[APM] Lint rule for explicit return types (#124771) (#125619)

(cherry picked from commit 0202164)

.eslintrc.js

@@ -885,6 +885,18 @@ module.exports = {
         ],
       },
     },
+    {
+      // require explicit return types in route handlers for performance reasons
+      files: ['x-pack/plugins/apm/server/**/route.ts'],
+      rules: {
+        '@typescript-eslint/explicit-function-return-type': [
+          'error',
+          {
+            allowTypedFunctionExpressions: false,
+          },
+        ],
+      },
+    },
 
     /**
      * Fleet overrides

x-pack/plugins/apm/server/routes/backends/route.ts

@@ -21,6 +21,7 @@ import { getTopBackends } from './get_top_backends';
 import { getUpstreamServicesForBackend } from './get_upstream_services_for_backend';
 import { getThroughputChartsForBackend } from './get_throughput_charts_for_backend';
 import { getErrorRateChartsForBackend } from './get_error_rate_charts_for_backend';
+import { ConnectionStatsItemWithImpact } from './../../../common/connections';
 
 const topBackendsRoute = createApmServerRoute({
   endpoint: 'GET /internal/apm/backends/top_backends',
@@ -105,10 +106,11 @@ const topBackendsRoute = createApmServerRoute({
     ]);
 
     return {
+      // eslint-disable-next-line @typescript-eslint/explicit-function-return-type
       backends: currentBackends.map((backend) => {
         const { stats, ...rest } = backend;
         const prev = previousBackends.find(
-          (item) => item.location.id === backend.location.id
+          (item): boolean => item.location.id === backend.location.id
         );
         return {
           ...rest,
@@ -221,17 +223,24 @@ const upstreamServicesForBackendRoute = createApmServerRoute({
     ]);
 
     return {
-      services: currentServices.map((service) => {
-        const { stats, ...rest } = service;
-        const prev = previousServices.find(
-          (item) => item.location.id === service.location.id
-        );
-        return {
-          ...rest,
-          currentStats: stats,
-          previousStats: prev?.stats ?? null,
-        };
-      }),
+      services: currentServices.map(
+        (
+          service
+        ): Omit<ConnectionStatsItemWithImpact, 'stats'> & {
+          currentStats: ConnectionStatsItemWithImpact['stats'];
+          previousStats: ConnectionStatsItemWithImpact['stats'] | null;
+        } => {
+          const { stats, ...rest } = service;
+          const prev = previousServices.find(
+            (item): boolean => item.location.id === service.location.id
+          );
+          return {
+            ...rest,
+            currentStats: stats,
+            previousStats: prev?.stats ?? null,
+          };
+        }
+      ),
     };
   },
 });

x-pack/plugins/apm/server/routes/correlations/route.ts

@@ -27,6 +27,13 @@ import { withApmSpan } from '../../utils/with_apm_span';
 
 import { createApmServerRoute } from '../apm_routes/create_apm_server_route';
 import { environmentRt, kueryRt, rangeRt } from '../default_api_types';
+import { LatencyCorrelation } from './../../../common/correlations/latency_correlations/types';
+import {
+  FieldStats,
+  TopValuesStats,
+} from './../../../common/correlations/field_stats_types';
+import { FieldValuePair } from './../../../common/correlations/types';
+import { FailedTransactionsCorrelation } from './../../../common/correlations/failed_transactions_correlations/types';
 
 const INVALID_LICENSE = i18n.translate('xpack.apm.correlations.license.text', {
   defaultMessage:
@@ -59,7 +66,7 @@ const fieldCandidatesRoute = createApmServerRoute({
 
     return withApmSpan(
       'get_correlations_field_candidates',
-      async () =>
+      async (): Promise<{ fieldCandidates: string[] }> =>
         await fetchTransactionDurationFieldCandidates(esClient, {
           ...resources.params.query,
           index: indices.transaction,
@@ -106,7 +113,7 @@ const fieldStatsRoute = createApmServerRoute({
 
     return withApmSpan(
       'get_correlations_field_stats',
-      async () =>
+      async (): Promise<{ stats: FieldStats[]; errors: any[] }> =>
         await fetchFieldsStats(
           esClient,
           {
@@ -155,7 +162,7 @@ const fieldValueStatsRoute = createApmServerRoute({
 
     return withApmSpan(
       'get_correlations_field_value_stats',
-      async () =>
+      async (): Promise<TopValuesStats> =>
         await fetchFieldValueFieldStats(
           esClient,
           {
@@ -206,7 +213,7 @@ const fieldValuePairsRoute = createApmServerRoute({
 
