From 0483a6ad0f7da906d39fdec84ab17c5b47c4a28d Mon Sep 17 00:00:00 2001
From: George Robinson <george.robinson@grafana.com>
Date: Mon, 15 Jan 2024 17:30:29 +0000
Subject: [PATCH] Fix missing check for len(name) == 0

Signed-off-by: George Robinson <george.robinson@grafana.com>
---
 matchers/compat/parse.go      |  3 +++
 matchers/compat/parse_test.go | 24 ++++++++++++++++--------
 2 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/matchers/compat/parse.go b/matchers/compat/parse.go
index 541b7a1b..4a9bfe89 100644
--- a/matchers/compat/parse.go
+++ b/matchers/compat/parse.go
@@ -244,6 +244,9 @@ func isValidClassicLabelName(_ log.Logger) func(model.LabelName) bool {
 // isValidUTF8LabelName returns true if the string is a valid UTF-8 label name.
 func isValidUTF8LabelName(_ log.Logger) func(model.LabelName) bool {
 	return func(name model.LabelName) bool {
+		if len(name) == 0 {
+			return false
+		}
 		return utf8.ValidString(string(name))
 	}
 }
diff --git a/matchers/compat/parse_test.go b/matchers/compat/parse_test.go
index a026b8f5..848231dc 100644
--- a/matchers/compat/parse_test.go
+++ b/matchers/compat/parse_test.go
@@ -172,19 +172,23 @@ func TestIsValidClassicLabelName(t *testing.T) {
 		input    model.LabelName
 		expected bool
 	}{{
-		name:     "is accepted",
+		name:     "foo is accepted",
 		input:    "foo",
 		expected: true,
 	}, {
-		name:     "is also accepted",
+		name:     "starts with underscore and ends with number is accepted",
 		input:    "_foo1",
 		expected: true,
 	}, {
-		name:     "is not accepted",
+		name:     "empty is not accepted",
+		input:    "",
+		expected: false,
+	}, {
+		name:     "starts with number is not accepted",
 		input:    "0foo",
 		expected: false,
 	}, {
-		name:     "is also not accepted",
+		name:     "contains emoji is not accepted",
 		input:    "foo🙂",
 		expected: false,
 	}}
@@ -203,21 +207,25 @@ func TestIsValidUTF8LabelName(t *testing.T) {
 		input    model.LabelName
 		expected bool
 	}{{
-		name:     "is accepted",
+		name:     "foo is accepted",
 		input:    "foo",
 		expected: true,
 	}, {
-		name:     "is also accepted",
+		name:     "starts with underscore and ends with number is accepted",
 		input:    "_foo1",
 		expected: true,
 	}, {
-		name:     "is accepted in UTF-8",
+		name:     "starts with number is accepted",
 		input:    "0foo",
 		expected: true,
 	}, {
-		name:     "is also accepted with UTF-8",
+		name:     "contains emoji is accepted",
 		input:    "foo🙂",
 		expected: true,
+	}, {
+		name:     "empty is not accepted",
+		input:    "",
+		expected: false,
 	}}
 
 	for _, test := range tests {