Detect duplicate bevy dependencies

[janhohenheim]

An issue that many beginners have when using Bevy is having duplicates of it within the dependencies. This usually happens when a user adds 3rd party crates that don't support the same major versions, such as one depending on Bevy 0.14 and the other depending on Bevy 0.13.

When this happens, users will get difficult error messages about type incompatibilities and conflicting versions, which can be really confusing! We should make a custom lint that specifically detects this in Cargo.lock and emits a clear error message on what happened and how to fix it.

[BD103]

Just as a note, I edited Jan's original message as part of my issue-pass in #34.

[TimJentzsch]

Note that the compiler errors generated in these cases might get improved soon, then we might not need this lint anymore.
See Estaban Kuber's work on the error messages.

[BD103]

Note that the compiler errors generated in these cases might get improved soon, then we might not need this lint anymore. See Estaban Kuber's work on the error messages.

Wonderful! @estebank is this something that can hit stable by November¹? If so, I'll just close out this issue as not planned. (Also I know you said you're offline for 3 weeks, so no worries about responding immediately!)

Footnotes

1. November is my deadline for getting bevy_lint released and useful. ↩

[BD103]

This can be done relatively easily with find_crates(), adding it to the 0.2.0 milestone.