fix #23558, bug in recursive let-bound functions

Ref #23561
(cherry picked from commit aee1aab)

src/julia-syntax.scm

@@ -1105,23 +1105,24 @@
               ;; some kind of assignment
               (cond
                ((eventually-call? (cadar binds))
-                ;; f()=c
+                ;; f() = c
                 (let ((asgn (butlast (expand-forms (car binds))))
                       (name (assigned-name (cadar binds))))
                   (if (not (symbol? name))
                       (error "invalid let syntax"))
                   (loop (cdr binds)
                         `(scope-block
                           (block
-                           (local-def ,name)
+                           ,(if (expr-contains-eq name (caddar binds))
+                                `(local ,name) ;; might need a Box for recursive functions
+                                `(local-def ,name))
                            ,asgn
                            ,blk)))))
                ((or (symbol? (cadar binds))
                     (decl?   (cadar binds)))
                 (let ((vname (decl-var (cadar binds))))
                   (loop (cdr binds)
-                        (if (contains (lambda (x) (eq? x vname))
-                                      (caddar binds))
+                        (if (expr-contains-eq vname (caddar binds))
                             (let ((tmp (make-ssavalue)))
                               `(scope-block
                                 (block (= ,tmp ,(caddar binds))

test/core.jl

@@ -343,6 +343,13 @@ let f = i18408()
     @test_throws UndefRefError f(0)
 end
 
+# issue #23558
+c23558(n,k) =
+    let fact(n) = if (n == 0) 1 else n*fact(n-1) end
+        fact(n)/fact(k)/fact(n-k)
+    end
+@test c23558(10, 5) == 252
+
 # variable scope, globals
 glob_x = 23
 function glotest()