expander: don't flip use-site scope in local-expand

Various parts of the expander, including `local-expand`, always
flipped the use-site scope when flipping an introduction scope. Onlt
`syntax-local-introduce` should flip both of them, though.

Closes #2112

pkgs/racket-test-core/tests/racket/macro.rktl

@@ -2155,6 +2155,25 @@
           [(_ e) (disarm #'e)]))
       (mapply m))))
 
+;; ----------------------------------------
+;; Make sure `local-expand` doesn't flip the use-site
+;; scope in addition to the introduction scope
+
+(module local-expand-result-depends-on-use-site-scope racket/base
+  (require (for-syntax racket/base))
+  (define x 1)
+  
+  (define-syntax (a stx)
+    (syntax-case stx ()
+      [(a id)
+       (local-expand #'(let ([id 3]) x) 'expression '())]))
+  
+  (define result (a x))
+  (provide result))
+
+(test 1 dynamic-require ''local-expand-result-depends-on-use-site-scope 'result)
+
+
 ;; ----------------------------------------
 
 (report-errs)

racket/src/expander/expand/context.rkt

@@ -56,6 +56,7 @@
           keep-#%expression? ; if `in-local-expand?`, keep `#%expression` forms
           stops      ; free-id-set; non-empty => `def-ctx-scopes` is a box
           * current-introduction-scopes ; scopes for current macro expansion
+          * current-use-scopes ; scopes for current macro expansion
           declared-submodule-names ; mutable hash table: symbol -> 'module or 'module*
           lifts      ; #f or lift-context, which contains a list of lifteds
           lift-envs  ; list of box of env for lifts to locals
@@ -103,6 +104,7 @@
                   #f   ; keep-#%expression?
                   empty-free-id-set ; stops
                   null ; current-introduction-scopes
+                  null ; current-use-scopes
                   #hasheq() ; declared-submodule-names
                   #f   ; lifts
                   '()  ; lift-envs

racket/src/expander/expand/definition-context.rkt

@@ -27,6 +27,7 @@
          
          make-local-expand-context
          flip-introduction-scopes
+         flip-introduction-and-use-scopes
 
          intdefs?
          intdefs?-string
@@ -299,3 +300,7 @@
 
 (define (flip-introduction-scopes s ctx)
   (flip-scopes s (expand-context-current-introduction-scopes ctx)))
+
+(define (flip-introduction-and-use-scopes s ctx)
+  (flip-scopes (flip-introduction-scopes s ctx)
+               (expand-context-current-use-scopes ctx)))

racket/src/expander/expand/main.rkt

@@ -410,8 +410,8 @@
         (accumulate-def-ctx-scopes ctx (expand-context-def-ctx-scopes ctx))
         ctx))
   (define m-ctx (struct*-copy expand-context accum-ctx
-                              [current-introduction-scopes (cons intro-scope
-                                                                 use-scopes)]
+                              [current-introduction-scopes (list intro-scope)]
+                              [current-use-scopes use-scopes]
                               [def-ctx-scopes
                                 (if confine-def-ctx-scopes?
                                     ;; Can confine tracking to this call

racket/src/expander/expand/syntax-local.rkt

@@ -92,7 +92,7 @@
 (define/who (syntax-local-introduce s)
   (check who syntax? s)
   (define ctx (get-current-expand-context 'syntax-local-introduce))
-  (flip-introduction-scopes s ctx))
+  (flip-introduction-and-use-scopes s ctx))
 
 (define/who (syntax-local-identifier-as-binding id)
   (check who identifier? id)