Tarpaulin: Nightly cargo changes can break tarpaulin compilation (remove cargo dep)

[Razican]

I'm getting an error when using cargo tarpaulin in the Rocket repository on the async branch. It turns out that they removed the extern crate proc_macro; from the ./contrib/codegen/ crate, which gave a warning in Rust 2018, since it's considered non-idiomatic.

It compiles fine with cargo build or cargo test, but it gives the following error when running the latest cargo tarpaulin:

[INFO tarpaulin] Running Tarpaulin
[INFO tarpaulin] Building project
error[E0432]: unresolved import `proc_macro`
  --> contrib/codegen/src/lib.rs:39:5
   |
39 | use proc_macro::TokenStream;
   |     ^^^^^^^^^^ help: a similar path exists: `quote::proc_macro`

error[E0432]: unresolved import `proc_macro`
 --> contrib/codegen/src/database.rs:1:5
  |
1 | use proc_macro::TokenStream;
  |     ^^^^^^^^^^ help: a similar path exists: `quote::proc_macro`

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0432`.
error: could not compile `rocket_contrib_codegen`.
Error: "Failed to compile tests! Error: build failed"

If you give me some pointers I can try to fix it :)

[xd009642]

I think this might be because proc-macro=true in a Cargo.toml allows certain extra nightly proc-macro features. I've had a brief look over the cargo source but can't find anything obvious I should be doing so raised this issue https://github.com/rust-lang/cargo/issues/7968

In the meantime I'll continue to look but it seems to be a cargo usage based issue

[xd009642]

So I moved my cargo dependency to the latest on master and it seems to solve the issue. You can try it out by installing from https://github.com/xd009642/tarpaulin/tree/issue_339

[xd009642]

So over this weekend I'm going to follow some advice of a cargo maintainer and move to using https://docs.rs/cargo_metadata/ to handle my interactions with cargo as this will keep tarpaulin more up-to-date with nightly features and stop issues like this in future. I'll close this issue when that's done, confirmed to work and released :smile:

[Razican]

This sounds great! Thanks for your work :) It really sounds promising, to be able to use the same binary that cargo test is using. It should also reduce tarpaulin compile times by removing the cargo dependency :)

[Razican]

Let me know if I can help with this!

[xd009642]

So far I've mostly got it down, just two more tests need move from red to green (and that's ignoring nightly only tests)

[xd009642]

This should be fixed in the 0.11.1 release since cargo was updated. I'm still working on removing cargo as a dependency though so I'll keep this issue open to track that (and slightly rename it)

[Razican]

Hi, so this particular issue is solved, cool!

How is the cargo dependency removal going?

[xd009642]

There's a version without cargo as a dependency on the develop branch if you want to try it. It works exactly the same on all the projects I've tested with but could do with more testing!

[xd009642]

This version is now released although it looks like there might be a regression with examples which is handled by another issue. So I'm going to close this

[Razican]

Great, thanks! Sorry I didn't have the time to check it.