Crate not found in integration tests if `crate-type = ["cdylib"]`

[ckaran]

Problem
I am developing code that needs to work with python, which requires me to have a crate type of cdylib. It turns out that when you follow the recommendation to use a tests directory, the code within the directory cannot find the crate, failing with an error like the following:

   Compiling cargo_issue_6659 v0.1.0 (/home/cfkaran2/Desktop/cargo_issue_6659)
     Running `rustc --edition=2018 --crate-name tester tests/tester.rs --color always --emit=dep-info,link -C debuginfo=2 --test -C metadata=0525a91fc572753f -C extra-filename=-0525a91fc572753f --out-dir /home/cfkaran2/Desktop/cargo_issue_6659/target/debug/deps -C incremental=/home/cfkaran2/Desktop/cargo_issue_6659/target/debug/incremental -L dependency=/home/cfkaran2/Desktop/cargo_issue_6659/target/debug/deps`
     Running `rustc --edition=2018 --crate-name cargo_issue_6659 src/lib.rs --color always --emit=dep-info,link -C debuginfo=2 --test -C metadata=b9fa70b838dfddae -C extra-filename=-b9fa70b838dfddae --out-dir /home/cfkaran2/Desktop/cargo_issue_6659/target/debug/deps -C incremental=/home/cfkaran2/Desktop/cargo_issue_6659/target/debug/incremental -L dependency=/home/cfkaran2/Desktop/cargo_issue_6659/target/debug/deps`
error[E0463]: can't find crate for `rustc_issue_report_cdylib`
 --> tests/tester.rs:1:1
  |
1 | extern crate rustc_issue_report_cdylib;
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ can't find crate

error: aborting due to previous error

For more information about this error, try `rustc --explain E0463`.
error: Could not compile `cargo_issue_6659`.

Caused by:
  process didn't exit successfully: `rustc --edition=2018 --crate-name tester tests/tester.rs --color always --emit=dep-info,link -C debuginfo=2 --test -C metadata=0525a91fc572753f -C extra-filename=-0525a91fc572753f --out-dir /home/cfkaran2/Desktop/cargo_issue_6659/target/debug/deps -C incremental=/home/cfkaran2/Desktop/cargo_issue_6659/target/debug/incremental -L dependency=/home/cfkaran2/Desktop/cargo_issue_6659/target/debug/deps` (exit code: 1)
warning: build failed, waiting for other jobs to finish...
error: build failed

Steps

1. Checkout the repository at https://github.com/ckaran/cargo_issue_6659.
2. Follow the instructions in the README.md

Possible Solution(s)

None known.

Notes

$ cargo -V -vvv
cargo 1.32.0 (8610973aa 2019-01-02)
release: 1.32.0
commit-hash: 8610973aaf48615ba7dc9a38a9a2795ba6f36a31
commit-date: 2019-01-02

$ rustc -Vv
rustc 1.32.0 (9fda7c223 2019-01-16)
binary: rustc
commit-hash: 9fda7c2237db910e41d6a712e9a2139b352e558b
commit-date: 2019-01-16
host: x86_64-unknown-linux-gnu
release: 1.32.0
LLVM version: 8.0

$ uname -a
Linux EMANE 4.15.0-45-generic #48-Ubuntu SMP Tue Jan 29 16:28:13 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

$ lsb_release --all
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 18.04.2 LTS
Release:    18.04
Codename:   bionic

[ehuss]

You can add rlib (or lib) to the crate-type list, and it should work. Tests can't link to the cdylib.

BTW, there's a typo in your example, tests/tester.rs should have extern crate cargo_issue_6659;.

[ckaran]

Ah, sorry, since there is a chicken & egg problem between creating a repo that has the same name as the issue it's for, I sometimes forget to change the names. Now fixed.

As for setting to an rlib or lib, the problem is that I'm using pyo3, which says that you must set the library type to cdylib, and not having my integration tests work was surprising to me. If it is known that tests can't link to cdylib type libraries, it may be worth updating cargo's (or maybe rustc's) documentation to reflect this fact.

[ehuss]

Yea, the documentation for crate-types could definitely be improved in general.

Feel free to leave more comments here if you run into any other issues. Otherwise I'll just leave this open as a documentation issue.

[vjpr]

There are some potential issues with just adding `lib' to get it to work. See: #4881.