Prometheus: Add metadata for summary metrics (#24201)

* Prometheus: Add metadata for summary metrics

- summary metrics don't have metadata available from the metadata API,
so Grafana can help and just add it
- given a summary metric `foo`, we add metadata info for `foo_sum` and
`foo_count`
- with tests

* Update public/app/plugins/datasource/prometheus/language_utils.ts

Co-authored-by: gotjosh <josue@grafana.com>

Co-authored-by: gotjosh <josue@grafana.com>

public/app/plugins/datasource/prometheus/language_provider.ts

@@ -5,7 +5,7 @@ import { Value } from 'slate';
 import { dateTime, LanguageProvider, HistoryItem } from '@grafana/data';
 import { CompletionItem, TypeaheadInput, TypeaheadOutput, CompletionItemGroup } from '@grafana/ui';
 
-import { parseSelector, processLabels, processHistogramLabels } from './language_utils';
+import { parseSelector, processLabels, processHistogramLabels, fixSummariesMetadata } from './language_utils';
 import PromqlSyntax, { FUNCTIONS, RATE_RANGES } from './promql';
 
 import { PrometheusDatasource } from './datasource';
@@ -118,7 +118,7 @@ export default class PromQlLanguageProvider extends LanguageProvider {
 
     this.metrics = await this.request('/api/v1/label/__name__/values', []);
     this.lookupsDisabled = this.metrics.length > this.lookupMetricsThreshold;
-    this.metricsMetadata = await this.request('/api/v1/metadata', {});
+    this.metricsMetadata = fixSummariesMetadata(await this.request('/api/v1/metadata', {}));
     this.processHistogramMetrics(this.metrics);
 
     return [];

public/app/plugins/datasource/prometheus/language_utils.test.ts

@@ -1,4 +1,4 @@
-import { expandRecordingRules, parseSelector } from './language_utils';
+import { expandRecordingRules, fixSummariesMetadata, parseSelector } from './language_utils';
 
 describe('parseSelector()', () => {
   let parsed;
@@ -70,6 +70,33 @@ describe('parseSelector()', () => {
   });
 });
 
+describe('fixSummariesMetadata', () => {
+  it('returns empty metadata', () => {
+    expect(fixSummariesMetadata({})).toEqual({});
+  });
+
+  it('returns unchanged metadata if no summary is present', () => {
+    const metadata = {
+      foo: [{ type: 'not_a_summary', help: 'foo help' }],
+    };
+    expect(fixSummariesMetadata(metadata)).toEqual(metadata);
+  });
+
+  it('returns metadata with added count and sum for a summary', () => {
+    const metadata = {
+      foo: [{ type: 'not_a_summary', help: 'foo help' }],
+      bar: [{ type: 'summary', help: 'bar help' }],
+    };
+    const expected = {
+      foo: [{ type: 'not_a_summary', help: 'foo help' }],
+      bar: [{ type: 'summary', help: 'bar help' }],
+      bar_count: [{ type: 'counter', help: 'Count of events that have been observed for the base metric (bar help)' }],
+      bar_sum: [{ type: 'counter', help: 'Total sum of all observed values for the base metric (bar help)' }],
+    };
+    expect(fixSummariesMetadata(metadata)).toEqual(expected);
+  });
+});
+
 describe('expandRecordingRules()', () => {
   it('returns query w/o recording rules as is', () => {
     expect(expandRecordingRules('metric', {})).toBe('metric');

public/app/plugins/datasource/prometheus/language_utils.ts

@@ -1,3 +1,5 @@
+import { PromMetricsMetadata } from './types';
+
 export const RATE_RANGES = ['1m', '5m', '10m', '30m', '1h'];
 
 export const processHistogramLabels = (labels: string[]) => {
@@ -111,3 +113,34 @@ export function expandRecordingRules(query: string, mapping: { [name: string]: s
   const rulesRegex = new RegExp(`(\\s|^)(${ruleNames.join('|')})(\\s|$|\\(|\\[|\\{)`, 'ig');
   return query.replace(rulesRegex, (match, pre, name, post) => `${pre}${mapping[name]}${post}`);
 }
+
+/**
+ * Adds metadata for synthetic metrics for which the API does not provide metadata.
+ * See https://github.com/grafana/grafana/issues/22337 for details.
+ *
+ * @param metadata HELP and TYPE metadata from /api/v1/metadata
+ */
+export function fixSummariesMetadata(metadata: PromMetricsMetadata): PromMetricsMetadata {
+  if (!metadata) {
+    return metadata;
+  }
+  const summaryMetadata: PromMetricsMetadata = {};
+  for (const metric in metadata) {
+    const item = metadata[metric][0];
+    if (item.type === 'summary') {
+      summaryMetadata[`${metric}_count`] = [
+        {
+          type: 'counter',
+          help: `Count of events that have been observed for the base metric (${item.help})`,
+        },
+      ];
+      summaryMetadata[`${metric}_sum`] = [
+        {
+          type: 'counter',
+          help: `Total sum of all observed values for the base metric (${item.help})`,
+        },
+      ];
+    }
+  }
+  return { ...metadata, ...summaryMetadata };
+}