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Disallow context bounds in type lambdas #22659

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Disallow context bounds in type lambdas #22659

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20 changes: 17 additions & 3 deletions compiler/src/dotty/tools/dotc/parsing/Parsers.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -1798,8 +1798,22 @@ object Parsers {
val start = in.offset
val tparams = typeParamClause(ParamOwner.Type)
if in.token == TLARROW then
atSpan(start, in.skipToken()):
LambdaTypeTree(tparams, toplevelTyp())
val hasContextBounds = tparams.exists(_.rhs match {
case x: ContextBounds => true
case _ => false
})
if hasContextBounds then
// Filter illegal context bounds and report syntax error
atSpan(start, in.skipToken()):
LambdaTypeTree(tparams.map {
case TypeDef(name, rhs: ContextBounds) =>
syntaxError(em"context bounds are not allowed in type lambdas", rhs.span)
TypeDef(name, TypeBoundsTree(EmptyTree, EmptyTree))
case other => other
}, toplevelTyp())
else
atSpan(start, in.skipToken()):
LambdaTypeTree(tparams, toplevelTyp())
else if in.token == ARROW || isPureArrow(nme.PUREARROW) then
val arrowOffset = in.skipToken()
val body = toplevelTyp(nestedIntoOK(in.token))
Expand Down Expand Up @@ -3475,7 +3489,7 @@ object Parsers {
*
* HkTypeParamClause ::= ‘[’ HkTypeParam {‘,’ HkTypeParam} ‘]’
* HkTypeParam ::= {Annotation} [‘+’ | ‘-’]
* (id | ‘_’) [HkTypePamClause] TypeBounds
* (id | ‘_’) [HkTypeParamClause] TypeBounds
*/
def typeParamClause(paramOwner: ParamOwner): List[TypeDef] = inBracketsWithCommas {

Expand Down
8 changes: 8 additions & 0 deletions tests/neg/i22552.check
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Original file line number Diff line number Diff line change
@@ -0,0 +1,8 @@
-- [E040] Syntax Error: tests/neg/i22552.scala:3:10 --------------------------------------------------------------------
3 | type A[X: TC] // error
| ^
| ']' expected, but ':' found
-- Error: tests/neg/i22552.scala:4:15 ----------------------------------------------------------------------------------
4 | type C = [X: TC] =>> List[X] // error
| ^^
| context bounds are not allowed in type lambdas
5 changes: 5 additions & 0 deletions tests/neg/i22552.scala
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
trait Foo:
type TC[T]
type A[X: TC] // error
type C = [X: TC] =>> List[X] // error
type D = [X: TC] => () => List[X] // allowed context bound
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