Fix recently-introduced expand-file-name bug

The bug was that (expand-file-name "~") returned something
like "/home/eggert/" instead of "/home/eggert".
Problem	reported by Mattias Engdegård (Bug#26911#27).
* src/fileio.c (Fexpand_file_name): When concatenating NEWDIR to
NM, instead of stripping trailing slashes from NEWDIR (which can
turn non-symlinks into symlinks), strip leading slashes from NM.
This also simplifies the code by removing no-longer-needed DOS_NT
special-casing.  Also, remove an unnecessary ‘target[length] = 0;’
as that byte will be overwritten by the next memcpy anyway.
* test/src/fileio-tests.el (fileio-tests--HOME-trailing-slash):
New test.

1 files changed, 8 insertions, 0 deletions

diff --git a/test/src/fileio-tests.el b/test/src/fileio-tests.el
index 1516590795e..8b76912f5e1 100644
--- a/test/src/fileio-tests.el
+++ b/test/src/fileio-tests.el
@@ -108,6 +108,14 @@ Also check that an encoding error can appear in a symlink."
       (should (equal (expand-file-name "~/bar") "x:/foo/bar")))
     (setenv "HOME" old-home)))
 
+(ert-deftest fileio-tests--HOME-trailing-slash ()
+  "Test that expand-file-name of \"~\" respects trailing slash."
+  (let ((old-home (getenv "HOME")))
+    (dolist (home '("/a/b/c" "/a/b/c/"))
+      (setenv "HOME" home)
+      (should (equal (expand-file-name "~") (expand-file-name home))))
+    (setenv "HOME" old-home)))
+
 (ert-deftest fileio-tests--expand-file-name-trailing-slash ()
   (dolist (fooslashalias '("foo/" "foo//" "foo/." "foo//." "foo///././."
                            "foo/a/.."))