     return withApmSpan(
       'get_correlations_field_value_pairs',
-      async () =>
+      async (): Promise<{ errors: any[]; fieldValuePairs: FieldValuePair[] }> =>
         await fetchTransactionDurationFieldValuePairs(
           esClient,
           {
@@ -268,7 +275,11 @@ const significantCorrelationsRoute = createApmServerRoute({
 
     return withApmSpan(
       'get_significant_correlations',
-      async () =>
+      async (): Promise<{
+        latencyCorrelations: LatencyCorrelation[];
+        ccsWarning: boolean;
+        totalDocCount: number;
+      }> =>
         await fetchSignificantCorrelations(
           esClient,
           paramsWithIndex,
@@ -321,7 +332,10 @@ const pValuesRoute = createApmServerRoute({
 
     return withApmSpan(
       'get_p_values',
-      async () => await fetchPValues(esClient, paramsWithIndex, fieldCandidates)
+      async (): Promise<{
+        failedTransactionsCorrelations: FailedTransactionsCorrelation[];
+        ccsWarning: boolean;
+      }> => await fetchPValues(esClient, paramsWithIndex, fieldCandidates)
     );
   },
 });

x-pack/plugins/apm/server/routes/data_view/route.ts

@@ -9,6 +9,7 @@ import { createStaticDataView } from './create_static_data_view';
 import { setupRequest } from '../../lib/helpers/setup_request';
 import { getDynamicDataView } from './get_dynamic_data_view';
 import { createApmServerRoute } from '../apm_routes/create_apm_server_route';
+import { ISavedObjectsRepository } from '../../../../../../src/core/server';
 
 const staticDataViewRoute = createApmServerRoute({
   endpoint: 'POST /internal/apm/data_view/static',
@@ -24,7 +25,10 @@ const staticDataViewRoute = createApmServerRoute({
     const setupPromise = setupRequest(resources);
     const clientPromise = core
       .start()
-      .then((coreStart) => coreStart.savedObjects.createInternalRepository());
+      .then(
+        (coreStart): ISavedObjectsRepository =>
+          coreStart.savedObjects.createInternalRepository()
+      );
 
     const setup = await setupPromise;
     const savedObjectsClient = await clientPromise;

x-pack/plugins/apm/server/routes/fleet/route.ts

@@ -105,16 +105,25 @@ const fleetAgentsRoute = createApmServerRoute({
     return {
       cloudStandaloneSetup,
       isFleetEnabled: true,
-      fleetAgents: fleetAgents.map((agent) => {
-        const packagePolicy = policiesGroupedById[agent.id];
-        const packagePolicyVars = packagePolicy.inputs[0]?.vars;
-        return {
-          id: agent.id,
-          name: agent.name,
-          apmServerUrl: packagePolicyVars?.url?.value,
-          secretToken: packagePolicyVars?.secret_token?.value,
-        };
-      }),
+      fleetAgents: fleetAgents.map(
+        (
+          agent
+        ): {
+          id: string;
+          name: string;
+          apmServerUrl: string | undefined;
+          secretToken: string | undefined;
+        } => {
+          const packagePolicy = policiesGroupedById[agent.id];
+          const packagePolicyVars = packagePolicy.inputs[0]?.vars;
+          return {
+            id: agent.id,
+            name: agent.name,
+            apmServerUrl: packagePolicyVars?.url?.value,
+            secretToken: packagePolicyVars?.secret_token?.value,
+          };
+        }
+      ),
     };
   },
 });

x-pack/plugins/apm/server/routes/observability_overview/route.ts

@@ -58,25 +58,36 @@ const observabilityOverviewRoute = createApmServerRoute({
       kuery: '',
     });
 
-    return withApmSpan('observability_overview', async () => {
-      const [serviceCount, transactionPerMinute] = await Promise.all([
-        getServiceCount({
-          setup,
-          searchAggregatedTransactions,
-          start,
-          end,
-        }),
-        getTransactionsPerMinute({
-          setup,
-          bucketSize,
-          searchAggregatedTransactions,
-          start,
-          end,
-          intervalString,
-        }),
-      ]);
-      return { serviceCount, transactionPerMinute };
-    });
+    return withApmSpan(
+      'observability_overview',
+      async (): Promise<{
+        serviceCount: number;
+        transactionPerMinute:
+          | { value: undefined; timeseries: never[] }
+          | {
+              value: number;
+              timeseries: Array<{ x: number; y: number | null }>;
+            };
+      }> => {
+        const [serviceCount, transactionPerMinute] = await Promise.all([
+          getServiceCount({
+            setup,
+            searchAggregatedTransactions,
+            start,
+            end,
+          }),
+          getTransactionsPerMinute({
+            setup,
+            bucketSize,
+            searchAggregatedTransactions,
+            start,
+            end,
+            intervalString,
+          }),
+        ]);
+        return { serviceCount, transactionPerMinute };
+      }
+    );
   },
 });
 

