Ensure FunctionInputs corresponding to results have an entry node

ql/src/semmle/go/dataflow/FunctionInputsAndOutputs.qll

@@ -107,15 +107,20 @@ private class ResultInput extends FunctionInput, TInResult {
   }
 
   override DataFlow::Node getEntryNode(DataFlow::CallNode c) {
-    exists(DataFlow::PostUpdateNode pun, DataFlow::Node init |
-      pun = result and
-      init = pun.(DataFlow::SsaNode).getInit()
-    |
+    exists(DataFlow::Node pred |
       index = -1 and
-      init = c.getResult()
+      pred = c.getResult()
       or
       index >= 0 and
-      init = c.getResult(index)
+      pred = c.getResult(index)
+    |
+      // if the result is assigned to an SSA variable, we want to propagate mutations backwards
+      // through that variable
+      exists(DataFlow::SsaNode ssa | ssa.getInit() = pred | result = ssa)
+      or
+      // otherwise the entry node is simply the result
+      not exists(DataFlow::SsaNode ssa | ssa.getInit() = pred) and
+      result = pred
     )
   }
 

ql/test/library-tests/semmle/go/dataflow/FunctionInputsAndOutputs/FunctionInput_getEntryNode.expected

@@ -3,6 +3,8 @@
 | parameter 0 | main.go:55:2:55:27 | call to Printf | main.go:55:13:55:20 | "%d, %d" |
 | parameter 0 | main.go:57:2:57:27 | call to Printf | main.go:57:13:57:20 | "%d, %d" |
 | parameter 0 | reset.go:12:2:12:21 | call to Reset | reset.go:12:15:12:20 | source |
+| parameter 0 | tst2.go:10:9:10:26 | call to NewEncoder | tst2.go:10:25:10:25 | w |
+| parameter 0 | tst2.go:10:9:10:39 | call to Encode | tst2.go:10:35:10:38 | data |
 | parameter 0 | tst.go:10:2:10:29 | call to ReadFrom | tst.go:10:23:10:28 | reader |
 | parameter 0 | tst.go:16:2:16:12 | call to test5 | tst.go:16:8:16:8 | x |
 | parameter 0 | tst.go:18:2:18:12 | call to test5 | tst.go:18:8:18:8 | s |
@@ -17,6 +19,21 @@
 | parameter 2 | main.go:57:2:57:27 | call to Printf | main.go:57:26:57:26 | y |
 | receiver | main.go:53:14:53:21 | call to bump | main.go:53:14:53:14 | c |
 | receiver | reset.go:12:2:12:21 | call to Reset | reset.go:12:2:12:7 | reader |
+| receiver | tst2.go:10:9:10:39 | call to Encode | tst2.go:10:9:10:26 | call to NewEncoder |
 | receiver | tst.go:10:2:10:29 | call to ReadFrom | tst.go:10:2:10:12 | bytesBuffer |
+| result | main.go:51:2:51:14 | call to op | main.go:51:2:51:14 | call to op |
+| result | main.go:53:2:53:22 | call to op2 | main.go:53:2:53:22 | call to op2 |
+| result | main.go:53:14:53:21 | call to bump | main.go:53:14:53:21 | call to bump |
+| result | tst2.go:10:9:10:26 | call to NewEncoder | tst2.go:10:9:10:26 | call to NewEncoder |
+| result | tst2.go:10:9:10:39 | call to Encode | tst2.go:10:2:10:4 | definition of err |
 | result | tst.go:9:17:9:33 | call to new | tst.go:9:2:9:12 | definition of bytesBuffer |
+| result 0 | main.go:51:2:51:14 | call to op | main.go:51:2:51:14 | call to op |
+| result 0 | main.go:53:2:53:22 | call to op2 | main.go:53:2:53:22 | call to op2 |
+| result 0 | main.go:53:14:53:21 | call to bump | main.go:53:14:53:21 | call to bump |
+| result 0 | main.go:54:10:54:15 | call to test | main.go:54:2:54:2 | definition of x |
+| result 0 | main.go:56:9:56:15 | call to test2 | main.go:56:2:56:2 | definition of x |
+| result 0 | tst2.go:10:9:10:26 | call to NewEncoder | tst2.go:10:9:10:26 | call to NewEncoder |
+| result 0 | tst2.go:10:9:10:39 | call to Encode | tst2.go:10:2:10:4 | definition of err |
 | result 0 | tst.go:9:17:9:33 | call to new | tst.go:9:2:9:12 | definition of bytesBuffer |
+| result 1 | main.go:54:10:54:15 | call to test | main.go:54:5:54:5 | definition of y |
+| result 1 | main.go:56:9:56:15 | call to test2 | main.go:56:5:56:5 | definition of y |

ql/test/library-tests/semmle/go/dataflow/FunctionInputsAndOutputs/FunctionInput_getExitNode.expected

