improve error messages by filtering out highly unlikely mismatches

compiler/semcall.nim

@@ -164,8 +164,18 @@ proc presentFailedCandidates(c: PContext, n: PNode, errors: CandidateErrors):
       prefer = preferModuleInfo
       break
 
+  # we pretend procs are attached to the type of the first
+  # argument in order to remove plenty of candidates. This is
+  # comparable to what C# does and C# is doing fine.
+  var filterOnlyFirst = false
+  for err in errors:
+    if err.firstMismatch > 1:
+      filterOnlyFirst = true
+      break
+
   var candidates = ""
   for err in errors:
+    if filterOnlyFirst and err.firstMismatch == 1: continue
     if err.sym.kind in routineKinds and err.sym.ast != nil:
       add(candidates, renderTree(err.sym.ast,
             {renderNoBody, renderNoComments, renderNoPragmas}))