Go: fix CFG bug - implicit field selections with depth 0

go/ql/lib/semmle/go/controlflow/ControlFlowGraphImpl.qll

@@ -679,7 +679,7 @@ module CfgImpl {
           e.(Go::PromotedSelector).refersTo(explicitField) and
           baseType.getFieldAtDepth(_, explicitFieldDepth) = explicitField
         |
-          index = explicitFieldDepth - implicitFieldDepth
+          index = explicitFieldDepth - implicitFieldDepth and index > 0
         )
       )
       or
@@ -689,7 +689,8 @@ module CfgImpl {
         baseType = e.(Go::PromotedSelector).getSelectedStructType() and
         e.(Go::PromotedSelector).refersTo(method) and
         baseType.getMethodAtDepth(_, mDepth) = method and
-        index = mDepth - implicitFieldDepth
+        index = mDepth - implicitFieldDepth and
+        index > 0
       |
         method = baseType.getMethodOfEmbedded(implicitField, _, implicitFieldDepth + 1)
         or

go/ql/test/query-tests/RedundantCode/UnreachableStatement/main.go

@@ -159,4 +159,21 @@ func test19() mystruct {
 	return mystruct{test10(1), test10(2) == 2} // $ Alert
 }
 
+type (
+	embedded  struct{}
+	recursive struct {
+		*embedded
+		value int
+		*recursive
+	}
+)
+
+func test20(x *recursive) []int {
+	values := []int{0}
+	if x.value != 0 {
+		values = append(values, x.value)
+	}
+	return values // OK: reachable because value is a direct field of recursive
+}
+
 func main() {}