@@ -2,6 +2,7 @@
 | parameter 0 | main.go:13:1:20:1 | function declaration | main.go:13:10:13:11 | definition of op |
 | parameter 0 | main.go:40:1:48:1 | function declaration | main.go:40:12:40:12 | definition of b |
 | parameter 0 | reset.go:8:1:16:1 | function declaration | reset.go:8:27:8:27 | definition of r |
+| parameter 0 | tst2.go:8:1:12:1 | function declaration | tst2.go:8:12:8:15 | definition of data |
 | parameter 0 | tst.go:8:1:11:1 | function declaration | tst.go:8:12:8:17 | definition of reader |
 | parameter 0 | tst.go:15:1:19:1 | function declaration | tst.go:15:12:15:12 | definition of x |
 | parameter 1 | main.go:5:1:11:1 | function declaration | main.go:5:20:5:20 | definition of x |

ql/test/library-tests/semmle/go/dataflow/FunctionInputsAndOutputs/FunctionModelStep.expected

@@ -1,2 +1,4 @@
+| file://:0:0:0:0 | Encode | tst2.go:10:35:10:38 | data | tst2.go:10:9:10:26 | call to NewEncoder |
+| file://:0:0:0:0 | NewEncoder | tst2.go:10:9:10:26 | call to NewEncoder | tst2.go:9:6:9:6 | definition of w |
 | file://:0:0:0:0 | ReadFrom | tst.go:10:23:10:28 | reader | tst.go:9:2:9:12 | definition of bytesBuffer |
 | file://:0:0:0:0 | Reset | reset.go:12:15:12:20 | source | reset.go:11:6:11:11 | definition of reader |

ql/test/library-tests/semmle/go/dataflow/FunctionInputsAndOutputs/FunctionOutput_getEntryNode.expected

@@ -11,10 +11,12 @@
 | result 0 | main.go:40:1:48:1 | function declaration | main.go:40:21:40:23 | zero value for int |
 | result 0 | main.go:40:1:48:1 | function declaration | main.go:45:10:45:10 | 0 |
 | result 0 | main.go:40:1:48:1 | function declaration | main.go:47:9:47:9 | 0 |
+| result 0 | tst2.go:8:1:12:1 | function declaration | tst2.go:11:9:11:9 | w |
 | result 1 | main.go:31:1:33:1 | function declaration | main.go:32:13:32:14 | 42 |
 | result 1 | main.go:35:1:38:1 | function declaration | main.go:35:22:35:22 | zero value for y |
 | result 1 | main.go:35:1:38:1 | function declaration | main.go:36:9:36:10 | 42 |
 | result 1 | main.go:40:1:48:1 | function declaration | main.go:40:26:40:26 | zero value for y |
 | result 1 | main.go:40:1:48:1 | function declaration | main.go:42:3:42:5 | rhs of increment statement |
 | result 1 | main.go:40:1:48:1 | function declaration | main.go:45:13:45:13 | 1 |
 | result 1 | main.go:40:1:48:1 | function declaration | main.go:47:12:47:12 | 4 |
+| result 1 | tst2.go:8:1:12:1 | function declaration | tst2.go:11:12:11:14 | err |

ql/test/library-tests/semmle/go/dataflow/FunctionInputsAndOutputs/FunctionOutput_getExitNode.expected

