chore(jest-config): util types (#8437)

Author: JoshRosenstein

packages/jest-config/src/normalize.ts

@@ -659,14 +659,19 @@ export default function normalize(
               ? _replaceRootDirTags(options.rootDir, project)
               : project,
           )
-          .reduce((projects, project) => {
-            // Project can be specified as globs. If a glob matches any files,
-            // We expand it to these paths. If not, we keep the original path
-            // for the future resolution.
-            const globMatches =
-              typeof project === 'string' ? glob.sync(project) : [];
-            return projects.concat(globMatches.length ? globMatches : project);
-          }, []);
+          .reduce(
+            (projects, project) => {
+              // Project can be specified as globs. If a glob matches any files,
+              // We expand it to these paths. If not, we keep the original path
+              // for the future resolution.
+              const globMatches =
+                typeof project === 'string' ? glob.sync(project) : [];
+              return projects.concat(
+                globMatches.length ? globMatches : project,
+              );
+            },
+            [] as Array<string>,
+          );
         break;
       case 'moduleDirectories':
       case 'testMatch':

packages/jest-config/src/utils.ts

@@ -48,8 +48,8 @@ export const resolve = (
          ${chalk.bold('<rootDir>')} is: ${rootDir}`,
     );
   }
-
-  return module;
+  /// can cast as string since nulls will be thrown
+  return module as string;
 };
 
 export const escapeGlobCharacters = (path: Config.Path): Config.Glob =>
@@ -69,37 +69,50 @@ export const replaceRootDirInPath = (
   );
 };
 
-// TODO: Type as returning same type as input
-const _replaceRootDirInObject = (
+const _replaceRootDirInObject = <T extends ReplaceRootDirConfigObj>(
   rootDir: Config.Path,
-  config: any,
-): {[key: string]: unknown} => {
-  if (config !== null) {
-    const newConfig: {[key: string]: unknown} = {};
-    for (const configKey in config) {
-      newConfig[configKey] =
-        configKey === 'rootDir'
-          ? config[configKey]
-          : _replaceRootDirTags(rootDir, config[configKey]);
-    }
-    return newConfig;
+  config: T,
+): T => {
+  const newConfig = {} as T;
+  for (const configKey in config) {
+    newConfig[configKey] =
+      configKey === 'rootDir'
+        ? config[configKey]
+        : _replaceRootDirTags(rootDir, config[configKey]);
   }
-  return config;
+  return newConfig;
 };
 
-// TODO: Type as returning same type as input
-export const _replaceRootDirTags = (rootDir: Config.Path, config: any): any => {
+type OrArray<T> = T | Array<T>;
+type ReplaceRootDirConfigObj = {[key: string]: Config.Path};
+type ReplaceRootDirConfigValues =
+  | OrArray<ReplaceRootDirConfigObj>
+  | OrArray<RegExp>
+  | OrArray<Config.Path>;
+
+export const _replaceRootDirTags = <T extends ReplaceRootDirConfigValues>(
+  rootDir: Config.Path,
+  config: T,
+): T => {
+  if (config == null) {
+    return config;
+  }
   switch (typeof config) {
     case 'object':
       if (Array.isArray(config)) {
-        return config.map(item => _replaceRootDirTags(rootDir, item));
+        /// can be string[] or {}[]
+        return config.map(item => _replaceRootDirTags(rootDir, item)) as T;
       }
       if (config instanceof RegExp) {
         return config;
       }
-      return _replaceRootDirInObject(rootDir, config);
+
+      return _replaceRootDirInObject(
+        rootDir,
+        config as ReplaceRootDirConfigObj,
+      ) as T;
     case 'string':
-      return replaceRootDirInPath(rootDir, config);
+      return replaceRootDirInPath(rootDir, config) as T;
   }
   return config;
 };