Add error message when trait parameter prefixes are used for its parent #7393
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dottybot
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Oct 8, 2019
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kubukoz
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compiler/test/dotty/tools/dotc/reporting/ErrorMessagesTests.scala
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| val paramRefs = ref.namedPartsWith(ntp => ntp.symbol.enclosingClass == cls) | ||
| if (paramRefs.nonEmpty) | ||
| ctx.error("trait parameters cannot be used as parent prefixes", parent.sourcePos) | ||
| ctx.error(TraitParameterUsedAsParentPrefix(paramRefs.tail.head), parent.sourcePos) |
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What happens here if paramRefs has only one element? What is in paramRefs.head?
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paramRefs.head contains the enclosing class/trait and the second element in paramRefs is the trait which has the reference error. Given the nature of the error, paramRefs should always have 2 elements if it's nonEmpty.
Nonetheless, paramRefs.tail.head.symbol is the same as the parameter cls, so it's probably safer to use that instead. I'll make that change!
nicolasstucki
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Oct 13, 2019
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Tackling lampepfl#1589. More specifically, added an explanation for the compiler error when a trait with parameters is extended from a parent that is accessed via any of the parameters of the same trait.
For example: