x_estimator bars now inherit scatter_kws alpha

[milo-trujillo]

x_estimator error bars were previously always opaque, but now inherit alpha parameter from scatterplot settings (if present), since the error bars replace the scatterplot.

Fixes #2538

[codecov]

Codecov Report

Merging #2540 (f7f7831) into master (0f538fb) will decrease coverage by 0.01%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master    #2540      +/-   ##
==========================================
- Coverage   97.45%   97.43%   -0.02%     
==========================================
  Files          17       17              
  Lines        6325     6327       +2     
==========================================
+ Hits         6164     6165       +1     
- Misses        161      162       +1     

Impacted Files	Coverage Δ
seaborn/regression.py	97.50% <50.00%> (-0.30%)	⬇️

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[mwaskom]

👍 on the change; it would be good to cover this line in the tests though. I think adding a simple sub-case to this function should do it.

Also I edited your summary text to use github's (somewhat restricted) vernacular for linking issues such that they auto-close when the PR is merged.

[milo-trujillo]

Agreed on testing. What's the correct variable to check to confirm that the error bars have the desired transparency? Would it still be ax.collections[0]._alpha? If so I can add another trivial sub-case that uses alpha and x_estimator.

[mwaskom]

Hm that test shouldn't be accessing those private attributes ... but also the error bars will be in the ax.lines list.

[mwaskom]

@milo-trujillo let me know if you need help putting a test together ... I think the basic idea is something like this:

alpha = .3
ax = sns.regplot(
    data=tips, x="x", y="y",
    x_bins=5, fit_reg=False, scatter_kws=dict(alpha=alpha)
)
for line in ax.lines:
    assert line.get_alpha() == alpha