Support UTF-8 label matchers: Do not allow unquoted escape sequences (#3571)

* Do not allow unquoted escape sequences

This commit updates the matchers parser to reject unquoted
openmetrics escape sequences. As an example, foo=bar\n
will no longer parse, and must instead be written as
foo="bar\n". This avoids an issue where the input is valid
in both the matchers and classic parsers, but results
in two different parsings.

---------

Signed-off-by: George Robinson <george.robinson@grafana.com>

matchers/compat/parse_test.go

@@ -38,8 +38,8 @@ func TestFallbackMatcherParser(t *testing.T) {
 		expected: mustNewMatcher(t, labels.MatchEqual, "foo🙂", "bar"),
 	}, {
 		name:     "is accepted in old parser but not new",
-		input:    "foo=!bar",
-		expected: mustNewMatcher(t, labels.MatchEqual, "foo", "!bar"),
+		input:    "foo=!bar\\n",
+		expected: mustNewMatcher(t, labels.MatchEqual, "foo", "!bar\n"),
 	}, {
 		name:  "is accepted in neither",
 		input: "foo!bar",
@@ -81,10 +81,10 @@ func TestFallbackMatchersParser(t *testing.T) {
 		},
 	}, {
 		name:  "is accepted in old parser but not new",
-		input: "{foo=!bar,bar=$baz}",
+		input: "{foo=!bar,bar=$baz\\n}",
 		expected: labels.Matchers{
 			mustNewMatcher(t, labels.MatchEqual, "foo", "!bar"),
-			mustNewMatcher(t, labels.MatchEqual, "bar", "$baz"),
+			mustNewMatcher(t, labels.MatchEqual, "bar", "$baz\n"),
 		},
 	}, {
 		name:  "is accepted in neither",

matchers/compliance/compliance_test.go

@@ -76,6 +76,7 @@ func TestCompliance(t *testing.T) {
 				m, _ := labels.NewMatcher(labels.MatchEqual, "foo", "\\t")
 				return append(ms, m)
 			}(),
+			skip: true,
 		},
 		{
 			input: `{foo=bar\t}`,
@@ -84,6 +85,7 @@ func TestCompliance(t *testing.T) {
 				m, _ := labels.NewMatcher(labels.MatchEqual, "foo", "bar\\t")
 				return append(ms, m)
 			}(),
+			skip: true,
 		},
 		{
 			input: `{foo=bar\}`,
@@ -92,6 +94,7 @@ func TestCompliance(t *testing.T) {
 				m, _ := labels.NewMatcher(labels.MatchEqual, "foo", "bar\\")
 				return append(ms, m)
 			}(),
+			skip: true,
 		},
 		{
 			input: `{foo=bar\\}`,

matchers/parse/lexer.go

@@ -25,7 +25,7 @@ const (
 )
 
 func isReserved(r rune) bool {
-	return unicode.IsSpace(r) || strings.ContainsRune("{}!=~,\"'`", r)
+	return unicode.IsSpace(r) || strings.ContainsRune("{}!=~,\\\"'`", r)
 }
 
 // expectedError is returned when the next rune does not match what is expected.

matchers/parse/parse_test.go

@@ -195,6 +195,10 @@ func TestMatchers(t *testing.T) {
 		name:  "invalid escape sequence",
 		input: "{foo=\"bar\\w\"}",
 		error: "5:12: \"bar\\w\": invalid input",
+	}, {
+		name:  "no unquoted escape sequences",
+		input: "{foo=bar\\n}",
+		error: "8:9: \\: invalid input: expected a comma or close brace",
 	}}
 
 	for _, test := range tests {