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Oct 27, 2025
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document -Xsource-features:eta-expand-always #3225

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4 changes: 2 additions & 2 deletions _overviews/scala3-migration/tooling-scala2-xsource3.md
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Expand Up @@ -46,7 +46,6 @@ The `-Xsource:3` flag enables the following Scala 3 syntaxes in Scala 2:
- `import p.{given, *}`
- `case C(xs*)` as an alias for `case C(xs @ _*)`
- `A & B` type intersection as an alias for `A with B`
- Selecting a method `x.f` performs an eta-expansion (`x.f _`), even without an expected type

## Scala 3 migration warnings in detail

Expand Down Expand Up @@ -106,6 +105,7 @@ The following table shows backported Scala 3 language semantics available in `-X
| `case-companion-function`: companions are Functions | fatal warning at use site | synthetic case companion objects no longer extend FunctionN, but are adapted at use site with warning |
| `infer-override`: override type inference | fatal warning | inferred type of member uses type of overridden member |
| `double-definitions`: definitions differing in empty parens <sup>2</sup> | fatal warning | double definition error |
| `eta-expand-always`: `x.f` eta-expands (`x.f _`) even without an expected type | compilation error ("missing argument list") | `x.f` expands to a function value |

Example 1:

Expand All @@ -125,7 +125,7 @@ class C(x: Int) {

### Changes affecting binary encoding

As of Scala 2.13.15, there are 3 changes in `-Xsource-features` that affect binary encoding of classfiles:
As of Scala 2.13.17, there are 3 changes in `-Xsource-features` that affect binary encoding of classfiles:

1. `case-apply-copy-access`: the constructor modifiers of case classes (`case class C private[p] (x: Int)`) are copied to the synthetic `apply` and `copy` methods.
1. `case-companion-function`: the synthetic companion objects of case classes no longer extend `FunctionN`.
Expand Down