bring back ${ foo;} sans dot.mkshrc patch, using a temporary file, and as experimental feature

lex.c

@@ -23,7 +23,7 @@
 
 #include "sh.h"
 
-__RCSID("$MirOS: src/bin/mksh/lex.c,v 1.168 2012/10/03 17:24:20 tg Exp $");
+__RCSID("$MirOS: src/bin/mksh/lex.c,v 1.169 2012/10/22 20:19:13 tg Exp $");
 
 /*
  * states while lexing word
@@ -109,7 +109,7 @@ void yyskiputf8bom(void);
 static int backslash_skip;
 static int ignore_backslash_newline;
 static struct sretrace_info *retrace_info;
-uint8_t subshell_nesting_level = 0;
+int subshell_nesting_type = 0;
 
 /* optimised getsc_bn() */
 #define o_getsc()	(*source->str != '\0' && *source->str != '\\' && \
@@ -262,6 +262,13 @@ yylex(int cf)
 	while (!((c = getsc()) == 0 ||
 	    ((state == SBASE || state == SHEREDELIM || state == SHERESTRING) &&
 	    ctype(c, C_LEX1)))) {
+#ifndef MKSH_DISABLE_EXPERIMENTAL
+		if (state == SBASE &&
+		    subshell_nesting_type == /*{*/ '}' &&
+		    c == /*{*/ '}')
+			/* possibly end ${ :;} */
+			break;
+#endif
  accept_nonword:
 		Xcheck(ws, wp);
 		switch (state) {
@@ -395,14 +402,30 @@ yylex(int cf)
 					} else {
 						ungetsc(c);
  subst_command:
-						sp = yyrecursive();
+						c = COMSUB;
+#ifndef MKSH_DISABLE_EXPERIMENTAL
+ subst_command2:
+#endif
+						sp = yyrecursive(c);
 						cz = strlen(sp) + 1;
 						XcheckN(ws, wp, cz);
-						*wp++ = COMSUB;
+						*wp++ = c;
 						memcpy(wp, sp, cz);
 						wp += cz;
 					}
 				} else if (c == '{') /*}*/ {
+#ifndef MKSH_DISABLE_EXPERIMENTAL
+					c = getsc();
+					if (ctype(c, C_IFSWS)) {
+						/*
+						 * non-subenvironment
+						 * "command" substitution
+						 */
+						c = FUNSUB;
+						goto subst_command2;
+					}
+					ungetsc(c);
+#endif
 					*wp++ = OSUBST;
 					*wp++ = '{'; /*}*/
 					wp = get_brace_var(&ws, wp);
@@ -1171,7 +1194,7 @@ readhere(struct ioword *iop)
 		/* end of here document marker, what to do? */
 		switch (c) {
 		case /*(*/ ')':
-			if (!subshell_nesting_level)
+			if (!subshell_nesting_type)
 				/*-
 				 * not allowed outside $(...) or (...)
 				 * => mismatch