From 44d6fd9091985b94a0a83edacd560a2a1bba4237 Mon Sep 17 00:00:00 2001
From: Antonio Nuno Monteiro <anmonteiro@gmail.com>
Date: Wed, 18 Jun 2025 00:17:29 -0700
Subject: [PATCH 1/3] test: show regression with `const` assignment to function
 variables

---
 .../function-assignment-const.t               | 52 +++++++++++++++++++
 1 file changed, 52 insertions(+)
 create mode 100644 test/blackbox-tests/function-assignment-const.t

diff --git a/test/blackbox-tests/function-assignment-const.t b/test/blackbox-tests/function-assignment-const.t
new file mode 100644
index 000000000..02309935d
--- /dev/null
+++ b/test/blackbox-tests/function-assignment-const.t
@@ -0,0 +1,52 @@
+
+  $ . ./setup.sh
+  $ cat >dune-project <<EOF
+  > (lang dune 3.8)
+  > (using melange 0.1)
+  > EOF
+
+  $ cat > main.ml <<EOF
+  > let f x =
+  >   let rec aux x k =
+  >     match x with
+  >     | 0 -> k 0
+  >     | x -> aux (x - 1) (fun x -> x)
+  >   in
+  >   aux x (fun x -> x)
+  > let _: int = f 3
+  > EOF
+
+  $ melc main.ml | tee main.js
+  // Generated by Melange
+  'use strict';
+  
+  const Curry = require("melange.js/curry.js");
+  
+  function f(x) {
+    let _x = x;
+    const _k = function (x) {
+      return x;
+    };
+    while (true) {
+      const k = _k;
+      const x$1 = _x;
+      if (x$1 === 0) {
+        return Curry._1(k, 0);
+      }
+      _k = (function (x) {
+        return x;
+      });
+      _x = x$1 - 1 | 0;
+      continue;
+    };
+  }
+  
+  f(3);
+  
+  module.exports = {
+    f,
+  }
+  /*  Not a pure module */
+  $ node ./main.js 2>&1 | grep -i typeerror
+  TypeError: Assignment to constant variable.
+

From d7b64896787556e013ba3659d468b77f6e235e90 Mon Sep 17 00:00:00 2001
From: Antonio Nuno Monteiro <anmonteiro@gmail.com>
Date: Wed, 18 Jun 2025 00:26:28 -0700
Subject: [PATCH 2/3] fix: account for `Lam_group.let_kind` when assigning
 functions to variables

---
 jscomp/core/js_dump.ml                        | 21 ++++++++-------
 jscomp/test/dist/jscomp/test/bench.js         |  6 ++---
 .../dist/jscomp/test/earger_curry_test.js     |  6 ++---
 .../dist/jscomp/test/ocaml_parsetree_test.js  |  6 ++---
 jscomp/test/dist/jscomp/test/ocaml_re_test.js |  2 +-
 .../dist/jscomp/test/ocaml_typedtree_test.js  | 26 +++++++++----------
 jscomp/test/dist/jscomp/test/qcc.js           |  2 +-
 jscomp/test/dist/jscomp/test/sexpm.js         |  2 +-
 .../function-assignment-const.t               |  4 +--
 9 files changed, 38 insertions(+), 37 deletions(-)

diff --git a/jscomp/core/js_dump.ml b/jscomp/core/js_dump.ml
index 5d5a9569e..b75170849 100644
--- a/jscomp/core/js_dump.ml
+++ b/jscomp/core/js_dump.ml
@@ -323,8 +323,8 @@ let is_var (b : J.expression) a =
 
 type fn_exp_state =
   | Is_return (* for sure no name *)
-  | Name_top of Ident.t
-  | Name_non_top of Ident.t
+  | Name_top of { name : Ident.t; property : Lam_group.let_kind }
+  | Name_non_top of { name : Ident.t; property : Lam_group.let_kind }
   | No_name of { single_arg : bool }
 (* true means for sure, false -- not sure *)
 