@@ -1,19 +1,26 @@
 | parameter 0 | reset.go:12:2:12:21 | call to Reset | reset.go:9:2:9:7 | definition of source |
+| parameter 0 | tst2.go:10:9:10:26 | call to NewEncoder | tst2.go:9:6:9:6 | definition of w |
+| parameter 0 | tst2.go:10:9:10:39 | call to Encode | tst2.go:8:12:8:15 | definition of data |
 | parameter 0 | tst.go:10:2:10:29 | call to ReadFrom | tst.go:8:12:8:17 | definition of reader |
 | parameter 0 | tst.go:16:2:16:12 | call to test5 | tst.go:15:12:15:12 | definition of x |
 | parameter 1 | tst.go:16:2:16:12 | call to test5 | tst.go:15:15:15:15 | definition of y |
 | receiver | main.go:53:14:53:21 | call to bump | main.go:52:2:52:2 | definition of c |
 | receiver | reset.go:12:2:12:21 | call to Reset | reset.go:11:6:11:11 | definition of reader |
+| receiver | tst2.go:10:9:10:39 | call to Encode | tst2.go:10:9:10:26 | call to NewEncoder |
 | receiver | tst.go:10:2:10:29 | call to ReadFrom | tst.go:9:2:9:12 | definition of bytesBuffer |
 | result | main.go:51:2:51:14 | call to op | main.go:51:2:51:14 | call to op |
 | result | main.go:53:2:53:22 | call to op2 | main.go:53:2:53:22 | call to op2 |
 | result | main.go:53:14:53:21 | call to bump | main.go:53:14:53:21 | call to bump |
+| result | tst2.go:10:9:10:26 | call to NewEncoder | tst2.go:10:9:10:26 | call to NewEncoder |
+| result | tst2.go:10:9:10:39 | call to Encode | tst2.go:10:9:10:39 | call to Encode |
 | result | tst.go:9:17:9:33 | call to new | tst.go:9:17:9:33 | call to new |
 | result 0 | main.go:51:2:51:14 | call to op | main.go:51:2:51:14 | call to op |
 | result 0 | main.go:53:2:53:22 | call to op2 | main.go:53:2:53:22 | call to op2 |
 | result 0 | main.go:53:14:53:21 | call to bump | main.go:53:14:53:21 | call to bump |
 | result 0 | main.go:54:10:54:15 | call to test | main.go:54:2:54:15 | ... := ...[0] |
 | result 0 | main.go:56:9:56:15 | call to test2 | main.go:56:2:56:15 | ... = ...[0] |
+| result 0 | tst2.go:10:9:10:26 | call to NewEncoder | tst2.go:10:9:10:26 | call to NewEncoder |
+| result 0 | tst2.go:10:9:10:39 | call to Encode | tst2.go:10:9:10:39 | call to Encode |
 | result 0 | tst.go:9:17:9:33 | call to new | tst.go:9:17:9:33 | call to new |
 | result 1 | main.go:54:10:54:15 | call to test | main.go:54:2:54:15 | ... := ...[1] |
 | result 1 | main.go:56:9:56:15 | call to test2 | main.go:56:2:56:15 | ... = ...[1] |

ql/test/library-tests/semmle/go/dataflow/FunctionInputsAndOutputs/FunctionOutput_isResult.expected

@@ -1,4 +1,6 @@
 | main.go:51:2:51:14 | call to op | main.go:51:2:51:14 | call to op | result |
 | main.go:53:2:53:22 | call to op2 | main.go:53:2:53:22 | call to op2 | result |
 | main.go:53:14:53:21 | call to bump | main.go:53:14:53:21 | call to bump | result |
+| tst2.go:10:9:10:26 | call to NewEncoder | tst2.go:10:9:10:26 | call to NewEncoder | result |
+| tst2.go:10:9:10:39 | call to Encode | tst2.go:10:9:10:39 | call to Encode | result |
 | tst.go:9:17:9:33 | call to new | tst.go:9:17:9:33 | call to new | result |

ql/test/library-tests/semmle/go/dataflow/FunctionInputsAndOutputs/FunctionOutput_isResult_int.expected

@@ -8,5 +8,9 @@
 | main.go:54:10:54:15 | call to test | main.go:54:2:54:15 | ... := ...[1] | 1 | result 1 |
 | main.go:56:9:56:15 | call to test2 | main.go:56:2:56:15 | ... = ...[0] | 0 | result 0 |
 | main.go:56:9:56:15 | call to test2 | main.go:56:2:56:15 | ... = ...[1] | 1 | result 1 |
+| tst2.go:10:9:10:26 | call to NewEncoder | tst2.go:10:9:10:26 | call to NewEncoder | 0 | result |
+| tst2.go:10:9:10:26 | call to NewEncoder | tst2.go:10:9:10:26 | call to NewEncoder | 0 | result 0 |
+| tst2.go:10:9:10:39 | call to Encode | tst2.go:10:9:10:39 | call to Encode | 0 | result |
+| tst2.go:10:9:10:39 | call to Encode | tst2.go:10:9:10:39 | call to Encode | 0 | result 0 |
 | tst.go:9:17:9:33 | call to new | tst.go:9:17:9:33 | call to new | 0 | result |
 | tst.go:9:17:9:33 | call to new | tst.go:9:17:9:33 | call to new | 0 | result 0 |

ql/test/library-tests/semmle/go/dataflow/FunctionInputsAndOutputs/tst2.go

@@ -0,0 +1,12 @@
+package main
+
+import (
+	"encoding/json"
+	"io"
+)
+
+func test7(data interface{}) (io.Writer, error) {
+	var w io.Writer
+	err := json.NewEncoder(w).Encode(data)
+	return w, err
+}