Variables: add graceful circular dependency failure (#46590)

* adds circular dependency check

* adds circular dep test

public/app/features/variables/state/actions.test.ts

@@ -149,6 +149,22 @@ describe('shared actions', () => {
   });
 
   describe('when processVariables is dispatched', () => {
+    it('then circular dependencies fail gracefully', async () => {
+      const key = 'key';
+      const var1 = queryBuilder().withName('var1').withQuery('$var2').build();
+      const var2 = queryBuilder().withName('var2').withQuery('$var1').build();
+      const dashboard: any = { templating: { list: [var1, var2] } };
+      const preloadedState = getPreloadedState(key, {});
+
+      await expect(async () => {
+        await reduxTester<TemplatingReducerType>({ preloadedState })
+          .givenRootReducer(getTemplatingRootReducer())
+          .whenActionIsDispatched(toKeyedAction(key, variablesInitTransaction({ uid: key })))
+          .whenActionIsDispatched(initDashboardTemplating(key, dashboard))
+          .whenAsyncActionIsDispatched(processVariables(key), true);
+      }).rejects.toThrow(/circular dependency in dashboard variables detected/i);
+    });
+
     it('then correct actions are dispatched', async () => {
       const key = 'key';
       const query = queryBuilder().build();

public/app/features/variables/state/actions.ts

@@ -271,20 +271,12 @@ export const processVariableDependencies = async (variable: VariableModel, state
     throw new Error(`rootStateKey not found for variable with id:${variable.id}`);
   }
 
-  const dependencies: VariableModel[] = [];
-
-  for (const otherVariable of getVariablesByKey(variable.rootStateKey, state)) {
-    if (variable === otherVariable) {
-      continue;
-    }
-
-    if (variableAdapters.getIfExists(variable.type)) {
-      if (variableAdapters.get(variable.type).dependsOn(variable, otherVariable)) {
-        dependencies.push(otherVariable);
-      }
-    }
+  if (isDependencyGraphCircular(variable, state)) {
+    throw new Error('Circular dependency in dashboard variables detected. Dashboard may not work as expected.');
   }
 
+  const dependencies = getDirectDependencies(variable, state);
+
   if (!isWaitingForDependencies(variable.rootStateKey, dependencies, state)) {
     return;
   }
@@ -303,6 +295,44 @@ export const processVariableDependencies = async (variable: VariableModel, state
   });
 };
 
+const isDependencyGraphCircular = (
+  variable: VariableModel,
+  state: StoreState,
+  encounteredDependencyIds: Set<string> = new Set()
+): boolean => {
+  if (encounteredDependencyIds.has(variable.id)) {
+    return true;
+  }
+
+  encounteredDependencyIds = new Set([...encounteredDependencyIds, variable.id]);
+
+  return getDirectDependencies(variable, state).some((dependency) => {
+    return isDependencyGraphCircular(dependency, state, encounteredDependencyIds);
+  });
+};
+
+const getDirectDependencies = (variable: VariableModel, state: StoreState) => {
+  if (!variable.rootStateKey) {
+    return [];
+  }
+
+  const directDependencies: VariableModel[] = [];
+
+  for (const otherVariable of getVariablesByKey(variable.rootStateKey, state)) {
+    if (variable === otherVariable) {
+      continue;
+    }
+
+    if (variableAdapters.getIfExists(variable.type)) {
+      if (variableAdapters.get(variable.type).dependsOn(variable, otherVariable)) {
+        directDependencies.push(otherVariable);
+      }
+    }
+  }
+
+  return directDependencies;
+};
+
 const isWaitingForDependencies = (key: string, dependencies: VariableModel[], state: StoreState): boolean => {
   if (dependencies.length === 0) {
     return false;