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Avoid unnecessary under-constrained implicit searches #14353

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Jan 26, 2022
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Avoid unnecessary under-constrained implicit searches #14353

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19 changes: 11 additions & 8 deletions compiler/src/dotty/tools/dotc/typer/Applications.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -433,15 +433,18 @@ trait Applications extends Compatibility {

protected def init(): Unit = methType match {
case methType: MethodType =>
// apply the result type constraint, unless method type is dependent
val resultApprox = resultTypeApprox(methType)
if (!constrainResult(methRef.symbol, resultApprox, resultType))
if (ctx.typerState.isCommittable)
// defer the problem until after the application;
// it might be healed by an implicit conversion
()
else
fail(TypeMismatch(methType.resultType, resultType, None))
val sym = methRef.symbol
if ctx.typerState.isCommittable then
// Here we call `resultType` only to accumulate constraints (even if
// it fails, we might be able to heal the expression to conform to the
// result type) so don't check for views since `viewExists` doesn't
// have any side-effect and would only slow the compiler down (cf #14333).
NoViewsAllowed.constrainResult(sym, resultApprox, resultType)
else if !constrainResult(sym, resultApprox, resultType) then
// Here we actually record that this alternative failed so that
// overloading resolution might prune it.
fail(TypeMismatch(methType.resultType, resultType, None))

// match all arguments with corresponding formal parameters
matchArgs(orderedArgs, methType.paramInfos, 0)
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