From d1e647e025e428ba765b2b56f57846193f141e07 Mon Sep 17 00:00:00 2001
From: Maxime Mangel <me@mangelmaxime.fr>
Date: Sat, 26 Oct 2024 10:06:29 +0200
Subject: [PATCH] [TS] Prevent generics to be duplicated (#3942)

---
 src/Fable.Cli/CHANGELOG.md          |  1 +
 src/Fable.Transforms/Fable2Babel.fs |  1 +
 tests/Js/Main/DictionaryTests.fs    | 18 ++++++++++++++++++
 3 files changed, 20 insertions(+)

diff --git a/src/Fable.Cli/CHANGELOG.md b/src/Fable.Cli/CHANGELOG.md
index 240427a312..ef70e9d49e 100644
--- a/src/Fable.Cli/CHANGELOG.md
+++ b/src/Fable.Cli/CHANGELOG.md
@@ -24,6 +24,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * [JS/TS/Python/Rust] Fixed String.StartsWith/EndsWith (#3934) (by @ncave)
 * [All/Rust] Removed Regex.Replace from hot paths (by @ncave)
 * [JS] Fix regression, generate `let` variable when using `import` on a private mutable variable (by @MangelMaxime)
+* [TS] Prevent generics to be duplicated (by @MangelMaxime)
 
 ## 4.22.0 - 2024-10-02
 
diff --git a/src/Fable.Transforms/Fable2Babel.fs b/src/Fable.Transforms/Fable2Babel.fs
index c0d9bbf1e3..3f81237302 100644
--- a/src/Fable.Transforms/Fable2Babel.fs
+++ b/src/Fable.Transforms/Fable2Babel.fs
@@ -565,6 +565,7 @@ module Annotation =
                 TypeParameter.typeParameter (name, ?bound = bound) |> Some
             | _ -> None
         )
+        |> Array.distinct
 
     let makeTypeParamInstantiation (com: IBabelCompiler) ctx genArgs =
         if List.isEmpty genArgs then
diff --git a/tests/Js/Main/DictionaryTests.fs b/tests/Js/Main/DictionaryTests.fs
index 30a1385fb8..29d7fb1f51 100644
--- a/tests/Js/Main/DictionaryTests.fs
+++ b/tests/Js/Main/DictionaryTests.fs
@@ -12,6 +12,17 @@ type MyRecord = { a: int }
 
 type R = { i: int; s: string }
 
+type Table<'K,'V when 'K:equality> () =
+
+    let dic = new Dictionary<'K,'V>()
+
+    let addKeyValue key value =
+        dic.[key] <- value
+
+    member _.add key value =
+        addKeyValue key value
+
+    member _.Dic = dic
 let tests =
   testList "Dictionaries" [
     testCase "Dictionary KeyValuePattern works" <| fun () -> // See #509
@@ -251,4 +262,11 @@ let tests =
         equal cache.[typeof<int>] 1
         equal cache.[typeof<string>] 2
         equal cache.[typeof<int64>] 3
+
+    testCase "Check that generics are not duplicated " <| fun _ -> // See #3911
+        let table = Table<_,_>()
+        table.add "A" 1
+        table.add "B" 2
+        table.add "C" 3
+        table.Dic.Count |> equal 3
   ]