[5.3] [Function builders] Use one-way constraints for closure parameters. #32323
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Introduce an experimental mode (behind the flag
`experimental-one-way-closure-params`) that places one-way
constraints between closure parameter types and references to those
parameters within the body of the closure. The intent here is to
break up constraint systems further, potentially improving type
checking performance and making way for larger closure bodies to be
supported.
This is a source-breaking change when the body of a single-expression
closure is used to determine the parameter types. One obvious example
is when there is no contextual type, e.g.,
let _ = { $0 + 1 }
this type-checks today because `1` becomes `Int`, which matches the
`+` overload with the type `(Int, Int) -> Int`, determining the
parameter type `Int` for the closure. Such code would not type-check
with one-way constraints.
(cherry picked from commit 64f903f)
Introduce one-way constraints for the parameters of closures to which a function builder is being applied. This was an intended part of the model when one-way constraints were introduced, but somehow got missed. This should further break up large constraints systems for faster solving, and *most likely* won't break much source code in practice. Fixes rdar://problem/64231116. (cherry picked from commit f60d17b)
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devincoughlin
approved these changes
Jun 12, 2020
AnthonyLatsis
added
swift 5.3
🍒 release cherry pick
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Introduce one-way constraints for the parameters of closures to which a
function builder is being applied. This was an intended part of the
model when one-way constraints were introduced, but somehow got
missed. This should further break up large constraints systems for
faster solving, and most likely won't break much source code in
practice.
Fixes rdar://problem/64231116.