Change a bit behavior of MatchJournal.reset* methods

Now after MatchJournal.reset(pos) cursor points before
the `pos`, not at it. So cursor.next will return 'pos'
It's required for MPSCR-67

reactor/Core/src/jetbrains/mps/logic/reactor/core/internal/MatchJournal.kt

@@ -76,15 +76,21 @@ interface MatchJournal : Iterable<MatchJournal.Chunk>, EvidenceSource {
     val cursor: RemovingJournalIterator
 
     /**
-     * Reset journal's position to the beginning, don't modify journal.
+     * Same as [resetCursor], moves [cursor] before [initialChunk].
      */
-    fun resetCursor()
+    fun resetCursor() = resetCursor(Pos(initialChunk(), 0))
 
     /**
-     * Erase part of the journal between [currentPos] and [pastPos].
+     * Moves [cursor] before [pastPos], so that [ChunkReader.next] is [pastPos].
-     * Resets journal position to specified position.
+     * Doesn't modify journal contents, as opposed to [reset].
+     */
+    fun resetCursor(pastPos: Pos)
+
+    /**
+     * Erase journal between [currentPos] (erased) and [pastPos] (not erased).
+     * Moves [cursor] at [pastPos], so that [ChunkReader.current] is [pastPos].
      * @param pastPos position to reset to.
-     * @throws IllegalStateException when position is not from the past (relative to current pos).
+     * @throws IllegalStateException when position is not from the past (relative to [cursor]).
      */
     fun reset(pastPos: Pos)
 
@@ -92,7 +98,7 @@ interface MatchJournal : Iterable<MatchJournal.Chunk>, EvidenceSource {
      * Replay activated and discarded occurrences logged in journal between current
      * and provided positions. Advances journal position to specified position.
      * Idempotent operation (can be called multiple times on same [Pos]]).
-     * @throws IllegalStateException when position is not from the future (relative to current pos).
+     * @throws IllegalStateException when [futurePos] is not from the future (relative to [cursor]).
      */
     fun replay(futurePos: Pos)
 
@@ -131,6 +137,12 @@ interface MatchJournal : Iterable<MatchJournal.Chunk>, EvidenceSource {
          */
         fun isKnown(chunk: Chunk): Boolean
 
+        /**
+         * Same as [isKnown], but for [Occurrence].
+         * Returns [true] for indexed [Occurrence]s.
+         */
+        fun isKnown(occ: Occurrence): Boolean = activatingChunkOf(occ) != null
+
         /**
          * Returns [Chunk] where [occ] was activated.
          * Returns null for non-principal occurrences & those not from indexed session.

reactor/Core/src/jetbrains/mps/logic/reactor/core/internal/MatchJournalImpl.kt

@@ -189,19 +189,25 @@ internal open class MatchJournalImpl(
     override fun isFront(): Boolean = __cursor.atEnd()
 
 
-    override fun reset(pastPos: MatchJournal.Pos) = reset(pastPos, true)
+    override fun reset(pastPos: MatchJournal.Pos) {
+        reset(pastPos, true)
+        replay(pastPos)
+    }
 
-    override fun resetCursor() = reset(Pos(initialChunk(), 0), false)
+    override fun resetCursor(pastPos: Pos) {
+        reset(pastPos, false)
+    }
 
-    private fun reset(pastPos: MatchJournal.Pos, removing: Boolean) = with(__cursor) {
+    private fun reset(pastPos: MatchJournal.Pos, removing: Boolean) {
-        moveToPastRemoving(pastPos) {
+        __cursor.moveToPastRemoving(pastPos) {
             popAncestor()
             resetOccurrences(it.entries())
-            removing
+            removing && it !== pastPos.chunk
         }
         // drop occurrences at final chunk
-        if (removing) current.entries = current.entries.subList(0, pastPos.entriesCount)
+        if (removing) with(pastPos.chunk as ChunkImpl) {
-        resetOccurrences(current.entries.drop(pastPos.entriesCount))
+            entries = entries.subList(0, pastPos.entriesCount)
+        }
     }
 
     private fun popAncestor() {
@@ -324,8 +330,9 @@ internal open class MatchJournalImpl(
 
 
         /**
-         * Walk in journal in direct order ([from] -> [next])
+         * Walk in journal in direct order ([from] -> [current])
-         * while applying [action] to each visited [Chunk].
+         * while applying [action] to each visited [Chunk]
+         * (not including [from], but including [__current]).
          * No journal state is changed, except by [action] effects
          * (i.e. no reset or replay of occurrences is performed).
          */
@@ -343,21 +350,24 @@ internal open class MatchJournalImpl(
         }
 
         /**
-         * Walk in journal in inverse order ([next] -> [pastPos])
+         * Walk in journal in inverse order ([pastPos] <- [current]) while
-         * while applying [action] to each visited [Chunk]
+         * applying [action] to each [Chunk] (including [pastPos])
-         * and removing it if [action] return [true] for it.
+         * and removing it if [action] returns true for it.
+         *
+         * Contract: after the call [__next] points to [pastPos].
          */
         inline fun moveToPastRemoving(pastPos: Pos, action: (Chunk) -> Boolean) {
             while (!atStart()) {
                 __current = it.previous()
+                if (action(__current)) {
+                    it.remove()
+                }
                 if (this at pastPos) {
-                    it.next() // make it point right after _previous_
+                    __current = it.previous()
+                    it.next() // make it point right after __current
                     updateNext()
                     return
                 }
-                if (action(current)) {
-                    it.remove()
-                }
             }
             this assertAt pastPos
         }