Extract let bindings from inside variable definitions (#255)

default-recommendations/let-binding-suggestions-test.rkt

@@ -417,3 +417,43 @@ test: "let binding with obfuscated conflicting define inside"
         x))
     (m x)))
 ------------------------------
+
+
+test: "variable definition with nested let binding refactorable to two variable definitions"
+------------------------------
+(define (f)
+  (define y (let ([x 1]) (* x 2)))
+  (* y 3))
+------------------------------
+------------------------------
+(define (f)
+  (define x 1)
+  (define y (* x 2))
+  (* y 3))
+------------------------------
+
+
+test: "variable definition with nested let binding of same name not refactorable"
+------------------------------
+(define (f)
+  (define y (let ([y 1]) (* y 2)))
+  (* y 3))
+------------------------------
+
+
+test: "variable definition with nested let binding of name bound later not refactorable"
+------------------------------
+(define (f)
+  (define y (let ([x 1]) (* x 2)))
+  (define x 5)
+  (* y 3))
+------------------------------
+
+
+test: "variable definition with nested let binding of name bound earlier not refactorable"
+------------------------------
+(define (f)
+  (define x 5)
+  (define y (let ([x 1]) (* x 2)))
+  (* y 3))
+------------------------------

default-recommendations/let-binding-suggestions.rkt

@@ -66,7 +66,24 @@
    (call-with-values (λ () expr) receiver)])
 
 
+(define-refactoring-rule define-let-to-double-define
+  #:description "This `let` expression can be pulled up into a `define` expression."
+  #:literals (define let)
+  [(header:header-form-allowing-internal-definitions
+    (define id:id (let ([nested-id:id nested-expr:expr]) expr:expr))
+    body ...)
+   #:when (not (set-member? (syntax-bound-identifiers #'(id body ...)) #'nested-id))
+   (header.formatted ...
+    (define nested-id nested-expr)
+    (define id expr)
+    body ...)])
+
+
 (define let-binding-suggestions
   (refactoring-suite
    #:name (name let-binding-suggestions)
-   #:rules (list let-to-define let-values-then-call-to-call-with-values named-let-to-plain-let)))
+   #:rules
+   (list define-let-to-double-define
+         let-to-define
+         let-values-then-call-to-call-with-values
+         named-let-to-plain-let)))