Fix matchersToPostingGroups vals variable shadow bug (thanos-io#6817)

* fix matchersToPostingGroups vals variable shadow bug

Signed-off-by: Ben Ye <benye@amazon.com>

* update changelog

Signed-off-by: Ben Ye <benye@amazon.com>

---------

Signed-off-by: Ben Ye <benye@amazon.com>

CHANGELOG.md

@@ -12,6 +12,8 @@ We use *breaking :warning:* to mark changes that are not backward compatible (re
 
 ### Fixed
 
+- [#6817](https://github.com/thanos-io/thanos/pull/6817) Store Gateway: fix `matchersToPostingGroups` label values variable got shadowed bug.
+
 ### Added
 
 ### Changed

pkg/store/bucket.go

@@ -2503,8 +2503,9 @@ func matchersToPostingGroups(ctx context.Context, lvalsFn func(name string) ([]s
 			}
 			// Cache label values because label name is the same.
 			if !valuesCached && vals != nil {
+				lvals := vals
 				lvalsFunc = func(_ string) ([]string, error) {
-					return vals, nil
+					return lvals, nil
 				}
 				valuesCached = true
 			}

pkg/store/bucket_test.go

@@ -3076,6 +3076,29 @@ func TestMatchersToPostingGroup(t *testing.T) {
 				},
 			},
 		},
+		{
+			name: "Reproduce values shadow bug",
+			matchers: []*labels.Matcher{
+				labels.MustNewMatcher(labels.MatchRegexp, "name", "test.*"),
+				labels.MustNewMatcher(labels.MatchNotRegexp, "name", "testfoo"),
+				labels.MustNewMatcher(labels.MatchNotEqual, "name", ""),
+			},
+			labelValues: map[string][]string{
+				"name": {"testbar", "testfoo"},
+			},
+			expected: []*postingGroup{
+				{
+					name:    "name",
+					addAll:  false,
+					addKeys: []string{"testbar"},
+					matchers: []*labels.Matcher{
+						labels.MustNewMatcher(labels.MatchNotEqual, "name", ""),
+						labels.MustNewMatcher(labels.MatchRegexp, "name", "test.*"),
+						labels.MustNewMatcher(labels.MatchNotRegexp, "name", "testfoo"),
+					},
+				},
+			},
+		},
 	} {
 		t.Run(tc.name, func(t *testing.T) {
 			actual, err := matchersToPostingGroups(ctx, func(name string) ([]string, error) {