Improve show for 0-dim array

NEWS.md

@@ -13,6 +13,8 @@ Language changes
 
 * Calling `show` or `repr` on an `undef`/`UndefInitializer()` array initializer now shows valid Julia code ([#33211]).
 
+* Calling `show` or `repr` on a 0-dimensional `AbstractArray` now shows valid code for creating an equivalent 0-dimensional array, instead of only showing the contained value. ([#33206])
+
 Multi-threading changes
 -----------------------
 
@@ -38,6 +40,7 @@ Standard library changes
 
 * Verbose `display` of `Char` (`text/plain` output) now shows the codepoint value in standard-conforming `"U+XXXX"` format ([#33291]).
 
+
 #### Libdl
 
 #### LinearAlgebra

base/arrayshow.jl

@@ -299,14 +299,12 @@ end
 
 # print_array: main helper functions for show(io, text/plain, array)
 # typeinfo agnostic
-
-# 0-dimensional arrays
-print_array(io::IO, X::AbstractArray{T,0} where T) =
-    isassigned(X) ? show(io, X[]) :
-                    print(io, undef_ref_str)
-
+# Note that this is for showing the content inside the array, and for `MIME"text/plain".
+# There are `show(::IO, ::A) where A<:AbstractArray` methods that don't use this
+# e.g. show_vector, show_zero_dim
+print_array(io::IO, X::AbstractArray{<:Any, 0}) =
+    isassigned(X) ? show(io, X[]) : print(io, undef_ref_str)
 print_array(io::IO, X::AbstractVecOrMat) = print_matrix(io, X)
-
 print_array(io::IO, X::AbstractArray) = show_nd(io, X, print_matrix, true)
 
 # typeinfo aware
@@ -415,6 +413,7 @@ _show_empty(io, X) = nothing # by default, we don't know this constructor
 
 # typeinfo aware (necessarily)
 function show(io::IO, X::AbstractArray)
+    ndims(X) == 0 && return show_zero_dim(io, X)
     ndims(X) == 1 && return show_vector(io, X)
     prefix = typeinfo_prefix(io, X)
     io = IOContext(io, :typeinfo => eltype(X))
@@ -423,6 +422,18 @@ function show(io::IO, X::AbstractArray)
         _show_nonempty(io, X, prefix)
 end
 
+### 0-dimensional arrays (#31481)
+function show_zero_dim(io::IO, X::AbstractArray{T, 0}) where T
+    if isassigned(X)
+        print(io, "fill(")
+        show(io, X[])
+    else
+        print(io, "Array{$T,0}(")
+        show(io, undef)
+    end
+    print(io, ")")
+end
+
 ### Vector arrays
 
 # typeinfo aware

test/offsetarray.jl

@@ -210,7 +210,7 @@ targets1 = ["0-dimensional $OAs_name.OffsetArray{Float64,0,Array{Float64,0}}:\n1
             "1×1 $OAs_name.OffsetArray{Float64,2,Array{Float64,2}} with indices 2:2×3:3:\n 1.0",
             "1×1×1 $OAs_name.OffsetArray{Float64,3,Array{Float64,3}} with indices 2:2×3:3×4:4:\n[:, :, 4] =\n 1.0",
             "1×1×1×1 $OAs_name.OffsetArray{Float64,4,Array{Float64,4}} with indices 2:2×3:3×4:4×5:5:\n[:, :, 4, 5] =\n 1.0"]
-targets2 = ["(1.0, 1.0)",
+targets2 = ["(fill(1.0), fill(1.0))",
             "([1.0], [1.0])",
             "([1.0], [1.0])",
             "([1.0], [1.0])",

test/show.jl

@@ -1583,3 +1583,30 @@ end
     @test sdastr(2, 2) == "[2, 3]"
     @test sdastr(3, 3) == "[3, 4, 5]"
 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
+    end
+    @test showstr(zeros(Int32)) == "fill(0)"
+    @test showstr(collect('b')) == "fill('b')"
+    @test showstr(fill(nothing)) == "fill(nothing)"
+    @test showstr(BitArray(0)) == "fill(false)"
+
+    @test replstr(zeros(Int32)) == "0-dimensional Array{Int32,0}:\n0"
+    @test replstr(collect('b')) == "0-dimensional Array{Char,0}:\n'b'"
+    @test replstr(fill(nothing)) == "0-dimensional Array{Nothing,0}:\nnothing"
+    @test replstr(BitArray(0)) == "0-dimensional BitArray{0}:\n0"
+
+    # UndefInitializer
+    @test showstr(fill(undef)) == "fill($undef)"
+    @test replstr(fill(undef)) == "0-dimensional Array{UndefInitializer,0}:\n$undef"
+
+    # `#undef` values
+    @test showstr(Array{String, 0}(undef)) == "Array{String,0}($undef)"
+    @test replstr(Array{String, 0}(undef)) == "0-dimensional Array{String,0}:\n$(Base.undef_ref_str)"
+
+    # "undef" with isbits type
+    @test startswith(showstr(Array{Int32, 0}(undef)), "fill(")
+    @test startswith(replstr(Array{Int32, 0}(undef)), "0-dimensional Array{Int32,0}:\n")
+end