Ignore true/false/1/0 values for CACHE_DIR environment variable (#27)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>

index.js

@@ -5,6 +5,8 @@ const commonDir = require('commondir');
 const pkgDir = require('pkg-dir');
 const makeDir = require('make-dir');
 
+const {env, cwd} = process;
+
 const isWritable = path => {
 	try {
 		fs.accessSync(path, fs.constants.W_OK);
@@ -40,11 +42,11 @@ function getNodeModuleDirectory(directory) {
 }
 
 module.exports = (options = {}) => {
-	if (process.env.CACHE_DIR) {
-		return useDirectory(path.join(process.env.CACHE_DIR, 'find-cache-dir'), options);
+	if (env.CACHE_DIR && !['true', 'false', '1', '0'].includes(env.CACHE_DIR)) {
+		return useDirectory(path.join(env.CACHE_DIR, 'find-cache-dir'), options);
 	}
 
-	let {cwd: directory = process.cwd()} = options;
+	let {cwd: directory = cwd()} = options;
 
 	if (options.files) {
 		directory = commonDir(directory, options.files);

readme.md

@@ -42,7 +42,7 @@ findCacheDir({name: 'unicorns'});
 
 ### findCacheDir(options?)
 
-Finds the cache directory using the supplied options. The algorithm checks for the `CACHE_DIR` environmental variable, and if one is not found, it tries to find a `package.json` file, searching every parent directory of the `cwd` specified (or implied from other options). It returns a `string` containing the absolute path to the cache directory, or `undefined` if `package.json` was never found or if the `node_modules` directory is unwritable.
+Finds the cache directory using the supplied options. The algorithm checks for the `CACHE_DIR` environmental variable and uses it if it is not set to `true`, `false`, `1` or `0`. If one is not found, it tries to find a `package.json` file, searching every parent directory of the `cwd` specified (or implied from other options). It returns a `string` containing the absolute path to the cache directory, or `undefined` if `package.json` was never found or if the `node_modules` directory is unwritable.
 
 #### options
 

test.js

@@ -57,3 +57,9 @@ test('supports CACHE_DIR environment variable', t => {
 
 	delete process.env.CACHE_DIR;
 });
+
+test('ignores `false` for CACHE_DIR environment variable', t => {
+	process.env.CACHE_DIR = 'false';
+
+	t.not(findCacheDir(), path.resolve(__dirname, 'false', 'find-cache-dir'));
+});