From 83802a81f1721987828b1a2d101a228ef0bc35f7 Mon Sep 17 00:00:00 2001
From: ncave <777696+ncave@users.noreply.github.com>
Date: Tue, 1 Oct 2024 15:12:36 -0700
Subject: [PATCH] Fixed #3915

---
 src/Fable.Transforms/FSharp2Fable.Util.fs |  9 +++++++--
 src/Fable.Transforms/Rust/Fable2Rust.fs   | 11 +++++++++--
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/src/Fable.Transforms/FSharp2Fable.Util.fs b/src/Fable.Transforms/FSharp2Fable.Util.fs
index e03de5f1b..6c4ad9db6 100644
--- a/src/Fable.Transforms/FSharp2Fable.Util.fs
+++ b/src/Fable.Transforms/FSharp2Fable.Util.fs
@@ -1075,8 +1075,13 @@ module Patterns =
     let (|UnionCaseTesterFor|_|) (memb: FSharpMemberOrFunctionOrValue) =
         match memb.DeclaringEntity with
         | Some ent when ent.IsFSharpUnion ->
-            // if memb.IsUnionCaseTester then // TODO: this currently fails, use when fixed
-            if memb.IsPropertyGetterMethod && memb.LogicalName.StartsWith("get_Is") then
+            // if memb.IsUnionCaseTester then // insufficient, could be an interface member
+            if
+                memb.IsPropertyGetterMethod
+                && not memb.IsDispatchSlot
+                && not memb.IsOverrideOrExplicitInterfaceImplementation
+                && memb.LogicalName.StartsWith("get_Is")
+            then
                 let unionCaseName = memb.LogicalName |> Naming.replacePrefix "get_Is" ""
                 ent.UnionCases |> Seq.tryFind (fun uc -> uc.Name = unionCaseName)
             else
diff --git a/src/Fable.Transforms/Rust/Fable2Rust.fs b/src/Fable.Transforms/Rust/Fable2Rust.fs
index 11e55adb4..ca896736f 100644
--- a/src/Fable.Transforms/Rust/Fable2Rust.fs
+++ b/src/Fable.Transforms/Rust/Fable2Rust.fs
@@ -1245,6 +1245,11 @@ module Util =
         else
             mkGenericPathExpr (splitNameParts ident.Name) None
 
+    let isThisArgumentIdentExpr (expr: Fable.Expr) =
+        match expr with
+        | Fable.IdentExpr ident -> ident.IsThisArgument
+        | _ -> false
+
     // let transformExprMaybeIdentExpr (com: IRustCompiler) ctx (expr: Fable.Expr) =
     //     match expr with
     //     | Fable.IdentExpr ident when ident.IsThisArgument ->
@@ -1602,7 +1607,9 @@ module Util =
     let prepareRefForPatternMatch (com: IRustCompiler) ctx typ (name: string option) fableExpr =
         let expr = com.TransformExpr(ctx, fableExpr)
 
-        if (name.IsSome && isRefScoped ctx name.Value) || (isInRefType com typ) then
+        if isThisArgumentIdentExpr fableExpr then
+            expr
+        elif (name.IsSome && isRefScoped ctx name.Value) || (isInRefType com typ) then
             expr
         elif shouldBeRefCountWrapped com ctx typ |> Option.isSome then
             expr |> makeAsRef
@@ -4576,7 +4583,7 @@ module Util =
         let isIgnoredMember (memb: Fable.MemberFunctionOrValue) = ent.IsFSharpExceptionDeclaration // to filter out compiler-generated exception equality
 
         let isInterfaceMember (memb: Fable.MemberFunctionOrValue) =
-            memb.IsDispatchSlot
+            (memb.IsDispatchSlot || memb.IsOverrideOrExplicitInterfaceImplementation)
             && (memb.DeclaringEntity
                 |> Option.bind com.TryGetEntity
                 |> Option.map (fun ent -> ent.IsInterface)