fix lazy stepper bug: annota of non-identifier fns

- fix lazy stepper bug where delaying of non-identifier fns
  wasnt being properly hidden
- add test case for this bug

include in 5.2
(cherry picked from commit 79dd7df945)

collects/lazy/lazy.rkt

@@ -78,7 +78,10 @@
   
   (define-syntax (mark-as-lazy-op stx)
     (syntax-case stx ()
-      [(_ arg) (stepper-add-lazy-op-prop (syntax/loc stx arg))]))
+      [(_ arg) 
+       (identifier? #'arg)
+       (stepper-add-lazy-op-prop (syntax/loc stx arg))]
+      [(_ arg) #'arg]))
     
   (define-syntax (hidden-~ stx)
     (syntax-case stx ()

collects/tests/stepper/automatic-tests.rkt

@@ -23,7 +23,7 @@
     lazy-length lazy-list-ref lazy-list-tail lazy-append lazy-reverse lazy-empty? 
     lazy-assoc lazy-assq lazy-assv lazy-cons? lazy-remove lazy-remq lazy-remv
     lazy-member lazy-memq lazy-memv lazy-filter1 lazy-filter2 lazy-fold
-    lazy-cyclic1))
+    lazy-cyclic1 lazy-fn-app))
 
 (let ((outer-namespace (current-namespace)))
   (parameterize ([display-only-errors #t]

collects/tests/stepper/test-cases.rkt

@@ -2132,8 +2132,16 @@
         -> ,def (+ 1 {1})
         :: ,def {(+ 1 1)} -> ,def {2}))
    
-         
+   ; application in function position -- checks bug fix
-    
+   (let* ([lxx '(lambda (x) x)]
+          [def `(define I ,lxx)])
+     (t 'lazy-fn-app m:lazy
+        ,def ((I I) I)
+        :: ,def (({I} I) I)       -> ,def (({,lxx} I) I)
+        :: ,def ((,lxx {I}) I)    -> ,def ((,lxx {,lxx}) I)
+        :: ,def ({(,lxx ,lxx)} I) -> ,def ({,lxx} I)
+        :: ,def (,lxx {I})        -> ,def (,lxx {,lxx})
+        :: ,def {(,lxx ,lxx)}     -> ,def {,lxx}))
     
    
   #;