Pub Package Layout Conventions

Part of a healthy code ecosystem is consistent conventions. When we all do the same thing the same way, it makes it easier for us to learn our way around each other’s work. It also makes it easier to write tools that can automatically do things for us.

When you build a pub package, we have a set of conventions we encourage you to follow. They describe how you organize the files and directories within your package, and how to name things. You don’t have to have every single thing these guidelines specify. If your package doesn’t have binaries, it doesn’t need a directory for them. But if it does, you’ll make everyone’s life easier if you call it bin.

To give you a picture of the whole enchilada, here’s what a complete package (conveniently named enchilada) that uses every corner of these guidelines would look like:

enchilada/
  pubspec.yaml
  pubspec.lock *
  README.md
  LICENSE
  benchmark/
    make_lunch.dart
    packages/ **
  bin/
    enchilada
    packages/ **
  doc/
    getting_started.md
  example/
    lunch.dart
    packages/ **
  lib/
    enchilada.dart
    tortilla.dart
    guacamole.css
    src/
      beans.dart
      queso.dart
  packages/ **
  test/
    enchilada_test.dart
    tortilla_test.dart
    packages/ **
  tool/
    generate_docs.dart
  web/
    index.html
    main.dart
    style.css

* The pubspec.lock will only be in source control if the package is an application package.

** The packages directories will exist locally after you’ve run pub get, but won’t be checked into source control.

The basics

enchilada/
  pubspec.yaml
  pubspec.lock

Every package will have a pubspec, a file named pubspec.yaml, in the root directory of the package. That’s what makes it a package.

Once you’ve run pub get or pub upgrade on the package, you will also have a lockfile, named pubspec.lock. If your package is an application package, this will be checked into source control. Otherwise, it won’t be.

enchilada/
  packages/
    ...

Running pub will also generate a packages directory. You will not check this into source control, and you won’t need to worry too much about its contents. Consider it pub magic, but not scary magic.

The open source community has a few other files that commonly appear at the top level of a project: LICENSE, AUTHORS, etc. If you use any of those, they can go in the top level of the package too.

For more information, see Pubspec Format.

README

enchilada/
  README.md

One file that’s very common in open source is a README file that describes the project. This is especially important in pub. When you upload to pub.dartlang.org, your README will be shown on the page for your package. This is the perfect place to introduce people to your code.

If your README ends in .md, .markdown, or .mdown, it will be parsed as Markdown.

Public libraries

enchilada/
  lib/
    enchilada.dart
    tortilla.dart

Many packages are library packages: they define Dart libraries that other packages can import and use. These public Dart library files go inside a directory called lib.

Most packages define a single library that users can import. In that case, its name should usually be the same as the name of the package, like enchilada.dart in the example here. But you can also define other libraries with whatever names make sense for your package.

When you do, users can import these libraries using the name of the package and the library file, like so:

import "package:enchilada/enchilada.dart";
import "package:enchilada/tortilla.dart";

If you want to organize your public libraries, you can also create subdirectories inside lib. If you do that, users will specify that path when they import it. Say you have the following file hierarchy:

enchilada/
  lib/
    some/
      path/
        olives.dart

Users will import olives.dart as follows:

import "package:enchilada/some/path/olives.dart";

Note that only libraries should be in lib. Entrypoints—Dart scripts with a main() function—cannot go in lib. If you place a Dart script inside lib, you will discover that any package: imports it contains don’t resolve. Instead, your entrypoints should go in the appropriate entrypoint directory.

Referencing packages

You can, of course, reference a package from within your app. For example, say your source tree looks like this:

myapp/
  example/
    one/
      sub/
        index.html

The resulting build directory has the following structure:

build/
  example/
    one/
      packages/
        myapp/
          style.css
      sub/
        index.html

In this scenario, index.html references the stylesheet using the relative path ../packages/myapp/style.css. (Note the leading ...)

You can also use a path relative to the root URL, such as /packages/myapp/style.css, but you must be careful on how you deploy your app.

