ARROW-4377: [Rust] Implement std::fmt::Debug for PrimitiveArrays

[ntrinquier]

No description provided.

[paddyhoran]

Thanks @ntrinquier, can you change the title to "ARROW-4377: [Rust] Implement std::fmt::Debug for PrimitiveArrays" please. I'll take a look when I get a chance.

[paddyhoran]

Also, CI is failing due to formatting issues. We use nightly compiler but stable rust fmt so you can run cargo +stable fmt --all -- --check.

[codecov-io]

Codecov Report

Merging #3663 into master will decrease coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3663      +/-   ##
==========================================
- Coverage   87.84%   87.78%   -0.06%     
==========================================
  Files         689      689              
  Lines       84014    84014              
  Branches     1081     1081              
==========================================
- Hits        73798    73752      -46     
- Misses      10103    10151      +48     
+ Partials      113      111       -2

Impacted Files	Coverage Δ
go/arrow/math/uint64_sse4_amd64.go	0% <0%> (-100%)	⬇️
go/arrow/math/float64_sse4_amd64.go	0% <0%> (-100%)	⬇️
go/arrow/memory/memory_sse4_amd64.go	0% <0%> (-100%)	⬇️
go/arrow/math/int64_sse4_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%)	⬇️
go/arrow/math/math_amd64.go	36.84% <0%> (-26.32%)	⬇️
go/arrow/memory/memory_amd64.go	42.85% <0%> (-14.29%)	⬇️
cpp/src/arrow/csv/column-builder.cc	95.39% <0%> (-1.98%)	⬇️

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[nevi-me]

Thanks for taking this on Nicolas, please see my inline comment.

[nevi-me]

May you please add tests for null values, I don't think you handle them because getting a null value returns invalid data.

[ntrinquier]

Will do! Thanks

[andygrove]

Looking good so far. I'd like to see those unwraps removed in favor of returning an error result though (I'm guilty of using unwrap too, but I think it won't be hard to make the change here).

[andygrove]

It would be better to return fmt::Result(Error) rather than call unwrap here

[paddyhoran]

@ntrinquier what do you think about displaying the array values vertically?

This would be more consistent with C++/Python and make it easier to debug larger arrays.

Also, if we want to debug nested arrays in the future we can use the vertical indentation to help display the nesting levels.

[ntrinquier]

@paddyhoran It leaves more unused space but I guess it is better to be consistent (plus as you said, with nesting it will actually be much better if displayed vertically).

[nevi-me]

I'm happy

[paddyhoran]

Yep, LGTM, thanks @ntrinquier

[kszucs]

CI failure is unrelated, merging. Thanks @ntrinquier!