Correct bounds checking for AbstractVectors with no indices specified (fixes #194)

[jishnub]

After this PR

julia> OffsetArray([0], 1)[]
ERROR: BoundsError: attempt to access 1-element OffsetArray(::Array{Int64,1}, 2:2) with eltype Int64 with indices 2:2 at index []

julia> OffsetArray([6], 1:1)[]
6

[codecov]

Codecov Report

Merging #195 (873cc30) into master (b20b4db) will decrease coverage by 0.34%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #195      +/-   ##
==========================================
- Coverage   99.28%   98.93%   -0.35%     
==========================================
  Files           5        5              
  Lines         280      283       +3     
==========================================
+ Hits          278      280       +2     
- Misses          2        3       +1     

Impacted Files	Coverage Δ
src/axes.jl	100.00% <100.00%> (ø)
src/precompile.jl	92.85% <0.00%> (-7.15%)	⬇️

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[yurivish]

Thank you for the quick fix!

Is it odd that coverage is reporting that the added Base.checkbounds_indices indices method is reported as not being covered by tests, even though the tests you've added presumably hit that method (otherwise they would not pass)?

[jishnub]

It's perhaps some inlining quirk. I've added an explicit test, hopefully coverage will be happy now.

[johnnychen94]

Nice detective work. No objection in merging this.

[mbauman]

The problem here isn't the bounds check. Indeed, the expression OffsetArray([6], 2:2)[] should work and return a 6. Where we are hardcoding a 1 is in the linear indexing transform:

julia> Base._to_linear_index(OffsetArray([6], 2:2))
1

This is where the problem is:

https://github.com/JuliaLang/julia/blob/69d24532980bda6db510b6d4b71f66e7ffff2e81/base/abstractarray.jl#L1196