[PATCH] POSIXBUILTINS: quieten 'unset -f nonexistentfunc'

[Martijn Dekker <martijn@xxxxxxxx>]

Doing 'unset -f' on an unset function outputs an error message and
causes an unsuccessful exit status. All other shells quietly ignore it.
POSIX specifies for 'unset' that "Unsetting a variable or function that
was not previously set shall not be considered an error [...]".
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_29_03

If I have figured this out correctly, then the attached patch causes
'unset -f nonexistent_function' to be quiet and return status 0 if
POSIXBUILTINS is active, without changing the behaviour of 'unfunction'
and 'unhash -f'.

- Martijn

diff --git a/Src/builtin.c b/Src/builtin.c
index 84a2bee..0ff9e4f 100644
--- a/Src/builtin.c
+++ b/Src/builtin.c
@@ -125,7 +125,7 @@ static struct builtin builtins[] =
     BUILTIN("unalias", 0, bin_unhash, 0, -1, BIN_UNALIAS, "ams", NULL),
     BUILTIN("unfunction", 0, bin_unhash, 1, -1, BIN_UNFUNCTION, "m", "f"),
     BUILTIN("unhash", 0, bin_unhash, 1, -1, BIN_UNHASH, "adfms", NULL),
-    BUILTIN("unset", BINF_PSPECIAL, bin_unset, 1, -1, 0, "fmv", NULL),
+    BUILTIN("unset", BINF_PSPECIAL, bin_unset, 1, -1, BIN_UNSET, "fmv", NULL),
     BUILTIN("unsetopt", 0, bin_setopt, 0, -1, BIN_UNSETOPT, NULL, NULL),
     BUILTIN("wait", 0, bin_fg, 0, -1, BIN_WAIT, NULL, NULL),
     BUILTIN("whence", 0, bin_whence, 0, -1, 0, "acmpvfsSwx:", NULL),
@@ -4158,6 +4158,10 @@ bin_unhash(char *name, char **argv, Options ops, int func)
     for (; *argv; argv++) {
 	if ((hn = ht->removenode(ht, *argv))) {
 	    ht->freenode(hn);
+	} else if (func == BIN_UNSET && isset(POSIXBUILTINS)) {
+	    /* POSIX: unset: "Unsetting a variable or function that was *
+	     * not previously set shall not be considered an error."    */
+	    returnval = 0;
 	} else {
 	    zwarnnam(name, "no such hash table element: %s", *argv);
 	    returnval = 1;
diff --git a/Src/hashtable.h b/Src/hashtable.h
index 3606e97..21398e1 100644
--- a/Src/hashtable.h
+++ b/Src/hashtable.h
@@ -62,6 +62,7 @@
 #define BIN_UNHASH   28
 #define BIN_UNALIAS  29
 #define BIN_UNFUNCTION  30
+#define BIN_UNSET    31
 
 /* These currently depend on being 0 and 1. */
 #define BIN_SETOPT    0