[JS/TS] Fix ResizeArray index getter/setter not throwing IndexOutOfRangeException when index is out of bounds

Co-authored-by: Mangel Maxime <me@mangelmaxime.fr>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: 3 people

src/Fable.Cli/CHANGELOG.md

@@ -9,6 +9,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+* [TS] Annotate `System.Collections.Generic.IList<T>` as `MutableArray<T>` (by @MangelMaxime)
+* [JS/TS] Fix `ResizeArray` index getter/setter not throwing `IndexOutOfRangeException` when index is out of bounds (fix #3812) (by @MangelMaxime)
 * [Beam] Fix unused term warning in try/catch when exception variable is not referenced (by @dbrattli)
 * [Beam] Fix "no effect" warning for pure BIF calls (`self/0`, `node/0`) in non-final block positions (by @dbrattli)
 * [Beam] Fix `reraise()` generating unbound `MatchValue` variable — use raw Erlang reason variable for re-throw (by @dbrattli)

src/Fable.Compiler/CHANGELOG.md

@@ -9,6 +9,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+* [TS] Annotate `System.Collections.Generic.IList<T>` as `MutableArray<T>` (by @MangelMaxime)
+* [JS/TS] Fix `ResizeArray` index getter/setter not throwing `IndexOutOfRangeException` when index is out of bounds (fix #3812) (by @MangelMaxime)
 * [Beam] Fix unused term warning in try/catch when exception variable is not referenced (by @dbrattli)
 * [Beam] Fix "no effect" warning for pure BIF calls (`self/0`, `node/0`) in non-final block positions (by @dbrattli)
 * [Beam] Fix `reraise()` generating unbound `MatchValue` variable — use raw Erlang reason variable for re-throw (by @dbrattli)

src/Fable.Transforms/Fable2Babel.fs

@@ -815,6 +815,7 @@ module Annotation =
         | Types.iobservableGeneric ->
             makeFableLibImportTypeAnnotation com ctx genArgs "Observable" "IObservable"
             |> Some
+        | Types.ilistGeneric -> makeFableLibImportTypeAnnotation com ctx genArgs "Util" "MutableArray" |> Some
         | "Microsoft.FSharp.Control.IEvent`1" ->
             makeFableLibImportTypeAnnotation com ctx genArgs "Event" "IEvent" |> Some
         | Types.ievent2 -> makeFableLibImportTypeAnnotation com ctx genArgs "Event" "IEvent$2" |> Some

src/Fable.Transforms/Replacements.fs

@@ -1921,8 +1921,9 @@ let resizeArrays (com: ICompiler) (ctx: Context) r (t: Type) (i: CallInfo) (this
         Helper.GlobalCall("Array", t, args, memb = "from", ?loc = r)
         |> withTag "array"
         |> Some
-    | "get_Item", Some ar, [ idx ] -> getExpr r t ar idx |> Some
-    | "set_Item", Some ar, [ idx; value ] -> setExpr r ar idx value |> Some
+    | "get_Item", Some ar, [ idx ] -> Helper.LibCall(com, "Array", "item", t, [ idx; ar ], ?loc = r) |> Some
+    | "set_Item", Some ar, [ idx; value ] ->
+        Helper.LibCall(com, "Array", "setItem", t, [ ar; idx; value ], ?loc = r) |> Some
     | "CopyTo", Some ar, [ target ] ->
         let count = getFieldWith r t ar "length"
         copyToArray com r t i [ ar; makeIntConst 0; target; makeIntConst 0; count ]

tests/Js/Main/ResizeArrayTests.fs

@@ -2,6 +2,7 @@ module Fable.Tests.ResizeArrays
 
 open System.Collections.Generic
 open Util.Testing
+open Fable.Tests.Util
 
 type Animal = Duck of int | Dog of int
 
@@ -264,14 +265,9 @@ let tests =
         equal 3. li.[0]
         equal 2. ar.[0]
 
-    testCase "ResizeArray.Item is undefined when index is out of range" <| fun () ->
+    testCase "ResizeArray.Item throws on out of bounds access" <| fun _ ->
         let xs = ResizeArray [0]
-        #if FABLE_COMPILER
-        isNull <| box (xs.Item 1)
-        #else
-        try (xs.Item 1) |> ignore; false with _ -> true
-        #endif
-        |> equal true
+        throwsAnyError (fun () -> xs.Item 1 |> ignore)
 
     testCase "ResizeArray.Remove works with non-primitive types" <| fun _ ->
         let myResizeArray = new ResizeArray<Animal>()
@@ -369,4 +365,15 @@ let tests =
         coll.Remove(("D", 3)) |> equal false
         coll.Remove(("B", 2)) |> equal true
         coll.Count |> equal 2
-  ]
+
+    testCase "ResizeArray index out of bounds get throws" <| fun _ -> // See #3812
+        let xs = ResizeArray [1; 2; 3]
+        throwsAnyError (fun () -> xs[-1] |> ignore)
+        throwsAnyError (fun () -> xs[10] |> ignore)
+
+
+    testCase "ResizeArray index out of bounds set throws" <| fun _ -> // See #3812
+        let xs = ResizeArray [1; 2; 3]
+        throwsAnyError (fun () -> xs.[-1] <- 42)
+        throwsAnyError (fun () -> xs.[10] <- 42)
+  ]