Add config validation for empty forking url

Author: kshyun28

packages/hardhat-core/src/internal/core/config/config-validation.ts

@@ -401,6 +401,18 @@ export function getValidationErrors(config: any): string[] {
         );
       }
 
+      if (hardhatNetwork.forking !== undefined) {
+        if (isEmptyString(hardhatNetwork.forking.url)) {
+          errors.push(
+            getEmptyErrorMessage(
+              `HardhatConfig.networks.${HARDHAT_NETWORK_NAME}.forking.url`,
+              hardhatNetwork.forking.url,
+              "string"
+            )
+          );
+        }
+      }
+
       // Validating the accounts with io-ts leads to very confusing errors messages
       const { accounts, ...configExceptAccounts } = hardhatNetwork;
 

packages/hardhat-core/test/internal/core/config/config-validation.ts

@@ -857,6 +857,30 @@ describe("Config validation", function () {
             ERRORS.GENERAL.INVALID_CONFIG
           );
 
+          expectHardhatError(
+            () =>
+              validateConfig({
+                networks: {
+                  [HARDHAT_NETWORK_NAME]: {
+                    forking: { url: "" },
+                  },
+                },
+              }),
+            ERRORS.GENERAL.INVALID_CONFIG
+          );
+
+          expectHardhatError(
+            () =>
+              validateConfig({
+                networks: {
+                  [HARDHAT_NETWORK_NAME]: {
+                    forking: { url: " " },
+                  },
+                },
+              }),
+            ERRORS.GENERAL.INVALID_CONFIG
+          );
+
           expectHardhatError(
             () =>
               validateConfig({