Check for Mono runtime

[tmds]

A lot of code checking for mono runtime does it by seeing the Mono.Runtime type exists.

It is the suggested answer in this stack overflow question and is based on the Mono documentation.

It seems this is not working with the runtime based mono builds. I've tested against 7.0 and main.

When I run:

foreach (var type in new[] { "Mono.Runtime", "Mono.RuntimeStructs" })
{
    Console.WriteLine($"{type}: {Type.GetType(type) != null}");
}

The output is:

Mono.Runtime: False
Mono.RuntimeStructs: True

The check can also be found in .NET sources, for example: aspnetcore, msbuild, nuget, roslyn.

Should the type be re-introduced so this check continues to work?

Should a public API be added to perform this check?

cc @akoeplinger @jkotas @omajid @uweigand

[ghost]

Tagging subscribers to this area: @directhex
See info in area-owners.md if you want to be subscribed.

Issue Details

---

A lot of code checking for mono runtime does it by seeing the Mono.Runtime type exists.

It is the suggested answer in this stack overflow question and is based on the Mono documentation.

It seems this is not working with the runtime based mono builds. I've tested against 7.0 and main.

When I run:

foreach (var type in new[] { "Mono.Runtime", "Mono.RuntimeStructs" })
{
    Console.WriteLine($"{type}: {Type.GetType(type) != null}");
}

The output is:

Mono.Runtime: False
Mono.RuntimeStructs: True

The check can also be found in .NET sources, for example: aspnetcore, msbuild, nuget, roslyn.

Should the type be re-introduced so this check continues to work?

Should a public API be added to perform this check?

cc @akoeplinger @jkotas @omajid @uweigand

Author:	tmds
Assignees:	-
Labels:	untriaged, area-Infrastructure-mono
Milestone:	-

[uweigand]

I'm not convinced this would be a good change. .NET using the Mono runtime is a quite different environment from Mono. Most users of those pre-existing checks were likely actually checking for Mono itself. Having them all activated in .NET just because we're using the Mono runtime doesn't look like a good idea to me - we ideally want .NET to behave the same no matter the underlying runtime.

[akoeplinger]

This was sort of intentional, like @uweigand said the Mono.Runtime type has long been used to check for legacy Mono (.NET Framework-based) so we left it out in dotnet/runtime to make sure code goes into the "modern" codepaths.

The Mono.RuntimeStructs is an alternative if you really need to know it even nowadays.

[tmds]

That makes sense.

Ideally, these runtimes behave the same.
In practice, they don't, which is why we have these checks.

It sounds like the use-case is considered too niche to add a public API.

Anyone looking for code to check for the variants (from BenchmarkDotNet's RuntimeInformation class):

public static bool IsMono { get; } = Type.GetType("Mono.RuntimeStructs") != null;
public static bool IsOldMono { get; } = Type.GetType("Mono.Runtime") != null;
public static bool IsNewMono { get; } = IsMono && !IsOldMono;

[stephentoub]

Ideally, these runtimes behave the same.
In practice, they don't, which is why we have these checks.

What are the differences that are causing you problems?

[tmds]

I still have to create an issue about it in this repo: running a webapp using dotnet run and then pressing Ctrl+C, gives a 143 exit code with Mono runtime, and a 0 exit code with CoreCLR.
Such a check is part of source-build's smoke tests, and it is failing on Mono: dotnet/source-build#3174.

To make the test pass on existing releases, I was looking for a way to check for Mono runtime.

[tmds]

I still have to create an issue about it

I've written up an issue in the sdk repo: #81093.