PATCH: partial [perl #86972]: Allow /aia

This allows a second /a modifier to not have to be contiguous with the
first.  This patch changes only the part in toke.c where the modifiers
are in suffix form.

pod/perldiag.pod

@@ -4014,15 +4014,16 @@ discovered.
 (P) The regular expression engine got confused by what the regular
 expression compiler gave it.
 
+=item Regexp modifier "/%c" may appear a maximum of twice
+
 =item Regexp modifier "/%c" may not appear twice
 
-(F syntax) The regular expression pattern had one of the
-mutually exclusive modifiers repeated.  Remove all but one of the
-occurrences.
+(F syntax) The regular expression pattern had too many occurrences
+of the specified modifier.  Remove the extraneous ones.
 
 =item Regexp modifiers "/%c" and "/%c" are mutually exclusive
 
-(F syntax) The regular expression pattern had more than one of the
+(F syntax) The regular expression pattern had more than one of these
 mutually exclusive modifiers.  Retain only the modifier that is
 supposed to be there.
 

t/lib/warnings/toke

@@ -960,12 +960,15 @@ EXPECT
 # toke.c
 use warnings 'syntax' ;
 my $a = qr/foo/du;
-$a = qr/foo/laai;
+$a = qr/foo/lai;
 $a = qr/foo/lil;
+$a = qr/foo/aia;
+$a = qr/foo/aaia;
 no warnings 'syntax' ;
 my $a = qr/foo/du;
 EXPECT
 Regexp modifiers "/d" and "/u" are mutually exclusive at - line 3, near "= "
 Regexp modifiers "/l" and "/a" are mutually exclusive at - line 4, near "= "
 Regexp modifier "/l" may not appear twice at - line 5, near "= "
-BEGIN not safe after errors--compilation aborted at - line 6.
+Regexp modifier "/a" may appear a maximum of twice at - line 7, near "= "
+BEGIN not safe after errors--compilation aborted at - line 8.

toke.c

@@ -8877,17 +8877,21 @@ S_pmflag(pTHX_ const char* const valid_flags, U32 * pmfl, char** s, char* charse
 	    if (*((*s) + 1) == 'n') {
 		goto deprecate;
 	    }
-	    if (*((*s) + 1) == ASCII_RESTRICT_PAT_MOD) {
-		/* Doubled modifier implies more restricted */
-		set_regex_charset(pmfl, REGEX_ASCII_MORE_RESTRICTED_CHARSET);
-		(*s)++;
-	    }
-	    else {
+
+	    if (! *charset) {
 		set_regex_charset(pmfl, REGEX_ASCII_RESTRICTED_CHARSET);
 	    }
-	    if (*charset) { /* Do this after the increment of *s in /aa, so
-			       the return advances the ptr correctly */
-		goto multiple_charsets;
+	    else {
+
+		/* Error if previous modifier wasn't an 'a', but if it was, see
+		 * if, and accept, a second occurrence (only) */
+		if (*charset != 'a'
+		    || get_regex_charset(*pmfl)
+			!= REGEX_ASCII_RESTRICTED_CHARSET)
+		{
+			goto multiple_charsets;
+		}
+		set_regex_charset(pmfl, REGEX_ASCII_MORE_RESTRICTED_CHARSET);
 	    }
 	    *charset = c;
 	    break;
@@ -8912,6 +8916,9 @@ S_pmflag(pTHX_ const char* const valid_flags, U32 * pmfl, char** s, char* charse
 	if (*charset != c) {
 	    yyerror(Perl_form(aTHX_ "Regexp modifiers \"/%c\" and \"/%c\" are mutually exclusive", *charset, c));
 	}
+	else if (c == 'a') {
+	    yyerror("Regexp modifier \"/a\" may appear a maximum of twice");
+	}
 	else {
 	    yyerror(Perl_form(aTHX_ "Regexp modifier \"/%c\" may not appear twice", c));
 	}