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[ty] Support __setitem__ and improve __getitem__ related diagnostics (#19578)

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## Summary

Adds validation to subscript assignment expressions.

```py
class Foo: ...

class Bar:
    __setattr__ = None

class Baz:
    def __setitem__(self, index: str, value: int) -> None:
        pass

# We now emit a diagnostic on these statements
Foo()[1] = 2
Bar()[1] = 2
Baz()[1] = 2

```

Also improves error messages on invalid `__getitem__` expressions

## Test Plan

Update mdtests and add more to `subscript/instance.md`

---------

Co-authored-by: David Peter <sharkdp@users.noreply.github.com>
Co-authored-by: David Peter <mail@david-peter.de>
This commit is contained in:
Matthew Mckee 2025-08-01 08:23:27 +01:00 • committed by GitHub
parent 5c5d50d57a
commit b30d97e5e0
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5 changed files with 196 additions and 17 deletions
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2
crates/ty_python_semantic/resources/mdtest/del.md
View file

@ -181,7 +181,7 @@ def f(l: list[int]):
# but if it was greater than that, it will not be an error.
reveal_type(l[0]) # revealed: int
# error: [call-non-callable]
# error: [invalid-argument-type]
del l["string"]
l[0] = 1

3
crates/ty_python_semantic/resources/mdtest/narrow/assignment.md
View file

@ -253,6 +253,7 @@ does["not"]["exist"] = 0
reveal_type(does["not"]["exist"]) # revealed: Unknown
non_subscriptable = 1
# error: [invalid-assignment]
non_subscriptable[0] = 0
# error: [non-subscriptable]
reveal_type(non_subscriptable[0]) # revealed: Unknown
@ -317,7 +318,7 @@ def f(c: C, s: str):
reveal_type(c.x) # revealed: int | None
s = c.x # error: [invalid-assignment]
# TODO: This assignment is invalid and should result in an error.
# error: [invalid-assignment] "Method `__setitem__` of type `Overload[(key: SupportsIndex, value: int, /) -> None, (key: slice[Any, Any, Any], value: Iterable[int], /) -> None]` cannot be called with a key of type `Literal[0]` and a value of type `str` on object of type `list[int]`"
c.l[0] = s
reveal_type(c.l[0]) # revealed: int
```

56
crates/ty_python_semantic/resources/mdtest/subscript/instance.md
View file

@ -14,7 +14,7 @@ a = NotSubscriptable()[0] # error: "Cannot subscript object of type `NotSubscri
class NotSubscriptable:
__getitem__ = None
# error: "Method `__getitem__` of type `Unknown | None` is not callable on object of type `NotSubscriptable`"
# error: "Method `__getitem__` of type `Unknown | None` is possibly not callable on object of type `NotSubscriptable`"
a = NotSubscriptable()[0]
```
@ -43,6 +43,18 @@ def _(flag: bool):
reveal_type(Identity()[0]) # revealed: int | str
```
## `__getitem__` with invalid index argument
```py
class Identity:
def __getitem__(self, index: int) -> int:
return index
a = Identity()
# error: [invalid-argument-type] "Method `__getitem__` of type `bound method Identity.__getitem__(index: int) -> int` cannot be called with key of type `Literal["a"]` on object of type `Identity`"
a["a"]
```
## `__setitem__` with no `__getitem__`
```py
@ -53,3 +65,45 @@ class NoGetitem:
a = NoGetitem()
a[0] = 0
```
## Subscript store with no `__setitem__`
```py
class NoSetitem: ...
a = NoSetitem()
a[0] = 0 # error: "Cannot assign to object of type `NoSetitem` with no `__setitem__` method"
```
## `__setitem__` not callable
```py
class NoSetitem:
__setitem__ = None
a = NoSetitem()
a[0] = 0 # error: "Method `__setitem__` of type `Unknown | None` is possibly not callable on object of type `NoSetitem`"
```
## Valid `__setitem__` method
```py
class Identity:
def __setitem__(self, index: int, value: int) -> None:
pass
a = Identity()
a[0] = 0
```
## `__setitem__` with invalid index argument
```py
class Identity:
def __setitem__(self, index: int, value: int) -> None:
pass
a = Identity()
# error: [invalid-assignment] "Method `__setitem__` of type `bound method Identity.__setitem__(index: int, value: int) -> None` cannot be called with a key of type `Literal["a"]` and a value of type `Literal[0]` on object of type `Identity`"
a["a"] = 0
```

8
crates/ty_python_semantic/resources/mdtest/subscript/lists.md
View file

@ -17,7 +17,7 @@ reveal_type(x[0]) # revealed: Unknown
# TODO reveal list[int]
reveal_type(x[0:1]) # revealed: list[Unknown]
# error: [call-non-callable]
# error: [invalid-argument-type]
reveal_type(x["a"]) # revealed: Unknown
```
@ -29,11 +29,9 @@ In assignment, we might also have a named assignment. This should also get type
x = [1, 2, 3]
x[0 if (y := 2) else 1] = 5
# TODO: better error than "method `__getitem__` not callable on type `list`"
# error: [call-non-callable]
# error: [invalid-assignment]
x["a" if (y := 2) else 1] = 6
