When using 'with' to construct a record based on another record, in a specific set of circumstances the compiler fails with the following errors:

error FS0073: internal error: TryOptimizeRecordFieldGet: term argument out of range
error FS0193: internal error: Index was outside the bounds of the array.

The following toy application reproduces the error:

type FooBar =
    { xyz : string }
    static let staticLet = 1

let doThing (foo : FooBar) =
    let bar = { foo with xyz = foo.xyz }
    let baz = { bar with xyz = bar.xyz }
    printfn "%O" baz

doThing { xyz = "" }

Note that the following are required:

• baz must use with based on another record type that also uses with based on another record type: if baz is changed to = { foo with... the code builds correctly.
• The record type must contain a static let: if staticLet is removed then the code builds correctly.
• The code must be in a function: if doThing is removed and replaced with let foo = { Field = "" } then the code builds correctly.

This error only happens when building with optimisations switched on.

Tested using the 9.0.101 SDK.