Fix regression in expand-file-name with drive-relative HOME

* src/fileio.c (get_homedir) [DOS_NT]: Expand drive-relative
$HOME to begin with "X:/".

* test/src/fileio-tests.el (fileio-tests--relative-HOME): Add
testing of drive-relative value of $HOME on MS-Windows and
MS-DOS.

1 files changed, 4 insertions, 0 deletions

diff --git a/test/src/fileio-tests.el b/test/src/fileio-tests.el
index b7b78bbda09..a74bcea41f2 100644
--- a/test/src/fileio-tests.el
+++ b/test/src/fileio-tests.el
@@ -102,4 +102,8 @@ Also check that an encoding error can appear in a symlink."
     (setenv "HOME" "a/b/c")
     (should (equal (expand-file-name "~/foo")
                    (expand-file-name "a/b/c/foo")))
+    (when (memq system-type '(ms-dos windows-nt))
+      ;; Test expansion of drive-relative file names.
+      (setenv "HOME" "x:foo")
+      (should (equal (expand-file-name "~/bar") "x:/foo/bar")))
     (setenv "HOME" old-home)))