[exporter/datadog] Add empty removedSettings list (#9090)

exporter/datadogexporter/config/config.go

@@ -443,6 +443,10 @@ func (c *Config) Validate() error {
 }
 
 func (c *Config) Unmarshal(configMap *config.Map) error {
+	if err := handleRemovedSettings(configMap); err != nil {
+		return err
+	}
+
 	err := configMap.UnmarshalExact(c)
 	if err != nil {
 		return err

exporter/datadogexporter/config/warning_deprecated.go

@@ -38,7 +38,7 @@ type renameError struct {
 	issueNumber uint
 }
 
-// List of settings that are deprecated.
+// List of settings that are deprecated but not yet removed.
 var renamedSettings = []renameError{
 	{
 		oldName:      "metrics::send_monotonic_counter",
@@ -86,6 +86,9 @@ var renamedSettings = []renameError{
 	},
 }
 
+// List of settings that have been removed, but for which we keep a custom error.
+var removedSettings = []renameError{}
+
 // Error implements the error interface.
 func (e renameError) Error() string {
 	return fmt.Sprintf(
@@ -97,6 +100,19 @@ func (e renameError) Error() string {
 	)
 }
 
+// RemovedErr returns an error describing that the old name was removed in favor of the new name.
+func (e renameError) RemovedErr(configMap *config.Map) error {
+	if configMap.IsSet(e.oldName) {
+		return fmt.Errorf(
+			"%q was removed in favor of %q. See github.com/open-telemetry/opentelemetry-collector-contrib/issues/%d",
+			e.oldName,
+			e.newName,
+			e.issueNumber,
+		)
+	}
+	return nil
+}
+
 // Check if the deprecated option is being used.
 // Error out if both the old and new options are being used.
 func (e renameError) Check(configMap *config.Map) (bool, error) {
@@ -126,3 +142,10 @@ func handleRenamedSettings(configMap *config.Map, cfg *Config) (warnings []error
 	}
 	return
 }
+
+func handleRemovedSettings(configMap *config.Map) (err error) {
+	for _, removed := range removedSettings {
+		err = multierr.Append(err, removed.RemovedErr(configMap))
+	}
+	return
+}