[JS/TS] Don't generate the setter code if a property is decorated with [<Erase>] (#3997)

Fix #3948

Author: MangelMaxime

src/Fable.Cli/CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * [TS] Make discriminated union `.Is*` properties works (@MangelMaxime)
 * [JS/TS/Python] Fix `h` in `DateTime.ToString` (@MangelMaxime)
 * [JS/TS] Fix `hh` in `DateTime.ToString` (@MangelMaxime)
+* [JS/TS] Don't generate the setter code if a property is decorated with `[<Erase>]` (@MangelMaxime)
 
 ## 5.0.0-alpha.3 - 2024-12-18
 

src/Fable.Transforms/FSharp2Fable.fs

@@ -1899,6 +1899,22 @@ let private transformMemberDecl
             UsedNamesInDeclarationScope = HashSet()
         }
 
+    let isErasedPropertySetter (memb: FSharpMemberOrFunctionOrValue) =
+        if memb.IsPropertySetterMethod then
+            match memb.DeclaringEntity with
+            | Some ent ->
+                // Remove the "set_" prefix
+                let logicalName = memb.LogicalName.Substring(4)
+
+                ent.MembersFunctionsAndValues
+                |> Seq.tryFind (fun (m: FSharpMemberOrFunctionOrValue) ->
+                    m.LogicalName = logicalName && hasAttrib Atts.erase m.Attributes
+                )
+                |> Option.isSome
+            | _ -> false
+        else
+            false
+
     if isIgnoredNonAttachedMember memb then
         if memb.IsMutable && isNotPrivate memb && hasAttrib Atts.global_ memb.Attributes then
             "Global members cannot be mutable and public, please make it private: "
@@ -1921,7 +1937,11 @@ let private transformMemberDecl
     elif isCompilerGenerated memb args then
         []
     // Ignore members that are decorated with [<Erase>]
-    elif hasAttrib Atts.erase memb.Attributes then
+    elif
+        hasAttrib Atts.erase memb.Attributes || isErasedPropertySetter memb
+    // Attributes are not universally propagated so for setter properties we need
+    // to check the declaring entity, https://github.com/fable-compiler/Fable/issues/3948
+    then
         []
     elif memb.IsOverrideOrExplicitInterfaceImplementation then
         if not memb.IsCompilerGenerated then

tests/Integration/Integration/data/eraseAttribute/ErasedProperty.fs

@@ -0,0 +1,12 @@
+module ErasedProperty
+
+open Fable.Core
+
+
+// This test is to make sure that we are retrieving the Erase attribute from the erased property
+// and not the declaring type
+
+type internal LanguageInjectionAttribute() =
+
+    [<Erase>]
+    member val Prefix = "" with get, set

tests/Integration/Integration/data/eraseAttribute/ErasedProperty.js.expected

@@ -0,0 +1,16 @@
+import { class_type } from "./fable_modules/fable-library-js.5.0.0-alpha.3/Reflection.js";
+
+export class LanguageInjectionAttribute {
+    constructor() {
+        this["Prefix@"] = "";
+    }
+}
+
+export function LanguageInjectionAttribute_$reflection() {
+    return class_type("ErasedProperty.LanguageInjectionAttribute", undefined, LanguageInjectionAttribute);
+}
+
+export function LanguageInjectionAttribute_$ctor() {
+    return new LanguageInjectionAttribute();
+}
+

tests/Integration/Integration/data/eraseAttribute/ErasedTypeWithProperty.fs

@@ -0,0 +1,12 @@
+module ErasedTypeWithProperty
+
+open Fable.Core
+
+[<Erase>]
+type internal LanguageInjectionAttribute() =
+
+    [<Erase>]
+    member val Prefix = "" with get, set
+
+// Force Fable to generate a file, otherwise because everything is erased, it will not generate anything
+let a = 0

tests/Integration/Integration/data/eraseAttribute/ErasedTypeWithProperty.js.expected

@@ -0,0 +1,3 @@
+
+export const a = 0;
+

tests/Integration/Integration/data/eraseAttribute/eraseAttribute.fsproj

@@ -8,6 +8,8 @@
 
   <ItemGroup>
     <Compile Include="Members.fs" />
+    <Compile Include="ErasedTypeWithProperty.fs" />
+    <Compile Include="ErasedProperty.fs" />
   </ItemGroup>
 
   <ItemGroup>