Fix inheritance through redefined type

Author: owen-mc

go/ql/lib/semmle/go/dataflow/internal/FlowSummaryImpl.qll

@@ -377,7 +377,8 @@ module SourceSinkInterpretationInput implements
       or
       n2.asExpr() = n.asInstruction().(IR::EvalImplicitDerefInstruction).getOperand()
     |
-      result = lookThroughPointerType(skipImplicitFieldReads(n2).getType())
+      result =
+        maybeLookThroughNamedType(lookThroughPointerType(skipImplicitFieldReads(n2).getType()))
     )
   }
 
@@ -395,6 +396,12 @@ module SourceSinkInterpretationInput implements
           .getBaseInstruction()
   }
 
+  private DefinedType maybeLookThroughNamedType(DefinedType t) {
+    // We do not have information on what a defined type is defined to be, only
+    // the underlying type, so we have to be a bit imprecise.
+    result.getBaseType() = t.getBaseType()
+  }
+
   /** Provides additional sink specification logic. */
   bindingset[c]
   predicate interpretOutput(string c, InterpretNode mid, InterpretNode node) {

go/ql/test/library-tests/semmle/go/dataflow/ExternalFlowInheritance/test_fields.go

@@ -91,5 +91,5 @@ func TestFieldsRedefinedP1(t test.RedefinedP1) {
 
 func TestFieldsRedefinedS1(t test.RedefinedS1) {
 	a := t.SourceField
-	t.SinkField = a // $ ql_S1 MISSING: S1[f] S1[t]
+	t.SinkField = a // $ S1[f] S1[t] ql_S1
 }

go/ql/test/library-tests/semmle/go/dataflow/ExternalFlowInheritance/test_methods.go

@@ -175,5 +175,5 @@ func TestMethodsSEmbedS1AndSEmbedS1(t test.SEmbedS1AndSEmbedS1) {
 func TestMethodsRedefinedI1(t test.RedefinedI1) {
 	x := t.Source()
 	y := t.Step(x)
-	t.Sink(y) // $ ql_I1 MISSING: I1[f] I1[t] SPURIOUS: ql_P1 ql_S1
+	t.Sink(y) // $ I1[f] I1[t] ql_I1 SPURIOUS: ql_P1 ql_S1
 }