Dotnet fsi broken on inputs that take more than 1 line

[ieviev]

Please provide a succinct description of the issue.

dotnet fsi breaks because it cannot read multiline expressions

Provide the steps required to reproduce the problem:

1 run dotnet fsi
2 insert any expr taking more than 1 line in console
3 reach the bottom of console
4 the interpreter goes crazy

7.0.2xx sdk:

issue does not exist in 7.0.1** sdk:

workaround is to revert back to 7.0.1

sudo apt-get install dotnet-sdk-7.0=7.0.104-1

[KevinRansom]

This repros on linux, not windows.

[NatElkins]

I also experienced this on macOS.

[bonjune]

Repros on MacOS

Screen.Recording.2023-05-02.at.5.12.09.PM.mov

$ dotnet fsi

Microsoft (R) F# Interactive version 12.5.0.0 for F# 7.0
Copyright (c) Microsoft Corporation. All Rights Reserved.

For help type #help;;

> adjksbfaksdlbfjaklsdfjbasdklfjbdskljfbadjkslbfasdjklfbksadjfbk
lsadjfbadklsjbfskladjbfajklsbfadjksbfadjksbfsjkldbfjklasbfjklasb
fjklsafkadlsfhajklsfhaklsjfhskljfahsdklfjhasdklfjhsadjkfhadjksfh
ajklsfhadsjkfhajklsfhklajsfhklajsfhajkslfhajklsfhjklshfjksafklds

System.PlatformNotSupportedException: Operation is not supported on this platform.
   at System.ConsolePal.set_BufferHeight(Int32 value)
   at <StartupCode$fsi>.$Console.moveCursorToNextLine@345(ReadLineConsole x, Char c) in D:\a\_work\1\s\src\fsi\console.fs:line 350
   at <StartupCode$fsi>.$Console.writeChar@358(ReadLineConsole x, FSharpRef`1 rendered, Char c) in D:\a\_work\1\s\src\fsi\console.fs:line 367
   at <StartupCode$fsi>.$Console.insertChar@402(ReadLineConsole x, StringBuilder input, FSharpRef`1 anchor, FSharpRef`1 rendered, FSharpRef`1 current, Char c) in D:\a\_work\1\s\src\fsi\console.fs:line 410
   at <StartupCode$fsi>.$Console.read@544(ReadLineConsole x, StringBuilder input, FSharpRef`1 anchor, FSharpRef`1 rendered, FSharpRef`1 changed, FSharpRef`1 optionsCache, FSharpRef`1 current, Unit unitVar0) in D:\a\_work\1\s\src\fsi\console.fs:line 634
   at FSharp.Compiler.Interactive.ReadLineConsole.ReadLine() in D:\a\_work\1\s\src\fsi\console.fs:line 643
   at FSharp.Compiler.Interactive.Shell.-ctor@1182-163.Invoke() in D:\a\_work\1\s\src\Compiler\Interactive\fsi.fs:line 1186
   at System.Threading.Thread.StartCallback()
Stopped due to error
Unhandled exception. System.PlatformNotSupportedException: Operation is not supported on this platform.
   at System.ConsolePal.set_BufferHeight(Int32 value)
   at <StartupCode$fsi>.$Console.moveCursorToNextLine@345(ReadLineConsole x, Char c) in D:\a\_work\1\s\src\fsi\console.fs:line 350
   at <StartupCode$fsi>.$Console.writeChar@358(ReadLineConsole x, FSharpRef`1 rendered, Char c) in D:\a\_work\1\s\src\fsi\console.fs:line 367
   at <StartupCode$fsi>.$Console.insertChar@402(ReadLineConsole x, StringBuilder input, FSharpRef`1 anchor, FSharpRef`1 rendered, FSharpRef`1 current, Char c) in D:\a\_work\1\s\src\fsi\console.fs:line 410
   at <StartupCode$fsi>.$Console.read@544(ReadLineConsole x, StringBuilder input, FSharpRef`1 anchor, FSharpRef`1 rendered, FSharpRef`1 changed, FSharpRef`1 optionsCache, FSharpRef`1 current, Unit unitVar0) in D:\a\_work\1\s\src\fsi\console.fs:line 634
   at FSharp.Compiler.Interactive.ReadLineConsole.ReadLine() in D:\a\_work\1\s\src\fsi\console.fs:line 643
   at FSharp.Compiler.Interactive.Shell.-ctor@1182-163.Invoke() in D:\a\_work\1\s\src\Compiler\Interactive\fsi.fs:line 1186
   at System.Threading.Thread.StartCallback()

[sgoguen]

It appears #14365 rewrote how line advances on FSharp.Compiler.Interactive.ReadLineConsole() to accommodate East Asian Width characters per https://www.unicode.org/reports/tr11/

Unfortunately, this fix advances the next line by setting Console.BufferHeight by incrementing it (which is not supported in UNIX).

        let moveCursorToNextLine c =
            let charSize = x.GetCharacterSize(c)

            if Console.CursorLeft + charSize > Utils.bufferWidth () then
                if Console.CursorTop + 1 = Console.BufferHeight then
                    Console.BufferHeight <- Console.BufferHeight + 1

                Cursor.Move(0)

I was able to fix it from catastrophically failing on my Mac by wrapping the code that sets the BufferHeight it in a try block and writing a new line, but that breaks any editing functionality.

[sgoguen]

The following update to console.fs to the function seems to resolve the issue on my Mac.

        let moveCursorToNextLine c =
            let charSize = x.GetCharacterSize(c)

            if Console.CursorLeft + charSize > Utils.bufferWidth () then
                if Console.CursorTop + 1 = Console.BufferHeight then
                    try
                        Console.BufferHeight <- Console.BufferHeight + 1
                    with _ ->
                        // If we can't increase the buffer height, just write a newline.
                        Console.WriteLine()
                        // When we add a newline, we need to reflect the change in the anchor.
                        anchor <- { anchor with top = (anchor).top - 1 }
                    
                Cursor.Move(0)

[MrLuje]

Got bitten by this today once again (#14160 (comment)) 😞

@sgoguen are you going to make a PR for it ?
I confirm this fix this issue. I guess we could even get rid of the try block and only go with the with part, since only windows will go to the happy path

        let moveCursorToNextLine c =
            let charSize = x.GetCharacterSize(c)

            if Console.CursorLeft + charSize > Utils.bufferWidth () then
                if Console.CursorTop + 1 = Console.BufferHeight then
                    Console.WriteLine()
                    // When we add a newline, we need to reflect the change in the anchor.
                    anchor <- { anchor with top = (anchor).top - 1 }
                    
                Cursor.Move(0)

[vzarytovskii]

It seems I'm not able to see it on macOS on 8.0rc2 not sure how to reproduce it.

[MrLuje]

@vzarytovskii Assign a long string to a variable (string longer than terminal's width) and do it enough times to hit the bottom of the terminal (to trigger the scrolling)

I was having it with RC1 this weekend, I'll try again with RC2
EDIT: still have it on RC2 (devcontainers from WSL2)

[athrun]

I can reproduce this bug in Homebrew's currently shipping dotnet 8 build: #16251 (comment)

[vzarytovskii]

It didn't get to release for 8.0.100 for sure, I'd expect it in 8.0.200