Jon Ross-Perkins

FYI: creating PRs doesn't require contributor access (see the last paragraph of [getting access](https://github.com/carbon-language/carbon-lang/blob/trunk/CONTRIBUTING.md#getting-access) for an explanation of what access is appropriate when)

> The idea of these tests was to make sure these interfaces are properly implemented for builtin types. The revised tests would pass if the interfaces don't work for builtin...

``` // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/operators/mul_builtin.carbon:[[@LINE+2]]: type error in `*`: // CHECK: could not find implementation of interface MulWith(U = T:! MulWith(i32) where .Self.Result == i32) for T:! MulWith(i32) where...

@zygoloid Pinging here, did you have any remaining concerns?

We've added [docs](https://github.com/carbon-language/carbon-lang/blob/trunk/docs/project/contribution_tools.md#troubleshooting-build-issues) to help troubleshoot build issues. I'm closing this issue because I think there's a limit to how much we can detect here right now.

Created a proposal on #1983 -- let me know if I've misunderstood leads direction there, I can always flip around alternatives if the leads want a different choice. > I...

I believe this is resolved by #1983 though I still need to update the design (but I think we can call the leads question closed).

@josh11b Loooking through https://github.com/carbon-language/carbon-lang/blob/trunk/docs/design/generics/details.md#external-impl, is `impl LazyNe.Make as true` actually invalid because `LazyNe.Make` shouldn't be allowed there without it being a `external impl` outside a class? Is this even valid...

Note, this is blocked on #2110

This was mostly done in https://github.com/carbon-language/carbon-lang/pull/1883 but it looks like `!=` is still missing.