JuliaLang / julia / 1464

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Committed by web-flow

Commit Message

typegroup: Allow `TypeApp` bounds in `TypeVar` (#64691)

Since struct definitions go through the typegroup mechanism (#61306), a
self-reference applied to parameters such as `S{T}` evaluates to a
`Core.TypeApp` placeholder, so using it as a bound, as in
`x::Vector{<:S{T}}`, failed in the `TypeVar` constructor.

A `TypeVar` bound may now be a `TypeApp`, and the `lb`/`ub` fields of
`TypeVar` are declared accordingly once `TypeApp` is defined, since
compiled code relies on the declared field types. `resolve_type_refs`
already rebuilds a `TypeVar` whose bounds reference group members, so
such bounds resolve like any other once the group types exist, with no
change to lowering. `typevar_tfunc` no longer considers a `TypeApp` bound
to always throw, and `TypeApp` gets its own `show` method, so that
inferring the printing of `TypeVar` bounds does not pull in
`show_default`.

A struct type parameter bound that still contains a `TypeApp` (which can
only come from applying a `TypeVar`, as in `T<:F{Int}`) is rejected
instead of leaking into the type's parameters, and applying a `TypeVar`
during resolution raises the same `TypeError` as eager evaluation.

Fixes #63827
Assisted-by: Claude Code (Opus 5.5)

Coverage Stats

12 of 12 new or added lines in 2 files covered. (100.0%)

56 existing lines in 11 files now uncovered.

98880 of 107207 relevant lines covered (92.23%)

384.18 hits per line