# TODO: better error than "method `__getitem__` not callable on type `list`"
# error: [call-non-callable]
# error: [invalid-assignment]
x["a" if (y := 2) else "b"] = 6
```

130
crates/ty_python_semantic/src/types/infer.rs
View file

@ -89,7 +89,7 @@ use crate::semantic_index::symbol::ScopedSymbolId;
use crate::semantic_index::{
ApplicableConstraints, EnclosingSnapshotResult, SemanticIndex, place_table, semantic_index,
};
use crate::types::call::{Binding, Bindings, CallArguments, CallError};
use crate::types::call::{Binding, Bindings, CallArguments, CallError, CallErrorKind};
use crate::types::class::{CodeGeneratorKind, DataclassField, MetaclassErrorKind, SliceLiteral};
use crate::types::diagnostic::{
self, CALL_NON_CALLABLE, CONFLICTING_DECLARATIONS, CONFLICTING_METACLASS,
@ -3619,6 +3619,99 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
self.infer_target_impl(target, assigned_ty);
}
/// Make sure that the subscript assignment `obj[slice] = value` is valid.
fn validate_subscript_assignment(
&mut self,
target: &ast::ExprSubscript,
assigned_ty: Type<'db>,
) -> bool {
let ast::ExprSubscript {
range: _,
node_index: _,
value,
slice,
ctx: _,
} = target;
let value_ty = self.infer_expression(value);
let slice_ty = self.infer_expression(slice);
let db = self.db();
let context = &self.context;
match value_ty.try_call_dunder(
db,
"__setitem__",
CallArguments::positional([slice_ty, assigned_ty]),
) {
Ok(_) => true,
Err(err) => match err {
CallDunderError::PossiblyUnbound { .. } => {
if let Some(builder) =
context.report_lint(&POSSIBLY_UNBOUND_IMPLICIT_CALL, &**value)
{
builder.into_diagnostic(format_args!(
"Method `__setitem__` of type `{}` is possibly unbound",
value_ty.display(db),
));
}
false
}
CallDunderError::CallError(call_error_kind, bindings) => {
match call_error_kind {
CallErrorKind::NotCallable => {
if let Some(builder) = context.report_lint(&CALL_NON_CALLABLE, &**value)
{
builder.into_diagnostic(format_args!(
"Method `__setitem__` of type `{}` is not callable \
on object of type `{}`",
bindings.callable_type().display(db),
value_ty.display(db),
));
}
}
CallErrorKind::BindingError => {
if let Some(builder) =
context.report_lint(&INVALID_ASSIGNMENT, &**value)
{
builder.into_diagnostic(format_args!(
"Method `__setitem__` of type `{}` cannot be called with \
a key of type `{}` and a value of type `{}` on object of type `{}`",
bindings.callable_type().display(db),
slice_ty.display(db),
assigned_ty.display(db),
value_ty.display(db),
));
}
}
CallErrorKind::PossiblyNotCallable => {
if let Some(builder) = context.report_lint(&CALL_NON_CALLABLE, &**value)
{
builder.into_diagnostic(format_args!(
"Method `__setitem__` of type `{}` is possibly not \
callable on object of type `{}`",
bindings.callable_type().display(db),
value_ty.display(db),
));
}
}
}
false
}
CallDunderError::MethodNotAvailable => {
if let Some(builder) = context.report_lint(&INVALID_ASSIGNMENT, &**value) {
builder.into_diagnostic(format_args!(
"Cannot assign to object of type `{}` with no `__setitem__` method",
value_ty.display(db),
));
}
false
}
},
}
}
/// Make sure that the attribute assignment `obj.attribute = value` is valid.
///
/// `target` is the node for the left-hand side, `object_ty` is the type of `obj`, `attribute` is
@ -4191,6 +4284,13 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
);
}
}
ast::Expr::Subscript(subscript_expr) => {
self.store_expression_type(target, assigned_ty.unwrap_or(Type::unknown()));
if let Some(assigned_ty) = assigned_ty {
self.validate_subscript_assignment(subscript_expr, assigned_ty);
}
}
_ => {
// TODO: Remove this once we handle all possible assignment targets.
self.infer_expression(target);
@ -8616,7 +8716,9 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
return err.fallback_return_type(db);
}
Err(CallDunderError::CallError(_, bindings)) => {
Err(CallDunderError::CallError(call_error_kind, bindings)) => {
match call_error_kind {
CallErrorKind::NotCallable => {
if let Some(builder) = context.report_lint(&CALL_NON_CALLABLE, value_node) {
builder.into_diagnostic(format_args!(
"Method `__getitem__` of type `{}` \
@ -8625,6 +8727,30 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
value_ty.display(db),
));
}
}
CallErrorKind::BindingError => {
if let Some(builder) =
context.report_lint(&INVALID_ARGUMENT_TYPE, value_node)
{
builder.into_diagnostic(format_args!(
"Method `__getitem__` of type `{}` cannot be called with key of \
type `{}` on object of type `{}`",
bindings.callable_type().display(db),
slice_ty.display(db),
value_ty.display(db),
));
}
}
CallErrorKind::PossiblyNotCallable => {
if let Some(builder) = context.report_lint(&CALL_NON_CALLABLE, value_node) {
builder.into_diagnostic(format_args!(
"Method `__getitem__` of type `{}` is possibly not callable on object of type `{}`",
bindings.callable_type().display(db),
value_ty.display(db),
));
}
}
}
return bindings.return_type(db);
}