Work-in-progress: Implement a PPC0031-style eq:u flagged operator

Adds:
 * operator flag parser token type (OPFLAGS)
 * expected next token to be opflags or term (XOPFLAGTERM)
 * internal API function to modify operator opcode to add private flags
   (apply_opflags)

Still TODO:
 * More robustness testing, especially around new PL_expect value
 * Think about and test how actual chaining works with multiple of these

Author: leonerd

embed.fnc

@@ -701,6 +701,8 @@ Apx	|void	|apply_attrs_string					\
 Adp	|OP *	|apply_builtin_cv_attributes				\
 				|NN CV *cv				\
 				|NULLOK OP *attrlist
+Xp	|U32	|apply_opflags	|U32 optype				\
+				|NULLOK char *flagstr
 CTp	|void	|atfork_lock
 CTp	|void	|atfork_unlock
 Cop	|SV **	|av_arylen_p	|NN AV *av

embed.h

@@ -999,6 +999,7 @@
 #   define amagic_applies(a,b,c)                Perl_amagic_applies(aTHX_ a,b,c)
 #   define amagic_is_enabled(a)                 Perl_amagic_is_enabled(aTHX_ a)
 #   define apply(a,b,c)                         Perl_apply(aTHX_ a,b,c)
+#   define apply_opflags(a,b)                   Perl_apply_opflags(aTHX_ a,b)
 #   define av_extend_guts(a,b,c,d,e)            Perl_av_extend_guts(aTHX_ a,b,c,d,e)
 #   define av_nonelem(a,b)                      Perl_av_nonelem(aTHX_ a,b)
 #   define av_remove_offset(a)                  Perl_av_remove_offset(aTHX_ a)

op.c

@@ -16192,6 +16192,28 @@ Perl_rcpv_copy(pTHX_ char *pv) {
     return pv;
 }
 
+U32
+Perl_apply_opflags(pTHX_ U32 opcode, char *flagstr)
+{
+    U16 opcode_base = opcode & 0xFFFF;
+    U8 priv = (opcode_base >> 16) & 0xFF;
+
+    for(char flag; (flag = *flagstr); flagstr++) {
+        switch(opcode_base) {
+            case OP_SEQ:
+            case OP_EQ:
+                switch(flag) {
+                    case 'u':
+                        priv |= OPpEQ_UNDEF;
+                        continue;
+                }
+        }
+        croak("Unrecognized flag '%c' for %s", flag, PL_op_desc[opcode_base]);
+    }
+
+    return opcode_base | (priv << 16);
+}
+
 /*
  * ex: set ts=8 sts=4 sw=4 et:
  */

perl.h

@@ -5898,7 +5898,8 @@ typedef enum {
     XTERMBLOCK,
     XBLOCKTERM,
     XPOSTDEREF,
-    XTERMORDORDOR /* evil hack */
+    XTERMORDORDOR, /* evil hack */
+    XOPFLAGSTERM, /* next token should be opflags or a term */
     /* update exp_name[] in toke.c if adding to this enum */
 } expectation;