1404894 - forbid multiple crate versions when vendoring

Status: NEW

(Firefox Build System :: General, enhancement)

Description

[Nathan Froyd [:froydnj]]

We have a number of crates that have multiple versions vendored.  The "unnecessary" crates and versions are:

aho-corasick-0.6.2
bindgen-0.29.0
bitflags-0.7.0
bitflags-0.8.2
cfg-if-0.1.0
core-foundation-sys-0.3.1
env_logger-0.4.1
gcc-0.3.42
kernel32-sys-0.1.4
lazy_static-0.1.16
lazy_static-0.2.2
log-0.3.6
num-traits-0.1.37
regex-0.2.1
regex-syntax-0.4.0
rustc-serialize-0.3.22
semver-0.1.20
thread-id-3.0.0

I think servo has a lint set up that will complain if the dependency graph has multiple versions of a given crate, save for a few exceptional ones.  We should adopt a similar policy:

1. Set up a whitelist of the crates above.
2. Modify `mach vendor rust` to check for multiple crate versions.
3. If we try to vendor multiple versions of a crate not on the above list, print a nice error message and refuse to vendor.
4. If we vendor and one of the above crates suddenly doesn't have multiple versions, print a message about removing the appropriate crate from the whitelist prior to vendoring, and refuse to vendor.

Ideally, this plan will get us to a cleaner dependency graph and fewer unnecessary vendorings into m-c.  The only wrinkle I can think of--besides annoying people who now feel like they have to go clean up a bunch of crates which might not be their problem--is that auto-vendoring on servo imports might now go horribly wrong.  Not sure what to do about that.

Comment 1

[Kartikaya Gupta (email:[e-mail])]

I'm not sure this is a good idea. I think it will increase the burden on importing rust code significantly. Even totally unrelated projects (e.g. rust-url and webrender) that are vendored into m-c would need to make sure their entire dependency trees use compatible versions which IMO might be excessive. And there might be good reasons for needing different versions of a crate in different places (presumably this is why servo has an exceptions list).

Comment 2

[Gregory Szorc [:gps]]

Presumably multiple versions of the same create will increase binary size? Some people are quite sensitive to installer/binary size bloat and incurring work to avoid extra kilobytes due to multiple crate versions could be justified...