Fix bug - implicit field selection created with depth 0

Author: owen-mc

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/UnreachableStatement.expected

@@ -10,4 +10,3 @@
 | main.go:147:2:147:17 | return statement | This statement is unreachable. |
 | main.go:153:2:153:22 | return statement | This statement is unreachable. |
 | main.go:159:2:159:43 | return statement | This statement is unreachable. |
-| main.go:176:2:176:14 | return statement | This statement is unreachable. |

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

@@ -173,7 +173,7 @@ func test20(x *recursive) []int {
 	if x.value != 0 {
 		values = append(values, x.value)
 	}
-	return values // $ SPURIOUS: Alert // BUG: reachable because value is a direct field of recursive
+	return values // OK: reachable because value is a direct field of recursive
 }
 
 func main() {}