From: Bram <perl-rt@wizbit.be>
Date: Thu, 24 Jul 2008 18:14:27 +0000 (+0200)
Subject: Unintented interpolation of $/ in regex (was: Re: [perl
X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=commitdiff_plain;h=777723442a58c6c86c224d8d746a30441a5bdfbd;p=p5sagit%2Fp5-mst-13.2.git

Unintented interpolation of $/ in regex (was: Re: [perl
Message-ID: <20080724181427.aiml4sdvr40k4coc@horde.wizbit.be>

Note that the Subject: has a typo - it should be $\

This adds a new warning.
I moved the tests from the original patch to t/lib/warnings/toke.

p4raw-id: //depot/perl@34224
---

diff --git a/pod/perldiag.pod b/pod/perldiag.pod
index c512559..775e274 100644
--- a/pod/perldiag.pod
+++ b/pod/perldiag.pod
@@ -3419,6 +3419,20 @@ but there was no array C<@foo> in scope at the time. If you wanted a
 literal @foo, then write it as \@foo; otherwise find out what happened
 to the array you apparently lost track of.
 
+=item Possible unintended interpolation of $\ in regex
+
+(W ambiguous) You said something like C<m/$\/> in a regex.
+The regex C<m/foo$\s+bar/m> translates to: match the word 'foo', the output
+record separartor (see L<perlvar/$\>) and the letter 's' (one time or more)
+followed by the word 'bar'.
+
+If this is what you intended then you can silence the warning by using 
+C<m/${\}/> (for example: C<m/foo${\}s+bar/>).
+
+If instead you intended to match the word 'foo' at the end of the line
+followed by whitespace and the word 'bar' on the next line then you can use
+C<m/$(?)\/> (for example: C<m/foo$(?)\s+bar/>).
+
 =item pragma "attrs" is deprecated, use "sub NAME : ATTRS" instead
 
 (D deprecated) You have written something like this:
diff --git a/t/lib/warnings/toke b/t/lib/warnings/toke
index 1bd8f8f..04c41d5 100644
--- a/t/lib/warnings/toke
+++ b/t/lib/warnings/toke
@@ -875,3 +875,18 @@ Prototype after '@' for main::proto_after_array : @$ at - line 3.
 Prototype after '%' for main::proto_after_hash : %$ at - line 7.
 Illegal character after '_' in prototype for main::underscore_fail : $_$ at - line 12.
 Prototype after '@' for main::underscore_after_at : @_ at - line 13.
+########
+# toke.c
+use warnings "ambiguous";
+"foo\nn" =~ /^foo$\n/;
+"foo\nn" =~ /^foo${\}n/;
+my $foo = qr/^foo$\n/;
+my $bar = qr/^foo${\}n/;
+no warnings "ambiguous";
+"foo\nn" =~ /^foo$\n/;
+"foo\nn" =~ /^foo${\}n/;
+my $foo = qr/^foo$\n/;
+my $bar = qr/^foo${\}n/;
+EXPECT
+Possible unintended interpolation of $\ in regex at - line 3.
+Possible unintended interpolation of $\ in regex at - line 5.
diff --git a/toke.c b/toke.c
index e98e47c..b2ba362 100644
--- a/toke.c
+++ b/toke.c
@@ -2173,8 +2173,13 @@ S_scan_const(pTHX_ char *start)
 	else if (*s == '$') {
 	    if (!PL_lex_inpat)	/* not a regexp, so $ must be var */
 		break;
-	    if (s + 1 < send && !strchr("()| \r\n\t", s[1]))
+	    if (s + 1 < send && !strchr("()| \r\n\t", s[1])) {
+		if (s[1] == '\\' && ckWARN(WARN_AMBIGUOUS)) {
+		    Perl_warner(aTHX_ packWARN(WARN_AMBIGUOUS),
+				"Possible unintended interpolation of $\\ in regex");
+		}
 		break;		/* in regexp, $ might be tail anchor */
+            }
 	}
 
 	/* End of else if chain - OP_TRANS rejoin rest */