chmod: ugo perms sees effects from same clause.

This is Coreutils chmod behavior.

* sysif.c (chmod_wrap): Sample cmode into oldm at the start of
every assigment before punching the masked hole into cmode.

* tests/018/chmod.tl: Breaking test case added.

2 files changed, 2 insertions, 0 deletions

diff --git a/sysif.c b/sysif.c
index 444f8326..638f9642 100644
--- a/sysif.c
+++ b/sysif.c
@@ -673,6 +673,7 @@ static val chmod_wrap(val target, val mode)
           case chm_sub: cmode &= ~bits; break;
           case chm_set:
             if (cs == chm_perm) {
+              oldm = cmode;
               cmode &= ~mask;
               if (implicit_all || (who & CHM_O) != 0)
                 cmode &= ~S_ISVTX; /* GNU Coreutils 8.28 chmod behavior */
diff --git a/tests/018/chmod.tl b/tests/018/chmod.tl
index 93739c48..8cde28eb 100644
--- a/tests/018/chmod.tl
+++ b/tests/018/chmod.tl
@@ -46,3 +46,4 @@
 (cht "-----x------" "=,a+X"             "------------")
 (cht "-----x------" "a-x+X"             "------------")
 (cht "------------" "u+x-X"             "------------")
+(cht "------------" "o+x=o"             "-----------x")