Feature request: Format XML documentation comments

[FelixZY]

This is related to #667 but, I think, more narrow in scope.

We use xml documentation comments in code but have not been able to find a way to standardize formatting. Since we are already using csharpier to format our c# files, it would be really helpful if xml documentation comments were supported as well.

[FelixZY]

This is not a fix for the original problem but a manual workaround if you are simply looking to format the documentation you are currently writing.

Dirty workaround using prettier manually

1. Install prettier

$ npm install prettier

2. Copy documentation to a new .html file

Also remove leading ///

`MyClass.cs`

/// <summary>Some summary</summary>
/// <remarks>
///     <para>
///         This documentation is really long and requires that the formatter produces multiple lines when
///         formatted with
///         the <c>printWidth</c>
///         we are going with.
///     </para>
///     <code>
///         Console.WriteLine(
///             """
///             Hello World!
///             """
///         );
///     </code>
///     <para>
///         Another
///         badly <see cref="Formatting"/> formatted
///         para.
///     </para>
/// </remarks>
public class MyClass
{ }

documentation.html (input)

<summary>Some summary</summary>
<remarks>
    <para>
        This documentation is really long and requires that the formatter produces multiple lines when
        formatted with
        the <c>printWidth</c>
        we are going with.
    </para>
    <code>
        Console.WriteLine(
            """
            Hello World!
            """
        );
    </code>
    <para>
        Another
        badly <see cref="Formatting"/> formatted
        para.
    </para>
</remarks>

4. Add <!-- prettier-ignore --> before any <code> blocks etc. that should not be formatted

This will only affect the tag immediately following.

<summary>Some summary</summary>
<remarks>
    <para>
        This documentation is really long and requires that the formatter produces multiple lines when
        formatted with
        the <c>printWidth</c>
        we are going with.
    </para>
+   <!-- prettier-ignore -->
    <code>
        Console.WriteLine(
            """
            Hello World!
            """
        );
    </code>
    <para>
        Another
        badly <see cref="Formatting"/> formatted
        para.
    </para>
</remarks>

4. Run prettier

$ prettier --tab-width 4 --write documentation.html

documentation.html (output):

<summary>Some summary</summary>
<remarks>
    <para>
        This documentation is really long and requires that the formatter
        produces multiple lines when formatted with the <c>printWidth</c>
        we are going with.
    </para>
    <!-- prettier-ignore -->
    <code>
        Console.WriteLine(
            """
            Hello World!
            """
        );
    </code>
    <para> Another badly <see cref="Formatting" /> formatted para. </para>
</remarks>

5. Reinsert ///, remove <!-- prettier-ignore --> and copy back to your .cs file

You can use search and replace by regex ^ -> /// (note the trailing space in the replace expression!) to reinsert /// easily.