[659038] Check interface hierarchy before reporting ambiguous errors

mcs/mcs/ecore.cs

@@ -4175,8 +4175,39 @@ namespace Mono.CSharp {
 										continue;
 								}
 
-								// Is the new candidate better
-								if (BetterFunction (rc, candidate_args, member, pm.Parameters, params_expanded_form, best_candidate, best_parameter_member.Parameters, best_candidate_params)) {
+								bool is_better;
+								if (best_candidate.DeclaringType.IsInterface && member.DeclaringType.ImplementsInterface (best_candidate.DeclaringType, false)) {
+									//
+									// We pack all interface members into top level type which makes the overload resolution
+									// more complicated for interfaces. We accomodate for this by removing methods with same
+									// signature when building the cache hence this path should not really be hit often
+									//
+									// Example:
+									// interface IA { void Foo (int arg); }
+									// interface IB : IA { void Foo (params int[] args); }
+									//
+									// IB::Foo is the best overload when calling IB.Foo (1)
+									//
+									is_better = true;
+									if (ambiguous_candidates != null) {
+										foreach (var amb_cand in ambiguous_candidates) {
+											if (member.DeclaringType.ImplementsInterface (best_candidate.DeclaringType, false)) {
+												continue;
+											}
+
+											is_better = false;
+											break;
+										}
+
+										if (is_better)
+											ambiguous_candidates = null;
+									}
+								} else {
+									// Is the new candidate better
+									is_better = BetterFunction (rc, candidate_args, member, pm.Parameters, params_expanded_form, best_candidate, best_parameter_member.Parameters, best_candidate_params);
+								}
+
+								if (is_better) {
 									best_candidate = member;
 									best_candidate_args = candidate_args;
 									best_candidate_params = params_expanded_form;
@@ -4253,6 +4284,33 @@ namespace Mono.CSharp {
 			}
 
 			if (ambiguous_candidates != null) {
+				if (best_candidate.DeclaringType.IsInterface) {
+					ambiguous_candidates.Add (new AmbiguousCandidate (best_candidate, best_parameter_member.Parameters, best_candidate_params));
+					for (int cix = 0; cix < ambiguous_candidates.Count; ++cix) {
+						var tested_type = ambiguous_candidates[cix].Member.DeclaringType;
+
+						int ix = 0;
+						for (; ix < ambiguous_candidates.Count; ++ix) {
+							var amb_cand_type = ambiguous_candidates[ix].Member.DeclaringType;
+							if (amb_cand_type == tested_type)
+								continue;
+
+							if (tested_type.ImplementsInterface (amb_cand_type, false))
+								continue;
+
+							break;
+						}
+
+						if (ix != ambiguous_candidates.Count)
+							continue;
+
+						best_candidate = ambiguous_candidates[cix].Member;
+						//best_parameter_member = ambiguous_candidates
+
+						throw new NotImplementedException ();
+					}
+				}
+
 				//
 				// Now check that there are no ambiguities i.e the selected method
 				// should be better than all the others

mcs/tests/ver-il-gmcs.xml

@@ -8986,6 +8986,13 @@
       </method>
     </type>
   </test>
+  <test name="gtest-333.cs">
+    <type name="Program">
+      <method name="Void Main()">
+        <size>13</size>
+      </method>
+    </type>
+  </test>
   <test name="gtest-334.cs">
     <type name="Test">
       <method name="Void .ctor()">
@@ -9521,6 +9528,56 @@
       </method>
     </type>
   </test>
+  <test name="gtest-353.cs">
+    <type name="A`3[D1,D2,D3]">
+      <method name="Void Foo[T]()">
+        <size>1</size>
+      </method>
+      <method name="Void .ctor()">
+        <size>7</size>
+      </method>
+    </type>
+    <type name="B`1[DD2]">
+      <method name="Void .ctor()">
+        <size>7</size>
+      </method>
+    </type>
+    <type name="C">
+      <method name="Void Foo[T]()">
+        <size>1</size>
+      </method>
+      <method name="Void .ctor()">
+        <size>7</size>
+      </method>
+    </type>
+    <type name="Program">
+      <method name="Void Main()">
+        <size>11</size>
+      </method>
+      <method name="Void .ctor()">
+        <size>7</size>
+      </method>
+    </type>
+  </test>
+  <test name="gtest-354.cs">
+    <type name="M">
+      <method name="Void IC.Method(System.Int32[])">
+        <size>1</size>
+      </method>
+      <method name="System.String IA&lt;string&gt;.Method(Int32)">
+        <size>6</size>
+      </method>
+      <method name="Void IB.Method(Int32)">
+        <size>6</size>
+      </method>
+      <method name="Void Main()">
+        <size>23</size>
+      </method>
+      <method name="Void .ctor()">
+        <size>7</size>
+      </method>
+    </type>
+  </test>
   <test name="gtest-355.cs">
     <type name="A">
       <method name="Void .ctor()">
@@ -39774,16 +39831,6 @@
       </method>
     </type>
   </test>
-  <test name="test-679.cs">
-    <type name="Program">
-      <method name="Void .ctor()">
-        <size>7</size>
-      </method>
-      <method name="Int32 Main()">
-        <size>12</size>
-      </method>
-    </type>
-  </test>
   <test name="test-68.cs">
     <type name="Y">
       <method name="Void .ctor()">