Fix bug - implicit field selection created with depth 0

Author: owen-mc

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

@@ -682,7 +682,7 @@ module CfgImpl {
           e.(Go::PromotedSelector).refersTo(explicitField) and
           baseType.getFieldAtDepth(_, explicitFieldDepth) = explicitField
         |
-          index = explicitFieldDepth - implicitFieldDepth
+          index = explicitFieldDepth - implicitFieldDepth and index > 0
         )
       )
       or
@@ -692,7 +692,8 @@ 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/CONSISTENCY/CfgConsistency.expected

@@ -1,6 +1,5 @@
 consistencyOverview
-| deadEnd | 12 |
-| missingInNodeForPostOrInOrder | 1 |
+| deadEnd | 11 |
 deadEnd
 | main.go:17:2:17:10 | select statement |
 | main.go:109:2:109:10 | select statement |
@@ -13,6 +12,3 @@ deadEnd
 | main.go:157:2:157:10 | select statement |
 | main.go:164:2:164:10 | select statement |
 | main.go:168:2:168:10 | select statement |
-| main.go:200:5:200:11 | implicit-field:0 selection of value |
-missingInNodeForPostOrInOrder
-| main.go:200:5:200:11 | selection of value |

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

@@ -11,4 +11,3 @@
 | 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:171:2:171:14 | expression statement | This statement is unreachable. |
-| main.go:203:2:203:14 | return statement | This statement is unreachable. |

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

@@ -200,7 +200,7 @@ func test24(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() {}