Fix topics in loki.source.kafka

CHANGELOG.md

@@ -81,6 +81,8 @@ Main (unreleased)
 
 - Change the log level in the `eventlogmessage` stage of the `loki.process` component from `warn` to `debug`. (@wildum)
 
+- Fix a bug in `loki.source.kafka` where the `topics` argument incorrectly used regex matching instead of exact matches. (@wildum)
+
 ### Other changes
 
 - Change the stability of the `livedebugging` feature from "experimental" to "generally available". (@wildum)

docs/sources/reference/components/loki/loki.source.kafka.md

@@ -49,6 +49,8 @@ loki.source.kafka "LABEL" {
 
 `assignor` values can be either `"range"`, `"roundrobin"`, or `"sticky"`.
 
+If a topic starts with a '^', it is treated as a regex and may match multiple topics.
+
 Labels from the `labels` argument are applied to every message that the component reads.
 
 The `relabel_rules` field can make use of the `rules` export value from a

docs/sources/release-notes.md

@@ -14,6 +14,14 @@ For a complete list of changes to {{< param "FULL_PRODUCT_NAME" >}}, with links
 
 [Changelog]: https://github.com/grafana/alloy/blob/main/CHANGELOG.md
 
+## v1.6
+
+### Breaking change: The `topics` argument in the component `loki.source.kafka` does not use regex by default anymore
+
+A bug in `loki.source.kafka` caused the component to treat all topics as regex. For example, setting the topic value to "foo" would match any topic containing the substring "foo".
+With the fix introduced in this version, topic values are now treated as exact matches by default.
+Regex matching is still supported by prefixing a topic with "^", allowing it to match multiple topics.
+
 ## v1.5
 
 ### Breaking change: Change default value of `max_streams` in `otelcol.processor.deltatocumulative`

internal/component/loki/source/internal/kafkatarget/topics.go

@@ -36,6 +36,7 @@ func newTopicManager(client topicClient, topics []string) (*topicManager, error)
 		}
 		if t[0] != '^' {
 			matches = append(matches, t)
+			continue
 		}
 		re, err := regexp.Compile(t)
 		if err != nil {

internal/component/loki/source/internal/kafkatarget/topics_test.go

@@ -91,6 +91,16 @@ func Test_Topics(t *testing.T) {
 			[]string{"foo", "foobar"},
 			false,
 		},
+		{
+			mustNewTopicsManager(&mockKafkaClient{topics: []string{"foo", "foobar", "buzz"}}, []string{"^foo$"}),
+			[]string{"foo"},
+			false,
+		},
+		{
+			mustNewTopicsManager(&mockKafkaClient{topics: []string{"foo", "foobar", "buzz"}}, []string{"foo"}),
+			[]string{"foo"},
+			false,
+		},
 		{
 			mustNewTopicsManager(&mockKafkaClient{topics: []string{"foo", "foobar", "buzz"}}, []string{"^foo.*", "buzz"}),
 			[]string{"buzz", "foo", "foobar"},