parser: Allow newlines within parameter substitution

On Fri, Mar 16, 2018 at 11:27:22AM +0800, Herbert Xu wrote:
> On Thu, Mar 15, 2018 at 10:49:15PM +0100, Harald van Dijk wrote:
> >
> > Okay, it can be trivially modified to something that does work in other
> > shells (even if it were actually executed), but gets rejected at parse time
> > by dash:
> >
> >   if false; then
> >     : ${$+
> >   }
> >   fi
>
> That's just a bug in dash's parser with ${} in general, because
> it bombs out without the if clause too:
>
> 	: ${$+
> 	}

This patch fixes the parsing of newlines with parameter substitution.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

src/parser.c

@@ -924,7 +924,8 @@ readtoken1(int firstc, char const *syntax, char *eofmark, int striptabs)
 			CHECKSTRSPACE(4, out);	/* permit 4 calls to USTPUTC */
 			switch(synstack->syntax[c]) {
 			case CNL:	/* '\n' */
-				if (synstack->syntax == BASESYNTAX)
+				if (synstack->syntax == BASESYNTAX &&
+				    !synstack->varnest)
 					goto endword;	/* exit outer loop */
 				USTPUTC(c, out);
 				nlprompt();