Parse-Error: new-line in string interpolation expressions

[bernd5]

Version Used: 16.9.0 Preview 3

Sample Code:

Link

using System;

struct Point
{
    public int X;
    public int Y;
    
    public override string ToString() => $"({X}, {Y})";
}

public class App
{

    public static void Main()
    {
        Console.WriteLine($"A Point: {new Point{ 
              X = 1, 
              Y = 2 
        }}");
    }
}

Expected Behavior:
According to csharplang every expression is allowed in an interpolation. So expressions with New-Line trivia should compile.

Actual Behavior:
Code does not compile, just with removing the new lines.

[CyrusNajmabadi]

You need to use $@""

Normal $"" strings do not allow newlines in them.

[bernd5]

The new line does not appear in the string itself! It is inside a normal expression. @ would dissallow escaping / change escaping rules.

Of course we could use verbatim interpolated strings here, string.operator+, local variables or simply string.Format.

[CyrusNajmabadi]

The new line does not appear in the string itself! It is inside a normal expression.

Yes. I understand that :-)

This is how we designed the language to work. The string literal start/end is discovered first, then internally parsed. Fur these strings, the end can't be found as they are supposed to be in a single line, but a new line is encountered before the end is reached.

@ would dissallow escaping / change escaping rules.

Yes. That is true.

Of course we could use verbatim interpolated strings here, string.operator+, local variables or simply string.Format.

Yes.

[bernd5]

Is it defined in the spec that expressions with newline trivia are dissallowed here?

A resulting bug is a call to aSyntaxTreeRoot.NormalizeWhitespace() with long interpolation expressions becomes invalid just because
this function produces nice formatted code which is unfortunately not valid / parsable anymore. NormalizeWhitespace inserts new lines here.
I would say NormalizeWhitespace() is not buggy here, it is the interpolated string parsing!

What's about comments, those are "real trivia" - but a multiline comment would break interpolated strings, too.

[CyrusNajmabadi]

NormalizeWhitespace inserts new lines here.

That is a bug.

[CyrusNajmabadi]

Please see the conversation in dotnet/csharplang#1409 for a better understanding of what's going on here.

In particular: dotnet/csharplang#1409 (comment)

[bernd5]

I understand the problem with the colon handling. But I think the issue with new lines is easy.

Coudn't we change the call at: Lexer-Source

To IsAtEnd(isHole).

New lines are generally allowed in those "holes".

[bernd5]

New lines in nested-interpolated-verbatim-string-expressions in suche "holes" are already working see:

using System;

Console.WriteLine($"Test { (@$"
12")}");

The code at: Link could be simplified very much.

[bernd5]

I fixed the code but it is still over-complicated and bug-prone.

One example.
The old implementation allowed:

using System;

Console.WriteLine($"Test { @$"
12"}");

But it rejected:

using System;

Console.WriteLine($"Test { $@"
12"}");

[CyrusNajmabadi]

New lines in nested-interpolated-verbatim-string-expressions in suche "holes" are already working

yes. this is as expected.

[bernd5]

Implemented via #56853