Atlas is a simple package cloner tool. It manages project dependencies in an isolated deps/ directory.
Atlas is compatible with Nimble in the sense that it supports the Nimble file format.
Atlas uses two main concepts:
A project is a directory that has a file atlas.config inside it. Use atlas init to create a project out of the current working directory.
Projects can share dependencies and be developed locally by using the link command. This creates nimble-link files that allow projects to share their dependencies.
The project structure looks like this:
$project / project.nimble $project / nim.cfg $project / other main project files... $project / deps / atlas.config $project / deps / dependency-A $project / deps / dependency-B $project / deps / dependency-C.nimble-link (for linked projects)
The deps directory can be set via --deps:DIR during atlas init.
Inside a project there is a deps directory where your dependencies are kept. It is easy to move a dependency one level up and out of the deps directory, turning it into a project. Likewise, you can move a project to the deps directory, turning it into a dependency.
The only distinction between a project and a dependency is its location. For dependency resolution a project always has a higher priority than a dependency.
Atlas works by managing two files for you, the project.nimble file and the nim.cfg file. You can edit these manually too, Atlas doesn't touch what should be left untouched.
Atlas uses git commits internally; version requirements are translated to git commits via git tags and a fallback of searching Nimble file commits.
Atlas uses URLs internally; Nimble package names are translated to URLs via Nimble's packages.json file. Atlas uses "shortnames" for known URLs from packages. Unofficial URLs, including forks, using a name triplet of the form projectName.author.host. For example Atlas would be atlas.nim-lang.github.com. Packages can be added using nameOverrides in atlas.config which adds a new name to URL mapping.
Atlas does not call the Nim compiler for a build, instead it creates/patches a nim.cfg file for the compiler. For example:
############# begin Atlas config section ########## --noNimblePath --path:"deps/nimx" --path:"deps/sdl2/src" --path:"deps/opengl/src" --path:"../linked-project/src" --path:"../linked-project/deps/msgpack4nim/" ############# end Atlas config section ##########
The version selection is deterministic, it picks up the minimum required version. Thanks to this design, lock files are much less important.
Atlas supports the following commands:
Clone the package behind url or package name and its dependencies into the deps directory and make it available for your current project. Atlas will create or patch the files $project.nimble and nim.cfg for you so that you can simply import the required modules.
For example:
mkdir newproject cd newproject git init atlas use lexim # add `import lexim` to your example.nim file nim c example.nim
Link another project into the current project to share its dependencies. This creates nimble-link files that allow the projects to share their dependencies.
For example:
atlas link ../other-project
This will link the other project and make its dependencies available to your current project. The other project must be another Atlas project and have a Nimble file.
The linked project will be added to this project's Nimble file if it's not already present.
Note, that the other project's nameOverrides and urlOverrides aren't imported. You may need to import the name-overrides to properly use the deps. This is due to the triplet-naming above.
Clones a URL and all of its dependencies (recursively) into the project. Creates or patches a nim.cfg file with the required --path entries.
Note: Due to the used algorithms an update is the same as a clone.
If a <package name> is given instead the name is first translated into an URL via packages.json or via a github search.
Search the package index packages.json for a package that contains the given terms in its description (or name or list of tags).
Use the .nimble file to setup the project's dependencies.
Update every project / dependency in the project that has a remote URL that matches filter if a filter is given. The project / dependency is only updated if there are no uncommitted changes.
Run atlas --help for more features.
Sometimes two URLs can conflict for the same dependency shortname. For example, when a project uses a forked dependency with bug fixes. These conflicts need to be manually resolved using pkgOverrides in atlas.config. The format is package name and the selected URL:
"pkgOverrides": {
"asynctools": "https://github.com/timotheecour/asynctools"
},
You can override how Atlas resolves a package name or a URL. The overrides use a simple pattern matching language and are flexible enough to integrate private gitlab repositories.
