Fix #1891: Don't add redundant constraint #1893
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Before adding a constraint, make sure there is no way the two types are already in a subtype relation. Adding redundant constraints is problematic because we might introduce cycles. See i1891.scala for a test.
smarter
reviewed
Jan 10, 2017
| // The following condition is carefully formulated to catch all cases | ||
| // where the subtype relation is true without needing to add a constraint | ||
| // It's tricky because we might need to either appriximate tp2 by its | ||
| // lower bound or else widen tp1 and check that the result is a subtype of tp2. |
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I don't see a widening of tp1 in the code below?
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The widening is done by all the other parts of subtyping. The important part is not to narrow the lower bound of tp2 before we had a chance to widen tp1.
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LGTM, though this is still a bit mysterious to me ;) |
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Before adding a constraint, make sure there is no way
the two types are already in a subtype relation.
Adding redundant constraints is problematic because we
might introduce cycles. See i1891.scala for a test.
Fixes #1891. Review by @OlivierBlanvillain or/and @smarter?