refactor(dev-infra): do not validate config file multiple times (#38808)

Currently we validate the configuration file on each `getConfig`
invocation. We can only validate once since the configuration
is cached.

Also while being at it, renames the cache variables to lower-case as those
do not represent constants (which are convention-wise upper case).

PR Close #38808

dev-infra/utils/config.ts

@@ -49,7 +49,7 @@ export type NgDevConfig<T = {}> = CommonConfig&T;
 const CONFIG_FILE_PATH = '.ng-dev/config';
 
 /** The configuration for ng-dev. */
-let CONFIG: {}|null = null;
+let cachedConfig: NgDevConfig|null = null;
 
 /**
  * The filename expected for local user config, without the file extension to allow a typescript,
@@ -58,23 +58,23 @@ let CONFIG: {}|null = null;
 const USER_CONFIG_FILE_PATH = '.ng-dev.user';
 
 /** The local user configuration for ng-dev. */
-let USER_CONFIG: {[key: string]: any};
+let userConfig: {[key: string]: any}|null = null;
 
 /**
  * Get the configuration from the file system, returning the already loaded
  * copy if it is defined.
  */
 export function getConfig(): NgDevConfig {
   // If the global config is not defined, load it from the file system.
-  if (CONFIG === null) {
+  if (cachedConfig === null) {
     // The full path to the configuration file.
     const configPath = join(getRepoBaseDir(), CONFIG_FILE_PATH);
-    // Set the global config object.
-    CONFIG = readConfigFile(configPath);
+    // Read the configuration and validate it before caching it for the future.
+    cachedConfig = validateCommonConfig(readConfigFile(configPath));
   }
-  // Return a clone of the global config to ensure that a new instance of the config is returned
-  // each time, preventing unexpected effects of modifications to the config object.
-  return validateCommonConfig({...CONFIG});
+  // Return a clone of the cached global config to ensure that a new instance of the config
+  // is returned each time, preventing unexpected effects of modifications to the config object.
+  return {...cachedConfig};
 }
 
 /** Validate the common configuration has been met for the ng-dev command. */
@@ -162,13 +162,13 @@ export function getRepoBaseDir() {
  */
 export function getUserConfig() {
   // If the global config is not defined, load it from the file system.
-  if (USER_CONFIG === undefined) {
+  if (userConfig === null) {
     // The full path to the configuration file.
     const configPath = join(getRepoBaseDir(), USER_CONFIG_FILE_PATH);
     // Set the global config object.
-    USER_CONFIG = readConfigFile(configPath, true);
+    userConfig = readConfigFile(configPath, true);
   }
-  // Return a clone of the global config to ensure that a new instance of the config is returned
+  // Return a clone of the user config to ensure that a new instance of the config is returned
   // each time, preventing unexpected effects of modifications to the config object.
-  return {...USER_CONFIG};
+  return {...userConfig};
 }