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Backport "Restore pre-3.3.2 behavior of inline implicit def" to LTS #20975

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merged 1 commit into from
Jul 3, 2024

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WojciechMazur
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Backports #19877 to the LTS branch.

PR submitted by the release tooling.
[skip ci]

`inline implicit def` is not really a supported feature since it combines Scala
3's `inline` with Scala 2's `implicit` where the latter should eventually be
deprecated. This however didn't prevent at least one project from using this
combination in a way that was broken by #18249, see #19862 for the details.

The issue is that when definining:

    implicit def foo(x: A): B = ...

Then `foo` is a valid implicit search candidate when looking up an implicit
`Function1[A, B]`. However, before #18249 if instead we wrote:

    inline implicit def foo(x: A): B = ...

Then `foo` would be considered as an implicit search candidate but discarded
because eta-expansion was disabled.

There is no particular reason for `inline implicit def` to behave differently
from `implicit def` here, but since `implicit def` is a legacy feature and since
Scala 3.3 is an LTS release, we choose to restore the pre-#18249 behavior for
compatibility reasons.

Fixes #19862.

[Cherry-picked af69895]
Base automatically changed from lts-19803 to lts-3.3 July 3, 2024 08:38
@WojciechMazur
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No regressions detected in the community build up to lts-19921.

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@WojciechMazur WojciechMazur merged commit f32fa2b into lts-3.3 Jul 3, 2024
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@WojciechMazur WojciechMazur deleted the lts-19877 branch July 3, 2024 08:38
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2 participants