Fix #4999: allow pattern matching against by-name arguments #5012
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In this testcase `tp` is `TermRef(NoPrefix, xs)` so widenExpr does nothing, but `widenTermRefExpr` is appropriate.
Since ExprType are unstable, we can keep stable TermRef alone, in case this provides more info to the pattern matcher/exhaustivity checker.
| @@ -116,7 +116,7 @@ object PatternMatcher { | |||
| /** Widen type as far as necessary so that it does not refer to a pattern- | |||
| * generated variable. | |||
| */ | |||
| private def sanitize(tp: Type): Type = tp.widenExpr match { | |||
| private def sanitize(tp: Type): Type = tp.widenIfUnstable match { | |||
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Yeah the first commit uses widenTermRefExpr. Maybe @liufengyun can think of examples where widening singletons would make a difference?
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What about x match { case _: x.type => ... } ?
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We concluded with @smarter that there is no need to widen singleton types
allanrenucci
approved these changes
Sep 5, 2018
| @@ -116,7 +116,7 @@ object PatternMatcher { | |||
| /** Widen type as far as necessary so that it does not refer to a pattern- | |||
| * generated variable. | |||
| */ | |||
| private def sanitize(tp: Type): Type = tp.widenExpr match { | |||
| private def sanitize(tp: Type): Type = tp.widenIfUnstable match { | |||
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We concluded with @smarter that there is no need to widen singleton types
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In this testcase
tpisTermRef(NoPrefix, xs)sowidenExprdoes nothing, butwidenTermRefExpris appropriate.