utils: Add 'readlink*'.

* guix/scripts/package.scm (readlink*): Move to...
* guix/utils.scm (readlink*): ... here.  New procedure.

1 files changed, 28 insertions, 0 deletions

diff --git a/guix/utils.scm b/guix/utils.scm
index 190b787185..f1317ac756 100644
--- a/guix/utils.scm
+++ b/guix/utils.scm
@@ -82,6 +82,7 @@
             fold-tree-leaves
             split
             cache-directory
+            readlink*
 
             filtered-port
             compressed-port
@@ -710,6 +711,33 @@ elements after E."
       (and=> (getenv "HOME")
              (cut string-append <> "/.cache/guix"))))
 
+(define (readlink* file)
+  "Call 'readlink' until the result is not a symlink."
+  (define %max-symlink-depth 50)
+
+  (let loop ((file  file)
+             (depth 0))
+    (define (absolute target)
+      (if (absolute-file-name? target)
+          target
+          (string-append (dirname file) "/" target)))
+
+    (if (>= depth %max-symlink-depth)
+        file
+        (call-with-values
+            (lambda ()
+              (catch 'system-error
+                (lambda ()
+                  (values #t (readlink file)))
+                (lambda args
+                  (let ((errno (system-error-errno args)))
+                    (if (or (= errno EINVAL))
+                        (values #f file)
+                        (apply throw args))))))
+          (lambda (success? target)
+            (if success?
+                (loop (absolute target) (+ depth 1))
+                file))))))
 
 ;;;
 ;;; Source location.