Add support for new feature syntax (RFC 3143)

[ehuss]

This adds support for the new feature syntax described in RFC 3143. There are two new feature values that are allowed in the [features] table: weak dependencies (foo?/feat-name) and namespaced dependencies (dep:bar). When these style of features are detected, they are placed in the index in a separate field called features2 to prevent older versions of cargo from breaking on them. Additionally, it sets a new version field called v to indicate that this new field is present, which prevents versions starting at 1.51 from selecting those versions.

[rust-highfive]

r? @smarnach

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[pksunkara]

Looks good except for a minor concern

[bors]

☔ The latest upstream changes (presumably #4096) made this pull request unmergeable. Please resolve the merge conflicts.

[djc]

Gentle ping? I think this should be labeled as waiting on review again?

[jhpratt]

I can't attest to the validity of the changes as a whole; I'm not familiar with the internals. The parsing of the feature seems correct. Just one minor nit on style.

[Turbo87]

FWIW we discussed this on Discord a few days ago: https://discord.com/channels/442252698964721669/448525639469891595/920823792631152691

the tl;dr is that we show features on the UI these days and we need to verify that this still works correctly with this new syntax

[ehuss]

the tl;dr is that we show features on the UI these days and we need to verify that this still works correctly with this new syntax

I'm not sure how you'd like to verify that. I could add something that did a database query in the features_version_2 test if you'd like.

The feature values themselves don't seem to be displayed in the UI:

I can confirm from the API that it is there:

curl http://localhost:4200/api/v1/crates/foo | jq .versions[0].features
{
  "f1": [
    "dep:bar"
  ],
  "f2": [
    "bar?/bar-feat"
  ]
}

And via psql:

cargo_registry=# select * from versions;
 id | crate_id |  num  |         updated_at         |         created_at         | downloads |                   features                   | yanked | license | crate_size | published_by
----+----------+-------+----------------------------+----------------------------+-----------+----------------------------------------------+--------+---------+------------+--------------
  1 |        1 | 0.1.0 | 2021-12-22 23:49:25.411573 | 2021-12-22 23:49:25.411573 |         0 | {}                                           | f      | MIT     |        702 |            1
  2 |        2 | 0.1.0 | 2021-12-22 23:51:35.513816 | 2021-12-22 23:51:35.513816 |         0 | {"bar-feat": []}                             | f      | MIT     |        719 |            1
  4 |        1 | 0.2.0 | 2021-12-22 23:56:47.374767 | 2021-12-22 23:56:47.374767 |         0 | {"f1": ["dep:bar"], "f2": ["bar?/bar-feat"]} | f      | MIT     |        772 |            1
(3 rows)

[Turbo87]

The feature values themselves don't seem to be displayed in the UI

you're absolutely right. now that I finally had time to take a detailed look at the RFC and PR changes, I agree that the frontend shouldn't be affected by this. since the split between features and features2 only happens for the index, but is otherwise kept in its merged form I don't see any issues with it.

nice work! and sorry for the huge review delay... 😞

@pietroalbini @jtgeibel unless you have any objections I plan to merge this on 2021-12-30 (one week from now), or earlier if you both signal your approval until then :)

[Turbo87]

@bors r+

[bors]

📌 Commit 2b4430c has been approved by Turbo87

[bors]

⌛ Testing commit 2b4430c with merge 91a2cd4...

[bors]

☀️ Test successful - checks-actions
Approved by: Turbo87
Pushing 91a2cd4 to master...

[Turbo87]

rebased, merged and deployed. thanks for working on this @ehuss!