CompilationUnitSyntax.Members[i].ToFullString() skips #endif if it's at the end of the file

[eduherminio]

Version Used:

Microsoft.CodeAnalysis.CSharp.Workspaces v4.4.0

Steps to Reproduce:

git clone https://github.com/eduherminio/roslyn-66019-compilationunitsyntax-endif
cd roslyn-66019-compilationunitsyntax-endif
dotnet run
# Compare output with file contents

Expected Behavior:

This piece of code:

using Microsoft.CodeAnalysis.CSharp;

var root = CSharpSyntaxTree.ParseText(await File.ReadAllTextAsync("valid_file.cs")).GetCompilationUnitRoot();
foreach (var member in root.Members)
{
    Console.Write(member.ToFullString());
}

prints the whole content of valid_file.cs:

namespace Endif;

#if DEBUG
public class A1
{

}
#else

public class B1
{

}

#endif

Actual Behavior:

The mentioned piece of code prints:

namespace Endif;

#if DEBUG
public class A1
{

}
#else

public class B1
{

}

Skipping the #endif

[DoctorKrolic]

The #endif is attached to the EndOfFileToken, that's why you don't see it: https://sharplab.io/#v2:C4LghgzsA0AmIGoA+A7MBbAphADmAxpgAQCiKsAlgGYDcAsAFCMDE1RASiQDIkCCAyiUYABAMxFhAJiK8AjIwDejRgF8WmADYRMyhmInSAQvIZKmDNeeaZy1IA==

[Youssef1313]

Yes. This is by-design.

[eduherminio]

I see, thanks both of you! I'm always impressed how awesome sharplab is, btw.

Do you folks happen to know/remember/can think of any other gotchas of the following approach to translate CompilationUnitSyntax back to the *.cs files they came from?

• CompilationUnitSyntax.Usings
• CompilationUnitSyntax.Members
• CompilationUnitSyntax.EndOfFileToken

I'd be happy to be pointed to any documentation/code if you know a good source to learn about it 😃

[DoctorKrolic]

If you have it as CompilationUnitSyntax you can just call ToFullString(). This preserves all necessary trivia

[eduherminio]

If you have it as CompilationUnitSyntax you can just call ToFullString(). This preserves all necessary trivia

I'm afraid that's not the case, since I'm mixing multiple files into one, but good to know, thanks!

[Youssef1313]

since I'm mixing multiple files into one

What exactly the scenario where you want to do this? Why it is needed to merge multiple trees?

Anyway, my suggestion for that is:

• Walk every tree you have, take strip all usings from it, and strip the leading trivia of the first member only if it is #endif.
• Now you got a bunch of usings and all the trees without the using.
• In the new file, concatenate all the usings that were stripped, then concatenate the rest of all trees.
• This will be trickier if trees have file-scoped namespaces.
• If one of the trees has top-level statements, it should be the first once to add after all the usings. What about multiple trees having top-level statements? Is that something that can happen for your scenario? I can't think of a good behavior for that case.

[eduherminio]

It's for dotnet-combine tool, which aims to do exactly that, merge multiple C# files into a single one and keep everything working.

I'm fully aware there are some scenarios that will very tricky or just impossible to support, such as the one with multiple top-level statements that you mention, but I'm fine with that.

I got it working more or less as I expected 2 years ago, following a process similar to what you described, but I'm revisiting now (i.e. added support for file-scoped namespaces) and realizing that the devil's in the detail, of course.

Walk every tree you have, take strip all usings from it, and strip the leading trivia of the first member only if it is #endif.

I need to have a look that last part of this, since I'm definitely not doing that right now.

[Youssef1313]

I need to have a look that last part of this, since I'm definitely not doing that right now.

Basically what I mean here is for something like this

#if DEBUG
using System;
#endif

public class C { }

In this case, #endif is attached to the class (the first member of compilation unit). So in a tree such as the above, you need to strip all the usings in addition to #endif

[eduherminio]

Thanks a lot @Youssef1313, good example of edge case that represents a bug in the tool as it is right now.

[svick]

@eduherminio If you want to figure out what are all the parts of a CompilationUnitSyntax, then they're here:

roslyn/src/Compilers/CSharp/Portable/Syntax/Syntax.xml

Lines 3020 to 3033 in 0d6ace5

	<Node Name="CompilationUnitSyntax" Base="CSharpSyntaxNode">
	<Kind Name="CompilationUnit"/>
	<Field Name="Externs" Type="SyntaxList&lt;ExternAliasDirectiveSyntax&gt;"/>
	<Field Name="Usings" Type="SyntaxList&lt;UsingDirectiveSyntax&gt;"/>
	<Field Name="AttributeLists" Type="SyntaxList&lt;AttributeListSyntax&gt;">
	<PropertyComment>
	<summary>Gets the attribute declaration list.</summary>
	</PropertyComment>
	</Field>
	<Field Name="Members" Type="SyntaxList&lt;MemberDeclarationSyntax&gt;"/>
	<Field Name="EndOfFileToken" Type="SyntaxToken">
	<Kind Name="EndOfFileToken"/>
	</Field>
	</Node>

[eduherminio]

Awesome, thanks a lot @svick!