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[ty] do nothing with store_expression_type if inner_expression_inference_state is Get #21718

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[ty] do nothing with store_expression_type if inner_expression_inference_state is Get #21718

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[ty] do nothing with `store_expression_type` if `inner_expression_inf…
mtshiba Dec 1, 2025
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Create inner_expression_inference_state.py
mtshiba Dec 1, 2025
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6 changes: 6 additions & 0 deletions crates/ty_python_semantic/resources/corpus/inner_expression_inference_state.py
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@@ -0,0 +1,6 @@
# This is a regression test for `store_expression_type`.
# ref: https://github.com/astral-sh/ty/issues/1688

x: int

type x[T] = x[T, U]
5 changes: 4 additions & 1 deletion crates/ty_python_semantic/src/types/infer/builder.rs
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Expand Up @@ -7093,10 +7093,13 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {

#[track_caller]
fn store_expression_type(&mut self, expression: &ast::Expr, ty: Type<'db>) {
if self.deferred_state.in_string_annotation() {
if self.deferred_state.in_string_annotation()
|| self.inner_expression_inference_state.is_get()
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@MichaReiser MichaReiser Dec 1, 2025

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Could we use multi_inference_state::Ignore instead of having two modes that represent "read-only" type inference?

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@Gankra Gankra Dec 1, 2025

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drive-by context: I am likely to modify this check for in_string_annotation to do the "store (Expr, Expr) for string annotation types" thing we've been discussing.

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@mtshiba mtshiba Dec 1, 2025

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Could we use multi_inference_state::Ignore instead of having two modes that represent "read-only" type inference?

I understand that MultiInferenceState::Ignore is an option to perform the same calculation twice and discard the second result.
Since all type inference for expressions is skipped while in InnerExpressionInferenceState::Get, I think it should be used whenever possible (for example, when only diagnostics are needed, such as the handling in infer_subscript_type_expression for union types).
But I'm not sure whether this can be assumed in all cases where MultiInferenceState::Ignore is used.

{
// Avoid storing the type of expressions that are part of a string annotation because
// the expression ids don't exists in the semantic index. Instead, we'll store the type
// on the string expression itself that represents the annotation.
// Also, if `inner_expression_inference_state` is `Get`, the expression type has already been stored.
return;
}

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