Graphite: Fallback to hardcoded list of functions when no functions are returned (#46681) (#46688)

(cherry picked from commit ed155e47c4)

Co-authored-by: Piotr Jamróz <pm.jamroz@gmail.com>

public/app/plugins/datasource/graphite/datasource.test.ts

@@ -292,6 +292,14 @@ describe('graphiteDatasource', () => {
         },
       });
     });
+
+    it('should use hardcoded list of functions when no functions are returned', async () => {
+      fetchMock.mockImplementation(() => {
+        return of(createFetchResponse('{}'));
+      });
+      const funcDefs = await ctx.ds.getFuncDefs();
+      expect(Object.keys(funcDefs)).not.toHaveLength(0);
+    });
   });
 
   describe('building graphite params', () => {

public/app/plugins/datasource/graphite/datasource.ts

@@ -769,6 +769,15 @@ export class GraphiteDatasource
           } else {
             this.funcDefs = gfunc.parseFuncDefs(results.data);
           }
+
+          // When /functions endpoint returns application/json response but containing invalid JSON the fix above
+          // wont' be triggered due to the changes in https://github.com/grafana/grafana/pull/45598 (parsing happens
+          // in fetch and Graphite receives an empty object and no error). In such cases, when the provided JSON
+          // seems empty we fallback to the hardcoded list of functions.
+          // See also: https://github.com/grafana/grafana/issues/45948
+          if (Object.keys(this.funcDefs).length === 0) {
+            this.funcDefs = gfunc.getFuncDefs(this.graphiteVersion);
+          }
           return this.funcDefs;
         }),
         catchError((error: any) => {