From d5094cb6aa5df578d6c8c4ea11f885e8d63cc513 Mon Sep 17 00:00:00 2001
From: Alfonso Garcia-Caro <alfonso.garcia-caro@outlook.com>
Date: Tue, 11 Feb 2025 20:57:45 +0900
Subject: [PATCH] [JS/TS/Python] Fix #4041: Replace idents with unit type

---
 src/Fable.Transforms/Fable2Babel.fs         | 16 ++++++++++------
 src/Fable.Transforms/Python/Fable2Python.fs | 10 ++++++++--
 2 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/src/Fable.Transforms/Fable2Babel.fs b/src/Fable.Transforms/Fable2Babel.fs
index fc1bba82c..12d25ef7a 100644
--- a/src/Fable.Transforms/Fable2Babel.fs
+++ b/src/Fable.Transforms/Fable2Babel.fs
@@ -2827,13 +2827,17 @@ module Util =
 
         | _ -> transformDecisionTreeWithExtraSwitch com ctx returnStrategy targets treeExpr
 
-    let transformIdent (com: IBabelCompiler) ctx id =
-        let e = identAsExpr id
+    let transformIdent (com: IBabelCompiler) ctx (id: Fable.Ident) =
+        match id.Type with
+        // Remove unit idents, because the declaration may have been erased #4041
+        | Fable.Unit -> undefined id.Range None
+        | _ ->
+            let e = identAsExpr id
 
-        if com.IsTypeScript && ctx.ForcedIdents.Contains id.Name then
-            Expression.unaryExpression (UnaryNot, e, isSuffix = true)
-        else
-            e
+            if com.IsTypeScript && ctx.ForcedIdents.Contains id.Name then
+                Expression.unaryExpression (UnaryNot, e, isSuffix = true)
+            else
+                e
 
     let rec transformAsExpr (com: IBabelCompiler) ctx (expr: Fable.Expr) : Expression =
         match expr with
diff --git a/src/Fable.Transforms/Python/Fable2Python.fs b/src/Fable.Transforms/Python/Fable2Python.fs
index a21d570e8..b55ab36cd 100644
--- a/src/Fable.Transforms/Python/Fable2Python.fs
+++ b/src/Fable.Transforms/Python/Fable2Python.fs
@@ -2950,6 +2950,12 @@ module Util =
         let name = Expression.name name
         Expression.call name, [ func ]
 
+    let transformIdent (com: IPythonCompiler) ctx (id: Fable.Ident) =
+        match id.Type with
+        // Remove unit idents, because the declaration may have been erased #4041
+        | Fable.Unit -> undefined id.Range
+        | _ -> identAsExpr com ctx id
+
     let rec transformAsExpr (com: IPythonCompiler) ctx (expr: Fable.Expr) : Expression * Statement list =
         // printfn "transformAsExpr: %A" expr
         match expr with
@@ -2959,7 +2965,7 @@ module Util =
 
         | Fable.Value(kind, r) -> transformValue com ctx r kind
 
-        | Fable.IdentExpr id -> identAsExpr com ctx id, []
+        | Fable.IdentExpr id -> transformIdent com ctx id, []
 
         | Fable.Import({
                            Selector = selector
@@ -3154,7 +3160,7 @@ module Util =
 
             stmts @ (expr |> resolveExpr ctx kind.Type returnStrategy)
 
-        | Fable.IdentExpr id -> identAsExpr com ctx id |> resolveExpr ctx id.Type returnStrategy
+        | Fable.IdentExpr id -> transformIdent com ctx id |> resolveExpr ctx id.Type returnStrategy
 
         | Fable.Import({
                            Selector = selector