Solution structure

Fantomas has a modular project structure.
The parser (Fantomas.FCS), the core library (Fantomas.Core) and the command line application (fantomas) are the main components of the solution.

graph TD
    A[Fantomas.FCS] --> B
    B[Fantomas.Core] --> J[Fantomas.EditorConfig]
    B --> C[Fantomas]
    J --> C
    B --> D[Fantomas.Benchmarks]
    B --> E[Fantomas.Core.Tests]
    B --> I[Fantomas.Core.SnapshotTests]
    J --> I
    C --> F[Fantomas.Tests]
    G[Fantomas.Client] --> H[Fantomas.Client.Tests]

Fantomas.FCS

This is a very custom fork of the F# compiler. We only expose a single parse function to construct the untyped syntax tree. We achieve this by taking the files necessary to compile the F# parser from source (via custom code in a Fun.Build pipeline). This limits the dependency footprint that our compiler has, compared to the official F# compiler NuGet package.

Note that the AST returned by Fantomas.FCS looks identical to what the official F# compiler returns. However, the AST is not binary compatible. It is most likely that Fantomas contains a newer version of the Syntax tree than the official F# compiler.

Fantomas.Core

The heart of Fantomas is the core library. It contains the core logic reconstructing source code from the AST. Fantomas can be used as a library, see CodeFormatter.fsi to learn what APIs are exposed.

Fantomas

The command line application is the main entry point of the solution.
It exposes the core functionality and also takes care of .editorconfig and .fantomasignore files.

Fantomas.EditorConfig

Reading Fantomas's settings from .editorconfig properties, and writing them back. It is a project of its own so that the snapshot cases read their settings with the same code as the tool. It is not a package: it ships inside the fantomas tool. Finding the .editorconfig files that apply to a file stays in Fantomas.

Fantomas.Benchmarks

A BenchmarkDotNet project used to measure the performance of the core library. We format a fixed revision of CodePrinter.fs as part of our CI process, to detect potential regressions.

Fantomas.Client

A standalone library project that editors can use to interact with the fantomas commandline application. Editors do not use Fantomas.Core, instead they use the Fantomas.Client library to connect to a fantomas dotnet tool. This allows end-users to bring their "own version" of Fantomas. This selected version could then later be re-used to verify if all files were formatted in a CI scenario.