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Fix problem in unapply typing. #177

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Fix problem in unapply typing. #177

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odersky
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@odersky odersky commented Sep 21, 2014

GADT bound resetting may only be applied when comparing
<: , not when comparing the
other way around.

The fix revealed an error in a test case (t1048) which looks like a real error.
Therefore the test got moved to neg.

Fixes #175 Review by @DarkDimius

@odersky
Fix problem in unapply typing.
4e2b284 
GADT bound resetting may only be applied when comparing
<pattern type> <: <expected type>, not when comparing the
other way around.

The fix revealed an error in a test case (t1048) which looks like a real error.
Therefore the test got moved to neg.
@DarkDimius
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after applying this commit to patmat branch new type-comparrer related errors appeared:

assertion failed: error at ./tests/pos/typers.scala:145
type mismatch:
 found   : String(x)
 required: String

While Y-checking a block
Block(List(ValDef(Modifiers(,,List()),x,TypeTree[TypeRef(ThisType(TypeRef(NoPrefix,lang)),String)],EXPR),Block(List(),Ident(x)))
with an expected type of String.

@odersky
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odersky commented Sep 23, 2014

It looks like there's something deeper going on. Did you run with -uniqid and -Xexplain-types. In cases like these you want to see the precise failed subtyping derivation.

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assertion failed: error at ./tests/pos/Patterns.scala:41
type mismatch:
 found   : String#6032(x#31720)
 required: String#6032
Constraint(
 uninstVars = ;
 constrained types = ;
 constraint = )
Subtype trace:
  ==> String#6032(x#31720) <:< String#6032
  <== String#6032(x#31720) <:< String#6032 = false

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incorporated in #174

@DarkDimius DarkDimius closed this Sep 26, 2014
WojciechMazur pushed a commit to WojciechMazur/dotty that referenced this pull request Mar 19, 2025
@tgodzik
Merge pull request scala#177 from scala/backport-lts-3.3-22353
75fe622 
Backport "fix: drop jackson-module-scala from CB" to 3.3 LTS
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Successfully merging this pull request may close these issues.

Incorrect infering "Nothing" as a type argument of fun in 'Unapply'
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@odersky @DarkDimius