On 10/10/16 22:20, Harald van Dijk wrote:
On 08/10/16 21:42, Martijn Dekker wrote:
Op 01-10-16 om 19:17 schreef Denys Vlasenko:
ash-vars/var_unbackslash.tests


ITYM ash-vars/var_unbackslash1.tests

    echo Forty two:$\
    (\
    (\
    42\
    )\
    )
    dash says: Syntax error: Missing '))'

Yes, but it's not clear to me that it shouldn't.

Hmm... maybe this is indeed a bug:
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_02_01

"A <backslash> that is not quoted shall preserve the literal value of
the following character, with the exception of a <newline>. If a
<newline> follows the <backslash>, the shell shall interpret this as
line continuation. The <backslash> and <newline> shall be removed before
splitting the input into tokens. Since the escaped <newline> is removed
entirely from the input and is not replaced by any white space, it
cannot serve as a token separator."

So, unless I'm misreading this, it looks like backslashes need to be
parsed before *any* other kind of lexical analysis.

There does appear to be one exception: a comment may end with a
backslash. This does not cause the next line to be treated as a comment:
once a # is seen, the remaining characters on the line are not subjected
to the regular lexical analysis, so the above does not apply.

I would have expected another exception to be in alias expansions that
end in a backslash. Shells are not entirely in agreement there, but most
appear to treat this the regular way, meaning

  dash -c 'alias bs=\\
  bs
  '

prints nothing.

dash has a pgetc_eatbnl function already in parser.c which skips any
backslash-newline combinations. It's not used everywhere it could be.
There is also some duplicated backslash-newline handling elsewhere in
parser.c. Replacing all the calls to pgetc() to call pgetc_eatbnl()
instead, with the exception of the one that handles comments, and
removing the duplicated backslash-newline handling, lets this test case
work, as well as several other similar ones, such as:

  : &\
  & :

  : \
  <\
  <\
  EO\
  F
  123
  E\
  OF

A nice benefit is that the removal of the duplicated BSNL handling
causes a reduction in code size.

There are probably a few corner cases I'm not handling correctly in this
patch, though. Feedback welcome.

With more extensive testing, the only issue I've seen is what Jilles Tjoelker had already mentioned, namely that backslash-newline should be preserved inside single-quoted strings, and also that it should be preserved inside heredocs where any part of the delimiter is quoted:

  cat <<\EOF
  \
  EOF

dash's parsing treats this mostly the same as a single-quoted string, and the same extra check handles both cases.

Here's an updated patch. Hoping this looks okay and can be applied.

