Fix typo in application of y value BCs

[ali-ramadhan]

No description provided.

[codecov]

Codecov Report

Merging #690 into master will increase coverage by 0.12%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##           master     #690      +/-   ##
==========================================
+ Coverage   78.05%   78.18%   +0.12%     
==========================================
  Files         120      120              
  Lines        2447     2443       -4     
==========================================
  Hits         1910     1910              
+ Misses        537      533       -4     

Impacted Files	Coverage Δ
src/BoundaryConditions/apply_value_gradient_bcs.jl	56.75% <75.00%> (+5.53%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 4ad7e93...fc94431. Read the comment docs.

[glwagner]

Hmm... I don’t think this is a typo. The functions *_gradient for “west”, “south”, and “bottom” are identical. Therefore we should use the alias “left” for all three to avoid copy-pasting identical functions. The same applies to the three “right” boundaries: “east”, “north”, and “top”.

If we want to use matching names in other functions then we should use ‘const’ aliases. I think copy-pasting function definitions is bad practice that decreases maintainability and can make bugs harder to catch and fix.

[glwagner]

This is not part of this PR, but these 4 functions have identical definitions:

@inline bottom_gradient(bc::GBC, c¹, Δ, i, j, args...) = getbc(bc, i, j, args...)
@inline    top_gradient(bc::GBC, cᴺ, Δ, i, j, args...) = getbc(bc, i, j, args...)
@inline south_gradient(bc::GBC, c¹, Δ, i, k, args...) = getbc(bc, i, k, args...)
@inline north_gradient(bc::GBC, cᴺ, Δ, i, k, args...) = getbc(bc, i, k, args...)

[glwagner]

This function's definition is identical to bottom_gradient.

I think we should have two functions, left_gradient and right_gradient. left_gradient should be called in _fill_bottom_halo!(c, bc::Union{VBC, GBC}, grid, args...), _fill_south_halo!(c, bc::Union{VBC, GBC}, grid, args...), and _fill_west_halo!(c, bc::Union{VBC, GBC}, grid, args...), while right_gradient should be called in the same functions for top, north, and east.

[ali-ramadhan]

Good observation. I've simplified the code down to just left_gradient and right_gradient as suggested so there's still one duplicate definition but it'll be much better than having 5 duplicates once we support Value and Gradient boundary conditions in x.