Support configuring dotnet-format with a configuration file

As we add more options to the configuration it is increasingly tedious to type them all out at the command line.

• We should add support for reading in options from a “format.json” file.
• We should look for the configuration file in the current working directory.
• We should support multiple configurations stored as top-level properties. The configuration can be specified from the command line with a new -c|--configuration {name} option. A “default” option can be configured which will be applied whenever a configuration is not specified.
• The option’s property name should match the long name for the option.
• Options that support multiple values provided as a comma separated string can be expressed as either a comma separated string or as an array of values.
• Options are optional in the configuration and will take their default value if missing or if null is specified for their value.

Example “format.json”:

{
    "default": {
        "folder": "./src",
        "workspace": null,
        "dry-run": false,
        "check": false,
    },
    "all": {
        "workspace": "format.sln",
        "dry-run": false,
        "check": false,
        "files": null
    },
    "validate": {
        "folder": "./src",
        "workspace": null,
        "dry-run": true,
        "check": true,
        "files": [ ]
    }
}

[sandyarmstrong]

My only addition here would be to make it a hidden file similar to .gitconfig and .editorconfig. I’d suggest .dotnetformatconfig or .formatconfig.

I really like the multiple configurations idea here. Cool stuff!

[jmarolf]

I am not opposed to this in theory. My main concern is that we create an alternative to .editorconfig. In most cases I would expect someone to update the .editorconfig in their project to exclude/include files. I can see the rare case where I have some set of submodules that I need to configure, but my hope is that we first find a way to specify formatting options so that dotnet format, Visual Studio for Mac, VS Code, and Visual Studio can all do the same thing.

All those concerns aside, I would tentatively accept a PR for this.