Improve buildProviderConfig helper function (#1346)

The network controller helper function `buildProviderConfig` now
ensures that the provider configuration returned is valid for Infura
networks. Previously it always returned valid RPC provider configs, but
if the config was an Infura type it might be missing some properties.

Relates to #1197

packages/network-controller/tests/NetworkController.test.ts

@@ -278,8 +278,6 @@ describe('NetworkController', () => {
                 state: {
                   providerConfig: buildProviderConfig({
                     type: networkType,
-                    chainId: '99999',
-                    nickname: 'some nickname',
                   }),
                 },
                 infuraProjectId: 'infura-project-id',
@@ -560,7 +558,6 @@ describe('NetworkController', () => {
         refreshNetworkTests({
           expectedProviderConfig: buildProviderConfig({
             type: networkType,
-            ...BUILT_IN_NETWORKS[networkType],
           }),
           operation: async (controller) => {
             await controller.setProviderType(networkType);
@@ -2341,7 +2338,6 @@ describe('NetworkController', () => {
               state: {
                 providerConfig: buildProviderConfig({
                   type: networkType,
-                  ...BUILT_IN_NETWORKS[networkType],
                 }),
                 networkConfigurations: {
                   testNetworkConfiguration: {
@@ -2395,7 +2391,6 @@ describe('NetworkController', () => {
               expect(controller.state.providerConfig).toStrictEqual(
                 buildProviderConfig({
                   type: networkType,
-                  ...BUILT_IN_NETWORKS[networkType],
                 }),
               );
             },
@@ -5041,16 +5036,23 @@ async function withController<ReturnValue>(
  * @param config - An incomplete ProviderConfig object.
  * @returns The complete ProviderConfig object.
  */
-function buildProviderConfig(config: Partial<ProviderConfig> = {}) {
+function buildProviderConfig(
+  config: Partial<ProviderConfig> = {},
+): ProviderConfig {
+  if (config.type && config.type !== NetworkType.rpc) {
+    return {
+      ...BUILT_IN_NETWORKS[config.type],
+      // This is redundant with the spread operation below, but this was
+      // required for TypeScript to understand that this property was set to an
+      // Infura type.
+      type: config.type,
+      ...config,
+    };
+  }
   return {
     type: NetworkType.rpc,
     chainId: '1337',
-    id: undefined,
-    nickname: undefined,
-    rpcUrl:
-      !config.type || config.type === NetworkType.rpc
-        ? 'http://doesntmatter.com'
-        : undefined,
+    rpcUrl: 'http://doesntmatter.com',
     ...config,
   };
 }