Fix #8976: Do not instantiate type variables outside bounds #9010
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odersky
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Using <:< leads to a non-terminating or very long compile when compiling scalatest
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May 20, 2020
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| * - It is checked that the resulting type still fits within | ||
| * bounds. If not, a `NoInstance` exception is thrown, | ||
| * but only after instantiating the variable anyway because | ||
| * this avoids follow-on errors. |
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I'm not convinced this is needed:
avoidCapturesalready checks that the approximation is within bound and throws an exception if it isn'twidenInferredwill not do any widening if that would be out of bounds
The only problematic piece is approximation in ConstraintHandling which will replace recursive occurences of the type variable being instantiated by TypeBounds.empty, which can indeed be unsound. Here's an alternative PR which tries to fix that specific problem: #9012
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Closed in favor of #9012 |
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Avoid instantiations of type variables that do not fit their bounds. Throw a TypeError instead.