Improve hash-update refactoring (#421)

Closes #419.

default-recommendations/hash-shortcuts-test.rkt

@@ -162,6 +162,19 @@ test: "hash-set! with hash-ref and literal keys can be simplified to hash-update
 ------------------------------
 
 
+test: "hash-set! with hash-ref can be simplified to hash-update! without lambda"
+------------------------------
+(define h (make-hash))
+(define k 'a)
+(hash-set! h k (add1 (hash-ref h k 0)))
+------------------------------
+------------------------------
+(define h (make-hash))
+(define k 'a)
+(hash-update! h k add1 0)
+------------------------------
+
+
 test: "hash-set! with hash-ref cannot be simplified when v would shadow"
 ------------------------------
 (define h (make-hash))

default-recommendations/hash-shortcuts.rkt

@@ -10,6 +10,7 @@
 
 
 (require (for-syntax racket/base)
+         racket/list
          racket/set
          rebellion/private/static-name
          resyntax/base
@@ -107,9 +108,11 @@
   #:when (syntax-free-identifier=? #'k1 #'k2)
   #:when (for/and ([id (in-syntax-identifiers #'(f arg-before ... arg-after ...))])
            (not (equal? (syntax-e id) 'v)))
-  (hash-update! h1 k1
-                (λ (v) (f arg-before ... v arg-after ...))
-                (~? failure-result)))
+  #:with updater
+  (if (and (empty? (attribute arg-before)) (empty? (attribute arg-after)))
+      #'f
+      #'(λ (v) (f arg-before ... v arg-after ...)))
+  (hash-update! h1 k1 updater (~? failure-result)))
 
 
 (define-refactoring-rule hash-map-to-hash-keys