fix #15756 (#15761)

* fix #15756

* simplify test

(cherry picked from commit 610e9b2fe9)

compiler/varpartitions.nim

@@ -126,7 +126,7 @@ proc hasSideEffect*(c: var Partitions; info: var MutationInfo): bool =
       return true
   return false
 
-template isConstParam(a): bool = a.kind == skParam and a.typ.kind != tyVar
+template isConstParam(a): bool = a.kind == skParam and a.typ.kind notin {tyVar, tySink}
 
 proc variableId(c: Partitions; x: PSym): int =
   for i in 0 ..< c.s.len:

tests/effects/tstrict_funcs.nim

@@ -15,3 +15,15 @@ proc get_Contig2Reads(sin: Stream, fn: string, contig2len: TableRef[string, int]
     if contig2len.haskey(parser.row[1]):
       mgetOrPut(result, parser.row[1], @[]).add(parser.row[0])
 
+
+
+block:
+  # issue #15756
+  func `&&&`[T](x: var seq[T], y: sink T): seq[T] =
+    newSeq(result, x.len + 1)
+    for i in 0..x.len-1:
+      result[i] = move(x[i])
+    result[x.len] = move(y)
+
+  var x = @[0, 1]
+  let z = x &&& 2