Fix #647: emit explicit nil in else of if branch (#648)

Author: borkdude

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 [Squint](https://github.com/squint-cljs/squint): Light-weight ClojureScript dialect
 
+## Unreleased
+
+- Fix [#647](https://github.com/squint-cljs/squint/issues/647): emit explicit `null` when written in else branch of `if`
+
 ## v0.8.142 (2025-03-19)
 
 - Fix [#640](https://github.com/squint-cljs/squint/issues/640): don't emit anonymous function if it is a statement ([@jonasseglare](https://github.com/jonasseglare))

src/squint/compiler_common.cljc

@@ -1080,7 +1080,7 @@ break;}" body)
       (str (format "if (%s) {\n" condition)
            (emit then env)
            "}"
-           (when (some? else)
+           (when (= 4 (count expr)) ;; explicit else branch
              (str " else {\n"
                   (emit else env)
                   "}"))))))

test/squint/compiler_test.cljs

@@ -199,7 +199,10 @@
   (let [s (jss! "(let [x (do 1 (if (inc 1) (inc 2) (inc 3)))]
                    x)")]
     (is (= 3 (js/eval s))))
-  (is (eq #js {:a 1} (jsv! "{:a (or 1 (cond true (prn :yes)) 2)}"))))
+  (is (eq #js {:a 1} (jsv! "{:a (or 1 (cond true (prn :yes)) 2)}")))
+  (is (let [v (jsv! "(let [x false] (if x 1 nil))")]
+        (and (nil? v)
+             (not (undefined? v))))))
 
 (deftest zero?-test
   (is (str/includes? (jss! "(if (zero? x) 1 2)") "== 0"))