Find a way to detect API breakage.

[steveklabnik]

Issue by mahkoh
Wednesday Sep 10, 2014 at 20:36 GMT

For earlier discussion, see rust-lang/rust#17152

This issue was labelled with: in the Rust repository

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Given that the current rust ecosystem tries very hard to force everyone to use semver, and given that rust code breaks the API easily, this is very important.

Some easy but surprising ways to break the API:

• Adding a field to a struct.
• Changing a struct from Copy to NoCopy (same with Send, Sync, etc.)
• Adding a variant to an enum.
• Adding a public method to a type (consider extension traits)
• Adding a method to a trait (consider #17151)

Therefore rustc needs to have something like this:

rustc --record-api out.json lib_old.rs

stores api information in out.json

rustc --compare-api out.json lib_new.rs

Checks if the new api is compatible with the old one.

[sinistersnare]

I feel like if a cargo add-on could do this it would be perfect. something like

$ cargo breakage record
$ cargo breakage compare

[nikomatsakis]

The general plan was to tie this analysis to publishing a new version.

[sinistersnare]

Does rustc have knowledge about 'versions' though?

[Kimundi]

We also need an actual definition of what is considered rusts API in regard to semver.

[Manishearth]

As a way to solve this problem specifically for rustc:

Write a script that detects if a test (rpass, cfail, etc) that has no #![feature] markers was changed in the PR. If the PR has no [breaking-change] markers, complain about it on the PR (via highfive).

[Centril]

Closing in favor of https://github.com/rust-lang-nursery/rust-semverver.