Work around SLY / rainbow-delimiter clash.

.emacs.d/lisp/init-sly.el

@@ -192,6 +192,7 @@ Good substitute for `sly-mrepl-indent-and-complete-symbol'."
 (setq sly-command-switch-to-existing-lisp 'always)
 (add-hook 'sly-mrepl-hook #'ambrevar/init-lispy)
 (add-hook 'sly-mrepl-hook #'rainbow-delimiters-mode)
+(require 'patch-sly-rainbow)
 
 ;; #p completion.  See https://github.com/joaotavora/sly/issues/405.
 (with-eval-after-load 'company
@@ -324,10 +325,7 @@ returns a string."
    (propertize "> " 'font-lock-face 'sly-mrepl-prompt-face)))
 
 (with-eval-after-load 'sly-mrepl
-  (if (boundp 'sly-mrepl-prompt-formatter)
-      (setq sly-mrepl-prompt-formatter
-            #'ambrevar/sly-new-prompt)
-    (advice-add 'sly-mrepl--insert-prompt :around #'ambrevar/sly-prepare-prompt)))
+  (setq sly-mrepl-prompt-formatter #'ambrevar/sly-new-prompt))
 
 (defun ambrevar/sly-end-of-prompt-p ()
   (and (not (= (point) (point-min)))

.emacs.d/lisp/patch-sly-rainbow.el

@@ -0,0 +1,19 @@
+;; Workaround for https://github.com/joaotavora/sly/issues/452.
+(defun ambrevar/disable-rainbow-delimiters (_orig &rest args)
+  "`rainbow-delimiters-mode' interferes with `ffap' (and thus Helm) in SLY mrepl.
+Example:
+
+> (princ \"/home\")
+/home
+\"/home\"
+
+Running `ffap' on the first /home would not work as expected."
+  (rainbow-delimiters-mode -1))
+(advice-add 'sly-mrepl-return :before 'ambrevar/disable-rainbow-delimiters)
+
+(defun ambrevar/enable-rainbow-delimiters (_orig &rest args)
+  "See `ambrevar/disable-rainbow-delimiters'."
+  (rainbow-delimiters-mode 1))
+(advice-add 'sly-mrepl--insert-prompt :before 'ambrevar/enable-rainbow-delimiters)
+
+(provide 'patch-sly-rainbow)