Fix #14144 confusing error message misusing a callable object

runtime/vm/flow_graph_inliner.cc

Index: runtime/vm/flow_graph_inliner.cc
diff --git a/runtime/vm/flow_graph_inliner.cc b/runtime/vm/flow_graph_inliner.cc
index 1d3937704a34d910e05de19ccb421b8a24a49274..50eac24972af3a40a8bc6f7b7ec949da0a563972 100644
--- a/runtime/vm/flow_graph_inliner.cc
+++ b/runtime/vm/flow_graph_inliner.cc
@@ -1261,6 +1261,12 @@ class CallSiteInliner : public ValueObject {
         TRACE_INLINING(THR_Print("     Bailout: non-closure operator\n"));
         continue;
       }
+
+      if (target.NumParameters() != call->ArgumentCount()) {

[Florian Schneider, 2017/03/30 20:18:05]

Good catch!

Your fix is safe, but it could be improved by taking the fixed parameter count
into account:

if (call->ArgumentCount() > target.NumParameters() ||
    call->ArgumentCount() < target.num_fixed_parameters()) {
  // Bailout
  continue;
}

This way the inliner can still inline the closure if it has optional parameters.
A function f(a, b, [c]) would be only valid to inline when called with 2 or 3
arguments.

Optional parameters are dealt with later in AdjustForOptionalParameters which
fills in the default values for missing optional arguments.

+        TRACE_INLINING(THR_Print("     Bailout: wrong parameter count\n"));
+        continue;
+      }
+
       GrowableArray<Value*> arguments(call->ArgumentCount());
       for (int i = 0; i < call->ArgumentCount(); ++i) {
         arguments.Add(call->PushArgumentAt(i)->value());