Cheers,
Harald van Dijk
--- a/src/parser.c
+++ b/src/parser.c
@@ -106,6 +106,7 @@ STATIC void parseheredoc(void);
 STATIC int peektoken(void);
 STATIC int readtoken(void);
 STATIC int xxreadtoken(void);
+STATIC int pgetc_eatbnl();
 STATIC int readtoken1(int, char const *, char *, int);
 STATIC void synexpect(int) __attribute__((__noreturn__));
 STATIC void synerror(const char *) __attribute__((__noreturn__));
@@ -656,8 +657,10 @@ parseheredoc(void)
 		if (needprompt) {
 			setprompt(2);
 		}
-		readtoken1(pgetc(), here->here->type == NHERE? SQSYNTAX : DQSYNTAX,
-				here->eofmark, here->striptabs);
+		if (here->here->type == NHERE)
+			readtoken1(pgetc(), SQSYNTAX, here->eofmark, here->striptabs);
+		else
+			readtoken1(pgetc_eatbnl(), DQSYNTAX, here->eofmark, here->striptabs);
 		n = (union node *)stalloc(sizeof (struct narg));
 		n->narg.type = NARG;
 		n->narg.next = NULL;
@@ -782,7 +785,7 @@ xxreadtoken(void)
 		setprompt(2);
 	}
 	for (;;) {	/* until token or start of word found */
-		c = pgetc();
+		c = pgetc_eatbnl();
 		switch (c) {
 		case ' ': case '\t':
 		case PEOA:
@@ -791,30 +794,23 @@ xxreadtoken(void)
 			while ((c = pgetc()) != '\n' && c != PEOF);
 			pungetc();
 			continue;
-		case '\\':
-			if (pgetc() == '\n') {
-				nlprompt();
-				continue;
-			}
-			pungetc();
-			goto breakloop;
 		case '\n':
 			nlnoprompt();
 			RETURN(TNL);
 		case PEOF:
 			RETURN(TEOF);
 		case '&':
-			if (pgetc() == '&')
+			if (pgetc_eatbnl() == '&')
 				RETURN(TAND);
 			pungetc();
 			RETURN(TBACKGND);
 		case '|':
-			if (pgetc() == '|')
+			if (pgetc_eatbnl() == '|')
 				RETURN(TOR);
 			pungetc();
 			RETURN(TPIPE);
 		case ';':
-			if (pgetc() == ';')
+			if (pgetc_eatbnl() == ';')
 				RETURN(TENDCASE);
 			pungetc();
 			RETURN(TSEMI);
@@ -822,11 +818,9 @@ xxreadtoken(void)
 			RETURN(TLP);
 		case ')':
 			RETURN(TRP);
-		default:
-			goto breakloop;
 		}
+		break;
 	}
-breakloop:
 	return readtoken1(c, BASESYNTAX, (char *)NULL, 0);
 #undef RETURN
 }
@@ -903,7 +897,7 @@ readtoken1(int firstc, char const *syntax, char *eofmark, int striptabs)
 			attyline();
 			if (syntax == BASESYNTAX)
 				return readtoken();
-			c = pgetc();
+			c = syntax == SQSYNTAX ? pgetc() : pgetc_eatbnl();
 			goto loop;
 		}
 #endif
@@ -916,7 +910,7 @@ readtoken1(int firstc, char const *syntax, char *eofmark, int striptabs)
 					goto endword;	/* exit outer loop */
 				USTPUTC(c, out);
 				nlprompt();
-				c = pgetc();
+				c = syntax == SQSYNTAX ? pgetc() : pgetc_eatbnl();
 				goto loop;		/* continue outer loop */
 			case CWORD:
 				USTPUTC(c, out);
@@ -933,8 +927,6 @@ readtoken1(int firstc, char const *syntax, char *eofmark, int striptabs)
 					USTPUTC(CTLESC, out);
 					USTPUTC('\\', out);
 					pungetc();
-				} else if (c == '\n') {
-					nlprompt();
 				} else {
 					if (
 						dblquote &&
@@ -997,7 +989,7 @@ quotemark:
 					USTPUTC(c, out);
 					--parenlevel;
 				} else {
-					if (pgetc() == ')') {
+					if (pgetc_eatbnl() == ')') {
 						USTPUTC(CTLENDARI, out);
 						if (!--arinest)
 							syntax = prevsyntax;
@@ -1025,7 +1017,7 @@ quotemark:
 					USTPUTC(c, out);
 				}
 			}
-			c = pgetc();
+			c = syntax == SQSYNTAX ? pgetc() : pgetc_eatbnl();
 		}
 	}
 endword:
@@ -1132,7 +1124,7 @@ parseredir: {
 	np = (union node *)stalloc(sizeof (struct nfile));
 	if (c == '>') {
 		np->nfile.fd = 1;
-		c = pgetc();
+		c = pgetc_eatbnl();
 		if (c == '>')
 			np->type = NAPPEND;
 		else if (c == '|')
@@ -1145,7 +1137,7 @@ parseredir: {
 		}
 	} else {	/* c == '<' */
 		np->nfile.fd = 0;
-		switch (c = pgetc()) {
+		switch (c = pgetc_eatbnl()) {
 		case '<':
 			if (sizeof (struct nfile) != sizeof (struct nhere)) {
 				np = (union node *)stalloc(sizeof (struct nhere));
@@ -1154,7 +1146,7 @@ parseredir: {
 			np->type = NHERE;
 			heredoc = (struct heredoc *)stalloc(sizeof (struct heredoc));
 			heredoc->here = np;
-			if ((c = pgetc()) == '-') {
+			if ((c = pgetc_eatbnl()) == '-') {
 				heredoc->striptabs = 1;
 			} else {
 				heredoc->striptabs = 0;
@@ -1336,21 +1328,12 @@ parsebackq: {
 			if (needprompt) {
 				setprompt(2);
 			}
-			switch (pc = pgetc()) {
+			switch (pc = pgetc_eatbnl()) {
 			case '`':
 				goto done;
 
 			case '\\':
-                                if ((pc = pgetc()) == '\n') {
-					nlprompt();
-					/*
-					 * If eating a newline, avoid putting
-					 * the newline into the new character
-					 * stream (via the STPUTC after the
-					 * switch).
-					 */
-					continue;
-				}
+                                pc = pgetc_eatbnl();
                                 if (pc != '\\' && pc != '`' && pc != '$'
                                     && (!dblquote || pc != '"'))
                                         STPUTC('\\', pout);
@@ -1529,7 +1512,7 @@ expandstr(const char *ps)
 	saveprompt = doprompt;
 	doprompt = 0;
 
-	readtoken1(pgetc(), DQSYNTAX, FAKEEOFMARK, 0);
+	readtoken1(pgetc_eatbnl(), DQSYNTAX, FAKEEOFMARK, 0);
 
 	doprompt = saveprompt;
 

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