Hi there! Lately I got an idea of extending libcore a little. First of all, I cloned rust/library/core. Then, I set the path in my Cargo.toml. Finally, I put

extern crate custom_core as core;
use core::prelude::*;

to my and… compiler told me that things defined in custom_core are already defined in the core…

I got the error while compiling custom_core, not the crate with

What am I doing wrong? Must I specify -Z build-std or something?

Every involved crate must specify #![no_core]. I suspect your custom_core or a dependency of it does not specify #![no_core].

custom_core is just a clone of rust-lang/rust/library/core :frowning:

Do you have any other dependencies? Those need to use your fork too.

Hm… looks like the problem may occur because I am using std. Compiler throws an error while compiling custom_core, not my crate tho :face_with_monocle:

You mean you made custom_core depend on libstd? That won't work as libstd pulls in the original libcore. It has to as custom_core isn't compiled yet when libstd is compiled.

No, I didn’t :joy:

I’m not as stupid as you think (or maybe I am). I imported println from libstd in my crate that depends on custom_core. Custom core isn’t really custom

I see. You will have to compile libstd and all it's dependencies against the patched libcore too.

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