Fix %external extension.

Fixes #7270

Author: cristianoc

CHANGELOG.md

@@ -19,6 +19,7 @@
 #### :bug: Bug fix
 
 - Fix async context checking for module await. https://github.com/rescript-lang/rescript/pull/7271
+- Fix `%external` extension. https://github.com/rescript-lang/rescript/pull/7272
 
 # 12.0.0-alpha.8
 

compiler/frontend/ast_exp_handle_external.ml

@@ -60,7 +60,7 @@ let handle_external loc (x : string) : Parsetree.expression =
   Ast_compatible.app1 ~loc undefined_typeof
     (Exp.ifthenelse ~loc
        (Ast_compatible.app2 ~loc
-          (Exp.ident ~loc {loc; txt = Ldot (Lident "Pervasives", "=")})
+          (Exp.ident ~loc {loc; txt = Lident "=="})
           (Ast_compatible.app1 ~loc typeof raw_exp)
           (Ast_compatible.const_exp_string ~loc "undefined"))
        empty (Some raw_exp))

tests/tests/src/ExternalExtension.mjs

@@ -0,0 +1,12 @@
+// Generated by ReScript, PLEASE EDIT WITH CARE
+
+
+let match = typeof __DEV__ === "undefined" ? undefined : __DEV__;
+
+if (match !== undefined) {
+  console.log("dev mode");
+} else {
+  console.log("production mode");
+}
+
+/* match Not a pure module */

tests/tests/src/ExternalExtension.res

@@ -0,0 +1,4 @@
+switch %external(__DEV__) {
+| Some(_) => Console.log("dev mode")
+| None => Console.log("production mode")
+}