From c2efd5bf961b6fe63c7a9a7ec2d12bb1cc60411e Mon Sep 17 00:00:00 2001
From: Bryan Boreham <bjboreham@gmail.com>
Date: Wed, 20 Oct 2021 15:03:02 +0100
Subject: [PATCH] promql: copy data when short-circuiting (#9552)

* promql: copy data when short-circuiting

Because the range query loop re-uses the output buffer each time round,
we must copy results into the buffer rather than using input as output.

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
(cherry picked from commit a278ea4b58226c3db271fb78703cd110089cba9b)
---
 promql/engine.go      |  9 ++++++---
 promql/engine_test.go | 26 ++++++++++++++++++++++++++
 2 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/promql/engine.go b/promql/engine.go
index e5dbcd2d77..7887e19f4a 100644
--- a/promql/engine.go
+++ b/promql/engine.go
@@ -1792,9 +1792,11 @@ func (ev *evaluator) VectorOr(lhs, rhs Vector, matching *parser.VectorMatching,
 		panic("set operations must only use many-to-many matching")
 	}
 	if len(lhs) == 0 { // Short-circuit.
-		return rhs
+		enh.Out = append(enh.Out, rhs...)
+		return enh.Out
 	} else if len(rhs) == 0 {
-		return lhs
+		enh.Out = append(enh.Out, lhs...)
+		return enh.Out
 	}
 
 	leftSigs := map[string]struct{}{}
@@ -1819,7 +1821,8 @@ func (ev *evaluator) VectorUnless(lhs, rhs Vector, matching *parser.VectorMatchi
 	// Short-circuit: empty rhs means we will return everything in lhs;
 	// empty lhs means we will return empty - don't need to build a map.
 	if len(lhs) == 0 || len(rhs) == 0 {
-		return lhs
+		enh.Out = append(enh.Out, lhs...)
+		return enh.Out
 	}
 
 	rightSigs := map[string]struct{}{}
diff --git a/promql/engine_test.go b/promql/engine_test.go
index c4eb07d523..7ac6ae1d2f 100644
--- a/promql/engine_test.go
+++ b/promql/engine_test.go
@@ -2410,6 +2410,32 @@ func TestRangeQuery(t *testing.T) {
 			End:      time.Unix(120, 0),
 			Interval: 1 * time.Minute,
 		},
+		{
+			Name: "short-circuit",
+			Load: `load 30s
+							foo{job="1"} 1+1x4
+							bar{job="2"} 1+1x4`,
+			Query: `foo > 2 or bar`,
+			Result: Matrix{
+				Series{
+					Points: []Point{{V: 1, T: 0}, {V: 3, T: 60000}, {V: 5, T: 120000}},
+					Metric: labels.Labels{
+						labels.Label{Name: "__name__", Value: "bar"},
+						labels.Label{Name: "job", Value: "2"},
+					},
+				},
+				Series{
+					Points: []Point{{V: 3, T: 60000}, {V: 5, T: 120000}},
+					Metric: labels.Labels{
+						labels.Label{Name: "__name__", Value: "foo"},
+						labels.Label{Name: "job", Value: "1"},
+					},
+				},
+			},
+			Start:    time.Unix(0, 0),
+			End:      time.Unix(120, 0),
+			Interval: 1 * time.Minute,
+		},
 	}
 	for _, c := range cases {
 		t.Run(c.Name, func(t *testing.T) {