fix(plan): fix logic bug in planner helper method (#5115)

Fixes #5114.

Author: Christopher M. Wolff

libflux/go/libflux/buildinfo.gen.go

@@ -581,7 +581,7 @@ var sourceHashes = map[string]string{
 	"stdlib/universe/simple_max_test.flux":                                                        "a63b3f530e4d81451e3c71a1abeea50cff02e743c9313ab3ffd5bc3b3ce9ad2e",
 	"stdlib/universe/skew_test.flux":                                                              "7782d41c563c77ba9f4176fa1b5f4f6107e418b7ea301e4896398dbcb514315a",
 	"stdlib/universe/sort2_test.flux":                                                             "1d2043c0d0b38abb8dc61fc1baa6d6052fae63fea55cc6e67fd1600911513bdb",
-	"stdlib/universe/sort_limit_test.flux":                                                        "c595da9613faf8734932d8c2e63291517b7842b5656f795b32d50e987493ec2a",
+	"stdlib/universe/sort_limit_test.flux":                                                        "32825b6b789c5b3287ae72967687a63fa3fee783e6626426c9b1cc7f39306dc8",
 	"stdlib/universe/sort_rules_test.flux":                                                        "0770ae42e99b04167ca5bef8340a310b224baf1ba1928997273de9663b64684a",
 	"stdlib/universe/sort_test.flux":                                                              "f69ebb5972762078e759af3c1cd3d852431a569dce74f3c379709c9e174bfa31",
 	"stdlib/universe/spread_test.flux":                                                            "1ddf25e4d86b6365da254229fc8f77bd838c24a79e6a08c9c4c50330ace0a6a3",

plan/types.go

@@ -265,8 +265,8 @@ func mergePlanNodes(top, bottom, merged Node) (Node, error) {
 	}
 
 	merged.AddPredecessors(bottom.Predecessors()...)
-	for i, pred := range merged.Predecessors() {
-		for _, succ := range pred.Successors() {
+	for _, pred := range merged.Predecessors() {
+		for i, succ := range pred.Successors() {
 			if succ == bottom {
 				pred.Successors()[i] = merged
 			}

stdlib/universe/sort_limit_test.flux

@@ -138,3 +138,37 @@ testcase sort_limit_zero_row_table {
 
     testing.diff(got, want)
 }
+
+testcase sort_limit_multi_successor {
+    input =
+        array.from(
+            rows: [
+                {_time: 2022-01-11T00:00:00Z, _value: 10.0},
+                {_time: 2022-01-11T01:00:00Z, _value: 12.0},
+                {_time: 2022-01-11T02:00:00Z, _value: 18.0},
+                {_time: 2022-01-11T03:00:00Z, _value: 4.0},
+                {_time: 2022-01-11T04:00:00Z, _value: 8.0},
+            ],
+        )
+    in0 =
+        input
+            |> bottom(n: 2)
+    in1 =
+        input
+            |> top(n: 2)
+    got =
+        union(tables: [in0, in1])
+            |> sort(columns: ["_time"])
+
+    want =
+        array.from(
+            rows: [
+                {_time: 2022-01-11T01:00:00Z, _value: 12.0},
+                {_time: 2022-01-11T02:00:00Z, _value: 18.0},
+                {_time: 2022-01-11T03:00:00Z, _value: 4.0},
+                {_time: 2022-01-11T04:00:00Z, _value: 8.0},
+            ],
+        )
+
+    testing.diff(got: got, want: want)
+}