core(budget): throw error on duplicate budget types

lighthouse-core/config/budget.js

@@ -46,6 +46,22 @@ class Budget {
     }
   }
 
+  /**
+   * Asserts that `strings` has no duplicate strings in it, throwing an error if
+   * it does. `arrayName` is included for nicer logging.
+   * @param {Array<string>} strings
+   * @param {string} arrayName
+   */
+  static assertNoDuplicateStrings(strings, arrayName) {
+    const foundStrings = new Set();
+    for (const string of strings) {
+      if (foundStrings.has(string)) {
+        throw new Error(`${arrayName} has duplicate entry of type '${string}'`);
+      }
+      foundStrings.add(string);
+    }
+  }
+
   /**
    * @param {Record<string, unknown>} resourceBudget
    * @return {LH.Budget.ResourceBudget}
@@ -136,18 +152,24 @@ class Budget {
 
       if (isArrayOfUnknownObjects(resourceSizes)) {
         budget.resourceSizes = resourceSizes.map(Budget.validateResourceBudget);
+        Budget.assertNoDuplicateStrings(budget.resourceSizes.map(r => r.resourceType),
+          `budgets[${index}].resourceSizes`);
       } else if (resourceSizes !== undefined) {
         throw new Error(`Invalid resourceSizes entry in budget at index ${index}`);
       }
 
       if (isArrayOfUnknownObjects(resourceCounts)) {
         budget.resourceCounts = resourceCounts.map(Budget.validateResourceBudget);
+        Budget.assertNoDuplicateStrings(budget.resourceCounts.map(r => r.resourceType),
+          `budgets[${index}].resourceCounts`);
       } else if (resourceCounts !== undefined) {
         throw new Error(`Invalid resourceCounts entry in budget at index ${index}`);
       }
 
       if (isArrayOfUnknownObjects(timings)) {
         budget.timings = timings.map(Budget.validateTimingBudget);
+        Budget.assertNoDuplicateStrings(budget.timings.map(r => r.metric),
+          `budgets[${index}].timings`);
       } else if (timings !== undefined) {
         throw new Error(`Invalid timings entry in budget at index ${index}`);
       }

lighthouse-core/test/config/budget-test.js

@@ -146,6 +146,18 @@ describe('Budget', () => {
       assert.throws(_ => Budget.initializeBudget(budget),
         /Resource Budget has unrecognized properties: \[browser\]/);
     });
+
+    it('throws when a duplicate resourceType is specified in resourceSizes', () => {
+      budget[1].resourceSizes.push({resourceType: 'script', budget: 100});
+      assert.throws(_ => Budget.initializeBudget(budget),
+        /budgets\[1\]\.resourceSizes has duplicate entry of type 'script'/);
+    });
+
+    it('throws when a duplicate resourceType is specified in resourceCounts', () => {
+      budget[0].resourceCounts.push({resourceType: 'third-party', budget: 100});
+      assert.throws(_ => Budget.initializeBudget(budget),
+        /budgets\[0\]\.resourceCounts has duplicate entry of type 'third-party'/);
+    });
   });
 
   describe('timing budget validation', () => {
@@ -172,5 +184,11 @@ describe('Budget', () => {
       assert.throws(_ => Budget.initializeBudget(budget),
         /Timing Budget has unrecognized properties: \[device, location\]/);
     });
+
+    it('throws when a duplicate metric type is specified in timings', () => {
+      budget[0].timings.push({metric: 'interactive', budget: 1000});
+      assert.throws(_ => Budget.initializeBudget(budget),
+        /budgets\[0\]\.timings has duplicate entry of type 'interactive'/);
+    });
   });
 });