Refactoring "Move type to ..." breaks preprocessor directives

[josefpihrt]

Version Used: Visual Studio 2017 15.2.0+26430.6

Code to Reproduce:

public class Foo
{
    #region Region
    public class Bar // Move type to 'Bar.cs'
    {
    }
    #endregion
}

Actual Behavior:

public partial class Foo
{
    #endregion
}

[sharwell]

📝 We had to deal with this for StyleCop Analyzers, and believe we found a rather clever solution in the end. Rather than construct a new file from a particular syntax node, we duplicate the entire tree and then selectively remove different sets of nodes from each file.

https://github.com/DotNetAnalyzers/StyleCopAnalyzers/blob/master/StyleCop.Analyzers/StyleCop.Analyzers.CodeFixes/MaintainabilityRules/SA1402CodeFixProvider.cs

[Pilchie]

This was fixed already for 15.3 (I think by #16300 - @CyrusNajmabadi does that look right), though it leaves the #region and removes it's indentation, which could be better.

[Pilchie]

@sharwell That's actually how this is implemented as well :)

[CyrusNajmabadi]

Yeah. This was fixed. But clearly the fix could use some work. If anyone wants to fix up the formatting, that would be totally great.

[CyrusNajmabadi]

@yvef I would not over complicate things. We can just detect some very common cases that go awry today and improve on them. :-)

[Rekkonnect]

This still applies (17.9.2) and also carries over #endregion directives that are not bound to any #region ones. Example:

We have this file:

public class Foo
{
    #region Region1
    public class NotBar
    {
    }
    #endregion

    #region Region2
    public class Bar // Move type to 'Bar.cs'
    {
    }
    #endregion
}

After moving Foo.Bar to Bar.cs, we have (indentation is preserved as-is):

// Foo.cs
public partial class Foo
{
    #region Region1
    public class NotBar
    {
    }

#endregion
#region Region2
    #endregion
}

// Bar.cs
public partial class Foo
{
    #endregion

    #region Region2
    public class Bar // Move type to 'Bar.cs'
    {
    }
    #endregion
}