.

wcfs/internal/xbtree/rangeset.go

@@ -193,7 +193,17 @@ func (S *RangeSet) DelRange(r Range) {
 	}
 
 	// [ilo+1:jhi-1] should be deleted
-	// [ilo] and [jhi-1] overlap with [r.lo,r.hi) - they shuold be deleted or shrinked.
+	// [ilo] and [jhi-1] overlap with [r.lo,r.hi) - they shuold be deleted, or shrinked,
+	// or split+shrinked if ilo==jhi-1 and r is inside [ilo]
+	if jhi-ilo == 1 && S.rangev[ilo].lo < r.lo && r.hi_ < S.rangev[ilo].hi_ {
+		x := S.rangev[ilo]
+		S.rangev = append(
+			S.rangev[:ilo],		append([]Range{
+			x, x},
+			S.rangev[ilo+1:]...)...)
+		jhi++
+		debugfRSet("\tpresplit copy %s\t-> %s\n", x, S)
+	}
 	if S.rangev[ilo].lo < r.lo { // shrink left
 		S.rangev = append(
 			S.rangev[:ilo],		append([]Range{