[bug#27566] [PATCH] ui: spinner-port: New variable. Export it.

[Danny Milosavljevic <dannym@scratchpost.org>]

* guix/ui.scm (spinner-port): New variable.  Export it.
---
 guix/ui.scm | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/guix/ui.scm b/guix/ui.scm
index 4bad00e8c..0930ed2b7 100644
--- a/guix/ui.scm
+++ b/guix/ui.scm
@@ -102,7 +102,8 @@
             guix-warning-port
             warning
             info
-            guix-main))
+            guix-main
+            spinner-port))
 
 ;;; Commentary:
 ;;;
@@ -110,6 +111,26 @@
 ;;;
 ;;; Code:
 
+(define spinner-port
+  (let ((index 0)
+        (spinner-chars "|\\-/"))
+    (define previous-output-port (current-error-port))
+    (define (spin)
+      (set! index (+ index 1))
+      (if (>= index (string-length spinner-chars))
+        (set! index 0))
+      (display (array-ref spinner-chars index) previous-output-port)
+      (display #\backspace previous-output-port)
+      (force-output previous-output-port))
+    (make-soft-port
+           (vector
+            (lambda (c) (if (char=? c #\newline) (spin))) ; putc
+            (lambda (s) (if (string-contains s "\n") (spin))) ; puts
+            (lambda () #t) ; flusher
+            (lambda () #f) ; getc
+            (lambda () #t)) ; close
+           "w")))
+
 (define %gettext-domain
   ;; Text domain for strings used in the tools.
   "guix")