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Fix HK type param bounds variance checking
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4 files changed

+145
-1
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‎compiler/src/dotty/tools/dotc/printing/Formatting.scala‎

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@@ -87,6 +87,10 @@ object Formatting {
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def show(x: H *: T) =
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CtxShow(toStr(x.head) *: toShown(x.tail).asInstanceOf[Tuple])
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given Show[typer.VarianceChecker.VarianceError] with
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def show(x: typer.VarianceChecker.VarianceError) =
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CtxShow("VarianceError(" + toStr(x.tvar) + ", " + toStr(x.required) + ")")
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given Show[FlagSet] with
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def show(x: FlagSet) = x.flagsString
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‎compiler/src/dotty/tools/dotc/typer/VarianceChecker.scala‎

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@@ -120,7 +120,7 @@ class VarianceChecker(using Context) {
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* explicitly (their TypeDefs will be passed here.) For MethodTypes, the
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* same is true of the parameters (ValDefs).
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*/
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def apply(status: Option[VarianceError], tp: Type): Option[VarianceError] = trace(s"variance checking $tp of $base at $variance", variances) {
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def apply(status: Option[VarianceError], tp: Type): Option[VarianceError] = trace(i"variance checking $tp of $base at $variance", variances) {
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try
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if (status.isDefined) status
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else tp match {
@@ -136,6 +136,14 @@ class VarianceChecker(using Context) {
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status
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case tp: ClassInfo =>
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foldOver(status, tp.parents)
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case tp @ TypeBounds(lo: LambdaType, hi) if lo ne hi =>
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// When checking the info of higher-kinded type members,
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// (such as the following from i21625)
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// type F_NL_LB[M <: L] >: LB[M]
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// we only check the lambda type param bounds (`>: L`)
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// when checking the upper bound, eg `<: [M <: L] =>> Any`,
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// not when checking the lower bound `>: [M <: L] =>> LB[M]`.
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foldOver(status, tp.derivedTypeBounds(lo.resultType, hi))
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case _ =>
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foldOver(status, tp)
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}

‎tests/neg/i21625.check‎

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-- Error: tests/neg/i21625.scala:5:7 -----------------------------------------------------------------------------------
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5 | type F_LA_LB[K >: L] >: LB[K] // error: >: L
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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| contravariant type L occurs in covariant position in type [K >: L] >: LB[K] of type F_LA_LB
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-- Error: tests/neg/i21625.scala:8:7 -----------------------------------------------------------------------------------
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8 | type F_NU_LB[V <: U] >: LB[V] // error: <: U
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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| covariant type U occurs in contravariant position in type [V <: U] >: LB[V] of type F_NU_LB
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-- Error: tests/neg/i21625.scala:10:7 ----------------------------------------------------------------------------------
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10 | type F_LA_UB[K >: L] <: UB[K] // error: >: L
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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| contravariant type L occurs in covariant position in type [K >: L] <: UB[K] of type F_LA_UB
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-- Error: tests/neg/i21625.scala:13:7 ----------------------------------------------------------------------------------
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13 | type F_NU_UB[V <: U] <: UB[V] // error: <: U
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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| covariant type U occurs in contravariant position in type [V <: U] <: UB[V] of type F_NU_UB
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-- Error: tests/neg/i21625.scala:17:7 ----------------------------------------------------------------------------------
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17 | F_NL_LB[M <: L] >: LB[M], // error: <: L
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| ^^^^^^^^^^^^^^^^^^^^^^^^
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| contravariant type L occurs in covariant position in type [M <: L] >: LB[M] of type F_NL_LB
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-- Error: tests/neg/i21625.scala:18:7 ----------------------------------------------------------------------------------
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18 | F_UA_LB[T >: U] >: LB[T], // error: >: U
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| ^^^^^^^^^^^^^^^^^^^^^^^^
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| covariant type U occurs in contravariant position in type [T >: U] >: LB[T] of type F_UA_LB
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-- Error: tests/neg/i21625.scala:22:7 ----------------------------------------------------------------------------------
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22 | F_NL_UB[M <: L] <: UB[M], // error: <: L
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| ^^^^^^^^^^^^^^^^^^^^^^^^
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| contravariant type L occurs in covariant position in type [M <: L] <: UB[M] of type F_NL_UB
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-- Error: tests/neg/i21625.scala:23:7 ----------------------------------------------------------------------------------
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23 | F_UA_UB[T >: U] <: UB[T], // error: >: U
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| ^^^^^^^^^^^^^^^^^^^^^^^^
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| covariant type U occurs in contravariant position in type [T >: U] <: UB[T] of type F_UA_UB
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-- Error: tests/neg/i21625.scala:28:7 ----------------------------------------------------------------------------------
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28 | type M <: L // error: <: L
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| ^^^^^^^^^^^
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| contravariant type L occurs in covariant position in type <: L of type M
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-- Error: tests/neg/i21625.scala:29:7 ----------------------------------------------------------------------------------
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29 | type T >: U // error: >: U
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| ^^^^^^^^^^^
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| covariant type U occurs in contravariant position in type >: U of type T
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-- Error: tests/neg/i21625.scala:32:10 ---------------------------------------------------------------------------------
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32 | def d_K[K >: L](): K // error: >: L
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| ^^^^^^
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| contravariant type L occurs in covariant position in type >: L of type K
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-- Error: tests/neg/i21625.scala:33:6 ----------------------------------------------------------------------------------
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33 | def d_L(): L // error: => L
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| ^^^^^^^^^^^^^^^^^^^^
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| contravariant type L occurs in covariant position in type (): L of method d_L
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-- Error: tests/neg/i21625.scala:37:10 ---------------------------------------------------------------------------------
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37 | def d_V[V <: U](): V // error: <: U
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| ^^^^^^
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| covariant type U occurs in contravariant position in type <: U of type V
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-- Error: tests/neg/i21625.scala:40:6 ----------------------------------------------------------------------------------
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40 | val v_L: L // error: L
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| ^^^^^^^^^^
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| contravariant type L occurs in covariant position in type L of value v_L
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-- Error: tests/neg/i21625.scala:48:15 ---------------------------------------------------------------------------------
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48 | def d_K_Unit[K >: L](): K => Unit // error: >: L
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| ^^^^^^
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| contravariant type L occurs in covariant position in type >: L of type K
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-- Error: tests/neg/i21625.scala:52:6 ----------------------------------------------------------------------------------
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52 | def d_U_Unit(): U => Unit // error: U =>
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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| covariant type U occurs in contravariant position in type (): U => Unit of method d_U_Unit
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-- Error: tests/neg/i21625.scala:53:15 ---------------------------------------------------------------------------------
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53 | def d_V_Unit[V <: U](): V => Unit // error: <: U
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| ^^^^^^
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| covariant type U occurs in contravariant position in type <: U of type V
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-- Error: tests/neg/i21625.scala:59:6 ----------------------------------------------------------------------------------
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59 | val v_U_Unit: U => Unit // error: U =>
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| ^^^^^^^^^^^^^^^^^^^^^^^
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| covariant type U occurs in contravariant position in type U => Unit of value v_U_Unit

