Static_vcruntime: Distribute Windows MSVC binaries without needing to deploy vcruntime.dll

[chrisd]

EDIT: Version 2 has been released. Now 50% less hacky.

static_vcruntime

When you build a Windows application using the MSVC toolchain, by default it will produce a .exe that dynamically links to vcruntime140.dll. This dll will then need to be deployed when distributing the application. The static_vcruntime crate makes it so when you build your application in release mode, the vcruntime is statically linked instead.

Usage

Add it as a build dependency:

[build-dependencies]
static_vcruntime = "2.0"

Then put this in your build.rs:

fn main() {
    static_vcruntime::metabuild();
}

That is all. Then when you build in release mode the vcruntime library will be statically linked instead of dynamically:

cargo build --release

FAQ

How is this different to +crt-static?

Using +crt-static does statically link the vcruntime but it also statically links the universal C runtime (ucrt). This is entirely unnecessary because the ucrt is included with Windows already.

Can I do this manually instead?

You can! But it requires making a special configuration file. To do so create a folder in your project called .cargo. In that folder make a file called config.toml. So the directory structure is like this:

.cargo
|    config.toml

Then copy this into config.toml:

# Statically link the vcruntime.
# This should go in `.cargo/config.toml`. It will not work in `cargo.toml`.
[target.'cfg(all(windows, target_env = "msvc"))']
rustflags = [
	"-C", "target-feature=+crt-static"
	"-C", "link-args=/DEFAULTLIB:ucrt.lib /DEFAULTLIB:libvcruntime.lib libcmt.lib",
	"-C", "link-args=/NODEFAULTLIB:libvcruntimed.lib /NODEFAULTLIB:vcruntime.lib /NODEFAULTLIB:vcruntimed.lib"
	"-C", "link-args=/NODEFAULTLIB:libcmtd.lib /NODEFAULTLIB:msvcrt.lib /NODEFAULTLIB:msvcrtd.lib"
	"-C", "link-args=/NODEFAULTLIB:libucrt.lib /NODEFAULTLIB:libucrtd.lib /NODEFAULTLIB:ucrtd.lib"
]

One issue with doing it manually is there's no way I know of to only apply it to release versions other than to abuse the way cargo looks for configuration files.

---

Alternatives

Instead of statically linking you can deploy the vcruntime in one of two ways. In either case, from the start menu open "Developer Powershell". Then type:

cd $env:VCToolsRedistDir

This will put you in the directory with redistributable files. You can then either redistribute the installers found there (typically either vcredist_x64.exe or vcredist_x86.exe) or you can only distribute the dll itself. The dll is found in the following sub-directories:

x64\Microsoft.VC142.CRT\vcruntime140.dll

Or:

x86\Microsoft.VC142.CRT\vcruntime140.dll

[blonk]

This is awesome -- thanks for putting this together.

[Yandros]

Nice job

One thing though: you mention the behavior only being enabled when on --release, but the truth is that your cfg is currently based off debug-assertions = false, so while it will work with default profile settings, it may not always match --release.

If you do want to match --release, the trick is to use a build.rs script:

//! build.rs

fn main ()
{
    println!("cargo:rerun-if-env-changed=PROFILE");
    println!("cargo:rerun-if-changed=build.rs"); // Optional
    if ::std::env::var("PROFILE").map_or(false, |s| s == "release") {
        println!("cargo:rustc-cfg=release");
    }
}

which will enable you to use cfg(release) in your lib.rs.

• Demo

[chrisd]

Thank you! I wasn't aware of this trick. I've updated the build script as you suggest and uploaded version 1.1.