From a95115a6da7aa46980f42d02cc9c2dd9faea08ea Mon Sep 17 00:00:00 2001
From: Thomas Jackson <jacksontj.89@gmail.com>
Date: Thu, 30 Mar 2023 08:10:25 -0700
Subject: [PATCH] Add missing lock to ExtractSelectors

Now that we are parallel walking we need to ensure that the visitor methods are concurrent-safe. Surprisingly this doesn't show up in `-race

Fixes https://github.com/jacksontj/promxy/issues/579
---
 promql/parser/ast.go | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/promql/parser/ast.go b/promql/parser/ast.go
index 4e8f4daa5f..d9117b988e 100644
--- a/promql/parser/ast.go
+++ b/promql/parser/ast.go
@@ -382,11 +382,16 @@ func Walk(ctx context.Context, v Visitor, s *EvalStmt, node Node, path []Node, n
 }
 
 func ExtractSelectors(expr Expr) [][]*labels.Matcher {
-	var selectors [][]*labels.Matcher
+	var (
+		selectors [][]*labels.Matcher
+		l         sync.Mutex
+	)
 	Inspect(context.TODO(), &EvalStmt{Expr: expr}, func(node Node, _ []Node) error {
 		vs, ok := node.(*VectorSelector)
 		if ok {
+			l.Lock()
 			selectors = append(selectors, vs.LabelMatchers)
+			l.Unlock()
 		}
 		return nil
 	}, nil)