Public assets

enchilada/
  lib/
    guacamole.css

While most library packages exist to let you reuse Dart code, you can also reuse other kinds of content. For example, a package for Bootstrap might include a number of CSS files for consumers of the package to use.

These go in the top-level lib directory. You can put any kind of file in there and organize it with subdirectories however you like.

Users can reference another package’s assets using URLs that contain /packages/<package>/<path> where <package> is the name of the package containing the asset and <path> is the relative path to the asset within that package’s lib directory.

For example, let’s say your package wanted to use enchilada’s guacamole.css styles. In an HTML file in your package, you can add:

<link href="packages/enchilada/guacamole.css" rel="stylesheet">

When you run your application using pub serve, or build it to something deployable using pub build, pub will copy over any referenced assets that your package depends on.

Implementation files

enchilada/
  lib/
    src/
      beans.dart
      queso.dart

The libraries inside “lib” are publicly visible: other packages are free to import them. But much of a package’s code is internal implementation libraries that should only be imported and used by the package itself. Those go inside a subdirectory of lib called src. You can create subdirectories in there if it helps you organize things.

You are free to import libraries that live in lib/src from within other Dart code in the same package (like other libraries in lib, scripts in bin, and tests) but you should never import from another package’s lib/src directory. Those files are not part of the package’s public API, and they might change in ways that could break your code.

When you use libraries from within your own package, even code in src, you can (and should) still use "package:" to import them. This is perfectly legit:

import "package:enchilada/src/beans.dart";

The name you use here (in this case enchilada) is the name you specify for your package in its pubspec.

Web files

enchilada/
  web/
    index.html
    main.dart
    style.css

Dart is a web language, so many pub packages will be doing web stuff. That means HTML, CSS, images, and, heck, probably even some JavaScript. All of that goes into your package’s web directory. You’re free to organize the contents of that to your heart’s content. Go crazy with subdirectories if that makes you happy.

Also, and this is important, any Dart web entrypoints (in other words, Dart scripts that are referred to in a <script> tag) go under web and not lib. That ensures that a packages directory is created nearby so that package: imports can be resolved correctly.

(You may be asking whether you should put your web-based example programs in example or web?” Put those in example.)

Command-line apps

enchilada/
  bin/
    enchilada

Some packages define programs that can be run directly from the command line. These can be shell scripts or any other scripting language, including Dart. The pub application itself is one example: it’s a simple shell script that invokes pub.dart.

If your package defines code like this, put it in a directory named bin.

Tests and benchmarks

enchilada/
  test/
    enchilada_test.dart
    tortilla_test.dart

Every package should have tests. With pub, the convention is that these go in a test directory (or some directory inside it if you like) and have _test at the end of their file names.

Typically, these use the unittest package.

enchilada/
  benchmark/
    make_lunch.dart

Packages that have performance critical code may also include benchmarks. These test the API not for correctness but for speed (or memory use, or maybe other empirical metrics).

Documentation

enchilada/
  doc/
    getting_started.md

If you’ve got code and tests, the next piece you might want is good documentation. That goes inside a directory named doc. We don’t currently have any guidelines about format or organization within that. Use whatever markup format that you prefer.

This directory should not just contain docs generated automatically from your source code using docgen. Since that’s pulled directly from the code already in the package, putting those docs in here would be redundant. Instead, this is for tutorials, guides, and other hand-authored documentation in addition to generated API references.

Examples

enchilada/
  example/
    lunch.dart

Code, tests, docs, what else could your users want? Standalone example programs that use your package, of course! Those go inside the example directory. If the examples are complex and use multiple files, consider making a directory for each example. Otherwise, you can place each one right inside example.

This is an important place to consider using package: to import files from your own package. That ensures the example code in your package looks exactly like code outside of your package would look.

Internal tools and scripts

enchilada/
  tool/
    generate_docs.dart

Mature packages often have little helper scripts and programs that people run while developing the package itself. Think things like test runners, documentation generators, or other bits of automation.

Unlike the scripts in bin, these are not for external users of the package. If you have any of these, place them in a directory called tool.