Infer latest matching record type for copy-and-update expressions

[cmeeren]

I'd like to see better type inference for record copy-and-update expressions. When there are multiple matching record types in scope, it should default to the latest one, just like when using ..

type Record1 = { X: int; Y: string }
type Record2 = { X: int }

// Successfully infers Record2
let getX a = a.X 

// Fails with FS0667: Labels do not uniquely determine a corresponding record type.
// Ideally it should infer Record2.
let setX value a = { a with X = value }

The existing way of approaching this problem in F# is using type annotations.

Pros and Cons

The advantages of making this adjustment to F# are: Improved usability and consistency.

The disadvantages of making this adjustment to F# are: Less explicit types (though again, it's consistent with . capabilities).

Extra information

Estimated cost (XS, S, M, L, XL, XXL): M

Related suggestions: (put links to related suggestions here)

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• This is not a question (e.g. like one you might ask on StackOverflow) and I have searched StackOverflow for discussions of this issue
• This is a language change and not purely a tooling change (e.g. compiler bug, editor support, warning/error messages, new warning, non-breaking optimisation) belonging to the compiler and tooling repository
• This is not something which has obviously "already been decided" in previous versions of F#. If you're questioning a fundamental design decision that has obviously already been taken (e.g. "Make F# untyped") then please don't submit it
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Please tick all that apply:

• This is not a breaking change to the F# language design
• I or my company would be willing to help implement and/or test this

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