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Postings from March 2014
Zefram <perlbug-followup@perl.org> wrote:
> $ perl5.19.10 -lwe 'print "wibble" =~ /\Awibble\z/m ? "yes" : "no"'
> no
> $ perl5.19.9 -lwe 'print "wibble" =~ /\Awibble\z/m ? "yes" : "no"'
> yes
This bisects to the following commit:
commit d0d4464849e2b30aee89c175ccb5465795de10ce
Author: David Mitchell <davem@iabyn.com>
Date: Tue Mar 18 20:15:27 2014 +0000
re_intuit_start(): reduce scope of /^...$/m test
Intuit has a quick reject test for a fixed pattern that is anchored at
both ends. For example, with the pattern /^abcd$/, only the exact strings
"abcd" or "abcd\n" will match; anything else, and the match immediately
fails.
A fix for [perl #115242] correctly made intuit skip the test in the
presence of //m, since in this case the $ doesn't necessarily correspond
to the end of the string.
However, the fix was too wide in scope; it caused //m patterns to skip
searching for a known string anchored just at the start, as well as one
anchored at both ends.
With this commit, the following code now runs in a few milliseconds rather
than a few seconds on my machine:
$s = "abcdefg" x 1_000_000;
$s =~ /(?-m:^)abcX?fg/m for 1..100;
AFAICT from a fairly cursory look, re_intuit_start() seems to be
failing to account for the "\n" at the end of the fixed check
substring.
This is Zefram's test case expressed in the language of t/re/re_tests:
diff --git i/t/re/re_tests w/t/re/re_tests
index 7ab7dc3..294032f 100644
--- i/t/re/re_tests
+++ w/t/re/re_tests
@@ -1884,5 +1884,21 @@ A+(*PRUNE)BC(?{}) AAABC y $& AAABC
[bcd].{2,3}aaaa XbXaaaaa y - -
[bcd].{2,3}aaaa Xb\x{100}aaaaa y - -
+# RT #121484 - /m causing false negative
+'\Awibble\z'm wibble y $& wibble
+'\A.ibble\z'm wibble y $& wibble
+'\Aw.bble\z'm wibble y $& wibble
+'\Awi.ble\z'm wibble y $& wibble
+'\Awib.le\z'm wibble y $& wibble
+'\Awibb.e\z'm wibble y $& wibble
+'\Awibbl.\z'm wibble y $& wibble
+'\Awibble$'m wibble y $& wibble
+'\A.ibble$'m wibble y $& wibble
+'\Aw.bble$'m wibble y $& wibble
+'\Awi.ble$'m wibble y $& wibble
+'\Awib.le$'m wibble y $& wibble
+'\Awibb.e$'m wibble y $& wibble
+'\Awibbl.$'m wibble y $& wibble
+
# Keep these lines at the end of the file
# vim: softtabstop=0 noexpandtab
--
Aaron Crane ** http://aaroncrane.co.uk/
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