Fix 1365: Fix bindings in patterns #1377
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We need to compare pattern types with expected types in order to derive knowledge about pattern-bound variables. This is done use the mechanism of gadt bounds.
| if (!ctx.isAfterTyper) { | ||
| val setBefore = ctx.mode is Mode.GADTflexible | ||
| tpt1.tpe.<:<(pt)(ctx.addMode(Mode.GADTflexible)) | ||
| if (!setBefore) ctx.retractMode(Mode.GADTflexible) |
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Why do you need to rectractMode? ctx here is not fresh and addMode should create a new one instead of mutating existing one.
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This is from the GADT fix, where I didn't want to change the state of the context apart from relaxing the solver for GADTs
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But as @DarkDimius notes it's a new context that gets created, so this should not be a problem.
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Otherwise LGTM |
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It would be also nice to add a test. |
The dropped lines were both pure functions whose result is ignored.
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@DarkDimius There is a test: pos/1365.scala. Should something else be added to it? |
| */ | ||
| private def newPatternBoundSym(name: Name, info: Type, pos: Position)(implicit ctx: Context) = { | ||
| val flags = if (name.isTypeName) BindDefinedType else EmptyFlags | ||
| val sym = ctx.newSymbol(ctx.owner, name, flags | Case, info, coord = pos) |
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Case is described as:
/** A case class or its companion object */
final val Case = commonFlag(17, "case")
final val CaseClass = Case.toTypeFlags
final val CaseVal = Case.toTermFlagsso I don't understand what it's supposed to do here
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We need to compare pattern types with expected types in order
to derive knowledge about pattern-bound variables. This is done
using the mechanism of gadt bounds.
This is a subtle aspect of type inference that was so far missing from dotty. scalac does it
differently, I would argue in a more ad-hoc way.
Review by @DarkDimius.