I had never intended to avoid pinning nightly. This is an unfortunate thing
to have to do---require a _specific_ version of a compiler to build your
software; it's madness. But the unstable features utilized by TAMER (as
rationalized in `src/lib.rs`) are still worth the effort.
It's not _actually_ that case that we need a specific version of the
compiler, granted; this is outlined in `rust-toolchain.toml`'s
rationale. You should look there for more information; my approach still
utilizes explicit channels via cargo. Unfortunately, I had hard-coded it
previously, putting me in a bit of a bind an unable to override the behavior
without modifying the software.
The reason for this change is that `adt_const_params` has a BC break
involving the introduction of `ConstParamTy`. This is only the second time
I've been bitten by a nightly BC break; the other was the renaming of
`int_log`'s API, as mentioned in
709291b107. This pinning will in fact
mitigate those future issues---TAMER will be able to resolve the issue at
its leisure, and will further be able to continue to build earlier commits
in the future by simply re-bootstrapping with the committed nightly
version.
If you're curious of my rationale for wanting to inhibit toolchain
downloading during build, or use system libraries, have a look at GNU Guix's
approach to building software safely and reproducibly. In particular,
dependencies are also built from source (rather than downloading binaries
from external sources), and builds take place in network-isolated
containers. The `TAMER_RUST_TOOLCHAIN` configure parameter is meant to
facilitate these situations by giving more flexibility to packagers.
DEV-14476
Mike Gerwitz