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.

6 files changed, 16 insertions, 12 deletions

diff --git a/t/comp/parser.t b/t/comp/parser.t
index 8fd94530cb..5c64d11fb2 100644
--- a/t/comp/parser.t
+++ b/t/comp/parser.t
@@ -125,7 +125,7 @@ is( $@, '', 'PL_lex_brackstack' );
     is("${a}[", "A[", "interpolation, qq//");
     my @b=("B");
     is("@{b}{", "B{", "interpolation, qq//");
-    is(qr/${a}{/, '(?-xism:A{)', "interpolation, qr//");
+    is(qr/${a}{/, '(?^:A{)', "interpolation, qr//");
     my $c = "A{";
     $c =~ /${a}{/;
     is($&, 'A{', "interpolation, m//");
diff --git a/t/lib/warnings/regcomp b/t/lib/warnings/regcomp
index 98280f61f4..2842882371 100644
--- a/t/lib/warnings/regcomp
+++ b/t/lib/warnings/regcomp
@@ -250,3 +250,8 @@ $a = qr/[\8\9]/;
 EXPECT
 Unrecognized escape \8 in character class passed through in regex; marked by <-- HERE in m/[\8 <-- HERE \9]/ at - line 3.
 Unrecognized escape \9 in character class passed through in regex; marked by <-- HERE in m/[\8\9 <-- HERE ]/ at - line 3.
+########
+# regcomp.c [Perl_re_compile]
+$a = qr/(?^-i:foo)/;
+EXPECT
+Sequence (?^-...) not recognized in regex; marked by <-- HERE in m/(?^- <-- HERE i:foo)/ at - line 2.
diff --git a/t/re/pat.t b/t/re/pat.t
index ba0efcdc98..3bc7f5d372 100644
--- a/t/re/pat.t
+++ b/t/re/pat.t
@@ -499,12 +499,12 @@ sub run_tests {
     }
 
     {
-        iseq qr/\b\v$/i,    '(?i-xsm:\b\v$)', 'qr/\b\v$/i';
-        iseq qr/\b\v$/s,    '(?s-xim:\b\v$)', 'qr/\b\v$/s';
-        iseq qr/\b\v$/m,    '(?m-xis:\b\v$)', 'qr/\b\v$/m';
-        iseq qr/\b\v$/x,    '(?x-ism:\b\v$)', 'qr/\b\v$/x';
+        iseq qr/\b\v$/i,    '(?^i:\b\v$)', 'qr/\b\v$/i';
+        iseq qr/\b\v$/s,    '(?^s:\b\v$)', 'qr/\b\v$/s';
+        iseq qr/\b\v$/m,    '(?^m:\b\v$)', 'qr/\b\v$/m';
+        iseq qr/\b\v$/x,    '(?^x:\b\v$)', 'qr/\b\v$/x';
         iseq qr/\b\v$/xism, '(?msix:\b\v$)',  'qr/\b\v$/xism';
-        iseq qr/\b\v$/,     '(?-xism:\b\v$)', 'qr/\b\v$/';
+        iseq qr/\b\v$/,     '(?^:\b\v$)', 'qr/\b\v$/';
     }
 
 
diff --git a/t/re/pat_re_eval.t b/t/re/pat_re_eval.t
index fab828d17d..6fcbb9360b 100644
--- a/t/re/pat_re_eval.t
+++ b/t/re/pat_re_eval.t
@@ -77,7 +77,7 @@ sub run_tests {
     {
         our $a = bless qr /foo/ => 'Foo';
         ok 'goodfood' =~ $a,     "Reblessed qr // matches";
-        iseq $a, '(?-xism:foo)', "Reblessed qr // stringifies";
+        iseq $a, '(?^:foo)', "Reblessed qr // stringifies";
         my $x = "\x{3fe}";
         my $z = my $y = "\317\276";  # Byte representation of $x
         $a = qr /$x/;
@@ -88,7 +88,7 @@ sub run_tests {
                         "Postponed interpolation of qr // preserves UTF-8";
         {
             local $BugId = '17776';
-            iseq length qr /##/x, 12, "## in qr // doesn't corrupt memory";
+            iseq length qr /##/x, 9, "## in qr // doesn't corrupt memory";
         }
         {
             use re 'eval';
diff --git a/t/re/re.t b/t/re/re.t
index 249c6ddf22..10e2ee2b64 100644
--- a/t/re/re.t
+++ b/t/re/re.t
@@ -21,12 +21,11 @@ use re qw(is_regexp regexp_pattern
 
     is((regexp_pattern($qr))[0],'foo','regexp_pattern[0] (ref)');
     is((regexp_pattern($qr))[1],'ip','regexp_pattern[1] (ref)');
-    is(regexp_pattern($qr),'(?pi-xsm:foo)','scalar regexp_pattern (ref)');
+    is(regexp_pattern($qr),'(?^pi:foo)','scalar regexp_pattern (ref)');
 
     is((regexp_pattern($rx))[0],'foo','regexp_pattern[0] (bare REGEXP)');
     is((regexp_pattern($rx))[1],'ip','regexp_pattern[1] (bare REGEXP)');
-    is(regexp_pattern($rx),'(?pi-xsm:foo)',
-                                    'scalar regexp_pattern (bare REGEXP)');
+    is(regexp_pattern($rx),'(?^pi:foo)', 'scalar regexp_pattern (bare REGEXP)');
 
     ok(!regexp_pattern(''),'!regexp_pattern("")');
 }
diff --git a/t/run/fresh_perl.t b/t/run/fresh_perl.t
index 2019d9b520..3666f0922e 100644
--- a/t/run/fresh_perl.t
+++ b/t/run/fresh_perl.t
@@ -605,7 +605,7 @@ EXPECT
 # reversed again as a result of [perl #17763]
 die qr(x)
 EXPECT
-(?-xism:x)
+(?^:x)
 ########
 # 20001210.003 mjd@plover.com
 format REMITOUT_TOP =