[5.5][CSBindings] Account for literal bindings when checking "subtype of existential" property #37672
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…xistential" property It's important to know whether a binding set has all of its bindings as subtypes of some existential type(s), type variables like that should be delayed. Incremental binding inference introduced a bug into computation of this property by checking only directly inferable bindings, but it's also important to check that there are no literal requirements that can produce bindings, because that would mean that type variable can never be just a subtype of existential type(s). Resolves: rdar://77570994 (cherry picked from commit cf13e29)
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airspeedswift
approved these changes
Jun 2, 2021
AnthonyLatsis
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🍒 release cherry pick
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Cherry-pick of #37643
Fixes a source compatibility regression introduced by incremental
binding inference that results in type-checker rejecting valid code.
It's important to know whether a binding set has all of its bindings
as subtypes of some existential type(s), type variables like that
should be delayed.
Incremental binding inference introduced a bug into computation of
this property by checking only directly inferable bindings, but
it's also important to check that there are no literal requirements
that can produce bindings, because that would mean that type variable
can never be just a subtype of existential type(s).
Scope: Nested literal array with ternary operators that are contextually converted to an existential type.
Main Branch PR: [CSBindings] Account for literal bindings when checking "subtype of e… #37643
Resolves: rdar://77570994
Risk: Low
Reviewed By: @hborla
Testing: Regression tests added to the suite
Resolves: rdar://77570994
(cherry picked from commit cf13e29)