Fix for build.rs: double colon issue

[jbinko]

Fix incorrect Cargo directive in build.rs

Description

The build.rs script currently uses a double colon (::) in the cargo directive, which is incorrect. Cargo expects a single colon (:) for key-value pairs in build script output.

Current Behavior

println!("cargo::rustc-link-search={}", out.display());

Expected Behavior

println!("cargo:rustc-link-search={}", out.display());

[finalyards]

Does it, though?

I discussed this with Copilot, in September, and it - like you - kept firm that one colon is the official and two would be "ignored".

This brings a couple of questions to my mind:

• why do things still work?
• ..or do they?
• why hasn't CI picked up anything?

But sometimes AI gets confused. Especially when things have changed over time.

Note that also Cargo book uses two colons:

println!("cargo::rerun-if-changed=src/hello.c");

I think I looked this back to the particular PR in Cargo that moved from one to two (keeping both equally functioning, for backwards compatibility). So, with the authority of the Book I think it's safe to say, a) it does not matter, b) two is more correct than one.

i.e. you've found an interesting spot, but ... the PR would be a step backwards, in time.

p.s. what we could do, is the reverse: add a clippy-like test that no such println! is with only one colon!! :)

[finalyards]

#!/bin/bash
if grep -r --include="build.rs" -n 'println!("cargo:[^:]' .; then
    echo "Found 'build.rs' directives with single colon. Would you mind changing them to 'cargo::'."
    false
else
    echo "'build.rs' directives ok!"
fi

[lulf]

I'd prefer to follow the cargo book and keep the existing double colon.

[finalyards]

@jbinko Would you like to close this, or comment.

[jbinko]

Will close this one.