Avoid accumulating ill-kinded bounds during unification #6270
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Turning partial unification on unconditionally revealed that in some error cases it was possible for the partial unification branch of unifySpecific to add inappropriately kinded bounds to the type variable being solved. These later blow up in matchingBounds in GlbLubs where the mismatched kinds result in a NoCommonType exception being thrown which crashes the compiler reporting "lub/glb of incompatible types". This commit prevents that from happening by checking that the added bounds will match the kind of the TypeVar they're being added to. If they don't then the bound is not added and unification fails.
adriaanm
approved these changes
Jan 24, 2018
lrytz
added a commit
to lrytz/scala
that referenced
this pull request
Jan 25, 2018
Race condition in the merges of scala#6270 (added the test) and scala#5310 (changes its output).
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This PR is a precondition for being able to enable partial unification unconditionally.
Turning partial unification on unconditionally revealed that in some error cases it was possible for the partial unification branch of
unifySpecificto add inappropriately kinded bounds to the type variablebeing solved. These later blow up in
matchingBoundsinGlbLubswhere the mismatched kinds result in aNoCommonTypeexception being thrown which crashes the compiler reporting "lub/glb of incompatible types".This commit prevents that from happening by checking that the added bounds will match the kind of the TypeVar they're being added to. If they don't then the bound is not added and unification fails.