[Fix] sync/async: when package.json main is not a string, throw an error

Fixes #178.

Author: ljharb

lib/async.js

@@ -161,6 +161,11 @@ module.exports = function resolve(x, options, callback) {
                 }
 
                 if (pkg.main) {
+                    if (typeof pkg.main !== 'string') {
+                        var mainError = new TypeError('package “' + pkg.name + '” `main` must be a string');
+                        mainError.code = 'INVALID_PACKAGE_MAIN';
+                        return cb(mainError);
+                    }
                     if (pkg.main === '.' || pkg.main === './') {
                         pkg.main = 'index';
                     }

lib/sync.js

@@ -101,21 +101,28 @@ module.exports = function (x, options) {
             try {
                 var body = readFileSync(pkgfile, 'UTF8');
                 var pkg = JSON.parse(body);
+            } catch (e) {}
 
-                if (opts.packageFilter) {
-                    pkg = opts.packageFilter(pkg, x);
-                }
+            if (opts.packageFilter) {
+                pkg = opts.packageFilter(pkg, x);
+            }
 
-                if (pkg.main) {
-                    if (pkg.main === '.' || pkg.main === './') {
-                        pkg.main = 'index';
-                    }
+            if (pkg.main) {
+                if (typeof pkg.main !== 'string') {
+                    var mainError = new TypeError('package “' + pkg.name + '” `main` must be a string');
+                    mainError.code = 'INVALID_PACKAGE_MAIN';
+                    throw mainError;
+                }
+                if (pkg.main === '.' || pkg.main === './') {
+                    pkg.main = 'index';
+                }
+                try {
                     var m = loadAsFileSync(path.resolve(x, pkg.main));
                     if (m) return m;
                     var n = loadAsDirectorySync(path.resolve(x, pkg.main));
                     if (n) return n;
-                }
-            } catch (e) {}
+                } catch (e) {}
+            }
         }
 
         return loadAsFileSync(path.join(x, '/index'));

test/resolver.js

@@ -376,6 +376,19 @@ test('not a directory', function (t) {
     });
 });
 
+test('non-string "main" field in package.json', function (t) {
+    t.plan(5);
+
+    var dir = path.join(__dirname, 'resolver');
+    resolve('./invalid_main', { basedir: dir }, function (err, res, pkg) {
+        t.ok(err, 'errors on non-string main');
+        t.equal(err.message, 'package “invalid main” `main` must be a string');
+        t.equal(err.code, 'INVALID_PACKAGE_MAIN');
+        t.equal(res, undefined, 'res is undefined');
+        t.equal(pkg, undefined, 'pkg is undefined');
+    });
+});
+
 test('browser field in package.json', function (t) {
     t.plan(3);
 

test/resolver/invalid_main/package.json

@@ -0,0 +1,7 @@
+{
+  "name": "invalid main",
+  "main": [
+    "why is this a thing",
+    "srsly omg wtf"
+  ]
+}

test/resolver_sync.js

@@ -294,6 +294,20 @@ test('not a directory', function (t) {
     t.end();
 });
 
+test('non-string "main" field in package.json', function (t) {
+    var dir = path.join(__dirname, 'resolver');
+    try {
+        var result = resolve.sync('./invalid_main', { basedir: dir });
+        t.equal(result, undefined, 'result should not exist');
+        t.fail('should not get here');
+    } catch (err) {
+        t.ok(err, 'errors on non-string main');
+        t.equal(err.message, 'package “invalid main” `main` must be a string');
+        t.equal(err.code, 'INVALID_PACKAGE_MAIN');
+    }
+    t.end();
+});
+
 test('browser field in package.json', function (t) {
     var dir = path.join(__dirname, 'resolver');
     var res = resolve.sync('./browser_field', {