Anonymous function which is not the last statement results in invalid JS output

[jonasseglare]

version

The latest commit fa434c1b719de62bd676acf27d440ffc8e3868bb after version v0.8.141

problem

Invalid JavaScript code is produced when an anonymous function appears in a body of statements, such as do or a function body but not at the last position among those statements.

The following code

(defn get-four []
  (fn [] 119)
  4)

compiles to

var get_four = function () {
function () {
return 119;
};
return 4;
};

which is not valid JavaScript. Here is part of the error message:

18:35:14 [vite] Internal server error: Transform failed with 1 error:
/Users/osdjn/prog/libtaxonomy-js/public/test/libtaxonomy/db.jsx:46:9: ERROR: Expected identifier but found "("
  Plugin: vite:esbuild
  File: /Users/osdjn/prog/libtaxonomy-js/public/test/libtaxonomy/db.jsx:46:9

  Expected identifier but found "("
  44 |  };
  45 |  var get_four = function () {
  46 |  function () {
     |           ^
  47 |  return 119;
  48 |  };

repro

Here is a good unit test that fails when I try to include it in compiler_test.cljs:

(deftest fn-statement-test
  (is (= 4 (jsv! "(do (fn [] 119) 4)"))))

expected behavior

Either Squint should not emit a function at all, or it should generate a name for the function so that the generated JavaScript code is valid. So I would suggest that Squint would output the following code for the function get-four:

var get_four = function () {
return 4;
};

attempted fix

I attempted to fix this issue with omit?, see below. That is, if the function doesn't have a name and we are generating code for a statement, we omit it. But with this fix, another unit test breaks.

(defn emit-function* [env expr opts]
  (let [name (when (symbol? (first expr)) (first expr))
        expr (if name (rest expr) expr)
        expr (if (seq? (first expr))
               ;; TODO: multi-arity:
               (first expr)
               expr)
        signature (first expr)
        arrow? (or (:arrow env) (:=> (meta signature)))
        env (assoc env :arrow arrow?)
        omit? (and (= :statement (:context env))
                   (nil? name))]
    (when-not omit?
      (if (some #(= '& %) signature)
         
         ...........

[borkdude]

You can fix the test by forcing the context to be :expr:

(testing "no paren wrapping"
    (is (str/starts-with? (:body (squint/compile-string* "(fn ^:=> [] 1)" {:context :expr})) "() =>")))

[borkdude]

I already committed the test change, so you just merge with main and provide the PR