How do relative TemplateUrls work

What you write

1. in web/path/*.dart - templateUrl: 'more_path/foo.html'
2. in pkg/lib/path/*.dart - templateUrl: 'more_path/foo.html' [1]

What transformer sees

1. web/path/more_path/foo.html
2. packages/pkg/lib/path/more_path/foo.html

What url is fetched

1. path/more_path/foo.html
2. /packages/pkg/path/more_path/foo.html

Urls are considered relative

1. if they start with /
2. if they start with package

[1] We make no difference between current package (the one on which you call pub serve/build) and dependencies here.