Improve fix for parentheses in param expansions (re: 5ed9ffd)

The fix was incomplete: expansions using '?' (${var?w(ord},
${var:?wo)rd}) still did not tolerate parentheses in the word
as regular characters.

It was also possible to simplify the fix by making use of the
ST_BRACE (sh_lexstate7[]) state table. See data/lexstates.c and
include/lexstates.h.

src/cmd/ksh93/sh/lex.c: sh_lex(): case S_MOD1:
- The previous fix tested for modifier operator characters : - + =
  as part of the S_MOD2 case, though they are defined as S_MOD1 in
  the ST_BRACE state table. It only worked because of the
  fallthrough. And it turns out the S_MOD1 case already had a
  similar fix, though incomplete. The new fix effectively cancelled
  the old one out as any S_MOD1 character eventually led to
  'continue'. So it can be simplified by removing most of that
  code, without causing any change in behaviour. Only the mode
  change to the ST_QUOTE state table followed by 'continue' is
  necessary. This also fixes it for the '?' operator as that is
  also defined as S_MOD1 in the ST_BRACE state table.

src/cmd/ksh93/sh/macro.c:
- When skipping a ${...} expansion using sh_lexskip(), use the
  ST_QUOTE state table if the character c is an S_MOD1 modifier
  operator character. This makes it consistent with the S_MOD1
  handling in sh_lex().

src/cmd/ksh93/tests/variables.sh:
- Update regression tests to include ? and :? operators.

src/cmd/ksh93/sh/lex.c

@@ -998,31 +998,13 @@ int sh_lex(Lex_t* lp)
 				mode = ST_NESTED;
 				continue;
 			case S_MOD1:
-				if(oldmode(lp)==ST_QUOTE || oldmode(lp)==ST_NONE)
-				{
-					/* allow ' inside "${...}" */
-					if(c==':' && fcgetc(n)>0)
-					{
-						n = state[n];
-						fcseek(-LEN);
-					}
-					if(n==S_MOD1)
-					{
-						mode = ST_QUOTE;
-						continue;
-					}
-				}
-				/* FALL THRU */
+				mode = ST_QUOTE;
+				continue;
 			case S_MOD2:
 #if SHOPT_KIA
 				if(lp->kiafile)
 					refvar(lp,1);
 #endif /* SHOPT_KIA */
-				if(c == ':' || c == '-' || c == '+' || c == '=')
-				{
-					mode = ST_QUOTE;
-					continue;
-				}
 				if(c!=':' && fcgetc(n)>0)
 				{
 					if(n!=c)

src/cmd/ksh93/sh/macro.c

@@ -1628,8 +1628,7 @@ static int varsub(Mac_t *mp)
 			}
 			else
 			{
-				int state = (!newops && mp->quote || c=='-' || c=='+' || c=='=') ? ST_QUOTE : ST_NESTED;
-				sh_lexskip(lp, RBRACE, 0, state);
+				sh_lexskip(lp, RBRACE, 0, sh_lexstates[ST_BRACE][c]==S_MOD1 ? ST_QUOTE : ST_NESTED);
 				stkseek(stkp,offset);
 			}
 			argp=stkptr(stkp,offset);

src/cmd/ksh93/tests/variables.sh

@@ -1044,7 +1044,7 @@ wait
 [[ $$ == ${.sh.pid} ]] || err_exit "\${.sh.pid} and \$$ differ in the parent shell (expected $$, got ${.sh.pid})"
 
 # ======
-# Parentheses after the '-', '+', and '=' expansion operators were causing syntax errors.
+# Parentheses after the '-', '+', '=', and '?' expansion operators were causing syntax errors.
 # Check both the unset variable case and the set variable case for each set of symbols.
 
 unset -v foo
@@ -1058,7 +1058,7 @@ do	for word in '(word)' 'w(or)d' '(wor)d' 'w(ord)' 'w(ord' 'wor)d'
 done
 
 foo=some_value
-for op in - :- = :=
+for op in - :- = := \? :\?
 do	for word in '(word)' 'w(or)d' '(wor)d' 'w(ord)' 'w(ord' 'wor)d'
 	do	exp=$(set +x; eval "echo \${foo${op}${word}}" 2>&1)
 		if	[[ $exp != "$foo" ]]
@@ -1077,5 +1077,15 @@ do	for word in '(word)' 'w(or)d' '(wor)d' 'w(ord)' 'w(ord' 'wor)d'
 	done
 done
 
+unset -v foo
+for op in \? :\?
+do	for word in '(word)' 'w(or)d' '(wor)d' 'w(ord)' 'w(ord' 'wor)d'
+	do	exp=$(set +x; eval "echo \${foo${op}${word}}" 2>&1)
+		if	[[ $exp != *": foo: $word" ]]
+		then	err_exit "\${foo${op}${word}} when foo is not set: expected *\": foo: $word\", got \"$exp\""
+		fi
+	done
+done
+
 # ======
 exit $((Errors<125?Errors:125))