Add (?^...) regex construct

This adds (?^...) to signify to use the default regex modifiers for the
cluster or embedded pattern-match modifier change.  The major purpose of
this is to simplify regex stringification, so that "^" is output in
place of "-xism".  As a result, the stringification will not change in
the future when new regex modifiers are added, so tests, etc. that rely
on a particular stringification will have to change now, but never
again.

Code that needs to work properly with both old- and new-style regexes
can use something like the following:

    # Accept both old and new-style stringification
    my $modifiers = (qr/foobar/ =~ /\Q(?^/) ? '^' : '-xism';

This construct is Ben Morrow's idea.

1 files changed, 4 insertions, 0 deletions

diff --git a/regexp.h b/regexp.h
index 298a417d26..198b51017c 100644
--- a/regexp.h
+++ b/regexp.h
@@ -236,6 +236,10 @@ and check for NULL.
     case SINGLE_PAT_MOD:    *(pmfl) |= RXf_PMf_SINGLELINE; break;   \
     case XTENDED_PAT_MOD:   *(pmfl) |= RXf_PMf_EXTENDED;   break
 
+/* Note, includes locale */
+#define STD_PMMOD_FLAGS_CLEAR(pmfl)                        \
+    *(pmfl) &= ~(RXf_PMf_FOLD|RXf_PMf_MULTILINE|RXf_PMf_SINGLELINE|RXf_PMf_EXTENDED|RXf_PMf_LOCALE)
+
 /* chars and strings used as regex pattern modifiers
  * Singlular is a 'c'har, plural is a "string"
  *