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fix(js/ts/python/dart/beam): raise typed exceptions from invalidArg and invalidOp - #5152
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MangelMaxime merged 3 commits intoOct 26, 2026
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…nd invalidOp `invalidArg` and `invalidOp` threw a plain `Exception`, so `:? ArgumentException` and `:? InvalidOperationException` handlers never caught them, nor the library errors raised through them. They now go through `FSharp.Core.Operators` like `nullArg`, raising the `System` exceptions the libraries already define. Beam tags its exception maps inline, as it does for those exceptions' constructors.
This was referenced Oct 23, 2026
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invalidArgandinvalidOpcompile to a plainExceptionon every target, so:? ArgumentExceptionand:? InvalidOperationExceptionhandlers never catch them, or the library errors raised through them (Array.init -1,List.item,Seq.headon an empty sequence, ...).Each library already defines these
Systemexceptions, andnullArgalready raisesArgumentNullExceptionthroughFSharp.Core.Operators. This routesinvalidArgandinvalidOpthe same way on JS/TS, Python and Dart. Beam builds its tagged exception map inline, as it does for those exceptions' constructors. Messages don't change.Rust is unchanged, since it can't type-test BCL exceptions yet.
With the types visible,
List.takeandSeq.takeraiseArgumentExceptionwhere .NET raisesInvalidOperationException, andList.reducethe reverse. I left those for a follow-up.The full CI passes on my fork: https://github.com/leonitousconforti/Fable/actions/runs/39982396840. I also ran the JS output under JavaScriptCore: a repro matches .NET for all of the above, and a library's JS suite that catches these by type passes in full.