do not fetch variance for items when equating #41913
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Fixes rust-lang#41849. Problem was that evaluating the constant expression required evaluating a trait, which would equate types, which would request variance information, which it would then discard. However, computing the variance information would require determining the type of a field, which would evaluate the constant expression. (This problem will potentially arise *later* as we move to more sophisticated constants, however, where we need to check subtyping. We can tackle that when we come to it.)
nikomatsakis
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Nominated for beta -- regression. |
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@bors r+ |
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📌 Commit d22d1fe has been approved by |
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do not fetch variance for items when equating Fixes #41849. Problem was that evaluating the constant expression required evaluating a trait, which would equate types, which would request variance information, which it would then discard. However, computing the variance information would require determining the type of a field, which would evaluate the constant expression. (This problem will potentially arise *later* as we move to more sophisticated constants, however, where we need to check subtyping. We can tackle that when we come to it.) r? @eddyb
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☀️ Test successful - status-appveyor, status-travis |
brson
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Accepted for beta because I trust niko. |
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Doesn't pick cleanly @nikomatsakis |
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Fixes #41849. Problem was that evaluating the constant expression
required evaluating a trait, which would equate types, which would
request variance information, which it would then discard. However,
computing the variance information would require determining the type of
a field, which would evaluate the constant expression.
(This problem will potentially arise later as we move to more sophisticated
constants, however, where we need to check subtyping. We can tackle that
when we come to it.)
r? @eddyb