Re: Misc. substitution things

[Peter Stephenson <p.w.stephenson@ntlworld.com>]

On Sun, 16 Dec 2007 13:02:54 -0800
Bart Schaefer <schaefer@brasslantern.com> wrote:
> This seems like a bug:
> 
> zsh% print $(( x + "45" ))
> dquote> 
> 
> It appears that (( and the first double-quote are taken as a matching
> pair of quotes.

I think it's more subtle, but better error checking when we resolve math
and command substitution seems to keep everything happy, including the
new tests.  The new error cases are partly paranoia because I don't
quite understand the way dquote_parse() is written.

> Less importantly, even after 24264 (of which I conceptually approve)
> there is some ambiguity with the (P) flag and subscripting.

I'm not sure there's anything there I feel like changing.  It doesn't
look like anything is more broken, only differently strange.

Index: Src/lex.c
===================================================================
RCS file: /cvsroot/zsh/zsh/Src/lex.c,v
retrieving revision 1.41
diff -u -r1.41 lex.c
--- Src/lex.c	23 Aug 2007 22:04:25 -0000	1.41
+++ Src/lex.c	16 Dec 2007 22:12:54 -0000
@@ -548,6 +548,11 @@
 		else\
 		    parend = inbufct;} }
 
+/*
+ * Return 1 for math, 0 for a command, 2 for an error.  If it couldn't be
+ * parsed as math, but there was no gross error, it's a command.
+ */
+
 static int
 cmd_or_math(int cs_type)
 {
@@ -558,14 +563,19 @@
     c = dquote_parse(')', 0);
     cmdpop();
     *bptr = '\0';
-    if (c)
-	return 1;
-    c = hgetc();
-    if (c == ')')
-	return 1;
-    hungetc(c);
-    lexstop = 0;
-    c = ')';
+    if (!c) {
+	/* Successfully parsed, see if it was math */
+	c = hgetc();
+	if (c == ')')
+	    return 1; /* yes */
+	hungetc(c);
+	lexstop = 0;
+	c = ')';
+    } else if (lexstop) {
+	/* we haven't got anything to unget */
+	return 2;
+    }
+    /* else unsuccessful: unget the whole thing */
     hungetc(c);
     lexstop = 0;
     while (len > oldlen) {
@@ -576,18 +586,25 @@
     return 0;
 }
 
+
+/*
+ * Parse either a $(( ... )) or a $(...)
+ * Return 0 on success, 1 on failure.
+ */
 static int
 cmd_or_math_sub(void)
 {
-    int c = hgetc();
+    int c = hgetc(), ret;
 
     if (c == '(') {
 	add(Inpar);
 	add('(');
-	if (cmd_or_math(CS_MATHSUBST)) {
+	if ((ret = cmd_or_math(CS_MATHSUBST)) == 1) {
 	    add(')');
 	    return 0;
 	}
+	if (ret == 2)
+	    return 1;
 	bptr -= 2;
 	len -= 2;
     } else {
@@ -781,7 +798,16 @@
 	    if (incmdpos) {
 		len = 0;
 		bptr = tokstr = (char *) hcalloc(bsiz = 32);
-		return cmd_or_math(CS_MATH) ? DINPAR : INPAR;
+		switch (cmd_or_math(CS_MATH)) {
+		case 1:
+		    return DINPAR;
+
+		case 0:
+		    return INPAR;
+
+		default:
+		    return LEXERR;
+		}
 	    }
 	} else if (d == ')')
 	    return INOUTPAR;
@@ -1328,6 +1354,9 @@
     return peek;
 }
 
+
+/* Return non-zero for error (character to unget), else zero */
+
 /**/
 static int
 dquote_parse(char endchar, int sub)
@@ -1466,6 +1495,10 @@
 	 * to hungetc() a character on an error.  However, I don't
 	 * understand what that actually gets us, and we can't guarantee
 	 * it's a character anyway, because of the previous test.
+	 *
+	 * We use the same feature in cmd_or_math we we actually do
+	 * need to unget if we decide it's really a command substitution.
+	 * We try to handle the other case by testing for lexstop.
 	 */
 	err = c;
     }
Index: Test/C01arith.ztst
===================================================================
RCS file: /cvsroot/zsh/zsh/Test/C01arith.ztst,v
retrieving revision 1.13
diff -u -r1.13 C01arith.ztst
--- Test/C01arith.ztst	18 Jun 2007 13:39:56 -0000	1.13
+++ Test/C01arith.ztst	16 Dec 2007 22:12:54 -0000
@@ -153,3 +153,12 @@
   print $(( 37#z ))
 1:bases beyond 36 don't work
 ?(eval):1: invalid base: 37
+
+  print $(( 3 + "fail" ))
+1:parse failure in arithmetic
+?(eval):1: bad math expression: operand expected at `"fail" '
+
+  alias 3=echo
+  print $(( 3 + "OK"); echo "Worked")
+0:not a parse failure because not arithmetic
+>+ OK Worked
-- 
Peter Stephenson <p.w.stephenson@ntlworld.com>
Web page now at http://homepage.ntlworld.com/p.w.stephenson/