Fabulous: Invalid IL code in AllControls sample

[TimLariviere]

I'm getting the following exception when starting the AllControls sample, for both iOS, Android and macOS (and I guess the other platforms too?):

System.InvalidProgramException: Invalid IL code in AllControls.AppModule:view (AllControls.Model,Microsoft.FSharp.Core.FSharpFunc`2<AllControls.Msg, Microsoft.FSharp.Core.Unit>): IL_28a2: stloc     953


  at <StartupCode$AllControls>[email protected] (AllControls.Model model, Microsoft.FSharp.Core.FSharpFunc`2[T,TResult] dispatch) [0x00000] in /Users/timothelariviere/Git/GitHub/Fabulous/Fabulous.XamarinForms/samples/AllControls/AllControls/AllControls.fs:1062
  at Fabulous.ProgramModule+traceView@210[model,msg,arg].Invoke (model model, Microsoft.FSharp.Core.FSharpFunc`2[T,TResult] dispatch) [0x00082] in /Users/timothelariviere/Git/GitHub/Fabulous/src/Fabulous/Program.fs:217
  at Fabulous.ProgramRunner`3[arg,model,msg]..ctor (Fabulous.IHost host, Fabulous.Program`3[arg,model,msg] program, Microsoft.FSharp.Core.Unit arg) [0x00078] in /Users/timothelariviere/Git/GitHub/Fabulous/src/Fabulous/Program.fs:55
  at Fabulous.ProgramModule.runWithFabulous[arg,model,msg] (Fabulous.IHost host, arg arg, Fabulous.Program`3[arg,model,msg] program) [0x00000] in /Users/timothelariviere/Git/GitHub/Fabulous/src/Fabulous/Program.fs:252
  at Fabulous.XamarinForms.XamarinFormsProgramModule.runWith[a,b,c] (Xamarin.Forms.Application app, a arg, Fabulous.Program`3[arg,model,msg] program) [0x00007] in /Users/timothelariviere/Git/GitHub/Fabulous/Fabulous.XamarinForms/src/Fabulous.XamarinForms.Core/Program.fs:35
  at Fabulous.XamarinForms.XamarinFormsProgramModule.run[a,b] (Xamarin.Forms.Application app, Fabulous.Program`3[arg,model,msg] program) [0x00000] in /Users/timothelariviere/Git/GitHub/Fabulous/Fabulous.XamarinForms/src/Fabulous.XamarinForms.Core/Program.fs:42
  at AllControls.App..ctor () [0x0003b] in /Users/timothelariviere/Git/GitHub/Fabulous/Fabulous.XamarinForms/samples/AllControls/AllControls/AllControls.fs:1061
  at iOS.AppDelegate.FinishedLaunching (UIKit.UIApplication uiApp, Foundation.NSDictionary options) [0x00034] in /Users/timothelariviere/Git/GitHub/Fabulous/Fabulous.XamarinForms/samples/AllControls/iOS/AppDelegate.fs:18
  at at (wrapper managed-to-native) UIKit.UIApplication.UIApplicationMain(int,string[],intptr,intptr)
  at UIKit.UIApplication.Main (System.String[] args, System.IntPtr principal, System.IntPtr delegate) [0x00005] in /Library/Frameworks/Xamarin.iOS.framework/Versions/13.4.0.2/src/Xamarin.iOS/UIKit/UIApplication.cs:86
  at UIKit.UIApplication.Main (System.String[] args, System.String principalClassName, System.String delegateClassName) [0x0000e] in /Library/Frameworks/Xamarin.iOS.framework/Versions/13.4.0.2/src/Xamarin.iOS/UIKit/UIApplication.cs:65
  at iOS.Main.main (System.String[] args) [0x00000] in /Users/timothelariviere/Git/GitHub/Fabulous/Fabulous.XamarinForms/samples/AllControls/iOS/AppDelegate.fs:32

The view function seems to produce invalid IL.

I don't know why, it stopped working after #530 apparently.
Almost same code in https://github.com/fsprojects/Fabulous/tree/0.43.0 doesn't trigger the issue.

I played a little with the view function, and found that if I extract the code for the last match case (that we added recently, but there wasn't the issue at that moment) into its own function, the issue disappears...

https://github.com/fsprojects/Fabulous/blob/5886acc0aecdb57da33799f52c080e6101d412b8/Fabulous.XamarinForms/samples/AllControls/AllControls/AllControls.fs#L1035-L1054

Versions log

Visual Studio Enterprise 2019 for Mac
Version 8.3.5 (build 13)
Installation UUID: 97b76ad0-1550-4a4e-8af6-781cda196581
    GTK+ 2.24.23 (Raleigh theme)
    Xamarin.Mac 5.16.1.24 (d16-3 / 08809f5b)

    Package version: 604000208

Mono Framework MDK
Runtime:
    Mono 6.4.0.208 (2019-06/07c23f2ca43) (64-bit)
    Package version: 604000208

