Make this crate compatible with embedded-hal master

[eldruin]

Hi,
I ran into a compilation problem when using this crate with the embedded-hal master version.
In my pcf857x crate, if changing the embedded-hal dependency in the Cargo.toml file to:

embedded-hal = { git = "https://github.com/rust-embedded/embedded-hal" }

The tests cannot be run as the compiler complains that the prelude::Read and prelude::Write trait bounds were not satisfied.
Am I doing something wrong or is this crate incompatible with embedded-hal master?
There were some changes to embedded-hal's prelude. Could this be the cause?

PS: Thanks for this crate! I use it all the time :)

[dbrgn]

Hi. I'm just back from vacations. I need a few days to clear my backlog and will revisit this issue later on.

At first glance, the problem is that your project depends on embedded-hal@master while the mock crate depends on embedded-hal@0.2. Even if the traits are compatible feature-wise, different versions are incompatible by design. I think a feature flag that uses master instead of a released version would help, although I'm not sure if that can be released to crates.io.

[dbrgn]

I don't think crates with dependency to non-published crates can be published.

I'm not sure what the best way to implement this would be. Maybe I'll maintain a next branch that points to master and that can be used directly from Cargo.toml using a git dependency.

[ryankurte]

Will this still be an issue when we've released embedded-hal v0.3.0 and updated this to point at it?

[dbrgn]

As long as people use the master version of embedded-hal, I think yes.

The dependency tree looks like this:

a
|- embedded-hal@master
|- embedded-hal-mock@0.4.0
   |- embedded-hal@0.3.0

This means that there are two versions of embedded-hal. The traits implemented by embedded-hal-mock for embedded-hal@0.3.0 are not compatible with the traits provided by embedded-hal@master, even if their source code is identical.

Of course if both @eldruin and we use the released embedded-hal 0.3.0, then it's going to work.

[eldruin]

The traits implemented by embedded-hal-mock for embedded-hal@0.3.0 are not compatible with the traits provided by embedded-hal@master, even if their source code is identical.

This is quite unfortunate and I did not know about it, although I can understand the reasoning now.
I would like to release a new version of my crate once embedded-hal 0.3.0 is out, since the changes in that version address issues which arose in the pcf857x crate.
I do not need embedded-hal@master, I was just trying to test my crate against the new embedded-hal trait versions.
It would be great for me if a new version of embedded-hal-mock would be published using embedded-hal 0.3.0 once it is available.

[dbrgn]

It would be great for me if a new version of embedded-hal-mock would be published using embedded-hal 0.3.0 once it is available.

That's the plan of course - we track embedded-hal releases 🙂

For development, would it help you if we had a branch called "next" that has a dependency on embedded-hal@master?

[eldruin]

I think it would. At least I would have a better alternative to test something in embedded-hal@master than to clone this crate locally, modify it and use that.
However, I do not know how often this situation would come up.

[ryankurte]

@eldruin can you use a patch in your top level Cargo.yml file to achieve this?

[patch.crates-io]
embedded-hal-mock = { git = https://github.com/dbrgn/embedded-hal-mock }

If that / something similar works maybe we could document it for others too.

[dbrgn]

Actually I created a branch, see d1c7248!

[ryankurte]

Oops, sorry, that should be:

[patch.crates-io]
embedded-hal = { git = "https://github.com/rust-embedded/embedded-hal" }

@dbrgn the branch works too, I was recently introduced to this / thought I would share the cargo way.

[dbrgn]

Ahh I see, I didn't realize that it was in a patch section 🙂

Yes, that should work, and it's probably a better solution than the branch - as long as there are no breaking changes in embedded-hal 🙂