The Rust SpiderMonkey bindings still build in C++14 mode.

This hasn't been visible until now, since none of the code used by the bindings used C++17 features, but this will be the case in the future, e.g. with Bug 1560664.

Hm, I tried to just change to -std=gnu++17 in js/rust/CMakeLists.txt, but this doesn't seem to make a difference regarding the availability of std::is_convertible_v. It is hard to see which compiler/toolset and libstdc++ is used there, maybe this needs to be updated as well?

Can you point me towards an automation job/configuration where this happens? I'm rather confused because I don't see js/rust hooked into our build.

(In reply to Chris Manchester (:chmanchester) from comment #2)

Can you point me towards an automation job/configuration where this happens? I'm rather confused because I don't see js/rust hooked into our build.

Sorry, I should have included that beforehand. I wasn't aware of that job either, so I just hit that issue when trying to land. This is the failing job log: https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=280297638&repo=autoland&lineNumber=242

Ah, ok, I think perhaps we need an update here: https://searchfox.org/mozilla-central/rev/690e903ef689a4eca335b96bd903580394864a1c/js/rust/build.rs#146

Nathan, does that look right?

I can confirm that changing --std there fixes the issue: https://treeherder.mozilla.org/logviewer.html#?job_id=280646795&repo=try

I will submit a patch for that.

https://hg.mozilla.org/mozilla-central/rev/9dabe8b90b73