Display linebreaks, TextDisplay vs REPLDisplay

[t-bltg]

As explained on discourse, we (ping @mkitti) feel that there might be an inconsistency in display(...) between TextDisplay and REPLDisplay.

Does anyone know why there is no trailing newline for TextDisplay ?

Would the following patch be acceptable ?

--- a/base/multimedia.jl	2022-01-11 21:00:42.765702329 +0100
+++ b/base/multimedia.jl	2022-01-11 21:02:53.377249363 +0100
@@ -239,14 +239,14 @@
 struct TextDisplay <: AbstractDisplay
     io::IO
 end
-display(d::TextDisplay, M::MIME"text/plain", @nospecialize x) = show(d.io, M, x)
+display(d::TextDisplay, M::MIME"text/plain", @nospecialize x) = (show(d.io, M, x); println(d.io))
 display(d::TextDisplay, @nospecialize x) = display(d, MIME"text/plain"(), x)
 
 # if you explicitly call display("text/foo", x), it should work on a TextDisplay:
 displayable(d::TextDisplay, M::MIME) = istextmime(M)
 function display(d::TextDisplay, M::MIME, @nospecialize x)
     displayable(d, M) || throw(MethodError(display, (d, M, x)))
-    show(d.io, M, x)
+    show(d.io, M, x); println(d.io)
 end
 
 import Base: close, flush

[JeffBezanson]

I guess we should do this. Normally I don't like building in extra trailing line breaks, because they're harder to remove than to add yourself. But given the nature of display it seems like the right thing.

[t-bltg]

Thanks @JeffBezanson for clarifying that.

Basically what I understood for MIME"text/plain" is:

• use show(...) when writing to files or streams (no trailing newline), easier to work with afterwards, needs println to be added explicitly (machines ?)
• use display(...) for richest output where the trailing newline is justified (humans ?)

I'll propose the PR and add some tests.

[mkitti]

I think these line breaks may be necessary here rather than extra.

$ julia -e "A = rand(5,5); display(A); display(A)"
5×5 Matrix{Float64}:
 0.558617   0.833546   0.534481  0.871176   0.81832
 0.667262   0.214333   0.557675  0.469011   0.733549
 0.0167319  0.772786   0.532067  0.0182531  0.362664
 0.162401   0.175737   0.958528  0.528862   0.0345345
 0.28226    0.0938108  0.405553  0.34604    0.9921985×5 Matrix{Float64}:
 0.558617   0.833546   0.534481  0.871176   0.81832
 0.667262   0.214333   0.557675  0.469011   0.733549
 0.0167319  0.772786   0.532067  0.0182531  0.362664
 0.162401   0.175737   0.958528  0.528862   0.0345345
 0.28226    0.0938108  0.405553  0.34604    0.992198$

I think there may be an extra line break here though:

julia> A = rand(5,5); display(A); display(A)
5×5 Matrix{Float64}:
 0.649867     0.498648    0.0749694   0.585428   0.645387
 0.440297     0.326395    0.558343    0.0917279  0.519926
 0.566742     0.573145    7.27435e-6  0.477407   0.418683
 0.584659     0.00708769  0.765285    0.346584   0.439672
 0.000295367  0.244561    0.787006    0.738048   0.736395
5×5 Matrix{Float64}:
 0.649867     0.498648    0.0749694   0.585428   0.645387
 0.440297     0.326395    0.558343    0.0917279  0.519926
 0.566742     0.573145    7.27435e-6  0.477407   0.418683
 0.584659     0.00708769  0.765285    0.346584   0.439672
 0.000295367  0.244561    0.787006    0.738048   0.736395

julia>

[t-bltg]

On your second example this is just the REPL displaying nothing which looks like a newline no ?

julia> nothing

julia> println()


julia>