Fix two more 'command' bugs

BUG 1: Though 'command' is specified/documented as a regular
builtin, preceding assignments survive the invocation (as with
special or declaration builtins) if 'command' has no command
arguments in these cases:

$ foo=wrong1 command; echo $foo
wrong1
$ foo=wrong2 command -p; echo $foo
wrong2
$ foo=wrong3 command -x; echo $foo
wrong3

Analysis: sh_exec(), case TCOM (simple command), contains the
following loop that skips over 'command' prefixes, preparsing any
options and remembering the offset in the 'command' variable:

src/cmd/ksh93/sh/xec.c
1059 while(np==SYSCOMMAND || !np && com0
     && nv_search(com0,shp->fun_tree,0)==SYSCOMMAND)
1060 {
1061         register int n = b_command(0,com,&shp->bltindata);
1062         if(n==0)
1063                 break;
1064         command += n;
1065         np = 0;
1066         if(!(com0= *(com+=n)))
1067                 break;
1068         np = nv_bfsearch(com0, shp->bltin_tree, &nq, &cp);
1069 }

This skipping is not done if the preliminary b_command() call on
line 1061 (with argc==0) returns zero. This is currently the case
for command -v/-V, so that 'command' is treated as a plain and
regular builtin for those options.

The cause of the bug is that this skipping is even done if
'command' has no arguments. So something like 'foo=bar command' is
treated as simply 'foo=bar', which of course survives.

So the fix is for b_command() to return zero if there are no
arguments. Then b_command() itself needs changing to not error out
on the second/main b_command() call if there are no arguments.

src/cmd/ksh93/bltins/whence.c: b_command():
- When called with argc==0, return a zero offset not just for -v
  (X_FLAG) or -V (V_FLAG), but also if there are no arguments left
  (!*argv) after parsing options.
- When called with argc>0, do not issue a usage error if there are
  no arguments, but instead return status 0 (or, if -v/-V was given,
  status 2 which was the status of the previous usage message).
  This way, 'command -v $emptyvar' now also works as you'd expect.

BUG 2: 'command -p' sometimes failed after executing certain loops.

src/cmd/ksh93/sh/path.c: defpath_init():
- astconf() returns a pointer to memory that may be overwritten
  later, so duplicate the string returned. Backported from ksh2020.
  (re: f485fe0f, aa4669ad, <https://github.com/att/ast/issues/959>)

src/cmd/ksh93/tests/builtins.sh:
- Update the test for BUG_CMDSPASGN to check every variant of
  'command' (all options and none; invoking/querying all kinds of
  command and none) with a preceding assignment. (re: fae8862c)
  This also covers bug 2 as 'command -p' was failing on macOS prior
  to the fix due to a loop executed earlier in another test.

NEWS

@@ -3,6 +3,15 @@ For full details, see the git log at: https://github.com/ksh93/ksh
 
 Any uppercase BUG_* names are modernish shell bug IDs.
 
+2021-05-05:
+
+- Fixed: a preceding variable assignment like foo=bar in 'foo=bar command'
+  (with no command arguments after 'command') incorrectly survived the
+  'command' regular built-in command invocation.
+
+- Fixed: 'command -p some_utility' intermittently failed to find the utility
+  under certain conditions due to a memory corruption issue.
+
 2021-05-03:
 
 - Subshells (even if non-forked) now keep a properly separated state of the

src/cmd/ksh93/bltins/whence.c

@@ -85,20 +85,22 @@ int	b_command(register int argc,char *argv[],Shbltin_t *context)
 		errormsg(SH_DICT,ERROR_usage(2), "%s", opt_info.arg);
 		UNREACHABLE();
 	}
+	argv += opt_info.index;
 	if(argc==0)
 	{
-		if(flags & (X_FLAG|V_FLAG))
-			return(0);	/* return no offset now; sh_exec() will treat command -v/-V as normal builtin */
+		if((flags & (X_FLAG|V_FLAG)) || !*argv)
+			return(0);	/* return no offset now; sh_exec() will treat command -v/-V/(null) as normal builtin */
 		if(flags & P_FLAG)
 			sh_onstate(SH_XARG);
 		return(opt_info.index); /* offset for sh_exec() to remove 'command' prefix + options */
 	}
-	argv += opt_info.index;
-	if(error_info.errors || !*argv)
+	if(error_info.errors)
 	{
 		errormsg(SH_DICT,ERROR_usage(2),"%s", optusage((char*)0));
 		UNREACHABLE();
 	}
+	if(!*argv)
+		return((flags & (X_FLAG|V_FLAG)) != 0 ? 2 : 0);
 	return(whence(shp,argv, flags));
 }
 

src/cmd/ksh93/include/version.h

@@ -21,7 +21,7 @@
 
 #define SH_RELEASE_FORK	"93u+m"		/* only change if you develop a new ksh93 fork */
 #define SH_RELEASE_SVER	"1.0.0-alpha"	/* semantic version number: https://semver.org */
-#define SH_RELEASE_DATE	"2021-05-03"	/* must be in this format for $((.sh.version)) */
+#define SH_RELEASE_DATE	"2021-05-05"	/* must be in this format for $((.sh.version)) */
 #define SH_RELEASE_CPYR	"(c) 2020-2021 Contributors to ksh " SH_RELEASE_FORK
 
 /* Scripts sometimes field-split ${.sh.version}, so don't change amount of whitespace. */

src/cmd/ksh93/sh/path.c

@@ -431,8 +431,12 @@ Pathcomp_t *path_nextcomp(Shell_t *shp,register Pathcomp_t *pp, const char *name
 
 static Pathcomp_t* defpath_init(Shell_t *shp)
 {
-	if(!std_path && !(std_path=astconf("PATH",NIL(char*),NIL(char*))))
-		abort();
+	if(!std_path)
+	{
+		if(!(std_path = astconf("PATH",NIL(char*),NIL(char*))))
+			abort();
+		std_path = sh_strdup(std_path);	/* the value returned by astconf() is short-lived */
+	}
 	Pathcomp_t *pp = (void*)path_addpath(shp,(Pathcomp_t*)0,(std_path),PATH_PATH);
 	return(pp);
 }

src/cmd/ksh93/tests/builtins.sh

@@ -768,8 +768,24 @@ printf '\\\000' | read -r -d ''
 
 # ======
 # BUG_CMDSPASGN: Preceding a special builtin with 'command' should disable its special properties.
-foo=BUG command eval ':'
-[[ $foo == BUG ]] && err_exit "'command' fails to disable the special properties of special builtins"
+# Test that assignments preceding 'command' are local.
+command -p ls
+for arg in '' -v -V -p -x
+do
+	for cmd in '' : true ls eval 'eval :' 'eval true' 'eval ls'
+	do
+		[[ $arg == -x ]] && ! command -xv "${cmd% *}" >/dev/null && continue
+		unset foo
+		eval "foo=BUG command $arg $cmd" >/dev/null 2>&1
+		got=$?
+		case $arg,$cmd in
+		-v, | -V, )	exp=2 ;;
+		*)		exp=0 ;;
+		esac
+		[[ $got == "$exp" ]] || err_exit "exit status of 'command $arg $cmd' is $got, expected $exp"
+		[[ -v foo ]] && err_exit "preceding assignment survives 'command $arg $cmd'"
+	done
+done
 
 # Regression that occurred after fixing the bug above: the += operator didn't work correctly.
 # https://www.mail-archive.com/ast-users@lists.research.att.com/msg00369.html