{
"resolver": "SemVer",
"nameOverrides": {
"customProject": "https://gitlab.company.com/customProject"
},
"urlOverrides": {
"https://github.com/araq/ormin": "https://github.com/useMyForkInstead/ormin"
},
"plugins": "",
}
The $ has a special meaning in a pattern:
| Syntax | Meaning |
|---|---|
| $$ | Matches a single dollar sign. |
| $* | Matches until the token following the $* was found. |
| The match is allowed to be of 0 length. | |
| $+ | Matches until the token following the $+ was found. |
| The match must consist of at least one char. | |
| $s | Skips optional whitespace. |
For example, here is how to override any github link:
"urlOverrides": {
"https://github.com/$+": "https://utopia.forall/$#"
}
You can use $1 or $# to refer to captures.
Atlas supports setting up a virtual Nim environment via the env command. You can even install multiple different Nim versions into the same project.
For example:
atlas env 1.6.12 atlas env devel
When completed, run source nim-1.6.12/activate.sh on UNIX and nim-1.6.12/activate.bat on Windows.
To change the used dependency resolution mechanism, edit the resolver value of your atlas.config file. The possible values are:
The default resolution mechanism is called "MaxVer" where the highest available version is selected that still fits the requirements.
Suppose you have a dependency called "mylibrary" with the following available versions: 1.0.0, 1.1.0, and 2.0.0. MaxVer selects the version 2.0.0.
Adhere to Semantic Versioning (SemVer) by selecting the highest version that satisfies the specified version range. SemVer follows the format of MAJOR.MINOR.PATCH, where:
MAJOR version indicates incompatible changes.
MINOR version indicates backward-compatible new features.
PATCH version indicates backward-compatible bug fixes.
Consider the same "mylibrary" dependency with versions 1.0.0, 1.1.0, and 2.0.0. If you set the resolver to SemVer and specify a version range requirement of >= 1.0.0, the highest version that satisfies the range that does not introduce incompatible changes will be selected. In this case, the selected version would be 1.1.0.
For the "mylibrary" dependency with versions 1.0.0, 1.1.0, and 2.0.0, if you set the resolver to MinVer and specify multiple minimum versions, the highest version among the minimum required versions will be selected. For example, if you specify a minimum requirement of both >=1.0.0 and >=2.0.0, the selected version would be 2.0.0.
Atlas supports lockfiles for reproducible builds via its pin and rep commands.
Notice: Atlas helps with reproducible builds, but it is not a complete solution. For a truely reproducible build you also need to pin the used C++ compiler, any third party dependencies ("libc" etc.) and the version of your operating system.
atlas pin can be run either in the project or in a specific project. It "pins" the used repositories to their current commit hashes. If run in the project the entire project is "pinned" in the atlas.lock file. If run in a project the project's dependencies but not the project itself is "pinned" in the lock file.
The rep command replays or repeats the projects to use the pinned commit hashes. If the projects have any "build" instructions these are performed too unless the --noexec switch is used.
Atlas operates on a graph of dependencies. A dependency is a git project of a specific commit. The graph and version selection algorithms are mostly programming language agnostic. Thus it is easy to integrate foreign projects as dependencies into your project.
This is accomplished by Atlas plugins. A plugin is a NimScript snippet that can call into external tools via exec.
To enable plugins, add the line plugins="_plugins" to your atlas.config file. Then create a directory _plugins in your project. Every *.nims file inside the plugins directory is integrated into Atlas.
A builder is a build tool like make or cmake. What tool to use is determined by the existence of certain files in the project's top level directory. For example, a file CMakeLists.txt indicates a cmake based build:
builder "CMakeLists.txt": mkDir "build" withDir "build": exec "cmake .." exec "cmake --build . --config Release"
Save this as _plugins/cmake.nims. Then every dependency that contains a CMakeLists.txt file will be build with cmake.
Note: To disable any kind of action that might run arbitrary code, use the --noexec switch.