Fix issue with pattern matching empty list which interferes with boolean optimisations.

The pattern matching case  for empty list `switch x { | list{} =>` used to compile to `if(x)`, which interferes with boolean optimisation.
Now it compiles to `if(x ==0)` which is the same output as for `if(x == list{})`.

Fixes rescript-lang#7235

Author: cristianoc

CHANGELOG.md

@@ -17,6 +17,7 @@
 - Editor: Fix issue where pipe completions would not trigger with generic type arguments. https://github.com/rescript-lang/rescript/pull/7231
 - Fix leftover assert false in code for `null != undefined`. https://github.com/rescript-lang/rescript/pull/7232
 - Editor: Fix issue where completions would not show up inside of object bodies. https://github.com/rescript-lang/rescript/pull/7230
+- Fix issue with pattern matching empty list which interferes with boolean optimisations. https://github.com/rescript-lang/rescript/pull/7237
 
 #### :house: Internal
 

compiler/ml/matching.ml

@@ -2245,7 +2245,8 @@ let combine_constructor sw_names loc arg ex_pat cstr partial ctx def
           let arg =
             if Datarepr.constructor_has_optional_shape cstr then
               Lprim (Pis_not_none, [arg], loc)
-            else arg
+            else
+              Lprim (Pjscomp Cneq, [arg; Lconst (Const_base (Const_int 0))], loc)
           in
           Lifthenelse (arg, act2, act1)
         | 2, 0, [(i1, act1); (_, act2)], []