Equality requirement in project ignored by sub-dependency requirement

[little-arhat]

Hi,

Problem
Both application and its sub-dependency depend on library: application has equality requirements "= X.Y.Z", while sub-dependency can work with range: ">= X.Y.Z, < F.V"`.

I expect Cargo to only pull "X.Y.Z" version of a dependency, while both are pulled. Since library defines unmangled symbols (or will use links feature in the near future), this is an error.

Steps

Application dependencies:

[dependencies]
cortex-m = "=0.5.8"
cortex-m-log = {version = "0.4.0", features = ["semihosting"]}
panic-abort = "0.3.1"
stm32f30x = {version = "0.8.0", features = ["rt"]}
cortex-m-rt = "0.6.8"

Dependency in question is cortex-m-log, which depends on cortex-m-semihosting:

[dependencies]
cortex-m = "0.5"

[dependencies.cortex-m-semihosting]
version = "0.3"
optional = true

[features]
semihosting = ["cortex-m-semihosting"]

And [cortex-m-semihosting/(https://github.com/rust-embedded/cortex-m-semihosting) depends on cortex-m as well:

[dependencies]
cortex-m = ">= 0.5.8, < 0.7"

Application code (not important, but for completeness):

#![no_main]
#![no_std]
#![allow(unused)]

use cortex_m_rt::entry;
use panic_abort;
use stm32f30x;
use cortex_m_log::printer::semihosting::Semihosting;
use cortex_m_log::printer::Printer;
use cortex_m_log::modes::InterruptOk;
use core::fmt::Write;

#[entry]
fn main() -> ! {
    let prphs = stm32f30x::Peripherals::take().unwrap();
    let core = cortex_m::Peripherals::take().unwrap();
    let mut d = Semihosting::<InterruptOk, _>::stdout().unwrap();
    loop {
        write!(d.destination(), ";");
        cortex_m::asm::wfi()
    }
}

Compilation error:

  = note: rust-lld: error: duplicate symbol: CORE_PERIPHERALS
          >>> defined at mod.rs:153 (/Users/r/.cargo/registry/src/github.jparrowsec.cn-1ecc6299db9ec823/cortex-m-0.6.0/src/peripheral/mod.rs:153)
          >>>            cortex_m-774979bd87405991.cortex_m.b30jt41x-cgu.0.rcgu.o:(CORE_PERIPHERALS) in archive /Users/r/stuff/coco-test/target/thumbv7m-none-eabi/debug/deps/libcortex_m-774979bd87405991.rlib
          >>> defined at mod.rs:153 (/Users/r/.cargo/registry/src/github.jparrowsec.cn-1ecc6299db9ec823/cortex-m-0.5.8/src/peripheral/mod.rs:153)
          >>>            cortex_m-769a472e04c23d44.cortex_m.9qln9imh-cgu.0.rcgu.o:(.bss.CORE_PERIPHERALS+0x0) in archive /Users/r/stuff/coco-test/target/thumbv7m-none-eabi/debug/deps/libcortex_m-769a472e04c23d44.rlib

Excerpt from Cargo.lock:

[[package]]
name = "cortex-m-semihosting"
version = "0.3.3"
source = "registry+https://github.com/rust-lang/crates.io-index"
dependencies = [
 "cortex-m 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)",
]

cargo --version
cargo 1.36.0-nightly (6be12653d 2019-04-19)

rustc --version
rustc 1.36.0-nightly (e305df184 2019-04-24)

Am I missing something? It seems that in this scenario I should only have one cortex-m dependency, and it should be the one specified by equality, 0.5.8.

[Eh2406]

cargo thinks cortex-m 0.7 is compatible with cortex-m 0.5, so it gives you the most recent one you can use for each part of the project. If there is only supposed to be one version of cortex-m in the dependency tree, for example as it links to a native dependency, then it should specify the links atribut in it cargo.toml.

[little-arhat]

@Eh2406 I don't think that's the case. Reading docs it seems semver compatibility will come into play only if caret dependencies are used. In this example both application and sub-dependency define (in)equality versions.

As for the links attribute, linked issue from cortex-m addresses that, I believe.

[epage]

This looks to be another variant of #9029, closing in favor of that one. If there is something I overlooked, let us know!