Set :multiline=>false in showcompact() and use it for enum printing

This provides a simple way of printing the short representation
of a type. Cf. #16817.

base/Enums.jl

@@ -97,7 +97,7 @@ macro enum(T,syms...)
  print(io, x)
  else
  print(io, x, "::")
- show(IOContext(io, :multiline => false), typeof(x))
+ showcompact(io, typeof(x))
  print(io, " = ", Int(x))
  end
  end

base/docs/helpdb/Base.jl

@@ -2855,12 +2855,14 @@ Show an expression and result, returning the result.
 """
  showcompact(x)
 
-Show a more compact representation of a value.
+Show a compact representation of a value.
 
-This is used for printing array elements. If a new type has a different compact representation,
-it should test `get(io, :compact, false)` in its normal `show` method.
-A compact representation should skip any type information, which would be redundant
-with that printed once for the whole array.
+This is used for printing array elements without repeating type information (which would
+be redundant with that printed once for the whole array), and without line breaks inside
+the representation of an element.
+
+To offer a compact representation different from its standard one, a custom type should
+test `get(io, :compact, false)` in its normal `show` method.
 """
 showcompact
 

base/show.jl

@@ -1542,9 +1542,18 @@ end
 showcompact(x) = showcompact(STDOUT, x)
 function showcompact(io::IO, x)
  if get(io, :compact, false)
- show(io, x)
+ if !get(io, :multiline, false)
+ show(io, x)
+ else
+ show(IOContext(io, :multiline => false), x)
+ end
  else
- show(IOContext(io, :compact => true), x)
+ if get(io, :multiline, false)
+ show(IOContext(io, :compact => true), x)
+ else
+ show(IOContext(IOContext(io, :compact => true),
+ :multiline => false), x)
+ end
  end
 end
 

doc/stdlib/io-network.rst

@@ -434,9 +434,11 @@ Text I/O
 
  .. Docstring generated from Julia source
 
- Show a more compact representation of a value.
+ Show a compact representation of a value.
 
- This is used for printing array elements. If a new type has a different compact representation, it should test ``get(io, :compact, false)`` in its normal ``show`` method. A compact representation should skip any type information, which would be redundant with that printed once for the whole array.
+ This is used for printing array elements without repeating type information (which would be redundant with that printed once for the whole array), and without line breaks inside the representation of an element.
+
+ To offer a compact representation different from its standard one, a custom type should test ``get(io, :compact, false)`` in its normal ``show`` method.
 
 .. function:: showall(x)
 

test/show.jl

@@ -447,3 +447,16 @@ end
 # PR #16651
 @test !contains(repr(ones(10,10)), "\u2026")
 @test contains(sprint((io,x)->show(IOContext(io,:limit=>true), x), ones(30,30)), "\u2026")
+
+# showcompact() also sets multiline=>false (#16817)
+let io = IOBuffer()
+ @enum TestShowEnum a b
+ showcompact(io, TestShowEnum)
+ @test takebuf_string(io) == "TestShowEnum"
+ showcompact(IOContext(io, :multiline=>true), TestShowEnum)
+ @test takebuf_string(io) == "TestShowEnum"
+ showcompact(IOContext(io, :compact=>true), TestShowEnum)
+ @test takebuf_string(io) == "TestShowEnum"
+ showcompact(IOContext(IOContext(io, :compact=>true), :multiline=>true), TestShowEnum)
+ @test takebuf_string(io) == "TestShowEnum"
+end