guix: Properly compute progress bar width.

* guix/progress.scm (progress-reporter/bar): Take font width into account to
compute progress bar width.
* guix/git.scm (show-progress): Take font width into account to compute
progress bar width.

Change-Id: I946e447c1ea7c6eb4ff805400280f39e8f1a7c02

guix/git.scm

@@ -33,6 +33,8 @@
   #:use-module (guix store)
   #:use-module (guix utils)
   #:use-module (guix records)
+  #:use-module ((guix build syscalls)
+                #:select (terminal-string-width))
   #:use-module (guix gexp)
   #:autoload   (guix git-download)
   (git-reference-url git-reference-commit git-reference-recursive?)
@@ -154,7 +156,7 @@ the 'SSL_CERT_FILE' and 'SSL_CERT_DIR' environment variables."
   ;; TODO: Both should be handled & exposed by the PROGRESS-BAR API instead.
   (define width
     (max (- (current-terminal-columns)
-            (string-length label) 7)
+            (terminal-string-width label) 7)
          3))
 
   (define grain

guix/progress.scm

@@ -21,6 +21,8 @@
 
 (define-module (guix progress)
   #:use-module (guix records)
+  #:use-module ((guix build syscalls)
+                #:select (terminal-string-width))
   #:use-module (srfi srfi-19)
   #:use-module (rnrs io ports)
   #:use-module (rnrs bytevectors)
@@ -307,7 +309,7 @@ tasks is performed.  Write PREFIX at the beginning of the line."
       (if (string-null? prefix)
           (display (progress-bar ratio (current-terminal-columns)) port)
           (let ((width (- (current-terminal-columns)
-                          (string-length prefix) 3)))
+                          (terminal-string-width prefix) 3)))
             (display prefix port)
             (display "  " port)
             (display (progress-bar ratio width) port)))