Fix iterator edge cases for [high(P),high(P)] (#129)

also:
  cascaded `if` in rbtree (for unrelated troubleshooting)

stew/interval_set.nim

@@ -849,13 +849,17 @@ iterator increasing*[P,S](
   ##    any interval already visited. Intervals not visited yet must not be
   ##    deleted as the loop would become unpredictable.
   var rc = ds.leftPos.ge(minPt)
-  while rc.isOk:
-    let key = rc.value.key
-    if high(P) <= rc.value.right and ds.lastHigh:
-      yield Interval[P,S].new(rc.value.left,high(P))
-    else:
-      yield Interval[P,S].new(rc.value)
-    rc = ds.leftPos.gt(key)
+  if rc.isErr:
+    if ds.lastHigh:
+      yield Interval[P,S].new(high(P),high(P))
+  else:
+    while rc.isOk:
+      let key = rc.value.key
+      if high(P) <= rc.value.right and ds.lastHigh:
+        yield Interval[P,S].new(rc.value.left,high(P))
+      else:
+        yield Interval[P,S].new(rc.value)
+      rc = ds.leftPos.gt(key)
 
 iterator decreasing*[P,S](
     ds: IntervalSetRef[P,S];
@@ -866,8 +870,10 @@ iterator decreasing*[P,S](
   ##
   ## See the note at the `increasing()` function comment about deleting items.
   var rc = ds.leftPos.le(maxPt)
-
-  if rc.isOk:
+  if rc.isErr:
+    if ds.lastHigh:
+      yield Interval[P,S].new(high(P),high(P))
+  else:
     let key = rc.value.key
     # last entry: check for additional point
     if high(P) <= rc.value.right and ds.lastHigh:
@@ -877,10 +883,10 @@ iterator decreasing*[P,S](
     # find the next smaller one
     rc = ds.leftPos.lt(key)
 
-  while rc.isOk:
-    let key = rc.value.key
-    yield Interval[P,S].new(rc.value)
-    rc = ds.leftPos.lt(key)
+    while rc.isOk:
+      let key = rc.value.key
+      yield Interval[P,S].new(rc.value)
+      rc = ds.leftPos.lt(key)
 
 # ------------------------------------------------------------------------------
 # Public interval operators

stew/sorted_set/rbtree_delete.nim

@@ -119,8 +119,9 @@ proc rbTreeDelete*[C,K](rbt: RbTreeRef[C,K]; key: K): RbResult[C] =
       dirY = q.linkLeft.isNil.toDir
     parent.link[dirX] = q.link[dirY];
     # clear node cache if this was the one to be deleted
-    if not rbt.cache.isNil and rbt.cmp(rbt.cache.casket,key) == 0:
-      rbt.cache = nil
+    if not rbt.cache.isNil:
+      if rbt.cmp(rbt.cache.casket,key) == 0:
+        rbt.cache = nil
     q = nil # some hint for the GC to recycle that node
 
     rbt.size.dec

stew/sorted_set/rbtree_find.nim

@@ -31,8 +31,9 @@ proc rbTreeFindEq*[C,K](rbt: RbTreeRef[C,K]; key: K): RbResult[C] =
   if rbt.root.isNil:
     return err(rbEmptyTree)
 
-  if not rbt.cache.isNil and rbt.cmp(rbt.cache.casket,key) == 0:
-    return ok(rbt.cache.casket)
+  if not rbt.cache.isNil:
+    if rbt.cmp(rbt.cache.casket,key) == 0:
+      return ok(rbt.cache.casket)
 
   var
     q = rbt.root

tests/test_interval_set.nim

@@ -177,6 +177,24 @@ suite "IntervalSet: Intervals of FancyPoint entries over FancyScalar":
     check br.total.truncate(uint64) == (uHigh - 10000000) + 1
     check br.verify.isOk
 
+    br.clear()
+    check br.total == 0 and br.chunks == 0
+    check br.merge(uHigh,uHigh) == 1
+
+    block:
+      var (ivVal, ivSet) = (iv(0,0), false)
+      for iv in br.increasing:
+        check ivSet == false
+        (ivVal, ivSet) = (iv, true)
+      check ivVal == iv(uHigh,uHigh)
+
+    block:
+      var (ivVal, ivSet) = (iv(0,0), false)
+      for iv in br.decreasing:
+        check ivSet == false
+        (ivVal, ivSet) = (iv, true)
+      check ivVal == iv(uHigh,uHigh)
+
   test "Merge disjunct intervals on 1st set":
     br.clear()
     check br.merge(  0,  99) == 100