Add macro-introduction scopes when expanding rename transformers

This can’t affect scoping, but it can affect `syntax-original?`, which
is important for Check Syntax.

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

@@ -2442,6 +2442,25 @@
 
 (test #t dynamic-require ''syntax-local-value-free-id-context 'result)
 
+;; ----------------------------------------
+;; Ensure the expansion of a rename transformer is not `syntax-original?`
+
+(module rename-transformer-introduction-scope racket/base
+  (require (for-syntax racket/base))
+  (provide sym free-id=? original?)
+  (define x #f)
+  (define-syntax y (make-rename-transformer #'x))
+  (define-syntax (m stx)
+    (define expanded-y (syntax-local-introduce (local-expand #'y 'expression '())))
+    #`(values '#,(syntax-e expanded-y)
+              '#,(free-identifier=? expanded-y #'x)
+              '#,(syntax-original? expanded-y)))
+  (define-values (sym free-id=? original?) (m)))
+
+(test 'x dynamic-require ''rename-transformer-introduction-scope 'sym)
+(test #t dynamic-require ''rename-transformer-introduction-scope 'free-id=?)
+(test #f dynamic-require ''rename-transformer-introduction-scope 'original?)
+
 ;; ----------------------------------------
 ;; Make sure replacing scopes of binding on reference does not
 ;; turn a non-`syntax-original?` identifier into a `syntax-original?`

racket/src/expander/expand/main.rkt

@@ -323,12 +323,7 @@
     (cond
      [(expand-context-just-once? ctx) exp-s]
      [else (expand exp-s re-ctx
-                   #:alternate-id (and (rename-transformer? t)
+                   #:alternate-id (and (rename-transformer? t) (apply-rename-transformer t id ctx))
-                                       (syntax-track-origin (transfer-srcloc
-                                                             (rename-transformer-target-in-context t ctx)
-                                                             id)
-                                                            id
-                                                            id))
                    #:skip-log? (or (expand-context-only-immediate? ctx)
                                    (rename-transformer? t))
                    #:fail-non-transformer (and (rename-transformer? t) fail-non-transformer))])]))
@@ -485,6 +480,17 @@
 
 ;; ----------------------------------------
 
+;; "Apply" a rename transformer, replacing it with its target.
+(define (apply-rename-transformer t id ctx)
+  (define target-id (rename-transformer-target-in-context t ctx))
+  ;; Adding a macro-introduction scope doesn't affect scoping at all, but it can affect
+  ;; whether the result is `syntax-original?`
+  (define intro-scope (new-scope 'macro))
+  (define intro-id (add-scope target-id intro-scope))
+  (syntax-track-origin (transfer-srcloc intro-id id) id id))
+
+;; ----------------------------------------
+
 ;; Helper to lookup a binding in an expansion context
 (define (lookup b ctx id
                 #:in [in-s #f]

racket/src/racket/src/startup.inc

@@ -43558,12 +43558,7 @@ static const char *startup_source =
 "((re-ctx195_0) re-ctx_0)"
 "((temp196_0)"
 "(if(1/rename-transformer? t_0)"
-"(syntax-track-origin$1"
+"(apply-rename-transformer t_0 id_0 ctx_0)"
-"(transfer-srcloc"
-"(rename-transformer-target-in-context t_0 ctx_0)"
-" id_0)"
-" id_0"
-" id_0)"
 " #f))"
 "((temp197_0)"
 "(let-values(((or-part_0)(expand-context-only-immediate? ctx_0)))"
@@ -43826,6 +43821,14 @@ static const char *startup_source =
 "(expand-context/outer-name the-struct_0)))"
 "              (raise-argument-error 'struct-copy \"expand-context/outer?\" the-struct_0))))))))"
 "(define-values"
+"(apply-rename-transformer)"
+"(lambda(t_0 id_0 ctx_0)"
+"(begin"
+"(let-values(((target-id_0)(rename-transformer-target-in-context t_0 ctx_0)))"
+"(let-values(((intro-scope_0)(new-scope 'macro)))"
+"(let-values(((intro-id_0)(add-scope target-id_0 intro-scope_0)))"
+"(syntax-track-origin$1(transfer-srcloc intro-id_0 id_0) id_0 id_0)))))))"
+"(define-values"
 "(lookup62.1)"
 "(lambda(in55_0 out-of-context-as-variable?56_0 b59_0 ctx60_0 id61_0)"
 "(begin"