Restore namespace's parent scope when exiting due to error

Reproducer:

    $ namespace test { x=123; typeset -g x=456; }
    $ echo $x ${.test.x}
    456 123
    $ namespace test { typeset -Q; }
    arch/darwin.i386-64/bin/ksh: typeset: -Q: unknown option
    [usage message snipped for brevity]
    $ echo $x ${.test.x}
    123 123	            <== expected: 123 456
    $ x=789
    $ echo $x ${.test.x}
    789 789                 <== expected: 789 456
    $ # look at that, we never left the namespace...

When prefixing the erroneous 'typeset' with 'command', the problem
does not occur. 'command' disables the properties of special
built-ins such as exit on error. So, when a special built-in exits
on error, the parent scope is not properly resotred.

This bug exists in every ksh93 version with SHOPT_NAMESPACE so far.

src/cmd/ksh93/sh/xec.c: sh_exec():
- Before entering a namespace, use sh_pushcontext and sigsetjmp to
  make sure we return here if sh_exit() is called, e.g. when a
  special builtin throws an error, to ensure the parent scope
  (oldnspace) is restored.

Thanks to @hyenias for making me aware of this bug.
Discussion: https://github.com/ksh93/ksh/issues/479#issuecomment-1140468965

NEWS

@@ -3,6 +3,11 @@ 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.
 
+2022-05-29:
+
+- Fixed a bug causing an inconsistent state after a special built-in command
+  threw an error within a namespace.
+
 2022-05-27:
 
 - Fixed a bug introduced on 2022-03-05 where 'set --default', while turning

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	"2022-05-27"	/* must be in this format for $((.sh.version)) */
+#define SH_RELEASE_DATE	"2022-05-29"	/* 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/xec.c

@@ -2487,6 +2487,8 @@ int sh_exec(register const Shnode_t *t, int flags)
 				Namval_t *oldnspace = sh.namespace;
 				int offset = stktell(stkp);
 				int	flags=NV_NOASSIGN|NV_NOARRAY|NV_VARNAME;
+				struct checkpt *chkp = (struct checkpt*)stakalloc(sizeof(struct checkpt));
+				int jmpval;
 				if(cp)
 				{
 					errormsg(SH_DICT,ERROR_exit(1),e_ident,fname);
@@ -2511,8 +2513,15 @@ int sh_exec(register const Shnode_t *t, int flags)
 					dtview(root,sh.var_base);
 				}
 				oldnspace = enter_namespace(np);
+				/* make sure to restore oldnspace if a special builtin throws an error */
+				sh_pushcontext(chkp,SH_JMPCMD);
+				jmpval = sigsetjmp(chkp->buff,1);
+				if(!jmpval)
 					sh_exec(t->for_.fortre,flags|sh_state(SH_ERREXIT));
+				sh_popcontext(chkp);
 				enter_namespace(oldnspace);
+				if(jmpval)	/* error occurred */
+					sh_exit(sh.exitval);
 				break;
 			}
 #endif /* SHOPT_NAMESPACE */

src/cmd/ksh93/tests/namespace.sh

@@ -130,5 +130,17 @@ got=$(typeset -p .foo_nam.three)
 	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
 set +o allexport
 
+# ======
+# A namespace's parent scope should be restored after an error occurs.
+# https://github.com/ksh93/ksh/issues/479#issuecomment-1140514159
+#
+# TODO: this test fails when run in a non-forking comsub: the trap
+# is not executed -- the zillionth bug with virtual subshells >:-/
+exp=$'123 456\n789 456'
+got=$(ulimit -t unlimited 2>/dev/null  # workaround: force fork
+	trap 'echo $x ${.test.x}; x=789; echo $x ${.test.x}' EXIT; x=123; namespace test { x=456; set -Q 2>/dev/null; })
+[[ $got == "$exp" ]] || err_exit 'Parent scope not restored after special builtin throws error in namespace' \
+	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
+
 # ======
 exit $((Errors<125?Errors:125))