Fix issue where exhaustiveness check for pattern matching char was no… (#5744)

* Fix issue where exhaustiveness check for pattern matching char was not working

Fixes #5557
Fixes #5743

Exhaustiveness check for pattern matching relies on checking that the pattern does not lead to a type error.
Since char constants are represented internally as int, this causes an internal type error when processing patterns of the form 'x', where the constant is represented as `Pconst_integer` but the expected type is `char`.

This PR intercepts this situation and changes the expected type to `int`.
A cleaner solution would be to represent chars differently (but we can't change the AST), or make it official that char and int is the same type (and lose some abstraction).

* comment

Author: cristianoc

CHANGELOG.md

@@ -12,6 +12,10 @@
 
 # 10.1.0-rc.3
 
+#### :bug: Bug Fix
+
+- Fix issue where exhaustiveness check for pattern matching char was not working  https://github.com/rescript-lang/rescript-compiler/issues/5557
+
 # 10.1.0-rc.2
 
 #### :bug: Bug Fix

jscomp/ml/typecore.ml

@@ -1350,6 +1350,11 @@ let partial_pred ~lev ?mode ?explode env expected_ty constrs labels p =
   let state = save_state env in
   try
     reset_pattern None true;
+    let expected_ty = match p.ppat_desc, expected_ty.desc with
+    | Ppat_constant (Pconst_integer _ ), Tconstr (path, [], _) when Path.same path Predef.path_char ->
+      (* Constants such as 'x' are represented as Pconst_integer but expected to have type char *)
+      Predef.type_int
+    | _ -> expected_ty in
     let typed_p =
       Ctype.with_passive_variants
         (type_pat ~allow_existentials:true ~lev

lib/4.06.1/unstable/js_compiler.ml

@@ -40301,6 +40301,11 @@ let partial_pred ~lev ?mode ?explode env expected_ty constrs labels p =
   let state = save_state env in
   try
     reset_pattern None true;
+    let expected_ty = match p.ppat_desc, expected_ty.desc with
+    | Ppat_constant (Pconst_integer _ ), Tconstr (path, [], _) when Path.same path Predef.path_char ->
+      (* Constants such as 'x' are represented as Pconst_integer but expected to have type char *)
+      Predef.type_int
+    | _ -> expected_ty in
     let typed_p =
       Ctype.with_passive_variants
         (type_pat ~allow_existentials:true ~lev

lib/4.06.1/unstable/js_playground_compiler.ml

@@ -40301,6 +40301,11 @@ let partial_pred ~lev ?mode ?explode env expected_ty constrs labels p =
   let state = save_state env in
   try
     reset_pattern None true;
+    let expected_ty = match p.ppat_desc, expected_ty.desc with
+    | Ppat_constant (Pconst_integer _ ), Tconstr (path, [], _) when Path.same path Predef.path_char ->
+      (* Constants such as 'x' are represented as Pconst_integer but expected to have type char *)
+      Predef.type_int
+    | _ -> expected_ty in
     let typed_p =
       Ctype.with_passive_variants
         (type_pat ~allow_existentials:true ~lev

lib/4.06.1/whole_compiler.ml

@@ -216688,6 +216688,11 @@ let partial_pred ~lev ?mode ?explode env expected_ty constrs labels p =
   let state = save_state env in
   try
     reset_pattern None true;
+    let expected_ty = match p.ppat_desc, expected_ty.desc with
+    | Ppat_constant (Pconst_integer _ ), Tconstr (path, [], _) when Path.same path Predef.path_char ->
+      (* Constants such as 'x' are represented as Pconst_integer but expected to have type char *)
+      Predef.type_int
+    | _ -> expected_ty in
     let typed_p =
       Ctype.with_passive_variants
         (type_pat ~allow_existentials:true ~lev