toke.c: Create function to see if an identifier is known

This checks first if there is a lexical variable in scope with the given
name, and if not, if there is a global

Author: khwilliamson

embed.fnc

@@ -6154,6 +6154,11 @@ S	|int	|intuit_method	|NN char *start 			\
 				|NULLOK NOCHECK CV *cv
 S	|int	|intuit_more	|NN char *s				\
 				|NN char *e
+S	|bool	|is_existing_identifier 				\
+				|NN char *s				\
+				|Size_t len				\
+				|char sigil				\
+				|bool is_utf8
 S	|I32	|lop		|enum yytokentype t			\
 				|I32 f					\
 				|U8 x					\

embed.h

@@ -1685,6 +1685,7 @@
 #     define incline(a,b)                       S_incline(aTHX_ a,b)
 #     define intuit_method(a,b,c)               S_intuit_method(aTHX_ a,b,c)
 #     define intuit_more(a,b)                   S_intuit_more(aTHX_ a,b)
+#     define is_existing_identifier(a,b,c,d)    S_is_existing_identifier(aTHX_ a,b,c,d)
 #     define lop(a,b,c,d)                       S_lop(aTHX_ a,b,c,d)
 #     define missingterm(a,b)                   S_missingterm(aTHX_ a,b)
 #     define parse_ident(a,b,c,d,e,f)           S_parse_ident(aTHX_ a,b,c,d,e,f)

proto.h

@@ -4464,6 +4464,33 @@ S_scan_const(pTHX_ char *start)
     return s;
 }
 
+STATIC bool
+S_is_existing_identifier(pTHX_ char *s, Size_t len, char sigil, bool is_utf8)
+{
+    PERL_ARGS_ASSERT_IS_EXISTING_IDENTIFIER;
+
+    /* This returns a boolean indicating if a string represents an identifier
+     * known to the program.  'sigil' is the character indicating the type of
+     * the identifier to look for. (though '%' is currently not specially
+     * handled.) The string from 's + 1' to (s + len) is looked at.  s[0] is
+     * ignored, but must exist; the function overwrites it temporarily,
+     * restoring it before returning */
+
+    char save_sigil = s[0];
+    s[0] = sigil;
+    PADOFFSET slot = pad_findmy_pv(s, 0);
+    s[0] = save_sigil;
+
+    return   slot != NOT_IN_PAD
+          || gv_fetchpvn_flags(s + 1, len - 1,
+                             (is_utf8) ? SVf_UTF8 : 0,
+                             (sigil == '@')
+                              ? SVt_PVAV
+                              : (sigil == '&')
+                                 ? SVt_PVCV
+                                 : SVt_PV);
+}
+
 /* S_intuit_more
  * Returns TRUE if there's more to the expression (e.g., a subscript),
  * FALSE otherwise.