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Add ability to attach labels to individual struct fields:
#[derive(Metrics)]
#[metrics(scope = "forwarder")]
struct TransactionMetrics {
#[metric(rename = "transactions", labels = [("outcome", "forwarded")])]
forwarded_transactions: Counter,
#[metric(rename = "transactions", labels = [("outcome", "dropped")])]
dropped_transactions: Counter,
}
Field-level labels are appended to struct-level labels passed via
new_with_labels().
Closes #1
- Add FieldLabelMetrics and DynamicFieldLabelMetrics test structs - Add field_labels_static and field_labels_dynamic tests - Add compile-fail tests for invalid label syntax
Add ability to specify labels at the struct level that apply to all fields:
#[derive(Metrics)]
#[metrics(scope = "api", labels = [("service", "gateway")])]
struct ApiMetrics {
/// Total requests.
requests: Counter,
}
Label order: instance labels (new_with_labels) → global labels → field labels.
Label values can now be constants or other expressions, not just string literals:
const SERVICE_NAME: &str = "gateway";
#[derive(Metrics)]
#[metrics(scope = "api", labels = [("service", SERVICE_NAME)])]
struct ApiMetrics {
requests: Counter,
}
Label keys must still be string literals.
mattsse
approved these changes
Feb 1, 2026
Error at compile time if the same label key is specified multiple times within a single labels attribute.
mattsse
approved these changes
Feb 1, 2026
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Add ability to attach labels to individual struct fields:
This allows multiple fields to share the same metric name while being distinguished by label values, which renders better in dashboards than separate metric names.
Field-level labels are appended to struct-level labels passed via
new_with_labels(), so both can coexist.Closes #1