rust-analyzer server binary on Windows doesn't ship required Visual C++ Runtime

[ColinFinck]

Running rust-analyzer 0.3.2667 on a fresh Windows installation fails, because VCRUNTIME140.DLL is missing on that system and doesn't come with a default Windows installation.

This error and the solution of installing the missing Visual C++ Redistributable is hard to grasp for the average user, because rust-analyzer fails silently. You need to open the OUTPUT tab in VS Code, jump to "rust-analyzer Language Server" and translate the error stating:

Server process exited with error code 3221225781.

I see two viable solutions here:

1. Auto-install the missing Visual C++ Runtime package. I remember a time when every Windows installer detected the presence of that package and auto-installed it if missing. Is that also possible when installing VS Code extensions?

2. Build the rust-analyzer server binary with a static CRT. This may marginally increase the size of the binary, but entirely removes the DLL dependency. Adding the Rust flag -Ctarget-feature=+crt-static should be sufficient to achieve that.

CC @Veykril

[ChayimFriedman2]

We should definitely not auto-install the runtime. We should also not need to, it should come preinstalled, unless you have a too old version of Windows.

[lnicola]

There are multiple versions of the C++ redistributable. We just build on windows-latest, I don't think we do anything special about it. Most software will bundle that installer, but I'm not convinced we want to do the same.

[ColinFinck]

@ChayimFriedman2: Neither Windows 10 nor Windows 11 bundle the required version of the Visual C++ Runtime. I have tested this with two clean installations in VMs.
The Runtime may very well be installed by other development tools, but this is not guaranteed. If you currently install rust-analyzer on 100 different Windows machines, you will surely run into one that lacks the required dependencies.

If this is something you don't want to deal with, I highly recommend adding -Ctarget-feature=+crt-static to your Rust flags and build statically linked binaries.

[ShoyuVanilla]

Static linking sounds plausible to me, but I'm not sure about its license policy for that

[Veykril]

I am confused as to why no one ever has apparently had a problem with this before. I'd expect that by just installing rustc dependencies you will likely already have the required dependencies here

[ColinFinck]

@Veykril There's at least one person that reported this bug before, albeit without a suggestion to improve things: #14013

You're right that most people on Windows likely use the x86_64-pc-windows-msvc target. This target requires a full Visual Studio installation to build even the simplest Rust programs, because it depends on the commercial Microsoft linker. And it's supposed to install the required runtime files too.

Installing the "free" Visual Studio Community Edition may be a solution for most individual developers. However, I know of at least 3 situations where Visual Studio (and thus, the x86_64-pc-windows-msvc target) is not an option at all:

1. You want to distribute a batteries-included Rust setup. The Visual Studio Community license doesn't permit this redistribution.
2. You are a company that isn't qualified to use the Visual Studio Community edition.
3. You want to cross-compile Windows binaries from another operating system.

For all these situations, I need to resort to the x86_64-pc-windows-gnu target or the emerging x86_64-pc-windows-gnullvm target instead. I'm at a point where they have become my default targets for Windows development, simply to eliminate the potential traps right from the start. And I would love to have a good rust-analyzer experience when using them. Which is best achieved by not depending on the Visual C++ Runtime files :)