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"Break expression error" when using inline JavaScript in async methods
websharperFixed in 4.0.190.100-rc

Here's a code example:

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namespace JavascriptInlineError
{
    [JavaScript]
    public static class Client
    {
        static Var<string> vr = Var.Create("");

        [Inline("parseInt($s)")]
        public static int ParseInt(string s) { return 0; }

        public static async void parse()
        {
            (ParseInt("12345") + 1).ToString();
        }

        static public IControlBody Main()
        {
            return div(
            );
        }
    }
}

The key elements are: an inlined javascript function (actually, Direct or WebSharper.JavaScipt.Pervasives.JS.Inline can be used with the same result) (ParseInt, in this case) an async method calling said function (parse). Note, the method itself is not called from anywhere. * a static variable (vr). Note, that it's unused, but somehow essential to reproduce the error.

Compiling this code fails with a weird long error message:

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WebSharper error : Global error 'Break expression error : Cctor  {Assembly = "JavascriptInlineError"; FullName = "JavascriptInlineError.Client";}' at    at WebSharper.Compiler.Breaker.breakExpr@820.Invoke(String message)   at Microsoft.FSharp.Primitives.Basics.List.map[T,TResult](FSharpFunc`2 mapping, FSharpList`1 x)   at WebSharper.Compiler.Breaker.brLR@398(FSharpList`1 l)   at WebSharper.Compiler.Breaker.breakExpr(Expression expr)   at WebSharper.Compiler.Breaker.breakExpr(Expression expr)   at WebSharper.Compiler.Breaker.breakSt(Statement statement)   at WebSharper.Compiler.Breaker.breakSt(Statement statement)   at Microsoft.FSharp.Collections.IEnumerator.map@114.DoMoveNext(b& )   at Microsoft.FSharp.Collections.IEnumerator.MapEnumerator`1.System-Collections-IEnumerator-MoveNext()   at Microsoft.FSharp.Core.CompilerServices.RuntimeHelpers.takeOuter@683[T,TResult](ConcatEnumerator`2 x, Unit unitVar0)   at Microsoft.FSharp.Collections.SeqModule.ToList[T](IEnumerable`1 source)   at WebSharper.Compiler.Breaker.breakSt(Statement statement)   at WebSharper.Compiler.Breaker.brCases@975.Invoke(Tuple`2 tupledArg)   at Microsoft.FSharp.Primitives.Basics.List.map[T,TResult](FSharpFunc`2 mapping, FSharpList`1 x)   at WebSharper.Compiler.Breaker.breakSt(Statement statement)   at WebSharper.Compiler.Breaker.breakSt@905-12.Invoke(Expression aE)   at WebSharper.Compiler.Breaker.toStatements@152.GenerateNext(IEnumerable`1& next)   at Microsoft.FSharp.Core.CompilerServices.GeneratedSequenceBase`1.MoveNextImpl()   at Microsoft.FSharp.Collections.SeqModule.ToList[T](IEnumerable`1 source)   at WebSharper.Compiler.Breaker.combine@838-1(IEnumerable`1 x)   at WebSharper.Compiler.Breaker.breakSt(Statement statement)   at WebSharper.Compiler.Breaker.BreakStatement(Statement statement)   at WebSharper.Compiler.Breaker.breakExpr(Expression expr)   at WebSharper.Compiler.Breaker.breakExpr(Expression expr)   at WebSharper.Compiler.Breaker.breakSt(Statement statement)   at Microsoft.FSharp.Collections.IEnumerator.map@114.DoMoveNext(b& )   at Microsoft.FSharp.Collections.IEnumerator.MapEnumerator`1.System-Collections-IEnumerator-MoveNext()   at Microsoft.FSharp.Core.CompilerServices.RuntimeHelpers.takeOuter@683[T,TResult](ConcatEnumerator`2 x, Unit unitVar0)   at Microsoft.FSharp.Collections.SeqModule.ToList[T](IEnumerable`1 source)   at WebSharper.Compiler.Breaker.breakSt(Statement statement)   at Microsoft.FSharp.Collections.IEnumerator.map@114.DoMoveNext(b& )   at Microsoft.FSharp.Collections.IEnumerator.MapEnumerator`1.System-Collections-IEnumerator-MoveNext()   at Microsoft.FSharp.Core.CompilerServices.RuntimeHelpers.takeOuter@683[T,TResult](ConcatEnumerator`2 x, Unit unitVar0)   at Microsoft.FSharp.Collections.SeqModule.ToList[T](IEnumerable`1 source)   at WebSharper.Compiler.Breaker.breakSt(Statement statement)   at WebSharper.Compiler.Breaker.BreakStatement(Statement statement)   at WebSharper.Core.AST.Transformer.TransformFunction(FSharpList`1 a, Statement b)   at WebSharper.Compiler.Translator.DotNetToJavaScript.breakExpr(Expression e)   at WebSharper.Compiler.Translator.DotNetToJavaScript.CompileMethod(CompilingMember info, Expression expr, Hashed`1 typ, Hashed`1 meth)   at WebSharper.Compiler.Translator.compileMethods@580(Compilation comp, Unit unitVar0)   at WebSharper.Compiler.Translator.DotNetToJavaScript.CompileFull(Compilation comp)   at WebSharper.Compiler.CSharp.WebSharperCSharpCompiler.Compile(Info refMeta, IEnumerable`1 argv, String path)   at WebSharper.CSharp.Program.Compile$cont@47(WsConfig config, Unit unitVar)   at WebSharper.CSharp.Program.compileMain$cont@168(String[] argv, Unit unitVar)

I can't seem to work around this problem, and it seems to be a WebSharper bug. Here's a minimal VS2015 project reproducing the error, if needed: https://github.com/LinesPrower/JavascriptInlineError

.

Thanks again for the report, the fix is released in https://github.com/intellifactory/websharper/releases/tag/WebSharper.4.0.190.100-rc

By on 9/15/2017 12:43 PM ()

Fixed at https://github.com/intellifactory/websharper/issues/770, will be released soon.

By on 9/12/2017 1:23 PM ()

Thanks for the detailed description!

This seems like an unintended side effect of https://github.com/intellifactory/websharper/issues/755, because now static constructor calls are not pre-translated inside inlines, so that they can be potentially optimized away at the point of use. Something is not handled right about C# static fields it seems, will look into this shortly.

By on 9/11/2017 9:40 AM ()

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