Fix variant coercion with as attribute (rescript-lang#7058)

* Use value from as attribute if available

* Add tests

* Update CHANGELOG

* Fix formatting

Author: shulhi

CHANGELOG.md

@@ -33,6 +33,7 @@
 - Fix bigint max, min https://github.com/rescript-lang/rescript-compiler/pull/7088
 - Fix parsing issue with nested variant pattern type spreads. https://github.com/rescript-lang/rescript-compiler/pull/7080
 - Fix JSX settings inheritance: only 'version' propagates to dependencies, preserving their 'mode' and 'module'. https://github.com/rescript-lang/rescript-compiler/pull/7094
+- Fix variant cast to int. https://github.com/rescript-lang/rescript-compiler/pull/7058
 
 #### :nail_care: Polish
 

compiler/core/lam_constant_convert.ml

@@ -48,6 +48,11 @@ let rec convert_constant (const : Lambda.structured_constant) : Lam_constant.t =
     | Pt_assertfalse -> Const_int {i = Int32.of_int i; comment = Pt_assertfalse}
     | Pt_constructor {name; const; non_const; attrs} ->
       let tag_type = Ast_untagged_variants.process_tag_type attrs in
+      let i =
+        match tag_type with
+        | Some (Ast_untagged_variants.Int v) -> v
+        | _ -> i
+      in
       Const_int
         {
           i = Int32.of_int i;

tests/tests/src/VariantCoercion.js

@@ -120,3 +120,33 @@ module CoerceFromPolyvariantToVariant = {
   let withUnboxedCatchAll: withUnboxedCatchAll = #One
   let withUnboxedCatchAllP = (withUnboxedCatchAll :> withUnboxedCatchAllP)
 }
+
+module CoerceVariantBinaryOp = {
+  type flag = | @as(0) A | @as(2) B
+
+  let x = 0->lor((B :> int))
+
+  let v = B
+  let f1 = () =>
+    switch v {
+    | A => "a"
+    | B => "b"
+    }
+  let f2 = () =>
+    switch (v :> int) {
+    | 2 => "b"
+    | _ => "a"
+    }
+
+  for x in 1 to (B :> int) {
+    Js.log(x)
+  }
+
+  type flagStr = | @as("one") One | @as("two") Two
+
+  let y = (One :> string)->String.length
+
+  type flagFloat = | @as(1.5) X | @as(2.0) Y
+
+  let z = (X :> float) +. (Y :> float) +. 1.5
+}