Compiler error with iteration and units of measure in F# 17.10 preview with LangVersion Preview

[marklam]

A for loop over units of measure can create a compiler error where compilation previously succeeded

Repro steps

Provide the steps required to reproduce the problem:

module Measures

// Visual Studio & F#
//    Microsoft Visual Studio Community 2022
//    Version 17.10.0 Preview 3.0
//    VisualStudio.17.Preview/17.10.0-pre.3.0+34804.81
//    Microsoft .NET Framework
//    Version 4.8.09032
//
//    Visual F# Tools   17.10.0-beta.24172.5+8d852e43d35fdac96b1ba52e3bd4b35350035914
//    Microsoft Visual F# Tools

// Compiled with
//     <TargetFramework>net8.0</TargetFramework>
//     <LangVersion>Preview</LangVersion>

type [<Measure>] m
let length = 10<m>

let tenth = length / 10

for i in tenth .. 1<m> .. (length-1<m>) do
    ()

// ...\Library.fs(22,7): error FS0073: internal error: Unrecognized numeric type '?12527 (solved)'.

Git repo:

https://github.com/marklam/FSharp17_10_LangVersion_Preview_MeasuresBug

Expected behavior

Compilation succeeds

Actual behavior

error FS0073: internal error: Unrecognized numeric type '?12527 (solved)'.

Known workarounds

Related information

• Microsoft Visual Studio Community 2022
• Version 17.10.0 Preview 3.0
• VisualStudio.17.Preview/17.10.0-pre.3.0+34804.81
• Microsoft .NET Framework
• Version 4.8.09032

[vzarytovskii]

If it's preview, might be related to something @brianrourkeboll was optimizing. I can look at it next week.

[brianrourkeboll]

I'll take a look.

[marklam]

Cool, I'm obviously not blocked by it, just exercising the preview while it's still in preview :-)

[brianrourkeboll]

@marklam I have a fix for this in #17040.

Thanks for giving the preview features a try — I'm glad this was found sooner rather than later!

[marklam]

@brianrourkeboll - did #17040 not make it into the release of 17.10?

[vzarytovskii]

@brianrourkeboll - did #17040 not make it into the release of 17.10?

No, only 17.11, cutoff for 17.10 was way before the fix was made, and unfortunately, since it's langversion preview, it doesn't meet the backport bar: