fix #15836 proc arg return type auto unexpectly match proc with concr… (#21065)

* fix #15836 proc arg return type auto unexpectly match proc with concrete type

* fix #16244

* add test case for #12869

tests/misc/t12869.nim

@@ -0,0 +1,14 @@
+discard """
+  errormsg: "type mismatch: got <bool> but expected 'int'"
+  line: 12
+"""
+
+import sugar
+from algorithm import sorted, SortOrder
+
+let a = 5
+
+proc sorted*[T](a: openArray[T], key: proc(v: T): int, order = SortOrder.Ascending): seq[T] =
+  sorted(a, (x, y) => key(x) < key(y), order)
+
+echo sorted(@[9, 1, 8, 2, 6, 4, 5, 0], (x) => (a - x).abs)

tests/misc/t16244.nim

@@ -0,0 +1,9 @@
+discard """
+  errormsg: "type mismatch: got <int, float64>"
+  line: 9
+"""
+
+proc g(): auto = 1
+proc h(): auto = 1.0
+
+var a = g() + h()