[connector/routing] warn if a routing table entry already exists (#31297

)

**Description:** <Describe what has changed.>
Based on discussion in #30663, a warning is logged if there are two or
more routing items with the same routing statement.

**Link to tracking Issue:** #30663

.chloggen/kristofgyuracz-routing-table-warning.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: routingconnector
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: "a warning is logged if there are two or more routing items with the same routing statement"
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [ 30663 ]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [user]

connector/routingconnector/router.go

@@ -6,6 +6,7 @@ package routingconnector // import "github.com/open-telemetry/opentelemetry-coll
 import (
 	"errors"
 	"fmt"
+	"strings"
 
 	"go.opentelemetry.io/collector/component"
 	"go.uber.org/zap"
@@ -119,6 +120,13 @@ func (r *router[C]) registerRouteConsumers() error {
 		route, ok := r.routes[key(item)]
 		if !ok {
 			route.statement = statement
+		} else {
+			pipelineNames := []string{}
+			for _, pipeline := range item.Pipelines {
+				pipelineNames = append(pipelineNames, pipeline.String())
+			}
+			exporters := strings.Join(pipelineNames, ", ")
+			r.logger.Warn(fmt.Sprintf(`Statement %q already exists in the routing table, the route with target pipeline(s) %q will be ignored.`, item.Statement, exporters))
 		}
 
 		consumer, err := r.consumerProvider(item.Pipelines...)