From 5709ca0cbd3eb9a5d03df3a4b32cd9b01fae4db1 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Mon, 15 Dec 2025 17:05:32 +0000
Subject: [PATCH 1/3] Initial plan


From 3cc4a3daf67d61a58e1b9fcbe291afdb034a6eb8 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Mon, 15 Dec 2025 17:26:41 +0000
Subject: [PATCH 2/3] Add flatten-apply-append-syntax-template refactoring rule

Co-authored-by: jackfirth <8175575+jackfirth@users.noreply.github.com>
---
 .../syntax-shortcuts-test.rkt                 | 15 +++++++++++++
 default-recommendations/syntax-shortcuts.rkt  | 22 ++++++++++++++++++-
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/default-recommendations/syntax-shortcuts-test.rkt b/default-recommendations/syntax-shortcuts-test.rkt
index 147ffdd3..3cc1ced9 100644
--- a/default-recommendations/syntax-shortcuts-test.rkt
+++ b/default-recommendations/syntax-shortcuts-test.rkt
@@ -53,3 +53,18 @@ test: "making a symbol with format from a keyword can be simplified to format-sy
 test: "making a symbol with format from a keyword syntax object can be simplified to format-symbol"
 - (string->symbol (format "make-~a" (keyword->string (syntax-e #'#:foo))))
 - (format-symbol "make-~a" #'#:foo)
+
+
+test: "flattening nested syntax templates with apply append can be simplified"
+--------------------
+(require racket/syntax)
+(define (f stx)
+  (with-syntax ([((a ...) ...) stx])
+    (apply append
+           (map syntax->list (syntax->list #'((a ...) ...))))))
+====================
+(require racket/syntax)
+(define (f stx)
+  (with-syntax ([((a ...) ...) stx])
+    (syntax->list (syntax (a ... ...)))))
+--------------------
diff --git a/default-recommendations/syntax-shortcuts.rkt b/default-recommendations/syntax-shortcuts.rkt
index 2ff8ce1e..21d118e2 100644
--- a/default-recommendations/syntax-shortcuts.rkt
+++ b/default-recommendations/syntax-shortcuts.rkt
@@ -11,6 +11,7 @@
 
 (require racket/string
          racket/syntax
+         racket/list
          rebellion/private/static-name
          resyntax/base
          syntax/parse)
@@ -103,6 +104,25 @@
   (format-symbol template (~replacement arg.simplified #:original arg) ...))
 
 
+(define-refactoring-rule flatten-apply-append-syntax-template
+  #:description
+  "Flattening nested syntax templates with `apply append` and `map syntax->list` can be simplified\
+ by using a single `syntax->list` call on a flattened template."
+  #:literals (apply append map syntax->list syntax ...)
+
+  (apply append (map syntax->list (syntax->list (syntax ((inner ...) ...)))))
+
+  #:with flattened-template
+  (let* ([inner-attrs (attribute inner)]
+         ; Wrap in list if it's not already a list
+         [inner-list (if (list? inner-attrs) inner-attrs (list inner-attrs))]
+         [ellipsis-sym (datum->syntax #'here '...)])
+    (datum->syntax #'here (append inner-list (list ellipsis-sym ellipsis-sym))))
+  
+  (syntax->list #'flattened-template))
+
+
 (define-refactoring-suite syntax-shortcuts
-  #:rules (format-string-to-format-symbol
+  #:rules (flatten-apply-append-syntax-template
+           format-string-to-format-symbol
            syntax-e-in-format-id-unnecessary))

From 8dfbc9a94b9e45fe5277bf850064d4b99630e405 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Mon, 15 Dec 2025 17:31:46 +0000
Subject: [PATCH 3/3] Improve code clarity in
 flatten-apply-append-syntax-template rule

Co-authored-by: jackfirth <8175575+jackfirth@users.noreply.github.com>
---
 default-recommendations/syntax-shortcuts.rkt | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/default-recommendations/syntax-shortcuts.rkt b/default-recommendations/syntax-shortcuts.rkt
index 21d118e2..7b4e29a5 100644
--- a/default-recommendations/syntax-shortcuts.rkt
+++ b/default-recommendations/syntax-shortcuts.rkt
@@ -114,10 +114,13 @@
 
   #:with flattened-template
   (let* ([inner-attrs (attribute inner)]
-         ; Wrap in list if it's not already a list
+         ; When matching ((inner ...) ...), the inner attribute contains the elements from
+         ; within each nested list. If there's only one element, inner-attrs will be a single
+         ; syntax object, otherwise it's a list. We need a list for appending the ellipses.
          [inner-list (if (list? inner-attrs) inner-attrs (list inner-attrs))]
          [ellipsis-sym (datum->syntax #'here '...)])
-    (datum->syntax #'here (append inner-list (list ellipsis-sym ellipsis-sym))))
+    ; Construct (inner-elements ... ...) by appending two ellipsis symbols
+    (datum->syntax #'here (append inner-list (make-list 2 ellipsis-sym))))
   
   (syntax->list #'flattened-template))