remove outplace version of 'merge' for CountTables (#13377)

* remove outplace version of 'merge' for CountTables

* remove 'merge' tests

changelog.md

@@ -21,6 +21,10 @@
   compiler type trait instead of macro. `distinctBase` in sugar module is now deprecated.
 - `CountTable.mget` has been removed from `tables.nim`. It didn't work, and it
   was an oversight to be included in v1.0.
+- `tables.merge(CountTable, CountTable): CountTable` has been removed.
+  It didn't work well together with the existing inplace version of the same proc
+  (`tables.merge(var CountTable, CountTable)`).
+  It was an oversight to be included in v1.0.
 
 
 ### Breaking changes in the compiler

lib/pure/collections/tables.nim

@@ -2487,18 +2487,19 @@ proc merge*[A](s: var CountTable[A], t: CountTable[A]) =
   for key, value in t:
     s.inc(key, value)
 
-proc merge*[A](s, t: CountTable[A]): CountTable[A] =
-  ## Merges the two tables into a new one.
-  runnableExamples:
-    let
-      a = toCountTable("aaabbc")
-      b = toCountTable("bcc")
-    doAssert merge(a, b) == toCountTable("aaabbbccc")
+when (NimMajor, NimMinor) <= (1, 0):
+  proc merge*[A](s, t: CountTable[A]): CountTable[A] =
+    ## Merges the two tables into a new one.
+    runnableExamples:
+      let
+        a = toCountTable("aaabbc")
+        b = toCountTable("bcc")
+      doAssert merge(a, b) == toCountTable("aaabbbccc")
 
-  result = initCountTable[A](nextPowerOfTwo(max(s.len, t.len)))
-  for table in @[s, t]:
-    for key, value in table:
-      result.inc(key, value)
+    result = initCountTable[A](nextPowerOfTwo(max(s.len, t.len)))
+    for table in @[s, t]:
+      for key, value in table:
+        result.inc(key, value)
 
 proc `$`*[A](t: CountTable[A]): string =
   ## The ``$`` operator for count tables. Used internally when calling `echo`
@@ -3006,13 +3007,6 @@ when isMainModule:
   t2l.inc("foo", 4)
   t2l.inc("bar")
   t2l.inc("baz", 11)
-  let
-    t1merging = t1l
-    t2merging = t2l
-  let merged = merge(t1merging, t2merging)
-  assert(merged["foo"] == 5)
-  assert(merged["bar"] == 3)
-  assert(merged["baz"] == 14)
 
   block:
     const testKey = "TESTKEY"