NuGet
Version: 5.3.0.6192

.NET Core SDK
SDK: /usr/local/share/dotnet/sdk/3.0.100/Sdks
SDK Versions:
    3.0.100
    2.2.301
    2.2.206
    2.2.109
MSBuild SDKs: /Library/Frameworks/Mono.framework/Versions/6.4.0/lib/mono/msbuild/Current/bin/Sdks

.NET Core Runtime
Runtime: /usr/local/share/dotnet/dotnet
Runtime Versions:
    3.0.0
    2.2.7
    2.2.6
    2.1.13

Xamarin.Profiler
Version: 1.6.12.29
Location: /Applications/Xamarin Profiler.app/Contents/MacOS/Xamarin Profiler

Updater
Version: 11

Xamarin Designer
Version: 16.3.0.247
Hash: 52eac1a9e
Branch: remotes/origin/d16-3
Build date: 2019-10-03 23:04:28 UTC

Apple Developer Tools
Xcode 11.1 (15405)
Build 11A1027

Xamarin.Mac
Version: 6.4.0.2 (Visual Studio Enterprise)
Hash: e37549bc
Branch: xcode11.1
Build date: 2019-10-07 22:43:23-0400

Xamarin.iOS
Version: 13.4.0.2 (Visual Studio Enterprise)
Hash: e37549bc
Branch: xcode11.1
Build date: 2019-10-07 22:43:23-0400

Xamarin.Android
Version: 10.0.3.0 (Visual Studio Enterprise)
Commit: xamarin-android/d16-3/4d45b41
Android SDK: /Users/timothelariviere/Library/Developer/Xamarin/android-sdk-macosx
    Supported Android versions:
        None installed

SDK Tools Version: 26.1.1
SDK Platform Tools Version: 29.0.1
SDK Build Tools Version: 28.0.3

Build Information: 
Mono: mono/mono/2019-06@5608fe0abb3
Java.Interop: xamarin/java.interop/d16-3@5836f58
LibZipSharp: grendello/LibZipSharp/d16-3@71f4a94
LibZip: nih-at/libzip/rel-1-5-1@b95cf3fd
ProGuard: xamarin/proguard/master@905836d
SQLite: xamarin/sqlite/3.27.1@8212a2d
Xamarin.Android Tools: xamarin/xamarin-android-tools/d16-3@cb41333

Microsoft Mobile OpenJDK
Java SDK: /Users/timothelariviere/Library/Developer/Xamarin/jdk/microsoft_dist_openjdk_1.8.0.25
1.8.0-25
Android Designer EPL code available here:
https://github.com/xamarin/AndroidDesigner.EPL

Android SDK Manager
Version: 1.4.0.65
Hash: c33b107
Branch: remotes/origin/d16-3
Build date: 2019-10-10 12:15:44 UTC

Android Device Manager
Version: 1.2.0.116
Hash: d2b2af0
Branch: remotes/origin/d16-3
Build date: 2019-10-10 12:16:06 UTC

Xamarin Inspector
Version: 1.4.3
Hash: db27525
Branch: 1.4-release
Build date: Mon, 09 Jul 2018 21:20:18 GMT
Client compatibility: 1

Build Information
Release ID: 803050013
Git revision: 9ea9458e434c7b9f4e53ace3a461e2cdf966317f
Build date: 2019-10-24 13:08:01+00
Build branch: release-8.3
Xamarin extensions: ade6d975df7634a5d81feda320a6102e5bacf309

Operating System
Mac OS X 10.15.0
Darwin 19.0.0 Darwin Kernel Version 19.0.0
    Wed Sep 25 20:18:50 PDT 2019
    root:xnu-6153.11.26~2/RELEASE_X86_64 x86_64

Anyone getting the same issue?

@dsyme This one might interest you

[TimLariviere]

Another interesting thing is that adding a new case in #576 (and extracting Effects into its own function) doesn't trigger the issue.

[SergejDK]

Is this only caused by effects ?
I mean extracting something else into a function still creates the issue ?

[dsyme]

Ouch

[dsyme]

If we can trim this down to a minimal repro that would be, well, fabulous....

[TimLariviere]

@dsyme I made a repro as minimal as I could: https://github.com/TimLariviere/Fabulous/blob/repro-invalid-il/Fabulous.XamarinForms/samples/AllControls/AllControls/AllControls.fs

You can clone the branch directly to test it.

Things I found while reproing:

• It's linked to the number of View.Something used inside the view function. Adding one too many crashes, removing whichever one fixes the issue.
• View.Something inside in a condition branch that doesn't execute counts toward the bug
• View.Something inside local functions (e.g. dependsOn) does not count toward the bug
• No specific control trigger the issue
• It applies only in Debug mode, even having Fabulous.XamarinForms in release mode fixes the issue
• Couldn't reproduce on UWP or WPF (with Visual Studio 2019 - latest version), I repro on iOS, Android, macOS (with VS for Mac - see Versions log in first post)

[dsyme]

Cool. May be hitting a JIT limit on number of locals or the like. Does PEVerify pass ok?

[TimLariviere]

PEVerify is not outputting anything for the AllControls.dll. I'm only getting an exit code of 0.
So I guess it's ok?

[dsyme]

So I guess it's ok?

Yes, it must be a mono/Xamarin limitation