Don't allow 'enum' and 'typeset -T' to override special built-ins

Special builtins are undeleteable for a reason. But 'enum' and
'typeset -T' allow overriding them, causing an inconsistent state.

@JohnoKing writes:
| The behavior is rather buggy, as it appears to successfully
| override normal builtins but fails to delete the special
| builtins, leading to scenarios where both the original builtin
| and type are run:
|
| $ typeset -T eval=(typeset BAD; typeset TYPE)  # This should have failed
| $ eval foo=BAD
| /usr/bin/ksh: eval: line 1: foo: not found
| $ enum trap=(BAD TYPE)   # This also should have failed
| $ trap foo=BAD
| /usr/bin/ksh: trap: condition(s) required
| $ enum umask=(BAD TYPE)
| $ umask foo=BAD
| $ echo $foo
| BAD
|
| # Examples of general bugginess
| $ trap bar=TYPE
| /usr/bin/ksh: trap: condition(s) required
| $ echo $bar
| TYPE
| $ eval var=TYPE
| /usr/bin/ksh: eval: line 1: var: not found
| $ echo $var
| TYPE

This commit fixes the following:

The 'enum' and 'typeset -T' commands are no longer allowed to
override and replace special built-in commands, except for type
definition commands previously created by these commands; these
are already (dis)allowed elsewhere.

A command like 'typeset -T foo_t' without any assignments no longer
creates an incompletely defined 'foo_t' built-in comamnd. Instead,
it is now silently ignored for backwards compatibility. This did
have a regression test checking for it, but I'm changing it because
that's just not a valid use case. An incomplete type definition
command does nothing useful and only crashes the shell when run.

src/cmd/ksh93/bltins/enum.c: b_enum():
- Do not allow overriding non-type special built-ins.

src/cmd/ksh93/sh/name.c: nv_setlist():
- Do not allow 'typeset -T' to override non-type special built-ins.
  To avoid an inconsistent state, this must be checked for while
  processing the assignments list before typeset is really invoked.

src/cmd/ksh93/bltins_typeset.c: b_typeset():
- Only create a type command if sh.envlist is set, i.e., if some
  shell assignment(s) were passed to the 'typeset -T' command.

Progresses: https://github.com/ksh93/ksh/issues/350

NEWS

@@ -3,6 +3,17 @@ For full details, see the git log at: https://github.com/ksh93/ksh/tree/1.0
 
 Any uppercase BUG_* names are modernish shell bug IDs.
 
+2022-02-08:
+
+- To avoid an inconsistent state, the 'enum' and 'typeset -T' commands are
+  no longer allowed to replace special built-in commands. For instance,
+  'enum trap=(a b c)' is now an error because 'trap' is a special built-in.
+  The ability of 'typeset -T' to redefine a type is not affected.
+
+- A command like 'typeset -T foo_t' without any assignment no longer creates
+  an incompletely defined 'foo_t' built-in comamnd that will crash the shell
+  when used. Instead, it is now silently ignored for backwards compatibility.
+
 2022-02-05:
 
 - Fixed: for indexed arrays, given an unset array member a[i] with i > 0,

src/cmd/ksh93/COMPATIBILITY

@@ -168,6 +168,10 @@ For more details, see the NEWS file and for complete details, see the git log.
 	return value that fits in a signed integer, typically a 32-bit value.
 	Note that $? is truncated to 8 bits when the current (sub)shell exits.
 
+31.	The 'enum' and 'typeset -T' commands are no longer allowed to
+	override and replace special built-in commands, except for type
+	definition commands previously created by these commands.
+
 ____________________________________________________________________________
 
 		KSH-93 VS. KSH-88

src/cmd/ksh93/bltins/enum.c

@@ -88,6 +88,8 @@ static const char enum_type[] =
 "[+SEE ALSO?\benum\b(1), \btypeset\b(1)]"
 ;
 
+extern const char is_spcbuiltin[];
+
 struct Enum
 {
 	Namfun_t	hdr;
@@ -243,6 +245,13 @@ int b_enum(int argc, char** argv, Shbltin_t *context)
 #endif
 	while(cp = *argv++)
 	{
+		/* Do not allow 'enum' to override special built-ins -- however, exclude
+		 * previously created type commands from this search as that is handled elsewhere. */
+		if((tp=nv_search(cp,sh.bltin_tree,0)) && nv_isattr(tp,BLT_SPC) && !nv_search(cp,sh.typedict,0))
+		{
+			errormsg(SH_DICT,ERROR_exit(1),"%s:%s",cp,is_spcbuiltin);
+			UNREACHABLE();
+		}
 		if(!(np = nv_open(cp, (void*)0, NV_VARNAME|NV_NOADD))  || !(ap=nv_arrayptr(np)) || ap->fun || (sz=ap->nelem&(((1L<<ARRAY_BITS)-1))) < 2)
 		{
 			error(ERROR_exit(1), "%s must name an array containing at least two elements",cp);

src/cmd/ksh93/bltins/typeset.c

@@ -536,7 +536,7 @@ endargs:
 			errormsg(SH_DICT,ERROR_exit(1),"%s: unknown type",tdata.prefix);
 			UNREACHABLE();
 		}
-		else if(nv_isnull(tdata.tp))
+		else if(nv_isnull(tdata.tp) && sh.envlist)   /* only create a type command if there were assignment(s) */
 			nv_newtype(tdata.tp);
 		tdata.tp->nvenv = tdata.help;
 		flag &= ~NV_TYPE;

