[BUG] Issue with errorbars and series properties

[orso82]

Details

When plotting with errorbars and alpha vectors, Plots.jl generates numerous confusing warnings about index mismatches. Also the plot itself that comes out is wrong. The warnings suggest expanding the alpha vector, but this doesn't suppress the warnings.

using Plots
plot([0,1],[0,1]; yerror=[0.1,0.2], seriesalpha=[0.2,0.6], lw=5)

This generates multiple warnings like:

┌ Warning: Indices Base.OneTo(2) of attribute `seriesalpha` does not match data indices 2:6.
└ @ Plots ~/.julia/packages/Plots/MR7sb/src/utils.jl:141
┌ Info: Data contains NaNs or missing values, and indices of `seriesalpha` vector do not match data indices.
│ If you intend elements of `seriesalpha` to apply to individual NaN-separated segments in the data,
│ pass each segment in a separate vector instead, and use a row vector for `seriesalpha`. Legend entries
│ may be suppressed by passing an empty label.
│ For example,
└     plot([1:2,1:3], [[4,5],[3,4,5]], label=["y" ""], seriesalpha=[1 2])

The same warning repeats for linealpha, fillalpha, markeralpha, and markerstrokealpha.

I think the issue occurs because:

• I provide 2 data points with alpha vector [0.2, 0.6] (length 2)
• Internally, errorbars create multiple line segments (indices 2:6, so 5 segments total)
• The alpha vector length doesn't match the internal data structure
• Expanding the alpha vector (e.g., seriesalpha=[0.2,0.6,0.2,0.6,0.2]) doesn't resolve the issue

Related to #2156

Backends

This bug occurs on ( insert x below )

Backend	yes	no	untested
gr (default)	X
pythonplot			X
plotlyjs			X
pgfplotsx			X
unicodeplots			X
inspectdr			X
gaston			X

Versions

Plots.jl version: Plots v1.40.13
Backend version (]st -m <backend(s)>): GR v0.73.14
Output of versioninfo():

Julia Version 1.11.5
Commit 760b2e5b739 (2025-04-14 06:53 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: macOS (arm64-apple-darwin24.0.0)
  CPU: 12 × Apple M2 Pro
  WORD_SIZE: 64
  LLVM: libLLVM-16.0.6 (ORCJIT, apple-m2)
Threads: 1 default, 0 interactive, 1 GC (on 8 virtual cores)