improve REPL printing of sets

NEWS.md

@@ -42,6 +42,8 @@ Standard library changes
 
 * Verbose `display` of `Char` (`text/plain` output) now shows the codepoint value in standard-conforming `"U+XXXX"` format ([#33291]).
 
+* Sets are now displayed less compactly in the REPL, as a column of elements, like vectors
+  and dictionaries ([#33300]).
 
 #### Libdl
 

base/abstractset.jl

@@ -35,7 +35,10 @@ julia> union([4, 2], 1:2)
  1
 
 julia> union(Set([1, 2]), 2:3)
-Set([2, 3, 1])
+Set{Int64} with 3 elements:
+  2
+  3
+  1
 ```
 """
 function union end
@@ -60,7 +63,12 @@ julia> a = Set([1, 3, 4, 5]);
 julia> union!(a, 1:2:8);
 
 julia> a
-Set([7, 4, 3, 5, 1])
+Set{Int64} with 5 elements:
+  7
+  4
+  3
+  5
+  1
 ```
 """
 function union!(s::AbstractSet, sets...)
@@ -105,7 +113,8 @@ julia> intersect([1, 4, 4, 5, 6], [4, 6, 6, 7, 8])
  6
 
 julia> intersect(Set([1, 2]), BitSet([2, 3]))
-Set([2])
+Set{Int64} with 1 element:
+  2
 ```
 """
 intersect(s::AbstractSet, itr, itrs...) = intersect!(intersect(s, itr), itrs...)
@@ -160,7 +169,8 @@ julia> a = Set([1, 3, 4, 5]);
 julia> setdiff!(a, 1:2:6);
 
 julia> a
-Set([4])
+Set{Int64} with 1 element:
+  4
 ```
 """
 function setdiff!(s::AbstractSet, itrs...)

base/array.jl

@@ -1076,13 +1076,16 @@ julia> A
  2
 
 julia> S = Set([1, 2])
-Set([2, 1])
+Set{Int64} with 2 elements:
+  2
+  1
 
 julia> pop!(S)
 2
 
 julia> S
-Set([1])
+Set{Int64} with 1 element:
+  1
 
 julia> pop!(Dict(1=>2))
 1 => 2

base/set.jl

@@ -439,7 +439,10 @@ julia> replace!([1, 2, 1, 3], 1=>0, 2=>4, count=2)
  3
 
 julia> replace!(Set([1, 2, 3]), 1=>0)
-Set([0, 2, 3])
+Set{Int64} with 3 elements:
+  0
+  2
+  3
 ```
 """
 replace!(A, old_new::Pair...; count::Integer=typemax(Int)) =
@@ -479,7 +482,9 @@ Dict{Int64,Int64} with 2 entries:
   1 => 3
 
 julia> replace!(x->2x, Set([3, 6]))
-Set([6, 12])
+Set{Int64} with 2 elements:
+  6
+  12
 ```
 """
 replace!(new::Callable, A; count::Integer=typemax(Int)) =

base/show.jl

@@ -113,7 +113,10 @@ function show(io::IO, ::MIME"text/plain", t::AbstractDict{K,V}) where {K,V}
 
     for (i, (k, v)) in enumerate(t)
         print(io, "\n  ")
-        i == rows < length(t) && (print(io, rpad("⋮", keylen), " => ⋮"); break)
+        if i == rows < length(t)
+            print(io, rpad("⋮", keylen), " => ⋮")
+            break
+        end
 
         if limit
             key = rpad(_truncate_at_width_or_chars(ks[i], keylen, "\r\n"), keylen)
@@ -132,6 +135,48 @@ function show(io::IO, ::MIME"text/plain", t::AbstractDict{K,V}) where {K,V}
     end
 end
 
+function summary(io::IO, t::AbstractSet)
+    n = length(t)
+    showarg(io, t, true)
+    print(io, " with ", n, (n==1 ? " element" : " elements"))
+end
+
+function show(io::IO, ::MIME"text/plain", t::AbstractSet{T}) where T
+    # show more descriptively, with one line per value
+    recur_io = IOContext(io, :SHOWN_SET => t)
+    limit::Bool = get(io, :limit, false)
+
+    summary(io, t)
+    isempty(t) && return
+    print(io, ":")
+    show_circular(io, t) && return
+    if limit
+        sz = displaysize(io)
+        rows, cols = sz[1] - 3, sz[2]
+        rows < 2   && (print(io, " …"); return)
+        cols -= 2 # Subtract the width of prefix "  "
+        cols < 4  && (cols = 4) # Minimum widths of 4 for value
+        rows -= 1 # Subtract the summary
+    else
+        rows = cols = typemax(Int)
+    end
+
+    for (i, v) in enumerate(t)
+        print(io, "\n  ")
+        if i == rows < length(t)
+            print(io, rpad("⋮", 2))
+            break
+        end
+
+        if limit
+            str = sprint(show, v, context=recur_io, sizehint=0)
+            print(io, _truncate_at_width_or_chars(str, cols, "\r\n"))
+        else
+            show(recur_io, v)
+        end
+    end
+end
+
 function show(io::IO, ::MIME"text/plain", opt::JLOptions)
     println(io, "JLOptions(")
     fields = fieldnames(JLOptions)

test/show.jl

@@ -452,9 +452,6 @@ let a = Expr(:quote,Expr(:$,:x8d003))
     @test eval(eval(Meta.parse(repr(a)))) == 2
 end
 
-# issue #9865
-@test occursin(r"^Set\(\[.+….+\]\)$", replstr(Set(1:100)))
-
 # issue #11413
 @test string(:(*{1, 2})) == "*{1, 2}"
 @test string(:(*{1, x})) == "*{1, x}"
@@ -1275,7 +1272,7 @@ end
     @test replstr(view(A, [1], :)) == "1×1 view(::Array{Float64,2}, [1], :) with eltype Float64:\n 0.0"
 
     # issue #27680
-    @test replstr(Set([(1.0,1.0), (2.0,2.0), (3.0, 3.0)])) == (sizeof(Int) == 8 ?
+    @test showstr(Set([(1.0,1.0), (2.0,2.0), (3.0, 3.0)])) == (sizeof(Int) == 8 ?
               "Set([(3.0, 3.0), (2.0, 2.0), (1.0, 1.0)])" :
               "Set([(1.0, 1.0), (2.0, 2.0), (3.0, 3.0)])")
 
@@ -1586,6 +1583,21 @@ end
     @test sdastr(3, 3) == "[3, 4, 5]"
 end
 
+@testset "show Set" begin
+    s = Set{Int}(1:22)
+    str = showstr(s)
+    @test startswith(str, "Set([")
+    @test endswith(str, "])")
+    @test occursin("  …  ", str)
+
+    str = replstr(s)
+    @test startswith(str, "Set{$Int} with 22 elements:\n")
+    @test endswith(str, "\n  ⋮ ")
+    @test count(==('\n'), str) == 20
+
+    @test replstr(Set(['a'^100])) == "Set{String} with 1 element:\n  \"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa…"
+end
+
 @testset "0-dimensional Array. Issue #31481" begin
     for x in (zeros(Int32), collect('b'), fill(nothing), BitArray(0))
         @test eval(Meta.parse(repr(x))) == x