@@ -401,8 +401,8 @@ and pp_function ~return_unit ~is_method cxt ~fn_state (l : Ident.t list)
       let len = List.length l in
       (* length *)
       match fn_state with
-      | Name_top i | Name_non_top i ->
-          let cxt = pp_const_assign cxt i in
+      | Name_top { name = i; property } | Name_non_top { name = i; property } ->
+          let cxt = pp_assign ~property cxt i in
           let cxt = optimize len ~p:(arity = NA && len <= 8) cxt v in
           semi cxt;
           cxt
@@ -414,7 +414,8 @@ and pp_function ~return_unit ~is_method cxt ~fn_state (l : Ident.t list)
         (* identifiers will be printed following*)
         match fn_state with
         | Is_return | No_name _ -> Js_fun_env.get_unbounded env
-        | Name_top id | Name_non_top id ->
+        | Name_top { name = id; property = _ }
+        | Name_non_top { name = id; property = _ } ->
             Ident.Set.add (Js_fun_env.get_unbounded env) id
       in
       (* the context will be continued after this function *)
@@ -462,13 +463,13 @@ and pp_function ~return_unit ~is_method cxt ~fn_state (l : Ident.t list)
               string cxt L.function_;
               space cxt;
               param_body ())
-      | Name_non_top x ->
-          ignore (pp_const_assign inner_cxt x : cxt);
+      | Name_non_top { name = x; property } ->
+          ignore (pp_assign ~property inner_cxt x : cxt);
           string cxt L.function_;
           space cxt;
           param_body ();
           semi cxt
-      | Name_top x ->
+      | Name_top { name = x; property = _ } ->
           string cxt L.function_;
           space cxt;
           ignore (ident inner_cxt x : cxt);
@@ -961,7 +962,9 @@ and variable_declaration top cxt (variable : J.variable_declaration) : cxt =
           match e.expression_desc with
           | Fun { method_ = is_method; params; body = b; env; return_unit } ->
               pp_function ~return_unit ~is_method cxt
-                ~fn_state:(if top then Name_top name else Name_non_top name)
+                ~fn_state:
+                  (if top then Name_top { name; property }
+                   else Name_non_top { name; property })
                 params b env
           | _ ->
               let cxt = pp_assign ~property cxt name in
diff --git a/jscomp/test/dist/jscomp/test/bench.js b/jscomp/test/dist/jscomp/test/bench.js
index d27128e50..de8d58f82 100644
--- a/jscomp/test/dist/jscomp/test/bench.js
+++ b/jscomp/test/dist/jscomp/test/bench.js
@@ -7,7 +7,7 @@ const Curry = require("melange.js/curry.js");
 const Stdlib = require("melange/stdlib.js");
 
 function map(f, a) {
-  const f$1 = Curry.__1(f);
+  let f$1 = Curry.__1(f);
   const l = a.length;
   if (l === 0) {
     return [];
@@ -20,7 +20,7 @@ function map(f, a) {
 }
 
 function init(l, f) {
-  const f$1 = Curry.__1(f);
+  let f$1 = Curry.__1(f);
   if (l === 0) {
     return [];
   }
@@ -38,7 +38,7 @@ function init(l, f) {
 }
 
 function fold_left(f, x, a) {
-  const f$1 = Curry.__2(f);
+  let f$1 = Curry.__2(f);
   let r = x;
   for (let i = 0, i_finish = a.length; i < i_finish; ++i) {
     r = f$1(r, a[i]);
diff --git a/jscomp/test/dist/jscomp/test/earger_curry_test.js b/jscomp/test/dist/jscomp/test/earger_curry_test.js
index 4fc5042f2..5dd4a87b7 100644
--- a/jscomp/test/dist/jscomp/test/earger_curry_test.js
+++ b/jscomp/test/dist/jscomp/test/earger_curry_test.js
@@ -8,7 +8,7 @@ const Mt = require("./mt.js");
 const Stdlib = require("melange/stdlib.js");
 
 function map(f, a) {
-  const f$1 = Curry.__1(f);
+  let f$1 = Curry.__1(f);
   const l = a.length;
   if (l === 0) {
     return [];
@@ -21,7 +21,7 @@ function map(f, a) {
 }
 
 function init(l, f) {
-  const f$1 = Curry.__1(f);
+  let f$1 = Curry.__1(f);
   if (l === 0) {
     return [];
   }
@@ -39,7 +39,7 @@ function init(l, f) {
 }
 
