r? @alexcrichton

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@bors: r+

📌 Commit 6c6947b has been approved by alexcrichton

⌛ Testing commit 6c6947b with merge c8c4ff8...

💔 Test failed - status-appveyor

For context, I left that in when I removed its use in #5651 because it was used by cargo-bloat and semverver. It looks like cargo-bloat has since been rewritten to no longer use cargo.

The failure looks spurious btw.

@bors: retry

⌛ Testing commit 6c6947b with merge 2d0863f...

☀️ Test successful - status-appveyor, status-travis
Approved by: alexcrichton
Pushing 2d0863f to master...

For context, I left that in when I removed its use in #5651 because it was used by [...] semverver.

So what should rust-semverver use now to find the path of rlibs from a PackageId now that libraries has been removed ?

Since the usage of this field by rust-semverver was known, I suppose there must be a way to do that, but after staring at this and related PRs for 45 minutes and the cargo docs, I have no idea how to do that. It would have been nice to give that project a heads up, e.g. by filling an issue, with migration instructions, so that one doesn't have to spend this much time trying to figure out things 2 months later..

So what should rust-semverver use now to find the path of rlibs from a PackageId now that libraries has been removed ?

The issue is that there is not a simple, correct mapping anymore. There might be multiple lib targets with different settings.

I took a look at the semverver code for a bit. I'm wondering if it really needs to use cargo as a library. Would it be possible to just call the cargo cli, and get the rlib path from the JSON output?

I'm wondering if it really needs to use cargo as a library. Would it be possible to just call the cargo cli, and get the rlib path from the JSON output?

rust-semverver compiles the current crate as an rlib, as well as the previous version of it from crates.io (which has often to be downloaded, and then also compiled), and then compares both rlibs. The compilation is done by calling cargo::ops::compile.

I've opened an issue about this on cargo_metadata: oli-obk/cargo_metadata#60 , there is some discussion there about how to tackle some of these issues.