Fix option optimisation compiler bug

CHANGELOG.md

@@ -20,6 +20,7 @@
 
 #### :bug: Bug fix
 
+- Fix option optimisation that resulted in incorrect JS output. https://github.com/rescript-lang/rescript/pull/7766
 - Fix formatting of nested records in `.resi` files. https://github.com/rescript-lang/rescript/pull/7741
 - Don't format and don't check formatting of dependencies. https://github.com/rescript-lang/rescript/pull/7748
 - Fix `rescript-editor-analysis semanticTokens` returning invalid JSON in certain cases. https://github.com/rescript-lang/rescript/pull/7750

compiler/core/lam_pass_remove_alias.ml

@@ -24,10 +24,19 @@
 
 type outcome = Eval_false | Eval_true | Eval_unknown
 
-let id_is_for_sure_true_in_boolean (tbl : Lam_stats.ident_tbl) id =
+let rec id_is_for_sure_true_in_boolean (tbl : Lam_stats.ident_tbl) id =
   match Hash_ident.find_opt tbl id with
-  | Some (ImmutableBlock _)
+  | Some
+      (Normal_optional
+         ( Lprim {loc = _; primitive = Psome_not_nest; args = [Lvar id']}
+         | Lvar id' )) ->
+    id_is_for_sure_true_in_boolean tbl id'
+  | Some
+      (Normal_optional
+         (Lconst (Const_js_false | Const_js_null | Const_js_undefined _))) ->
+    Eval_false
   | Some (Normal_optional _)
+  | Some (ImmutableBlock _)
   | Some (MutableBlock _)
   | Some (Constant (Const_block _ | Const_js_true)) ->
     Eval_true

tests/tests/src/option_optimisation.mjs

@@ -0,0 +1,35 @@
+// Generated by ReScript, PLEASE EDIT WITH CARE
+
+import * as Primitive_option from "rescript/lib/es6/Primitive_option.js";
+
+function boolean(val1, val2) {
+  let a = val1;
+  let b = val2;
+  if (b || a) {
+    return "a";
+  } else {
+    return "b";
+  }
+}
+
+function $$null(val1, val2) {
+  let a = Primitive_option.some(val1);
+  let b = Primitive_option.some(val2);
+  let tmp = Primitive_option.valFromOption(b);
+  if (tmp !== null && tmp !== undefined) {
+    return "a";
+  }
+  tmp === null;
+  let tmp$1 = Primitive_option.valFromOption(a);
+  if (tmp$1 == null) {
+    return "b";
+  } else {
+    return "a";
+  }
+}
+
+export {
+  boolean,
+  $$null,
+}
+/* No side effect */

tests/tests/src/option_optimisation.res

@@ -0,0 +1,21 @@
+let boolean = (~val1: bool, ~val2: bool) => {
+  let a = Some(val1)
+  let b = Some(val2)
+
+  switch (a, b) {
+  | (_, Some(true))
+  | (Some(true), _) => "a"
+  | _ => "b"
+  }
+}
+
+let null = (~val1: Nullable.t<int>, ~val2: Nullable.t<int>) => {
+  let a = Some(val1)
+  let b = Some(val2)
+
+  switch (a, b) {
+  | (_, Some(Value(_)))
+  | (Some(Value(_)), _) => "a"
+  | _ => "b"
+  }
+}