‎tests/neg/i21625.scala‎

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trait LB[X]; trait UB[Y]
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trait Foo[-L, +U]:
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type F_LA_LB[K >: L] >: LB[K] // error: >: L
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type F_NL_LB[M <: L] >: LB[M] // was: error: <: L
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type F_UA_LB[T >: U] >: LB[T] // was: error: >: U
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type F_NU_LB[V <: U] >: LB[V] // error: <: U
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type F_LA_UB[K >: L] <: UB[K] // error: >: L
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type F_NL_UB[M <: L] <: UB[M]
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type F_UA_UB[T >: U] <: UB[T]
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type F_NU_UB[V <: U] <: UB[V] // error: <: U
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def hk[
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F_LA_LB[K >: L] >: LB[K], // was: error: >: L
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F_NL_LB[M <: L] >: LB[M], // error: <: L
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F_UA_LB[T >: U] >: LB[T], // error: >: U
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F_NU_LB[V <: U] >: LB[V], // was: error: <: U
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F_LA_UB[K >: L] <: UB[K],
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F_NL_UB[M <: L] <: UB[M], // error: <: L
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F_UA_UB[T >: U] <: UB[T], // error: >: U
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F_NU_UB[V <: U] <: UB[V],
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]: Unit
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type K >: L
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type M <: L // error: <: L
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type T >: U // error: >: U
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type V <: U
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def d_K[K >: L](): K // error: >: L
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def d_L(): L // error: => L
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def d_M[M <: L](): M
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def d_T[T >: U](): T
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def d_U(): U
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def d_V[V <: U](): V // error: <: U
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val v_K: K
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val v_L: L // error: L
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val v_M: M // indirect error: M <: L
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val v_T: T // indirect error: T >: U
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val v_U: U
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val v_V: V
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// reverse
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def d_K_Unit[K >: L](): K => Unit // error: >: L
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def d_L_Unit(): L => Unit
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def d_M_Unit[M <: L](): M => Unit
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def d_T_Unit[T >: U](): T => Unit
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def d_U_Unit(): U => Unit // error: U =>
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def d_V_Unit[V <: U](): V => Unit // error: <: U
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val v_K_Unit: K => Unit
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val v_L_Unit: L => Unit
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val v_M_Unit: M => Unit
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val v_T_Unit: T => Unit
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val v_U_Unit: U => Unit // error: U =>
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val v_V_Unit: V => Unit

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