FIX: Parse rule fails when input is modified and so does not advance

resolves: Oldes/Rebol-issues#2452

src/core/u-parse.c

@@ -56,6 +56,7 @@ enum parse_flags {
 	PF_CHANGE,
 	PF_RETURN,
 	PF_WHILE,
+	PF_ADVANCE, // used to report that although index was not changed, rule is suppose to advance
 };
 
 #define MAX_PARSE_DEPTH 512
@@ -839,8 +840,8 @@ void Print_Parse_Index(REBCNT type, REBVAL *rules, REBSER *series, REBCNT index)
 					// #2269 - reset the position if we are not in the middle of any rule
 					// don't allow code like: [copy x :pos integer!]
 					if (flags != 0) Trap1(RE_PARSE_RULE, rules-1); 
-                    begin = index;
-
+					begin = index;
+					SET_FLAG(parse->flags, PF_ADVANCE);
 					continue;
 				}
 
@@ -978,10 +979,20 @@ void Print_Parse_Index(REBCNT type, REBVAL *rules, REBSER *series, REBCNT index)
 			if (i != NOT_FOUND) {
 				count++; // may overflow to negative
 				if (count < 0) count = MAX_I32; // the forever case
+
 				// If input did not advance:
-				if (i == index && !GET_FLAG(flags, PF_WHILE)) {
-					if (count < mincount) index = NOT_FOUND; // was not enough
-					break;
+				if (i == index) {
+					// check if there was processed some _modifying_ rule, which should advance
+					// even if index was not changed (https://github.com/Oldes/Rebol-issues/issues/2452)
+					if (GET_FLAG(parse->flags, PF_ADVANCE)) {
+						// clear the state in case, that there are other rules to be processed
+						// keep it in case that we were at the last one
+						if(count < maxcount) CLR_FLAG(parse->flags, PF_ADVANCE);
+					}
+					else if (!GET_FLAG(flags, PF_WHILE)) {
+						if (count < mincount) index = NOT_FOUND; // was not enough
+						break;
+					}
 				}
 			}
 			//if (i >= series->tail) {     // OLD check: no more input
@@ -1058,6 +1069,7 @@ void Print_Parse_Index(REBCNT type, REBVAL *rules, REBSER *series, REBCNT index)
 						if (IS_PROTECT_SERIES(series)) Trap0(RE_PROTECTED);
 						Remove_Series(series, begin, count);
 					}
+					SET_FLAG(parse->flags, PF_ADVANCE);
 					index = begin;
 				}
 				if (flags & (1<<PF_INSERT | 1<<PF_CHANGE)) {
@@ -1090,6 +1102,7 @@ void Print_Parse_Index(REBCNT type, REBVAL *rules, REBSER *series, REBCNT index)
 						index = Modify_String(GET_FLAG(flags, PF_CHANGE) ? A_CHANGE : A_INSERT,
 								series, begin, item, cmd, count, 1);
 					}
+					SET_FLAG(parse->flags, PF_ADVANCE);
 				}
 				if (GET_FLAG(flags, PF_AND)) index = begin;
 			}

src/tests/units/_known-issues_.r3

@@ -36,15 +36,6 @@ Rebol [
 ===end-group===
 
 
-===start-group=== "PARSE"
---test-- "parse remove"
-	--assert parse v: "yx" [some [remove #"y" | #"x"] ]
-	--assert v = "x"
-	--assert parse "yx" [copy v any [ remove #"y" | #"x" ] ]
-	--assert v = "x"
-===end-group===
-
-
 ===start-group=== "TIME"
 	;@@ https://github.com/Oldes/Rebol-issues/issues/2416
 	--test-- "time protect 1"

src/tests/units/parse-test.r3

@@ -113,10 +113,23 @@ Rebol [
 
 ===start-group=== "REMOVE"
 --test-- "remove"
-	;--assert parse v: "yx" [some [remove #"y" | #"x"] ]
-	;--assert v = "x"
-	;--assert parse "yx" [copy v any [ remove #"y" | #"x" ] ]
-	;--assert v = "x"
+;@@ https://github.com/Oldes/Rebol-issues/issues/2452
+	--assert parse v: "yx" [some [remove #"y" | #"x"]]
+	--assert v = "x"
+	--assert parse "yx" [copy v any [ remove #"y" | #"x" ]]
+	--assert v = "x"
+	--assert parse v: "yx" [some [change #"y" "" | #"x"]]
+	--assert v = "x"
+	--assert parse v: "ab" [any [s: 1 skip e: (e: remove/part s e) :e | skip]]
+	--assert empty? v
+	; and also:
+	lr: [s: #L integer! e: (s: remove/part s 2) :s]
+	--assert parse v: [#L 1 "a" #L 2 "b"][some [lr | string!]]
+	--assert v = ["a" "b"]
+	--assert parse v: [#L 1 "a" #L 2 "b"][some [string! | lr]]
+	--assert v = ["a" "b"]
+
+--test-- "while .. remove"
 	remove-any-y: [while [remove #"y" | #"x"]] 
 	--assert parse v: "" remove-any-y
 	--assert parse v: "yx" remove-any-y