[bug#65546] [PATCH] guix: Properly compute progress bar width.

[Julien Lepiller <julien@lepiller.eu>]

* guix/progress.scm (terminal-width): New procedure.
(progress-reporter/bar): Use it to compute progress bar width.
* guix/git.scm (show-progress): Use it to compute progress bar width.
---
 guix/git.scm      |  2 +-
 guix/progress.scm | 26 +++++++++++++++++++++++++-
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/guix/git.scm b/guix/git.scm
index dbc3b7caa7..870045cddf 100644
--- a/guix/git.scm
+++ b/guix/git.scm
@@ -153,7 +153,7 @@ (define %
   ;; TODO: Both should be handled & exposed by the PROGRESS-BAR API instead.
   (define width
     (max (- (current-terminal-columns)
-            (string-length label) 7)
+            (terminal-width label) 7)
          3))
 
   (define grain
diff --git a/guix/progress.scm b/guix/progress.scm
index 33cf6f4a1a..8a84bcd1b0 100644
--- a/guix/progress.scm
+++ b/guix/progress.scm
@@ -24,6 +24,7 @@ (define-module (guix progress)
   #:use-module (srfi srfi-19)
   #:use-module (rnrs io ports)
   #:use-module (rnrs bytevectors)
+  #:use-module (system foreign)
   #:use-module (ice-9 format)
   #:use-module (ice-9 match)
   #:export (<progress-reporter>
@@ -47,6 +48,7 @@ (define-module (guix progress)
             progress-bar
             byte-count->string
             current-terminal-columns
+            terminal-width
 
             dump-port*))
 
@@ -166,6 +168,28 @@ (define current-terminal-columns
   ;; Number of columns of the terminal.
   (make-parameter 80))
 
+(define (terminal-width str)
+  "Return the width of a string as it would be printed on the terminal.  This
+procedure accounts for characters that have a different width than 1, such as
+CJK double-width characters."
+  (define get-wchar-ffi
+    (pointer->procedure int
+                        (dynamic-func "mbstowcs" (dynamic-link))
+                        (list '* '* size_t)))
+  (define terminal-width-ffi
+    (pointer->procedure int
+                        (dynamic-func "wcswidth" (dynamic-link))
+                        (list '* size_t)))
+  (define (get-wchar str)
+    (let ((wchar (make-bytevector (* (+ (string-length str) 1) 4))))
+      (get-wchar-ffi (bytevector->pointer wchar)
+                     (string->pointer str)
+                     (string-length str))
+      wchar))
+  (terminal-width-ffi
+    (bytevector->pointer (get-wchar str))
+    (string-length str)))
+
 (define-record-type* <progress-bar-style>
   progress-bar-style make-progress-bar-style progress-bar-style?
   (start  progress-bar-style-start)
@@ -307,7 +331,7 @@ (define (draw-bar)
       (if (string-null? prefix)
           (display (progress-bar ratio (current-terminal-columns)) port)
           (let ((width (- (current-terminal-columns)
-                          (string-length prefix) 3)))
+                          (terminal-width prefix) 3)))
             (display prefix port)
             (display "  " port)
             (display (progress-bar ratio width) port)))
-- 
2.41.0