Prettier your CSharp with dotnet-format and lint-staged

Consistent formatting is a good thing. It makes code less confusing to newcomers and it allows whoever is working on the codebase to reliably focus on the task at hand. Not "fixing curly braces because Janice messed them up with her last commit". (A git commit message that would be tragic in so many ways.)

Once you've agreed that you want to have consistent formatting, you want it to be enforced. Enter, stage left, Prettier, the fantastic tool for formatting code. It rocks; I've been using on my JavaScript / TypeScript for the longest time. But what about C#? Well, there is a Prettier plugin for C#.... Sort of. It appears to be abandoned and contains the worrying message in the README.md:

Please note that this plugin is under active development, and might not be ready to run on production code yet. It will break your code.

Not a ringing endorsement.

dotnet-format: a new hope

Margarida Pereira recently pointed me in the direction of dotnet-format which is a formatter for .NET. It's a .NET tool which:

is a code formatter for dotnet that applies style preferences to a project or solution. Preferences will be read from an .editorconfig file, if present, otherwise a default set of preferences will be used.

It can be installed with:

dotnet tool install -g dotnet-format

The VS Code C# extension will make use of this formatter, you just need to set the following in your settings.json:

    "omnisharp.enableRoslynAnalyzers": true,
    "omnisharp.enableEditorConfigSupport": true

Customising your formatting

If you'd like to deviate from the default formatting options then create yourself a .editorconfig file in the root of your project. Let's say you prefer more of the K & R style approach to braces instead of the C# default of Allman style. To make dotnet-format use that you'd set the following:

# Remove the line below if you want to inherit .editorconfig settings from higher directories
root = true

# See https://github.com/dotnet/format/blob/master/docs/Supported-.editorconfig-options.md for reference
[*.cs]
csharp_new_line_before_open_brace = none
csharp_new_line_before_catch = false
csharp_new_line_before_else = false
csharp_new_line_before_finally = false
csharp_new_line_before_members_in_anonymous_types = false
csharp_new_line_before_members_in_object_initializers = false
csharp_new_line_between_query_expression_clauses = true

With this in place it's K & R all the way baby!

lint-staged integration

It's become somewhat standard to use the marvellous husky and lint-staged to enforce code quality. To quote the docs:

Run linters against staged git files and don't let 💩 slip into your code base!

So, before I happened upon dotnet-format I was already enforcing TypeScript / JavaScript style with the following entry in my package.json:

"husky": {
    "hooks": {
        "pre-commit": "lint-staged"
    }
},
"lint-staged": {
    "*.{js,ts,tsx}": "prettier --write"
}

The above configuration runs Prettier against files which have been staged for commit, provided they have the suffix .js or .ts or .tsx. How can we get dotnet-format in the mix also? Like so:

"husky": {
    "hooks": {
        "pre-commit": "lint-staged --relative"
    }
},
"lint-staged": {
    "*.cs": "dotnet format --include",
    "*.{js,ts,tsx}": "prettier --write"
}

We've done two things here. First, we've changed the lint-staged command to include the parameter --relative. This is because dotnet-format only deals with relative paths. Prettier is pretty flexible, so we can make this change without breaking anything.

Secondly we've added the *.cs task of dotnet format --include. This is the task that will be run on commit, when lint-staged runs, it will pass a list of relative file paths to dotnet format, the --include accepts a list of relative file or folder paths to include in formatting. So if you'd staged two files it might end up executing a command like this:

dotnet format --include src/server-app/Server/Controllers/UserController.cs src/server-app/Server/Controllers/WeatherForecastController.cs

By and large we don't have to think about this; the important take home is that we're now enforcing standardised formatting for all C# files upon commit. Everything that goes into the codebase will be formatted in a consistent fashion.