Allow coercing int to float (#6448)

* allow coercing int to float

* changelog

Author: zth

CHANGELOG.md

@@ -15,6 +15,7 @@
 #### :rocket: New Feature
 - Allow coercing unboxed variants with only strings (now including with a single payload of string) to the primitive string. https://github.com/rescript-lang/rescript-compiler/pull/6441
 - Allow coercing strings to unboxed variants that has a catch-all unboxed string case. https://github.com/rescript-lang/rescript-compiler/pull/6443
+- Allow coercing `int` to `float`. https://github.com/rescript-lang/rescript-compiler/pull/6448
 
 #### :bug: Bug Fix
 

jscomp/ml/ctype.ml

@@ -3951,6 +3951,8 @@ let rec subtype_rec env trace t1 t2 cstrs =
         end
     | (Tconstr(p1, _, _), _) when generic_private_abbrev env p1 ->
         subtype_rec env trace (expand_abbrev_opt env t1) t2 cstrs
+    | (Tconstr(p1, [], _), Tconstr(p2, [], _)) when Path.same p1 Predef.path_int && Path.same p2 Predef.path_float ->
+        cstrs 
     | (Tconstr(path, [], _), Tconstr(_, [], _)) when Path.same path Predef.path_string && 
         extract_concrete_typedecl env t2 |> Variant_coercion.can_try_coerce_variant_to_primitive |> Option.is_some
         ->

jscomp/test/Coercion.js

@@ -0,0 +1,3 @@
+let x = 1
+
+let xx = (x :> float)