[BUG][UnicodePlotsBackend] showable for image/png and UnicodePlotsBackend is unreliable

[david-macmahon]

Details

Displaying plots made by the UnicodePlots backend of Plots.jl throws an argument error in VS Code. The underlying cause is because showable for image/png and UnicodePlotsBackend (always) returns true, even when UnicodePlots.save_image has zero methods. The exact method call that (always) returns true:

showable(MIME("image/png"), Plots.Plot{Plots.UnicodePlotsBackend})

Defining the following showable method avoids this problem and Plots.jl plots made with the UnicodePlotsBackend display properly inline in the REPL.

Base.showable(::MIME"image/png", ::Plots.Plot{Plots.UnicodePlotsBackend}) = applicable(UnicodePlots.save_image, devnull)

Backends

This bug is specific to UnicodePlotsBackend.

Backend	yes	no	untested
unicodeplots	x

Versions

Plots.jl version: Plots v1.40.4
Backend version: UnicodePlots v3.6.4
Output of versioninfo():

julia> versioninfo()
Julia Version 1.10.4
Commit 48d4fd48430 (2024-06-04 10:41 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: macOS (arm64-apple-darwin22.4.0)
  CPU: 8 × Apple M2
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-15.0.7 (ORCJIT, apple-m1)
Threads: 1 default, 0 interactive, 1 GC (on 4 virtual cores)

[t-bltg]

The exact method call that (always) returns true:

showable(MIME("image/png"), Plots.Plot{Plots.UnicodePlotsBackend})

Where do you see this method ?