## Summary
For silencing `invalid-type-form` diagnostics in unreachable code, we
use the same approach that we use before and check the reachability that
we already record.
For silencing `invalid-bases`, we simply check if the type of the base
is `Never`. If so, we silence the diagnostic with the argument that the
class construction would never happen.
## Test Plan
Updated Markdown tests.
## Summary
Similar to what we did for `unresolved-reference` and
`unresolved-attribute`, we now also silence `unresolved-import`
diagnostics if the corresponding `import` statement is unreachable.
This addresses the (already closed) issue #17049.
## Test Plan
Adapted Markdown tests.
## Summary
Basically just repeat the same thing that we did for
`unresolved-reference`, but now for attribute expressions.
We now also handle the case where the unresolved attribute (or the
unresolved reference) diagnostic originates from a stringified type
annotation.
And I made the evaluation of reachability constraints lazy (will only be
evaluated right before we are about to emit a diagnostic).
## Test Plan
New Markdown tests for stringified annotations.
## Summary
Track the reachability of nested scopes within their parent scopes. We
use this as an additional requirement for emitting
`unresolved-reference` diagnostics (and in the future,
`unresolved-attribute` and `unresolved-import`). This means that we only
emit `unresolved-reference` for a given use of a symbol if the use
itself is reachable (within its own scope), *and if the scope itself is
reachable*. For example, no diagnostic should be emitted for the use of
`x` here:
```py
if False:
x = 1
def f():
print(x) # this use of `x` is reachable inside the `f` scope,
# but the whole `f` scope is not reachable.
```
There are probably more fine-grained ways of solving this problem, but
they require a more sophisticated understanding of nested scopes (see
#15777, in particular
https://github.com/astral-sh/ruff/issues/15777#issuecomment-2788950267).
But it doesn't seem completely unreasonable to silence *this specific
kind of error* in unreachable scopes.
## Test Plan
Observed changes in reachability tests and ecosystem.
## Summary
As discussed in https://github.com/astral-sh/ruff/issues/16983 and
"mitigate" said issue for the alpha.
This PR changes the default for `PythonPlatform` to be the current
platform rather than `all`.
I'm not sure if we should be as sophisticated as supporting `ios` and
`android` as defaults but it was easy...
## Test Plan
Updated Markdown tests.
---------
Co-authored-by: David Peter <mail@david-peter.de>
## Summary
This is a new test case that I don't know how to handle yet. It leads to
many false positives in `rich/tests/test_win32_console.py`, which does
something like:
```py
if sys.platform == "win32":
from windows_only_module import some_symbol
some_other_symbol = 1
def some_test_case():
use(some_symbol) # Red Knot: unresolved-reference
use(some_other_symbol) # Red Knot: unresolved-reference
```
Also adds a test for using unreachable symbols in type annotations or as
class bases.
## Summary
This implements a new approach to silencing `unresolved-reference`
diagnostics by keeping track of the reachability of each use of a
symbol. The changes merged in
https://github.com/astral-sh/ruff/pull/17169 are still needed for the
"Use of variable in nested function" test case, but that could also be
solved in another way eventually (see
https://github.com/astral-sh/ruff/issues/15777). We can use the same
technique to silence `unresolved-import` and `unresolved-attribute`
false-positives, but I think this could be merged in isolation.
## Test Plan
New Markdown tests, ecosystem tests
## Summary
This PR changes the inferred type for symbols in unreachable sections of
code to `Never` (instead of reporting them as unbound), in order to
silence false positive diagnostics. See the lengthy comment in the code
for further details.
## Test Plan
- Updated Markdown tests.
- Manually verified a couple of ecosystem diagnostic changes.
## Summary
Add an initial set of tests that will eventually document our behavior
around unreachable code. In the last section of this suite, I argue why
we should never type check unreachable sections and never emit any
diagnostics in these sections.