 function fold_left(f, x, a) {
-  const f$1 = Curry.__2(f);
+  let f$1 = Curry.__2(f);
   let r = x;
   for (let i = 0, i_finish = a.length; i < i_finish; ++i) {
     r = f$1(r, a[i]);
diff --git a/jscomp/test/dist/jscomp/test/ocaml_parsetree_test.js b/jscomp/test/dist/jscomp/test/ocaml_parsetree_test.js
index 0de06d12f..556a338f6 100644
--- a/jscomp/test/dist/jscomp/test/ocaml_parsetree_test.js
+++ b/jscomp/test/dist/jscomp/test/ocaml_parsetree_test.js
@@ -1897,7 +1897,7 @@ function errorf(locOpt, subOpt, if_highlightOpt, fmt) {
   const sub = subOpt !== undefined ? subOpt : /* [] */ 0;
   const if_highlight = if_highlightOpt !== undefined ? if_highlightOpt : "";
   let before = print_phanton_error_prefix;
-  const k = function (msg) {
+  let k = function (msg) {
     return {
       loc: loc,
       msg: msg,
@@ -13108,10 +13108,10 @@ function token$1(lexbuf) {
         switch (doc) {
           case /* SHARP */ 84 :
             if (at_bol(lexbuf)) {
-              const cont = function (lexbuf) {
+              let cont = function (lexbuf) {
                 return loop(lines, docs, lexbuf);
               };
-              const look_ahead = function (token) {
+              let look_ahead = function (token) {
                 sharp_look_ahead.contents = token;
                 return /* SHARP */ 84;
               };
diff --git a/jscomp/test/dist/jscomp/test/ocaml_re_test.js b/jscomp/test/dist/jscomp/test/ocaml_re_test.js
index e459230cd..764173c09 100644
--- a/jscomp/test/dist/jscomp/test/ocaml_re_test.js
+++ b/jscomp/test/dist/jscomp/test/ocaml_re_test.js
@@ -1782,7 +1782,7 @@ function is_charset(_param) {
 
 function split(s, cm) {
   let _t = s;
-  const f = function (i, j) {
+  let f = function (i, j) {
     Caml_bytes.set(cm, i, /* '\001' */1);
     Caml_bytes.set(cm, j + 1 | 0, /* '\001' */1);
   };
diff --git a/jscomp/test/dist/jscomp/test/ocaml_typedtree_test.js b/jscomp/test/dist/jscomp/test/ocaml_typedtree_test.js
index cb89f5408..cdde1de99 100644
--- a/jscomp/test/dist/jscomp/test/ocaml_typedtree_test.js
+++ b/jscomp/test/dist/jscomp/test/ocaml_typedtree_test.js
@@ -2176,7 +2176,7 @@ function errorf(locOpt, subOpt, if_highlightOpt, fmt) {
   const sub = subOpt !== undefined ? subOpt : /* [] */ 0;
   const if_highlight = if_highlightOpt !== undefined ? if_highlightOpt : "";
   let before = print_phanton_error_prefix;
-  const k = function (msg) {
+  let k = function (msg) {
     return {
       loc: loc,
       msg: msg,
@@ -11298,10 +11298,10 @@ function find_name$1(s, tbl) {
 
 function fold_name(f) {
   return function (param, param$1) {
-    const f$1 = function (k, param) {
+    let f$1 = function (k, param) {
       return Curry._2(f, k, param[0]);
     };
-    const f$2 = function (k) {
+    let f$2 = function (k) {
       return Curry._2(f$1, k.ident, k.data);
     };
     let _stack = /* [] */ 0;
@@ -12879,10 +12879,10 @@ function run_iter_cont(l) {
 
 function iter_types(f) {
   return function (param, param$1) {
-    const proj1 = function (env) {
+    let proj1 = function (env) {
       return env.types;
     };
-    const proj2 = function (sc) {
+    let proj2 = function (sc) {
       return sc.comp_types;
     };
     iter((function (id, param) {
@@ -25175,10 +25175,10 @@ function token$1(lexbuf) {
         switch (doc) {
           case /* SHARP */ 84 :
             if (at_bol(lexbuf)) {
-              const cont = function (lexbuf) {
+              let cont = function (lexbuf) {
                 return loop(lines, docs, lexbuf);
               };
-              const look_ahead = function (token) {
+              let look_ahead = function (token) {
                 sharp_look_ahead.contents = token;
                 return /* SHARP */ 84;
               };
@@ -42575,7 +42575,7 @@ function print_out_sig_item(ppf, param) {
               },
               _1: " =%a {%a@;<1 -2>}"
             }), print_private, td.otype_private, (function (param, param$1) {
-              const sep = function (ppf) {
+              let sep = function (ppf) {
                 Stdlib__Format.fprintf(ppf)({
                   TAG: /* Format */ 0,
                   _0: {
@@ -65328,7 +65328,7 @@ function partial_pred(lev, env, expected_ty, constrs, labels, p) {
 function check_partial$1(levOpt, env, expected_ty) {
   const lev = levOpt !== undefined ? levOpt : current_level.contents;
   return function (param, param$1) {
-    const pred = function (param, param$1, param$2) {
+    let pred = function (param, param$1, param$2) {
       return partial_pred(lev, env, expected_ty, param, param$1, param$2);
     };
     const first_check = check_partial(param, param$1);
@@ -70213,7 +70213,7 @@ function type_let(checkOpt, check_strictOpt, env, rec_flag, spat_sexp_list, scop
           
