ARROW-3868: [Rust] Switch to nightly Rust for required build, stable is now allowed to fail

[andygrove]

No description provided.

[paddyhoran]

@andygrove changes will be needed to windows CI also, right?

[andygrove]

@paddyhoran @sunchao This is ready for review again. The build failed on the R build but the Rust one passed.

[codecov-io]

Codecov Report

Merging #3034 into master will decrease coverage by 0.07%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master   #3034      +/-   ##
=========================================
- Coverage   87.07%     87%   -0.08%     
=========================================
  Files         496     496              
  Lines       70600   70602       +2     
=========================================
- Hits        61477   61427      -50     
- Misses       9024    9074      +50     
- Partials       99     101       +2

Impacted Files	Coverage Δ
rust/src/csv/reader.rs	87.5% <100%> (+0.12%)	⬆️
rust/src/tensor.rs	93.11% <100%> (ø)	⬆️
rust/src/buffer.rs	93.53% <100%> (+0.02%)	⬆️
go/arrow/math/int64_avx2_amd64.go	0% <0%> (-100%)	⬇️
go/arrow/memory/memory_avx2_amd64.go	0% <0%> (-100%)	⬇️
go/arrow/math/float64_avx2_amd64.go	0% <0%> (-100%)	⬇️
go/arrow/math/uint64_avx2_amd64.go	0% <0%> (-100%)	⬇️
go/arrow/math/float64_amd64.go	33.33% <0%> (-33.34%)	⬇️
go/arrow/math/int64_amd64.go	33.33% <0%> (-33.34%)	⬇️
go/arrow/math/uint64_amd64.go	33.33% <0%> (-33.34%)	⬇️
... and 3 more

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[sunchao]

Instead of having a separate file, can we use env variable such as RUSTUP_TOOLCHAIN to check this?

[andygrove]

Done

[sunchao]

Curious: will the build fail if it fails to build in stable? how is this done?

[paddyhoran]

I think it will right now (failure in stable will fail the build). @andygrove I don't think you needed to add the || exit /B below. This is the mechanism that fails the build AFAIK. Actually, I think we need to add the || exit /B to each of the examples above so that the build fails if they fail to run.

@kszucs could you comment on this?

[andygrove]

I have addressed this now. I had originally swapped the order of stable/nightly and that made the PR confusing to review. I added the || exit /B to the examples so it is consistent.