Prevent usage of 'in' with non-readonly structs by a compiler error

[dymanoid]

Using a Roslyn Analyzer ReflectionIT.Analyzer.Structs, issue a compiler error when a non-readonly struct is passed to a method using the in modifier.

Passing a non-readonly struct with an in modifier can drastically decrease performance, because in the called method, the compiler will create defensive struct copies on every method call or property access of that passed struct.

Closes #440.

[krzychu124]

Works only with VS 2019 because of missing dependency Microsoft.CodeAnalysis, Version=3.1.0.0 😕

[kvakvs]

Builds for me.
As I am not using in keyword anyway, i'm happy to have this. It will be up to @krzychu124 to make it work on CI, or something? :)

[dymanoid]

Okay, didn't know you're on VS2017. Should I fork that analyzer and downgrade it back to VS2017 toolset, or you'd rather prefer to upgrade your IDE?

[krzychu124]

I've upgraded my IDE 😃
I've had to change environment in AppVeyor to VS2019. Downside of that is longer queue for build 😕

[originalfoo]

Updated dev tools wiki page to note VS 2019 requirement: https://github.com/krzychu124/Cities-Skylines-Traffic-Manager-President-Edition/wiki/Dev-Tools

I assume it works on Rider too?

Will this also work on Visual Studio Code - I think @FireController1847 was using that for EVE dev.

[kvakvs]

Clean and rebuild in both FullDebug and Release, worked on Rider with no visible effect.

[dymanoid]

Maybe try to pass a non-readonly struct via in and see if that leads to a compile error?

[krzychu124]

Works on Rider 2019.1.3 but only while building project/solution. I will check 2019,2 Early Access Preview

[dymanoid]

On Rider, you need to explicitly enable Roslyn Analyzers somewhere in the settings. If I recall that correctly.

[originalfoo]

Regarding activating the Roslyn Analyzers on Rider, post some details in a comment and I'll update wiki. I think the two Build guides will also need updating.

[dymanoid]

https://www.jetbrains.com/help/rider/Settings_Roslyn_Analyzers.html

[krzychu124]

I wanted to add screenshot but I couldn't upload due to timeout to GitHub Amazon S3 server 😄

In Rider 2019.2 EAP works too.

[originalfoo]

Ah, the .dll has to be manually downloaded?

1>CSC : error CS0006: Metadata file '..\packages\ReflectionIT.Analyzer.Structs.0.1.0\analyzers\dotnet\cs\ReflectionIT.Analyzer.Structs.dll' could not be found

[dymanoid]

No, the NuGet package manager should automatically restore the packages and download the binaries.

[originalfoo]

Looks like I built before it finished downloading lol. It's working now. I've not tested non-readonly structs and the in keyword yet.

EDIT: Could we add a unit test for testing that the analyser is working?

[dymanoid]

This is not possible. The Analyzer will generate a compiler error, so the code won't compile and the unit test cannot be run. If the code compiles though and the test executes, that means the Analyzer doesn't work.

[krzychu124]

@aubergine10 what do you think? Looks good to me.
Can we merge it?

[originalfoo]

LGTM 👍

Note: I've not tested to see what happens when a non-readonly struct is used with in parameter (I don't really know how to as I've not worked with structs before). If that's not yet been tested merging would be premature.

[krzychu124]

I did a few tests
It's easy, look 😉
Method:

private void Test(in Vector2 vec){
    Debug.Log(vec); // whatever
}

Call

Vector2 vec = new Vector2(1f, 1f);
Test(vec); //this line should create compilation error because Vector2 is not readonly struct

[originalfoo]

👍