Allow let! and use! binding with type annotation without parentheses.

[edgarfgp]

Description

Allow let! and use! binding with type annotation without parentheses.

Fixes #10697

BEFORE

let f =
    async {
        let! (a: int) = async { return 1 } // Valid
        let! b: int = async { return 1 } // Error
        use! (a: int) = ...  //Error
        use! b: int = ... //Error
        return a
    }

AFTER

let f =
    async {
        let! (a: int) = ... // Valid
        let! b: int = ... // Valid
        return a
    }

Once #18487 is merged

let f =
    async {
        use! (a: int) = ...  // Valid
        use! b: int = ... // Valid
        return a
    }

Checklist

• Test cases added
• Release notes entry updated

[github-actions]

❗ Release notes required

---

✅ Found changes and release notes in following paths:

Change path	Release notes path	Description
src/Compiler	docs/release-notes/.FSharp.Compiler.Service/9.0.300.md

[edgarfgp]

This new rule allows type annotations without requiring parentheses in let!/use! bindings

let! x: int = ...
use! x: int = ...

It's worth noting that this is consistent with how patterns are handled in regular let bindings as well - e.g. when you want to annotate individual elements of a tuple, you need parentheses

let (a: int, b: string) = (1, "hello")  // Valid
let a: int, b: string = (1, "hello")  // Not valid

let! (a: int , b: int) = async { return 1, 3 } // Valid
let! a: int , b: int = async { return 1, 3 }  // Invalid

[edgarfgp]

This is the associated offside-sensitive version of the new type annotation rule. e.g. in cases where let! or use! bindings are used outside of the CE context. This is invalid code but we will want the tokens to be parsed.

let example=
    // No braces, indentation defines scope
    let! x = async { return 1 }
    let! y = async { return 2 }
    return x + y

[edgarfgp]

It might be interesting in a follow up PR to add error recovery for cases where we have a headBindingPattern COLON error

let! x: 
use! stream: 
let x: 
use x:

Where we can use reportParseErrorAt mColon (FSComp.SR.parsExpectingType())

[baronfel]

Love the depth of test coverage here.