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[JS-Bug?] Previously failing code now compiles to throw 1, without compile time error #5008
Description
This was tested with fable 5.18.0. I noticed this behavior because of the compile time tests in Feliz, in which a test, which should fail, did not fail anymore.
I expect the following code snippet to fail during fable transpilation.
Instead it transpiles without warning/error to throw 1;
#r "nuget: Feliz"
open Fable.Core
open Feliz
open Feliz.JSX
open System.IO
open System.Text.Json
[<Erase; Mangle(false)>]
type Components =
[<JSX.Component>]
static member FailsDuringTranspile() =
// minimal json serialization, this should fail!
let json = JsonSerializer.Serialize({| Message = "Hello, world!" |})
Html.div json
Transpiled Code:
export function FailsDuringTranspile($props) {
throw 1;
throw 1;
}Terminal output:
PS C:\Users\Kevin\Desktop\CodePlayground\fable_transpile> dotnet fable --version
5.18.0
PS C:\Users\Kevin\Desktop\CodePlayground\fable_transpile> dotnet fable .\test.fsx --noCache
Fable 5.18.0: F# to JavaScript compiler
Minimum @fable-org/fable-library-js version (when installed from npm): 2.8.0
Thanks to the contributor! @piaste
Stand with Ukraine! https://standwithukraine.com.ua/
Parsing test.fsx...
Some Nuget packages contain information about NPM dependencies that can be managed by Femto: https://github.com/Zaid-Ajaj/Femto
Project and references (33 source files) parsed in 5529ms
Loaded Feliz.HookAttribute from ..\..\..\.nuget\packages\feliz.compilerplugins\3.2.0\lib\netstandard2.0\Feliz.CompilerPlugins.dll
Loaded Feliz.ReactComponentAttribute from ..\..\..\.nuget\packages\feliz.compilerplugins\3.2.0\lib\netstandard2.0\Feliz.CompilerPlugins.dll
Loaded Feliz.ReactMemoComponentAttribute from ..\..\..\.nuget\packages\feliz.compilerplugins\3.2.0\lib\netstandard2.0\Feliz.CompilerPlugins.dll
Loaded Feliz.ReactLazyComponentAttribute from ..\..\..\.nuget\packages\feliz.compilerplugins\3.2.0\lib\netstandard2.0\Feliz.CompilerPlugins.dll
Started Fable compilation...
Compiled 31/33: ..\..\..\.packagemanagement\nuget\Projects\36700--b24040fd-5957-45c9-8b23-d4b6eb933361\Project.fsproj...Compiled 33/33: test.fsx
Fable compilation finished in 7292msMetadata
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MangelMaxime commentedon Oct 12, 2026
Hello,
I am not able to reproduce on Linux at the moment.
Could you please provide us with the full of log
dotnet fable .\test.fsx --noCache --verbose?MangelMaxime commentedon Oct 12, 2026
I think that your PR at fable-hub/Feliz#723 is failing because Fable now supports
File.ReadAllTextMangelMaxime commentedon Oct 12, 2026
However, this does not explain why you are seeing
Fable compilation finished in 7292mswithout the Error reported.In my case, I see
Freymaurer commentedon Oct 12, 2026
Yes! This is the first i checked. That is why my code example above actually uses the json call 🙂
Will give you the full log soon, i do currently not have access to my computer.
Freymaurer commentedon Oct 14, 2026
@MangelMaxime here is the output from
dotnet fable .\test.fsx --noCache --verbose. The output inTest.fs.jsis still unchanged (see above). Hope this helps 🙂full log