From 4fba6bea82f00ac811093681130ccf83a79dee63 Mon Sep 17 00:00:00 2001
From: Alan Bernstein <alan.aaron.bernstein@gmail.com>
Date: Fri, 29 Jan 2021 09:39:01 -0600
Subject: [PATCH 1/2] Prevent nil pointer exception during Distinct key
 translation

---
 executor.go | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/executor.go b/executor.go
index 9fa829aac..9b4ad515e 100644
--- a/executor.go
+++ b/executor.go
@@ -6572,6 +6572,9 @@ func (e *executor) translateResult(ctx context.Context, index string, idx *Index
 
 			if field.Keys() {
 				rslt := result.Pos
+				if rslt == nil {
+					return &SignedRow{Pos: &Row{}}, nil
+				}
 				other := &Row{Attrs: rslt.Attrs}
 				for _, segment := range rslt.Segments() {
 					keys, err := e.Cluster.translateIndexIDs(context.Background(), field.ForeignIndex(), segment.Columns())

From c4455acbd8df8bcdefc8c103f84673697f340fb3 Mon Sep 17 00:00:00 2001
From: Alan Bernstein <alan.aaron.bernstein@gmail.com>
Date: Fri, 29 Jan 2021 09:39:31 -0600
Subject: [PATCH 2/2] Use inconsistent JSON schema to reach Distinct
 translation error condition

---
 executor_test.go | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/executor_test.go b/executor_test.go
index 6a202ca3a..17ebbfc95 100644
--- a/executor_test.go
+++ b/executor_test.go
@@ -5397,6 +5397,19 @@ func TestExecutor_ForeignIndex(t *testing.T) {
 		pilosa.OptFieldKeys(),
 	)
 
+	// stepchild/other field needs to have usesKeys=true
+	crashSchemaJson := `{"indexes": [{"name": "stepparent","createdAt": 1611247966371721700,"options": {"keys": true,"trackExistence": true},"shardWidth": 1048576},{"name": "stepchild","createdAt": 1611247953796662800,"options": {"keys": true,"trackExistence": true},"shardWidth": 1048576,"fields": [{"name": "parent_id","createdAt": 1611247953797265700,"options": {"type": "int","base": 0,"bitDepth": 28,"min": -9223372036854776000,"max": 9223372036854776000,"keys": false,"foreignIndex": "stepparent"}},{"name": "other","createdAt": 1611247953796814000,"options": {"type": "int","base": 0,"bitDepth": 17,"min": -9223372036854776000,"max": 9223372036854776000,"keys": true,"foreignIndex": ""}}]}]}`
+
+	crashSchema := &pilosa.Schema{}
+	err := json.Unmarshal([]byte(crashSchemaJson), &crashSchema)
+	if err != nil {
+		t.Fatalf("json unmarshall: %v", err)
+	}
+	err = c.GetNode(0).API.ApplySchema(context.Background(), crashSchema, false)
+	if err != nil {
+		t.Fatalf("applying JSON schema: %v", err)
+	}
+
 	// Populate parent data.
 	c.Query(t, "parent", fmt.Sprintf(`
 			Set("one", general=1)
@@ -5442,6 +5455,12 @@ func TestExecutor_ForeignIndex(t *testing.T) {
 		t.Fatalf("unexpected keys: %v", row.Keys)
 	}
 
+	crash := c.Query(t, "stepchild", `Distinct(Row(parent_id=3), field=other)`).Results[0].(pilosa.SignedRow)
+	if !sameStringSlice(crash.Pos.Keys, []string{}) {
+		// empty result; error condition does not require data
+		t.Fatalf("unexpected columns: %v", crash.Pos.Keys)
+	}
+
 	eq := c.Query(t, "child", `Row(parent_id=="one")`).Results[0].(*pilosa.Row)
 	if !reflect.DeepEqual(eq.Columns(), []uint64{1, ShardWidth}) {
 		t.Fatalf("unexpected columns: %v", eq.Columns())