Allow nothin to be printed

fix missing bracket

fix up whitespace

Keep defining custom show for nothing

add printing of nothing

Let print of nothing fallback to show

NEWS.md

@@ -30,6 +30,7 @@ Standard library changes
 * Cmd interpolation (`` `$(x::Cmd) a b c` `` where) now propagates `x`'s process flags
   (environment, flags, working directory, etc) if `x` is the first interpolant and errors
   otherwise ([#24353]).
+* `nothing` can now be `print`ed, and interplated into strings etc. as the string `"nothing"`. It is still not permitted to be interplated into Cmds (i.e. ``echo `$(nothing)` `` will still error without running anything.) ([#32148])
 
 #### LinearAlgebra
 

base/process.jl

@@ -907,7 +907,7 @@ end
 
 cmd_interpolate(xs...) = cstr(string(map(cmd_interpolate1, xs)...))
 cmd_interpolate1(x) = x
-cmd_interpolate1(::Nothing) = throw(ArgumentError("`nothing` can not be interpolated into commands (`Cmd`)")
+cmd_interpolate1(::Nothing) = throw(ArgumentError("`nothing` can not be interpolated into commands (`Cmd`)"))
 
 arg_gen() = String[]
 arg_gen(x::AbstractString) = String[cstr(x)]

base/show.jl

@@ -585,7 +585,6 @@ function show(io::IO, tn::Core.TypeName)
 end
 
 show(io::IO, ::Nothing) = print(io, "nothing")
-print(io::IO, ::Nothing) = throw(ArgumentError("`nothing` should not be printed; use `show`, `repr`, or custom output instead."))
 show(io::IO, b::Bool) = print(io, get(io, :typeinfo, Any) === Bool ? (b ? "1" : "0") : (b ? "true" : "false"))
 show(io::IO, n::Signed) = (write(io, string(n)); nothing)
 show(io::IO, n::Unsigned) = print(io, "0x", string(n, pad = sizeof(n)<<1, base = 16))

test/show.jl

@@ -1459,15 +1459,19 @@ let src = code_typed(gcd, (Int, Int), debuginfo=:source)[1][1]
     @test pop!(lines) == "   ! ──       unreachable::#UNDEF"
 end
 
-# issue #27352
-@test_throws ArgumentError print(nothing)
-@test_throws ArgumentError print(stdout, nothing)
-@test_throws ArgumentError string(nothing)
-@test_throws ArgumentError string(1, "", nothing)
-@test_throws ArgumentError let x = nothing; "x = $x" end
-@test let x = nothing; "x = $(repr(x))" end == "x = nothing"
-@test_throws ArgumentError `/bin/foo $nothing`
-@test_throws ArgumentError `$nothing`
+@testset "printing and interpolating nothing" begin
+    @test sprint(print, nothing) == "nothing"
+    @test string(nothing) == "nothing"
+    @test repr(nothing) == "nothing"
+    @test string(1, "", nothing) == "1nothing"
+    @test let x = nothing; "x = $x" end == "x = nothing"
+    @test let x = nothing; "x = $(repr(x))" end == "x = nothing"
+
+    # issue #27352 : No interpolating nothing into commands
+    @test_throws ArgumentError `/bin/foo $nothing`
+    @test_throws ArgumentError `$nothing`
+    @test_throws ArgumentError let x = nothing; `/bin/foo $x` end
+end
 
 struct X28004
     value::Any