Add chmod builtin

[Matthew Martin <phy1729@xxxxxxxxx>]

Previously in #zsh "so sad that there is no zf_chmod". So here we are.

Since AT_SYMLINK_NOFOLLOW isn't implemented for some fchmodat
implementations (and modifying the mode of a symlink is usually
nonsensical), drop the -h that chgrp/chown support.

I realize Doc/Zsh/mod_files.yo uses behaviour while _chmod uses
behavior. I just matched the zf_chown docs and _chown.

- Matthew Martin

diff --git a/Completion/Unix/Command/_chmod b/Completion/Unix/Command/_chmod
index af64b9eb9..7a9769fd0 100644
--- a/Completion/Unix/Command/_chmod
+++ b/Completion/Unix/Command/_chmod
@@ -1,11 +1,19 @@
-#compdef chmod gchmod
+#compdef chmod gchmod zf_chmod

 local curcontext="$curcontext" state line expl ret=1
 local -a args privs

 args=( '*: :->files' '1: :_file_modes' )

-if _pick_variant gnu=Free\ Soft unix --version; then
+if zmodload -e zsh/files && [[ $words[1] != */* ]]; then
+  # Assign, not append because zf_chmod only supports octal modes.
+  args=(
+    '-R[change files and directories recursively]' \
+    '-s[enable paranoid behavior]' \
+    '1:octal mode:' \
+    '*: :->files'
+  )
+elif _pick_variant gnu=Free\ Soft unix --version; then
   args+=(
     '(-v --verbose -c --changes)'{-c,--changes}'[report changes made]'
     '(-v --verbose -c --changes)'{-v,--verbose}'[output a diagnostic
for every file processed]'
diff --git a/Doc/Zsh/mod_files.yo b/Doc/Zsh/mod_files.yo
index 90e988474..3cf7b61e3 100644
--- a/Doc/Zsh/mod_files.yo
+++ b/Doc/Zsh/mod_files.yo
@@ -23,6 +23,26 @@ item(tt(chgrp) [ tt(-hRs) ] var(group) var(filename) ...)(
 Changes group of files specified.  This is equivalent to tt(chown) with
 a var(user-spec) argument of `tt(:)var(group)'.
 )
+findex(chmod)
+item(tt(chmod) [ tt(-Rs) ] var(mode) var(filename) ...)(
+Changes mode of files specified.
+
+The specified var(mode) must be in octal.
+
+The tt(-R) option causes tt(chmod) to recursively descend into directories,
+changing the mode of all files in the directory after
+changing the mode of the directory itself.
+
+The tt(-s) option is a zsh extension to tt(chmod) functionality.  It enables
+paranoid behaviour, intended to avoid security problems involving
+a tt(chmod) being tricked into affecting files other than the ones
+intended.  It will refuse to follow symbolic links, so that (for example)
+``tt(chmod 600 /tmp/foo/passwd)'' can't accidentally chmod tt(/etc/passwd)
+if tt(/tmp/foo) happens to be a link to tt(/etc).  It will also check
+where it is after leaving directories, so that a recursive chmod of
+a deep directory tree can't end up recursively chmoding tt(/usr) as
+a result of directories being moved up the tree.
+)
 findex(chown)
 item(tt(chown) [ tt(-hRs) ] var(user-spec) var(filename) ...)(
 Changes ownership and group of files specified.
diff --git a/Src/Modules/files.c b/Src/Modules/files.c
index 6f816bac0..85764d55e 100644
--- a/Src/Modules/files.c
+++ b/Src/Modules/files.c
@@ -619,6 +619,45 @@ bin_rm(char *nam, char **args, Options ops,
UNUSED(int func))
     return OPT_ISSET(ops,'f') ? 0 : err;
 }

+/* chmod builtin */
+
+struct chmodmagic {
+    char *nam;
+    mode_t mode;
+};
+
+/**/
+static int
+chmod_dochmod(char *arg, char *rp, UNUSED(struct stat const *sp), void *magic)
+{
+    struct chmodmagic *chm = magic;
+
+    if(chmod(rp, chm->mode)) {
+ zwarnnam(chm->nam, "%s: %e", arg, errno);
+ return 1;
+    }
+    return 0;
+}
+
+/**/
+static int
+bin_chmod(char *nam, char **args, Options ops, int func)
+{
+    struct chmodmagic chm;
+    char *str = args[0], *ptr;
+
+    chm.nam = nam;
+
+    chm.mode = zstrtol(str, &ptr, 8);
+    if(!*str || *ptr) {
+ zwarnnam(nam, "invalid mode `%s'", str);
+ return 1;
+    }
+
+    return recursivecmd(nam, 0, OPT_ISSET(ops,'R'), OPT_ISSET(ops,'s'),
+ args + 1, chmod_dochmod, recurse_donothing, chmod_dochmod, &chm);
+}
+
 /* chown builtin */

 struct chownmagic {
@@ -754,6 +793,7 @@ static struct builtin bintab[] = {
     /* The names which overlap commands without necessarily being
      * fully compatible. */
     BUILTIN("chgrp", 0, bin_chown, 2, -1, BIN_CHGRP, "hRs",    NULL),
+    BUILTIN("chmod", 0, bin_chmod, 2, -1, 0,         "Rs",    NULL),
     BUILTIN("chown", 0, bin_chown, 2, -1, BIN_CHOWN, "hRs",    NULL),
     BUILTIN("ln",    0, bin_ln,    1, -1, BIN_LN,    LN_OPTS, NULL),
     BUILTIN("mkdir", 0, bin_mkdir, 1, -1, 0,         "pm:",   NULL),
@@ -763,6 +803,7 @@ static struct builtin bintab[] = {
     BUILTIN("sync",  0, bin_sync,  0,  0, 0,         NULL,    NULL),
     /* The "safe" zsh-only names */
     BUILTIN("zf_chgrp", 0, bin_chown, 2, -1, BIN_CHGRP, "hRs",    NULL),
+    BUILTIN("zf_chmod", 0, bin_chmod, 2, -1, 0,         "Rs",    NULL),
     BUILTIN("zf_chown", 0, bin_chown, 2, -1, BIN_CHOWN, "hRs",    NULL),
     BUILTIN("zf_ln",    0, bin_ln,    1, -1, BIN_LN,    LN_OPTS, NULL),
     BUILTIN("zf_mkdir", 0, bin_mkdir, 1, -1, 0,         "pm:",   NULL),