         });
       }
-      const callback = function (param) {
+      let callback = function (param) {
         const slot$1 = current_slot.contents;
         if (slot$1 !== undefined) {
           slot$1.contents = {
@@ -71350,7 +71350,7 @@ register_error_of_exn(function (err) {
             const name = kind$1 === "record" ? "field" : "constructor";
             let param$3 = param$1._2;
             let tpl = param$1._3;
-            const txt1 = function (ppf) {
+            let txt1 = function (ppf) {
               Curry._4(Stdlib__Format.fprintf(ppf)({
                 TAG: /* Format */ 0,
                 _0: {
@@ -71393,7 +71393,7 @@ register_error_of_exn(function (err) {
                 _1: "The %s %a@ belongs to the %s type"
               }), name, longident, lid$2, kind$1);
             };
-            const txt2 = function (ppf) {
+            let txt2 = function (ppf) {
               Curry._4(Stdlib__Format.fprintf(ppf)({
                 TAG: /* Format */ 0,
                 _0: {
@@ -71436,7 +71436,7 @@ register_error_of_exn(function (err) {
                 _1: "The %s %a@ belongs to one of the following %s types:"
               }), name, longident, lid$2, kind$1);
             };
-            const txt3 = function (ppf) {
+            let txt3 = function (ppf) {
               Curry._2(Stdlib__Format.fprintf(ppf)({
                 TAG: /* Format */ 0,
                 _0: {
diff --git a/jscomp/test/dist/jscomp/test/qcc.js b/jscomp/test/dist/jscomp/test/qcc.js
index 2ac96ad1b..2fc8dbaac 100644
--- a/jscomp/test/dist/jscomp/test/qcc.js
+++ b/jscomp/test/dist/jscomp/test/qcc.js
@@ -1965,7 +1965,7 @@ function main(param) {
         partial_arg_0,
         0
       ];
-      const c = function (param) {
+      let c = function (param) {
         return block(partial_arg, param);
       };
       let stk = /* [] */ 0;
diff --git a/jscomp/test/dist/jscomp/test/sexpm.js b/jscomp/test/dist/jscomp/test/sexpm.js
index 3a7749c9a..8e1b2b963 100644
--- a/jscomp/test/dist/jscomp/test/sexpm.js
+++ b/jscomp/test/dist/jscomp/test/sexpm.js
@@ -359,7 +359,7 @@ function to_chan(oc, t) {
 }
 
 function to_file_seq(filename, seq) {
-  const f = function (oc) {
+  let f = function (oc) {
     return Curry._1(seq, (function (t) {
       to_chan(oc, t);
       Caml_io.caml_ml_output_char(oc, /* '\n' */10);
diff --git a/test/blackbox-tests/function-assignment-const.t b/test/blackbox-tests/function-assignment-const.t
index 02309935d..1786ada5a 100644
--- a/test/blackbox-tests/function-assignment-const.t
+++ b/test/blackbox-tests/function-assignment-const.t
@@ -24,7 +24,7 @@
   
   function f(x) {
     let _x = x;
-    const _k = function (x) {
+    let _k = function (x) {
       return x;
     };
     while (true) {
@@ -47,6 +47,4 @@
     f,
   }
   /*  Not a pure module */
-  $ node ./main.js 2>&1 | grep -i typeerror
-  TypeError: Assignment to constant variable.
 

From b80fd67da42e9a3ec1d752da57ad68c17af8ad78 Mon Sep 17 00:00:00 2001
From: Antonio Nuno Monteiro <anmonteiro@gmail.com>
Date: Thu, 19 Jun 2025 00:00:02 -0700
Subject: [PATCH 3/3] changelos

---
 Changes.md | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Changes.md b/Changes.md
index d2b4d8c68..c95c2b81b 100644
--- a/Changes.md
+++ b/Changes.md
@@ -11,6 +11,8 @@ Unreleased
 - melange.ppx: improve the inference of `@mel.as` in polymorphic variant
   arguments to `external`s, allow to mix ints and strings in the different
   variant branches ([#1418](https://github.com/melange-re/melange/pull/1418))
+- Fix code generation bug when assigning functions to variables
+  ([#1429](https://github.com/melange-re/melange/pull/1429))
 
 5.1.0-53 2025-03-23
 ---------------