Print symbols in Tuple{:sym} type with colons (#42999)

Use `show` instead of `print` or `join`.

Author: inkydragon

base/show.jl

@@ -993,10 +993,17 @@ function show_datatype(io::IO, @nospecialize(x::DataType), wheres::Vector=TypeVa
     # Print homogeneous tuples with more than 3 elements compactly as NTuple{N, T}
     if istuple
         if n > 3 && all(@nospecialize(i) -> (parameters[1] === i), parameters)
-            print(io, "NTuple{", n, ", ", parameters[1], "}")
+            print(io, "NTuple{", n, ", ")
+            show(io, parameters[1])
+            print(io, "}")
         else
             print(io, "Tuple{")
-            join(io, parameters, ", ")
+            # join(io, params, ", ") params but `show` it
+            first = true
+            for param in parameters
+                first ? (first = false) : print(io, ", ")
+                show(io, param)
+            end
             print(io, "}")
         end
     else

test/show.jl

@@ -1347,6 +1347,20 @@ test_repr("(:).a")
 @test repr(Tuple{Float64, Float64, Float64, Float64}) == "NTuple{4, Float64}"
 @test repr(Tuple{Float32, Float32, Float32}) == "Tuple{Float32, Float32, Float32}"
 
+@testset "issue #42931" begin
+    @test repr(NTuple{4, :A}) == "NTuple{4, :A}"
+    @test repr(NTuple{3, :A}) == "Tuple{:A, :A, :A}"
+    @test repr(NTuple{2, :A}) == "Tuple{:A, :A}"
+    @test repr(NTuple{1, :A}) == "Tuple{:A}"
+    @test repr(NTuple{0, :A}) == "Tuple{}"
+
+    @test repr(Tuple{:A, :A, :A, :B}) == "Tuple{:A, :A, :A, :B}"
+    @test repr(Tuple{:A, :A, :A, :A}) == "NTuple{4, :A}"
+    @test repr(Tuple{:A, :A, :A}) == "Tuple{:A, :A, :A}"
+    @test repr(Tuple{:A}) == "Tuple{:A}"
+    @test repr(Tuple{}) == "Tuple{}"
+end
+
 # Test that REPL/mime display of invalid UTF-8 data doesn't throw an exception:
 @test isa(repr("text/plain", String(UInt8[0x00:0xff;])), String)