fixes #2625

lib/pure/collections/tables.nim

@@ -819,15 +819,18 @@ proc enlarge[A](t: var CountTable[A]) =
   swap(t.data, n)
 
 proc `[]=`*[A](t: var CountTable[A], key: A, val: int) =
-  ## puts a (key, value)-pair into `t`. `val` has to be positive.
+  ## puts a (key, value)-pair into `t`.
   assert val > 0
   var h = rawGet(t, key)
   if h >= 0:
     t.data[h].val = val
   else:
-    h = -1 - h
+    if mustRehash(len(t.data), t.counter): enlarge(t)
-    t.data[h].key = key
+    rawInsert(t, t.data, key, val)
-    t.data[h].val = val
+    inc(t.counter)
+    #h = -1 - h
+    #t.data[h].key = key
+    #t.data[h].val = val
 
 proc initCountTable*[A](initialSize=64): CountTable[A] =
   ## creates a new count table that is empty.

tests/collections/tcounttable.nim

@@ -0,0 +1,19 @@
+discard """
+  output: "And we get here"
+"""
+
+# bug #2625
+
+const s_len = 32
+
+import tables
+var substr_counts: CountTable[string] = initCountTable[string]()
+var my_string = "Hello, this is sadly broken for strings over 64 characters. Note that it *does* appear to work for short strings."
+for i in 0..(my_string.len - s_len):
+  let s = my_string[i..i+s_len-1]
+  substr_counts[s] = 1
+  # substr_counts[s] = substr_counts[s] + 1  # Also breaks, + 2 as well, etc.
+  # substr_counts.inc(s)  # This works
+  #echo "Iteration ", i
+
+echo "And we get here"