal[1]` and the type of `b` will be
`Literal[2]`.
There are a couple of follow-ups that can be done:
* Use this logic for other target positions like `for` loop
* Add diagnostics for mis-match length between LHS and RHS
## Test Plan
Add various test cases using the new markdown test framework.
Validate that existing test cases pass.
---------
Co-authored-by: Carl Meyer <carl@astral.sh>
