rust-lang / rust-lang/cargo

Cargo 1.52 causes a regression in dylib behaviour

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Description

Problem
Since Cargo 1.52, a change in behaviour of how dylibs are compiled has resulted in valid projects now failing to compile with rust 1.52. This is a little bit confusing because it compounds with an issue in the rust compiler but hopefully we can work around that.

Steps

  1. Clone this repo: https://github.com/alexkornitzer/dylib-errors/tree/error/nested
  2. Build with 1.51 we get the expected linker failure, we can circumvent this with hacks
  3. Build with 1.52 we now get dependency satisfaction errors
error: cannot satisfy dependencies so `std` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away

error: cannot satisfy dependencies so `core` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away

error: cannot satisfy dependencies so `compiler_builtins` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away

error: cannot satisfy dependencies so `rustc_std_workspace_core` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away

error: cannot satisfy dependencies so `alloc` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away

error: cannot satisfy dependencies so `libc` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away

error: cannot satisfy dependencies so `unwind` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away

error: cannot satisfy dependencies so `cfg_if` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away

error: cannot satisfy dependencies so `hashbrown` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away

error: cannot satisfy dependencies so `rustc_std_workspace_alloc` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away

error: cannot satisfy dependencies so `rustc_demangle` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away

error: cannot satisfy dependencies so `addr2line` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away

error: cannot satisfy dependencies so `gimli` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away

error: cannot satisfy dependencies so `object` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away

error: cannot satisfy dependencies so `panic_unwind` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away

error: cannot satisfy dependencies so `bar` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away

error: aborting due to 16 previous errors

error: could not compile `serverctl`

To learn more, run the command again with --verbose.

Possible Solution(s)
Originally we only had to handle this bug: https://github.com/rust-lang/rust/issues/82151. In this case the work around was to make sure that the dependant libraries were rlibs so that we compile down to a single dylib. Now with 1.52 we cant even get to this stage as cargo is blocking on dependency resolution.

As noted in the issue above, I assume we are getting to the stage here where we need a system in cargo that lets us specify which dependencies in the tree are what crate type. For example:

hyper = ['rlib', 'dylib']
mysharedlib = ['dylib']

where mysharedlib uses hyper, I want hyper to build as `rlib` and mysharedlib as `dylib` currently both would be compiled as dylibs resulting in satisfaction errors.

Notes

Output of cargo version:
cargo 1.52.0 (69767412a 2021-04-21)

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Clone the linked nested-repository example and reproduce the dependency-resolution errors with Cargo 1.51 and 1.52. Compare the two builds and investigate Cargo's dylib and rlib dependency handling; done means the valid project can proceed past dependency resolution under Cargo 1.52 without the reported errors.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
build-system
Issue type
Bug
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
25/100

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