Make reconciler tests build and run on macOS

[MaxDesiatov]

We can't run our basic reconciler tests in a WASI environment yet because XCTestExpectation is not available on WASI as it relies on the presence of Dispatch. We can run these tests on macOS though, and even on Linux in the future when Swift 5.3 is available for Linux on GitHub Actions.

My current OpenCombine fork doesn't build on macOS and it was much easier to add a new CombineShim module that uses native Combine there.

[carson-katri]

I wasn’t able to build the combine fork on Arch Linux either. Maybe use OpenCombine/OpenCombine instead of the fork for Linux? Unless that’s only a problem on Arch, which I don’t know for sure.

It’s the same error I get on macOS.

[MaxDesiatov]

No, I don't think my fork can be built on non-WASI platforms, I had a few things from COpenCombineHelpers torn out manually rushing to make it work on WASI 😅

[carson-katri]

Could you swap out the OpenCombine url in .package on line 34 when on Linux?

[MaxDesiatov]

I don't think so, at least after looking at the proposal. I'll try to submit my changes to the upstream OpenCombine repo to make it work on all platforms including WASI, I just have another old open PR there with the zip implementation that I need to finish first...

[j-f1]

Tests pass after linking the wasm version into ~/.swiftenv/versions and running swift test

[MaxDesiatov]

Yeah, that builds and runs on macOS though unless you pass the --triple wasm32-unknown-wasi option to it. This is what carton test does automatically, but it won't build because of XCTestExpectation unavailable on WASI.