Implement the fc keyword and the \F string escape.

Along with the simple_casefolding and full_casefolding features.

fc() stands for foldcase, a sort of pseudo case (like lowercase),
which is used to implement Unicode casefolding. It maps a string
to a form where all case differences are erased, so it's a
locale-independent way of checking if two strings are the same,
regardless of case.

This functionality was, and still is, available through the
regular expression engine -- /i matches would use casefolding
internally. The fc keyword merely exposes this for easier access.

Previously, one could attempt to case-insensitively test two strings
for equality by doing

   lc($a) eq lc($b)

But that might get you wrong results, for example in the case of
\x{DF}, LATIN SMALL LETTER SHARP S.

1 files changed, 10 insertions, 2 deletions

diff --git a/keywords.c b/keywords.c
index 169a41c411..23d550df83 100644
--- a/keywords.c
+++ b/keywords.c
@@ -51,7 +51,7 @@ Perl_keyword (pTHX_ const char *name, I32 len, bool all_keywords)
           goto unknown;
       }
 
-    case 2: /* 18 tokens of length 2 */
+    case 2: /* 19 tokens of length 2 */
       switch (name[0])
       {
         case 'd':
@@ -70,6 +70,14 @@ Perl_keyword (pTHX_ const char *name, I32 len, bool all_keywords)
 
           goto unknown;
 
+        case 'f':
+          if (name[1] == 'c')
+          {                                       /* fc               */
+            return (all_keywords || FEATURE_FC_IS_ENABLED ? -KEY_fc : 0);
+          }
+
+          goto unknown;
+
         case 'g':
           switch (name[1])
           {
@@ -3441,5 +3449,5 @@ unknown:
 }
 
 /* Generated from:
- * 29732a698b229f9e5f475fbb191f71c335c9e8d05b6168fe29e61c34c4f10bd2 regen/keywords.pl
+ * e5a540774760ea54c761ef17ee4a153cc264e9a700b817d561e390730c457406 regen/keywords.pl
  * ex: set ro: */