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-beta.2"	/* semantic version number: https://semver.org */
-#define SH_RELEASE_DATE	"2022-02-05"	/* must be in this format for $((.sh.version)) */
+#define SH_RELEASE_DATE	"2022-02-08"	/* must be in this format for $((.sh.version)) */
 #define SH_RELEASE_CPYR	"(c) 2020-2022 Contributors to ksh " SH_RELEASE_FORK
 
 /* Scripts sometimes field-split ${.sh.version}, so don't change amount of whitespace. */

src/cmd/ksh93/sh/name.c

@@ -319,6 +319,13 @@ void nv_setlist(register struct argnod *arg,register int flags, Namval_t *typ)
 					cp = sh_mactrim(fp->fornam,-1);
 				else
 					cp = fp->fornam;
+				/* Do not allow 'typeset -T' to override special built-ins -- however, exclude
+				 * previously created type commands from this search as that is handled elsewhere. */
+				if(maketype && (np=nv_search(cp,sh.bltin_tree,0)) && nv_isattr(np,BLT_SPC) && !nv_search(cp,sh.typedict,0))
+				{
+					errormsg(SH_DICT,ERROR_exit(1),"%s:%s",cp,is_spcbuiltin);
+					UNREACHABLE();
+				}
 				error_info.line = fp->fortyp-sh.st.firstline;
 				if(!array && tp->tre.tretyp!=TLST && tp->com.comset && !tp->com.comarg && tp->com.comset->argval[0]==0 && tp->com.comset->argval[1]=='[')
 					array |= (tp->com.comset->argflag&ARG_MESSAGE)?NV_IARRAY:NV_ARRAY;

src/cmd/ksh93/tests/enum.sh

@@ -161,5 +161,12 @@ then	enum PARSER2_t=(a b)
 fi
 PATH=/dev/null command -v PARSER2_t >/dev/null && err_exit "PARSER2_t incompletely defined though definition was never executed"
 
+# ======
+# https://github.com/ksh93/ksh/issues/350#issuecomment-982168684
+got=$("$SHELL" -c 'enum trap=(BAD TYPE)' 2>&1)
+exp=': trap: is a special shell builtin'
+[[ $got == *"$exp" ]] || err_exit "enum overrides special builtin" \
+	"(expected match of *$(printf %q "$exp"); got $(printf %q "$got"))"
+
 # ======
 exit $((Errors<125?Errors:125))

src/cmd/ksh93/tests/types.sh

@@ -565,8 +565,9 @@ unset z
 u_t -a x | read z
 [[ $z == unset ]]  && err_exit 'unset discipline called on type creation'
 
-{ z=$($SHELL 2> /dev/null 'typeset -T foo; typeset -T') ;} 2> /dev/null
+got=$("$SHELL" -c 'typeset -T foo; typeset -T' 2>&1)
-[[ $z == 'typeset -T foo' ]] || err_exit '"typeset -T foo; typeset -T" failed'
+[[ -z $got ]] || err_exit '"typeset -T foo; typeset -T" exposed incomplete type builtin' \
+	"(got $(printf %q "$got"))"
 
 { z=$($SHELL 2> /dev/null 'typeset -T foo=bar; typeset -T') ;} 2> /dev/null
 [[ $z ]] && err_exit '"typeset -T foo=bar" should not creates type foo'
@@ -657,5 +658,12 @@ exp='Subsh_t -a v=((typeset -i x=1) (typeset -i x=2) (typeset -i x=3))'
 	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
 PATH=/dev/null command -v Subsh_t >/dev/null && err_exit "Subsh_t leaked out of subshell"
 
+# ======
+# https://github.com/ksh93/ksh/issues/350#issuecomment-982168684
+got=$("$SHELL" -c 'typeset -T trap=( typeset -i i )' 2>&1)
+exp=': trap: is a special shell builtin'
+[[ $got == *"$exp" ]] || err_exit "typeset -T overrides special builtin" \
+	"(expected match of *$(printf %q "$exp"); got $(printf %q "$got"))"
+
 # ======
 exit $((Errors<125?Errors:125))