Add warnings for "\08", /\017/

This was discussed in thread
http://perl.markmail.org/thread/avtzvtpzemvg2ki2
but I never got around to this portion of the consensus, until now.

I did a cpan grep
http://grep.cpan.me/?q=%28^|[^\\]%29\\[0-7]{1%2C2}[8-9]&page=1

and eyeballing the results, saw three cases where this warning might
show up; one of which was for EBCDIC.  The others looked to be false
positives, such as in .css files.

1 files changed, 29 insertions, 0 deletions

diff --git a/dquote_static.c b/dquote_static.c
index 61845ccc92..5a22993ac0 100644
--- a/dquote_static.c
+++ b/dquote_static.c
@@ -297,6 +297,35 @@ S_grok_bslash_x(pTHX_ char **s, UV *uv, const char** error_msg,
     return TRUE;
 }
 
+STATIC char*
+S_form_short_octal_warning(pTHX_
+                           const char * const s, /* Points to first non-octal */
+                           const STRLEN len      /* Length of octals string, so
+                                                    (s-len) points to first
+                                                    octal */
+) {
+    /* Return a character string consisting of a warning message for when a
+     * string constant in octal is weird, like "\078".  */
+
+    const char * sans_leading_zeros = s - len;
+
+    PERL_ARGS_ASSERT_FORM_SHORT_OCTAL_WARNING;
+
+    assert(*s == '8' || *s == '9');
+
+    /* Remove the leading zeros, retaining one zero so won't be zero length */
+    while (*sans_leading_zeros == '0') sans_leading_zeros++;
+    if (sans_leading_zeros == s) {
+        sans_leading_zeros--;
+    }
+
+    return Perl_form(aTHX_
+                     "'%.*s' resolved to '\\o{%.*s}%c'",
+                     (int) (len + 2), s - len - 1,
+                     (int) (s - sans_leading_zeros), sans_leading_zeros,
+                     *s);
+}
+
 /*
  * Local variables:
  * c-indentation-style: bsd