From 9b2a267b2cfbf2a3ecadce8c9921b26476c8183d Mon Sep 17 00:00:00 2001
From: ncave <777696+ncave@users.noreply.github.com>
Date: Fri, 9 Oct 2026 14:10:54 -0700
Subject: [PATCH] fix(rust): Fix temporary struct locals type

---
 src/Fable.Build/Quicktest/Rust.fs       |  7 ++++-
 src/Fable.Transforms/Rust/Fable2Rust.fs | 34 +++++++++++++++++--------
 tests/Rust/tests/src/RecordTests.fs     | 12 +++++++--
 3 files changed, 40 insertions(+), 13 deletions(-)

diff --git a/src/Fable.Build/Quicktest/Rust.fs b/src/Fable.Build/Quicktest/Rust.fs
index 91fe780de6..d08715b24a 100644
--- a/src/Fable.Build/Quicktest/Rust.fs
+++ b/src/Fable.Build/Quicktest/Rust.fs
@@ -2,13 +2,18 @@ module Build.Quicktest.Rust
 
 open Build.FableLibrary
 open Build.Quicktest.Core
+open SimpleExec
 
 let handle (args: string list) =
+    let projectDir = "src/quicktest-rust"
+
+    Command.Run("cargo", "clean", workingDirectory = projectDir)
+
     genericQuicktest
         {
             Language = "rust"
             FableLibBuilder = BuildFableLibraryRust()
-            ProjectDir = "src/quicktest-rust"
+            ProjectDir = projectDir
             Extension = ".rs"
             RunMode = RunScript
         }
diff --git a/src/Fable.Transforms/Rust/Fable2Rust.fs b/src/Fable.Transforms/Rust/Fable2Rust.fs
index 229b582dcf..a86bfda20d 100644
--- a/src/Fable.Transforms/Rust/Fable2Rust.fs
+++ b/src/Fable.Transforms/Rust/Fable2Rust.fs
@@ -1469,6 +1469,14 @@ module Util =
     //         transformIdent com ctx None id
     //     | _ -> com.TransformExpr(ctx, expr)
 
+    let isTempLocal (ident: Fable.Ident) =
+        ident.IsCompilerGenerated
+        && (ident.Name = "copyOfStruct" || ident.Name = "inputRecord")
+
+    // let isMutableOrByRef (ident: Fable.Ident) =
+    //     (ident.IsMutable || isByRefType ident)
+    //     && not (isTempLocal ident)
+
     let transformIdentGet com ctx r (ident: Fable.Ident) =
         let expr = transformIdent com ctx r ident
 
@@ -1487,16 +1495,22 @@ module Util =
         mutableSet expr value
 
     let transformIdentType com ctx isCaptured (ident: Fable.Ident) =
-        let ty = transformType com ctx ident.Type
-
-        if isByRefType com ident.Type then
-            ty // already wrapped
-        elif ident.IsMutable && isCaptured then
-            ty |> makeMutTy com ctx |> makeLrcPtrTy com ctx
-        elif ident.IsMutable then
-            ty |> makeMutTy com ctx
-        else
-            ty
+        // let typ = Replacements.Util.getIdentValueType com ident ident.Type
+        match ident.Type with
+        | Replacements.Util.IsByRefType com typ when isTempLocal ident ->
+            // transform temporary local byref type to a reference type
+            transformType com ctx typ |> mkRefTy None
+        | _ ->
+            let ty = transformType com ctx ident.Type
+
+            if isByRefType com ident.Type then
+                ty // already wrapped
+            elif ident.IsMutable && isCaptured then
+                ty |> makeMutTy com ctx |> makeLrcPtrTy com ctx
+            elif ident.IsMutable then
+                ty |> makeMutTy com ctx
+            else
+                ty
 
     let getField r (expr: Rust.Expr) (fieldName: string) =
         mkFieldExpr expr (fieldName |> sanitizeMember) // ?loc=r)
diff --git a/tests/Rust/tests/src/RecordTests.fs b/tests/Rust/tests/src/RecordTests.fs
index ce0d9000ab..4913a83613 100644
--- a/tests/Rust/tests/src/RecordTests.fs
+++ b/tests/Rust/tests/src/RecordTests.fs
@@ -126,14 +126,22 @@ let processStructByValue (s: StructRecord) =
 
 [<Fact>]
 let ``Struct record works`` () =
-    let r1 = { i=1; s="hello" }
-    let r2 = { i=1; s="world" }
+    let r1 = { i = 1; s = "hello" }
+    let r2 = { i = 1; s = "world" }
     let (sres1, ires1) = r1 |> processStructByValue
     let (sres2, ires2) = r1 |> processStructByValue
     let (sres3, ires3) = r2 |> processStructByValue //cannot actually test this, but since this is the only reference, the output should not .clone()
     ires2 |> equal 2
     sres3.s |> equal "world"
 
+[<Fact>]
+let ``Struct record temp locals work`` () =
+    let r1 = { i = 1; s = "hello" }
+    let r2 = { i = 2; s = "world" }
+    let r3 = { r1 with i = r2.i ; s = r2.s }
+    r3.i |> equal 2
+    r3.s |> equal "world"
+
 type MutableRecord = {
     mutable MutValue: int
 }