Comment 11 for bug 1993819

> This is because Rust upstream has platform tiering. Some tests are not guaranteed to pass on certain operating systems + CPU combinations. For instance, upstream tests may include float-point arithmitics behavior validations that might not pass on architectures where float-point calculation does not conform fully to IEEE 754 (e.g. MIPS).
Rust upstream only gates the release depending on whether all the Tier 1 platforms pass the tests (see https://doc.rust-lang.org/rustc/platform-support.html for the Tiering, Tier 1 is considered to be both Tier 1 with Host Tools and Tier 1 without Host Tools).

This seems to be a little random. Shouldn't the tests which ought to pass on a given architecture be really identified as such? It seems that it’s an open gate for unnoticed regressions, or is there a some kind of manifest of "this tests passed in the previous build on that architecture, and so, it should pass again with the new build'?

> This is because Rust upstream adds new warnings to the compiler nearly every release. Cargo in the Debian tarball is usually pinned to a release branch and does not receive the fixes unless the fix is critical (and in Debian's case, some dependencies are probably not vendored correctly, thus producing warnings, but this will be changed in Ubuntu hopefully very soon).

So, what’s our strategy to read and ensure the warnings that are produced are under controlled and "expected"?