x-pack/plugins/apm/server/routes/rum_client/route.ts

@@ -407,6 +407,7 @@ function decodeUiFilters(
   }
 }
 
+// eslint-disable-next-line @typescript-eslint/explicit-function-return-type
 async function setupUXRequest<TParams extends SetupUXRequestParams>(
   resources: APMRouteHandlerResources & { params: TParams }
 ) {

x-pack/plugins/apm/server/routes/services/route.ts

@@ -49,6 +49,9 @@ import {
 } from '../../../../ml/server';
 import { getServiceInstancesDetailedStatisticsPeriods } from './get_service_instances/detailed_statistics';
 import { ML_ERRORS } from '../../../common/anomaly_detection';
+import { ScopedAnnotationsClient } from '../../../../observability/server';
+import { Annotation } from './../../../../observability/common/annotations';
+import { ConnectionStatsItemWithImpact } from './../../../common/connections';
 
 const servicesRoute = createApmServerRoute({
   endpoint: 'GET /internal/apm/services',
@@ -373,8 +376,10 @@ const serviceAnnotationsRoute = createApmServerRoute({
     const [annotationsClient, searchAggregatedTransactions] = await Promise.all(
       [
         observability
-          ? withApmSpan('get_scoped_annotations_client', () =>
-              observability.setup.getScopedAnnotationsClient(context, request)
+          ? withApmSpan(
+              'get_scoped_annotations_client',
+              (): Promise<undefined | ScopedAnnotationsClient> =>
+                observability.setup.getScopedAnnotationsClient(context, request)
             )
           : undefined,
         getSearchAggregatedTransactions({
@@ -443,8 +448,10 @@ const serviceAnnotationsCreateRoute = createApmServerRoute({
     } = resources;
 
     const annotationsClient = observability
-      ? await withApmSpan('get_scoped_annotations_client', () =>
-          observability.setup.getScopedAnnotationsClient(context, request)
+      ? await withApmSpan(
+          'get_scoped_annotations_client',
+          (): Promise<undefined | ScopedAnnotationsClient> =>
+            observability.setup.getScopedAnnotationsClient(context, request)
         )
       : undefined;
 
@@ -454,20 +461,22 @@ const serviceAnnotationsCreateRoute = createApmServerRoute({
 
     const { body, path } = params;
 
-    return withApmSpan('create_annotation', () =>
-      annotationsClient.create({
-        message: body.service.version,
-        ...body,
-        '@timestamp': new Date(body['@timestamp']).toISOString(),
-        annotation: {
-          type: 'deployment',
-        },
-        service: {
-          ...body.service,
-          name: path.serviceName,
-        },
-        tags: uniq(['apm'].concat(body.tags ?? [])),
-      })
+    return withApmSpan(
+      'create_annotation',
+      (): Promise<{ _id: string; _index: string; _source: Annotation }> =>
+        annotationsClient.create({
+          message: body.service.version,
+          ...body,
+          '@timestamp': new Date(body['@timestamp']).toISOString(),
+          annotation: {
+            type: 'deployment',
+          },
+          service: {
+            ...body.service,
+            name: path.serviceName,
+          },
+          tags: uniq(['apm'].concat(body.tags ?? [])),
+        })
     );
   },
 });
@@ -925,18 +934,25 @@ export const serviceDependenciesRoute = createApmServerRoute({
     ]);
 
     return {
-      serviceDependencies: currentPeriod.map((item) => {
-        const { stats, ...rest } = item;
-        const previousPeriodItem = previousPeriod.find(
-          (prevItem) => item.location.id === prevItem.location.id
-        );
-
-        return {
-          ...rest,
-          currentStats: stats,
-          previousStats: previousPeriodItem?.stats || null,
-        };
-      }),
+      serviceDependencies: currentPeriod.map(
+        (
+          item
+        ): Omit<ConnectionStatsItemWithImpact, 'stats'> & {
+          currentStats: ConnectionStatsItemWithImpact['stats'];
+          previousStats: ConnectionStatsItemWithImpact['stats'] | null;
+        } => {
+          const { stats, ...rest } = item;
+          const previousPeriodItem = previousPeriod.find(
+            (prevItem): boolean => item.location.id === prevItem.location.id
+          );
+
+          return {
+            ...rest,
+            currentStats: stats,
+            previousStats: previousPeriodItem?.stats || null,
+          };
+        }
+      ),
     };
   },
 });