fixing bug in local path resolve

if you have a local dep that points to a missing file, it will attempt to resolve it
as a remote. duo-parse treats something like `../../a/b/c` as `{ repo: '..' }`. if you
also have a manifest, it will attempt to find `..` via regexp in the `dependencies`
list. since it's a regexp, `..` will match just about anything.

the end result is that you have an extra dependency being added to your build. in the
case of css, it can be hard to trace this down.

this throws when the dep looks like a path (ie: begins with "." or "/") and is not
resolved locally. I don't believe it is possible to have a github repo that begins
with either of these chars, so we should be safe here.

lib/duo.js

@@ -774,6 +774,9 @@ Duo.prototype.dependency = function* (dep, file, entry) {
   if (local) {
     debug('%s: local dependency "%s"', file.id, dep);
     return relative(entry.root, local);
+  } else if (isLocal(dep)) {
+    debug('%s: local dependency "%s" not found', file.id, dep);
+    throw error('unable to resolve local dependency ' + dep + ' from ' + file.id);
   }
 
   // `dep` is a remote dependency
@@ -1383,3 +1386,13 @@ function isSlug(str) {
 
   return r.test(str);
 }
+
+/**
+ * Tells us whether or not the input path is a local path. (begins with . or /)
+ *
+ * @param {String} path
+ * @return {Boolean}
+ */
+function isLocal(path) {
+  return path[0] === '.' || path[0] === '/';
+}

test/api.js

@@ -398,6 +398,24 @@ describe('Duo API', function () {
       assert.strictEqual(ctx.a1, ctx.a2);
     });
 
+    it('should fail when relative requires are not found', function* () {
+      try {
+        var js = yield build('resolve-relative-missing', 'index.js').run();
+      } catch (err) {
+        assert(err instanceof Error);
+      }
+      assert(!js, 'should have failed');
+    });
+
+    it('should fail when absolute requires are not found', function* () {
+      try {
+        var js = yield build('resolve-absolute-missing', 'index.js').run();
+      } catch (err) {
+        assert(err instanceof Error);
+      }
+      assert(!js, 'should have failed');
+    });
+
     it('should fetch and build direct dependencies', function* () {
       this.timeout(15000);
       var js = yield build('simple-deps').run();

test/fixtures/resolve-absolute-missing/index.js

@@ -0,0 +1,2 @@
+
+module.exports = require('/lib'); // should not exist!

test/fixtures/resolve-relative-missing/index.js

@@ -0,0 +1,2 @@
+
+module.exports = require('./lib'); // should not exist!