Deprecate no space between pattern, following word

This patch raises a deprecated warning on constructs like
    $result = $a =~ m/$foo/sand $bar;
which means
    $result = $a =~ m/$foo/s and $bar;

3 files changed, 27 insertions, 2 deletions

diff --git a/pod/perldiag.pod b/pod/perldiag.pod
index 4d7d6adce8..26c35a0c30 100644
--- a/pod/perldiag.pod
+++ b/pod/perldiag.pod
@@ -1913,6 +1913,23 @@ spots.  This is now heavily deprecated.
 (F) The parser has given up trying to parse the program after 10 errors.
 Further error messages would likely be uninformative.
 
+=item Having no space between pattern and following word is deprecated
+
+(D syntax)
+
+You had a word that isn't a regex modifier immediately following a pattern
+without an intervening space.  For example, the two constructs:
+
+ $a =~ m/$foo/sand $bar
+ $a =~ m/$foo/s and $bar
+
+both currently mean the same thing, but it is planned to disallow the first form
+in Perl 5.16.  And,
+
+ $a =~ m/$foo/and $bar
+
+will be disallowed too.
+
 =item Hexadecimal number > 0xffffffff non-portable
 
 (W portable) The hexadecimal number you specified is larger than 2**32-1
@@ -2855,7 +2872,6 @@ your system.
 
 (F) The indicated command line switch needs a mandatory argument, but
 you haven't specified one.
-
 =item No such class field "%s" in variable %s of type %s
 
 (F) You tried to access a key from a hash through the indicated typed variable
diff --git a/t/lib/warnings/toke b/t/lib/warnings/toke
index 223644236b..6a1a6a579c 100644
--- a/t/lib/warnings/toke
+++ b/t/lib/warnings/toke
@@ -140,13 +140,16 @@ Use of comma-less variable list is deprecated at - line 4.
 Use of comma-less variable list is deprecated at - line 4.
 ########
 # toke.c
+$a =~ m/$foo/sand $bar;
 $a = <<;
 
 no warnings 'deprecated' ;
+$a =~ m/$foo/sand $bar;
 $a = <<;
 
 EXPECT
-Use of bare << to mean <<"" is deprecated at - line 2.
+Having no space between pattern and following word is deprecated at - line 2.
+Use of bare << to mean <<"" is deprecated at - line 3.
 ########
 # toke.c
 use warnings 'syntax' ;
diff --git a/toke.c b/toke.c
index daa60a18ed..a94753a0b8 100644
--- a/toke.c
+++ b/toke.c
@@ -11887,6 +11887,12 @@ S_scan_pat(pTHX_ char *start, I32 type)
 #endif
     while (*s && strchr(valid_flags, *s))
 	pm->op_pmflags = S_pmflag(pm->op_pmflags, *s++);
+
+    if (isALNUM(*s)) {
+	Perl_ck_warner_d(aTHX_ packWARN(WARN_SYNTAX),
+	    "Having no space between pattern and following word is deprecated");
+
+    }
 #ifdef PERL_MAD
     if (PL_madskills && modstart != s) {
 	SV* tmptoken = newSVpvn(modstart, s - modstart);