feat(ng-dev): support performing configuration assertions in the getC…

…onfig function (#204)

Allow the getConfig function take in a list of assertions functions which will assert against the
retrieved config object.  Errors from the assertions will be thrown as expected.  The returned config
object will has the asserted typings.

This will allow retrieving the config object already typed, which provides a convenience for cases
where getConfig is called on intialization.

PR Close #204

ng-dev/caretaker/cli.ts

@@ -8,7 +8,7 @@
 
 import {info} from 'console';
 import {Arguments, Argv} from 'yargs';
-import {getConfig} from '../utils/config';
+import {assertValidGithubConfig, getConfig} from '../utils/config';
 import {CheckModule} from './check/cli';
 import {assertValidCaretakerConfig} from './config';
 import {HandoffModule} from './handoff/cli';
@@ -22,9 +22,8 @@ export function buildCaretakerParser(yargs: Argv) {
 }
 
 function caretakerCommandCanRun(argv: Arguments) {
-  const config = getConfig();
   try {
-    assertValidCaretakerConfig(config);
+    getConfig([assertValidCaretakerConfig, assertValidGithubConfig]);
   } catch {
     info('The `caretaker` command is not enabled in this repository.');
     info(`   To enable it, provide a caretaker config in the repository's .ng-dev/ directory`);

ng-dev/utils/assertion-typings.d.ts

@@ -0,0 +1,17 @@
+type UnionToIntersection<U> = (U extends unknown ? (union: U) => void : never) extends (
+  intersection: infer I,
+) => void
+  ? I
+  : never;
+
+type AssertedType<A> = A extends AssertionFn<infer T> ? T : never;
+type AllAssertedTypes<A extends readonly AssertionFn<unknown>[]> = {
+  [K in keyof A]: AssertedType<A[K]>;
+};
+type ExtractValuesAsUnionFromObject<T> = T[keyof T & number];
+
+export type Assertions<A extends readonly AssertionFn<unknown>[]> = UnionToIntersection<
+  ExtractValuesAsUnionFromObject<AllAssertedTypes<A>>
+>;
+export type AssertionFn<T> = (value: Partial<T>) => asserts value is T;
+export type MultipleAssertions = AssertionFn<unknown>[];

ng-dev/utils/config.ts

@@ -8,6 +8,7 @@
 
 import {existsSync} from 'fs';
 import {dirname, join} from 'path';
+import {Assertions, MultipleAssertions} from './assertion-typings';
 
 import {debug, error} from './console';
 import {GitClient} from './git/git-client';
@@ -61,16 +62,30 @@ export function setConfig(config: {}) {
  * copy if it is defined.
  */
 export function getConfig(): {};
-export function getConfig(baseDir?: string): {};
-export function getConfig(baseDir?: string): {} {
+export function getConfig(baseDir: string): {};
+export function getConfig<A extends MultipleAssertions>(assertions: A): Assertions<A>;
+export function getConfig(baseDirOrAssertions?: unknown) {
+  let baseDir: string;
+  if (typeof baseDirOrAssertions === 'string') {
+    baseDir = baseDirOrAssertions;
+  } else {
+    baseDir = GitClient.get().baseDir;
+  }
+
   // If the global config is not defined, load it from the file system.
   if (cachedConfig === null) {
-    baseDir = baseDir || GitClient.get().baseDir;
     // The full path to the configuration file.
     const configPath = join(baseDir, CONFIG_FILE_PATH);
     // Read the configuration and validate it before caching it for the future.
     cachedConfig = readConfigFile(configPath);
   }
+
+  if (Array.isArray(baseDirOrAssertions)) {
+    for (const assertion of baseDirOrAssertions) {
+      assertion(cachedConfig);
+    }
+  }
+
   // 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};