From 7af94a9171dc52b84a783a8d90f1fda296972798 Mon Sep 17 00:00:00 2001
From: Jack Firth <jackhfirth@gmail.com>
Date: Sun, 9 Mar 2025 04:43:45 -0700
Subject: [PATCH] Add `format-string-to-format-symbol` rule

---
 .../syntax-shortcuts-test.rkt                 | 25 +++++++
 default-recommendations/syntax-shortcuts.rkt  | 65 ++++++++++++++++++-
 2 files changed, 88 insertions(+), 2 deletions(-)

diff --git a/default-recommendations/syntax-shortcuts-test.rkt b/default-recommendations/syntax-shortcuts-test.rkt
index 577cad69..548b1824 100644
--- a/default-recommendations/syntax-shortcuts-test.rkt
+++ b/default-recommendations/syntax-shortcuts-test.rkt
@@ -28,3 +28,28 @@ test: "syntax-e on a single format-id argument is removable"
 
 test: "format-id call without any syntax-e unwrapped arguments not refactorable"
 - (format-id #'foo "~a.~a.~a" #'bar #'baz #'blah)
+
+
+test: "making a symbol with format can be simplified to format-symbol"
+- (string->symbol (format "make-~a" "foo"))
+- (format-symbol "make-~a" "foo")
+
+
+test: "making a symbol with format from a symbol can be simplified to format-symbol"
+- (string->symbol (format "make-~a" (symbol->string 'foo)))
+- (format-symbol "make-~a" 'foo)
+
+
+test: "making a symbol with format from an identifier can be simplified to format-symbol"
+- (string->symbol (format "make-~a" (symbol->string (syntax-e #'foo))))
+- (format-symbol "make-~a" #'foo)
+
+
+test: "making a symbol with format from a keyword can be simplified to format-symbol"
+- (string->symbol (format "make-~a" (keyword->string '#:foo)))
+- (format-symbol "make-~a" '#:foo)
+
+
+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)
diff --git a/default-recommendations/syntax-shortcuts.rkt b/default-recommendations/syntax-shortcuts.rkt
index 5c10d942..2ff8ce1e 100644
--- a/default-recommendations/syntax-shortcuts.rkt
+++ b/default-recommendations/syntax-shortcuts.rkt
@@ -9,7 +9,8 @@
   [syntax-shortcuts refactoring-suite?]))
 
 
-(require racket/syntax
+(require racket/string
+         racket/syntax
          rebellion/private/static-name
          resyntax/base
          syntax/parse)
@@ -43,5 +44,65 @@
   (format-id lctx fmt arg.simplified ...))
 
 
+(define-syntax-class format-symbol-argument
+  #:attributes (simplified)
+  #:literals (syntax-e keyword->string symbol->string)
+
+  (pattern (syntax-e inner:format-symbol-argument) #:attr simplified (attribute inner.simplified))
+
+  (pattern (keyword->string inner:format-symbol-argument)
+    #:attr simplified (attribute inner.simplified))
+
+  (pattern (symbol->string inner:format-symbol-argument)
+    #:attr simplified (attribute inner.simplified))
+
+  (pattern simplified:expr))
+
+
+;; The format-symbol function only allows ~a placeholders. Rather a fancy generic utilty that finds
+;; all placeholders, we just explicitly list out all the other ones and check one-by-one whether any
+;; of them are contained in the template string. That's easier to implement and the performance
+;; doesn't matter at all since template strings are almost always short.
+(define disallowed-format-symbol-placeholders
+  (list "~n"
+        "~%"
+        "~s"
+        "~S"
+        "~v"
+        "~V"
+        "~.a"
+        "~.A"
+        "~.s"
+        "~.S"
+        "~.v"
+        "~.V"
+        "~e"
+        "~E"
+        "~c"
+        "~C"
+        "~b"
+        "~B"
+        "~o"
+        "~O"
+        "~x"
+        "~X"
+        "~ "
+        "~\n"
+        "~\t"))
+
+
+(define-refactoring-rule format-string-to-format-symbol
+  #:description
+  "This `format` expression can be simplified to an equivalent `format-symbol` expression."
+  #:literals (format string->symbol)
+
+  (string->symbol (format template:str arg:format-symbol-argument ...))
+  #:when (for/and ([disallowed (in-list disallowed-format-symbol-placeholders)])
+           (not (string-contains? (syntax-e #'template) disallowed)))
+
+  (format-symbol template (~replacement arg.simplified #:original arg) ...))
+
+
 (define-refactoring-suite syntax-shortcuts
-  #:rules (syntax-e-in-format-id-unnecessary))
+  #:rules (format-string-to-format-symbol
+           syntax-e-in-format-id-unnecessary))