DebuggingUtils syntax error for new projects

[KellyThomas]

Godot version:
Godot_v3.0-rc1_mono_win64

OS/device including version:
Windows XP

Issue description:
Build fails if my project includes a c# script.

Steps to reproduce:
I have Mono 4.5.0 5.4.0 and Microsoft Build Tools 2015 installed (these were working with 3.0 beta 2)

I have deleted my C:\Users\<username>\AppData\Roaming\Godot directory.

If I create a new project and attached a new c# script to a node then when I build I receive three errors:

Core\DebuggingUtils.cs(37,42): error CS1026: ) expected 
Core\DebuggingUtils.cs(37,52): error CS1002: ; expected 
Core\DebuggingUtils.cs(37,52): error CS1513: } expected 

My C:\Users\<username>\AppData\Roaming\Godot\mono\solutions\GodotSharp_-<somenumber>\Core\DebuggingUtils.cs contains the following lines:

// Lines 37-38
if (methodBase is MethodInfo methodInfo)
    sb.AppendTypeName(methodInfo.ReturnType);

If I modify them to this then no further errors occur:

// Lines 37-38
if (methodBase is MethodInfo)
    sb.AppendTypeName(((MethodInfo)methodBase).ReturnType);

Minimal reproduction project:
Attached zip contains example project and copy of my C:\Users\<username>\AppData\Roaming\Godot\mono directory

DebuggingUtils_test_files.zip

[akien-mga]

As far as I know Mono 4.5.0 is not supported, we recommend at least version 5.2.0 (earlier versions might work, but we don't test those).

In your case, your Mono version lacks support of the is type pattern matching in C# 7.0: https://docs.microsoft.com/en-us/dotnet/csharp/pattern-matching

CC @neikeq

[akien-mga]

(Closing as it's not a bug, but in case @neikeq wants to keep some support for older Mono versions, removing the use of C# 7.0 features could still be done I guess)

[KellyThomas]

@akien-mga Thanks the rapid response!

I have to confess to a typo in this report I was running mono-5.4.0.201-x64 when I first encountered this error.

Stepping forward to mono-5.4.1.6-x64-0 has not resolved it either.

I had not encountered the type pattern syntax until now so didn't recognise it as a recent language version feature.

Looking at my build log (full text in the attached zip) it ends with a reference to:

"C:\Users\Bill\AppData\Local\Temp\.NETFramework,Version=v4.5.AssemblyAttributes.cs"

This file contains the following content:

// <autogenerated />
using System;
using System.Reflection;
[assembly: global::System.Runtime.Versioning.TargetFrameworkAttribute(".NETFramework,Version=v4.5", FrameworkDisplayName = "")]

So it appears my build process is limiting itself to c# 5.0 for some reason.

[akien-mga]

Right, so we should likely avoid using C# 7.0 features for now.

[neikeq]

You need MSBuild 15 (2017) for C# 7 support. However, I wanted to keep these assemblies to C# 6 in order to support MSBuild 14, but looks like I forgot about that line.

[KellyThomas]

Thanks, I was using Build Tools 2015 as a workaround for encountering the \\csc.exe issue with Build Tools 2017.

I have now setup VS2017 / MS Build (System) as a workaround.

[akien-mga]

Can you make a PR with your changes if it's enough to fix building with VS 2015?