Noop locking

[furuholm]

This PR implements the noop locking part of #49.

[furuholm]

I added a static assertion as suggested in #49 but I am not sure I did it correctly. First of all the docs says that the following is to be added to lib.rs

#[macro_use]
extern crate static_assertions;

This lead to a unused `#[macro_use]` import warning so I didn't include those lines (the macro still worked).

I then verified that static_assertions::assert_not_impl_all!(Context: Send, Sync); worked by adding Send and Sync implementations for Context. As expected this caused a compilation error but the error message not very clarifying.

type annotations needed for `fn() {<context::Context as context::_::{{closure}}#0::AmbiguousIfImpl<_>>::some_item}

This may very well be correct, but I wasn't sure so it would be great if you could have an extra look at this.

Also: Travis failed. Not sure why.

$ cargo test --all --verbose --no-default-features --features="crypto-openssl"
error: --features is not allowed in the root of a virtual workspace
The command "cargo test --all --verbose --no-default-features --features="crypto-openssl"" exited with 101.

Not sure what this is about. The same command worked in the master build.

[furuholm]

I think the build failure is caused by rust-lang/cargo#7507. I will try to fix this in a separate PR in the coming days.

[Michael-F-Bryan]

Looks good to me. Other than my comment about moving the static assert next to the code that relies on the assertion, I'd be happy to merge this.

[Michael-F-Bryan]

Could this line be moved directly above lock_function()? That way our assertion that Context: !Send + !Sync is right next to the comment that says locking isn't required as long as Context doesn't implement Send and Sync.

[furuholm]

Agree. This looks better.

Fixed in eddb1cd

[furuholm]

The build failure is fixed by #52. I would like to have that merged before this change to not fail the build on master.

[Michael-F-Bryan]

@furuholm I've merged #52. If you do a rebase we should be good to merge.

[furuholm]

@Michael-F-Bryan rebase done...

[furuholm]

Build still fails for Rust: 1.34.0 though. Seems that the static_assertions lib does not compile.

[Michael-F-Bryan]

Looking at the .travis.yml for nvzqz/static-assertions-rs I think we need to bump the minimum rustc version to 1.37.0.

Would you be able to update this line with the new version and also add a comment saying it's needed for static_assertions?