Add comments noting methods from embedded interfaces are already included

Author: owen-mc

go/extractor/extractor.go

@@ -1618,6 +1618,9 @@ func extractType(tw *trap.Writer, tp types.Type) trap.Label {
 		case *types.Interface:
 			kind = dbscheme.InterfaceType.Index()
 			for i := 0; i < tp.NumMethods(); i++ {
+				// Note that methods coming from embedded interfaces can be
+				// accessed through `Method(i)`, so there is no need to
+				// deal with them separately.
 				meth := tp.Method(i)
 
 				// Note that methods do not have a parent scope, so they are

go/ql/lib/semmle/go/Types.qll

@@ -737,12 +737,17 @@ class TypeSetLiteralType extends @typesetliteraltype, CompositeType {
   override string toString() { result = "type set literal type" }
 }
 
+predicate foo(NamedType t, string name, Type mt) {
+  t.getUnderlyingType().(InterfaceType).getMethodType(name) = mt
+}
+
 /** An interface type. */
 class InterfaceType extends @interfacetype, CompositeType {
   /** Gets the type of method `name` of this interface type. */
   Type getMethodType(string name) {
     // Note that negative indices correspond to embedded interfaces and type
-    // set literals.
+    // set literals. Note also that methods coming from embedded interfaces
+    // have already been included in `component_types`.
     exists(int i | i >= 0 | component_types(this, i, name, result))
   }