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Retry constraint.replace after constraint.updateEntry #20399

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merged 4 commits into from
May 16, 2024
Merged

Retry constraint.replace after constraint.updateEntry #20399

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49940ee
Retry `constraint.replace` after `constraint.updateEntry`
EugeneFlesselle Apr 17, 2024
97ed37e
Fix: don't use oldBounds to re-tryReplace
EugeneFlesselle May 15, 2024
14a6cac
Do tryReplace using narrowedBounds instead of legalBound
EugeneFlesselle May 15, 2024
b1d7735
Fix doc position
EugeneFlesselle May 16, 2024
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22 changes: 14 additions & 8 deletions compiler/src/dotty/tools/dotc/core/ConstraintHandling.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -302,14 +302,18 @@ trait ConstraintHandling {
false
else
val bound = legalBound(param, rawBound, isUpper)
lazy val recBound = bound.existsPart(_ eq param, StopAt.Static)

// If the narrowed bounds are equal and not recursive,
// we can remove `param` from the constraint.
def tryReplace(lo: Type, hi: Type): Boolean =
val equalBounds = (if isUpper then lo else hi) eq bound
val canReplace = equalBounds && !recBound
if canReplace then constraint = constraint.replace(param, bound)
canReplace

val oldBounds @ TypeBounds(lo, hi) = constraint.nonParamBounds(param)
val equalBounds = (if isUpper then lo else hi) eq bound
if equalBounds && !bound.existsPart(_ eq param, StopAt.Static) then
// The narrowed bounds are equal and not recursive,
// so we can remove `param` from the constraint.
constraint = constraint.replace(param, bound)
true
else
tryReplace(lo, hi) || locally:
// Narrow one of the bounds of type parameter `param`
// If `isUpper` is true, ensure that `param <: `bound`, otherwise ensure
// that `param >: bound`.
Expand All @@ -328,7 +332,9 @@ trait ConstraintHandling {
|| {
constraint = c1
val TypeBounds(lo, hi) = constraint.entry(param): @unchecked
isSub(lo, hi)
val isSat = isSub(lo, hi)
if isSat then tryReplace(lo, hi) // isSub may have introduced new constraints
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isSat
}
end addOneBound

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