Make dump print const before const fields (#53492)

This provides more information to the user when dumping types, and also
makes the output of dump slightly more similar to the type definition
syntax.

EDIT: This has been changed to print:
* The kind of type before the type name `abstract type`, `mutable
struct`, etc.
* `const` only for `const` fields of `mutable struct`

New behaviour
```
julia> dump(Float32)
primitive type Float32 <: AbstractFloat

julia> dump(Signed)
abstract type Signed <: Integer

julia> dump(Pair{Int, String})
struct Pair{Int64, String} <: Any
  first::Int64
  second::String

julia> dump(BitSet)
mutable struct BitSet <: AbstractSet{Int64}
  const bits::Vector{UInt64}
  offset::Int64

julia> dump(Set)
UnionAll
  var: TypeVar
    name: Symbol T
    lb: Union{}
    ub: abstract type Any
  body: struct Set{T} <: AbstractSet{T}
    dict::Dict{T, Nothing}
```

---------

Co-authored-by: Shuhei Kadowaki <[email protected]>

Author: jakobnissen

base/show.jl

@@ -2986,6 +2986,13 @@ end
 
 # Types
 function dump(io::IOContext, x::DataType, n::Int, indent)
+    # For some reason, tuples are structs
+    is_struct = isstructtype(x) && !(x <: Tuple)
+    is_mut = is_struct && ismutabletype(x)
+    is_mut && print(io, "mutable ")
+    is_struct && print(io, "struct ")
+    isprimitivetype(x) && print(io, "primitive type ")
+    isabstracttype(x) && print(io, "abstract type ")
     print(io, x)
     if x !== Any
         print(io, " <: ", supertype(x))
@@ -3007,7 +3014,9 @@ function dump(io::IOContext, x::DataType, n::Int, indent)
         fieldtypes = datatype_fieldtypes(x)
         for idx in 1:length(fields)
             println(io)
-            print(io, indent, "  ", fields[idx])
+            print(io, indent, "  ")
+            is_mut && isconst(x, idx) && print(io, "const ")
+            print(io, fields[idx])
             if isassigned(fieldtypes, idx)
                 print(io, "::")
                 print(tvar_io, fieldtypes[idx])

doc/src/devdocs/types.md

@@ -93,13 +93,13 @@ UnionAll
   var: TypeVar
     name: Symbol T
     lb: Union{}
-    ub: Any
+    ub: abstract type Any
   body: UnionAll
     var: TypeVar
       name: Symbol N
       lb: Union{}
-      ub: Any
-    body: Array{T, N} <: DenseArray{T, N}
+      ub: abstract type Any
+    body: mutable struct Array{T, N} <: DenseArray{T, N}
       ref::MemoryRef{T}
       size::NTuple{N, Int64}
 ```
@@ -181,13 +181,13 @@ TypeName
     var: TypeVar
       name: Symbol T
       lb: Union{}
-      ub: Any
+      ub: abstract type Any
     body: UnionAll
       var: TypeVar
         name: Symbol N
         lb: Union{}
-        ub: Any
-      body: Array{T, N} <: DenseArray{T, N}
+        ub: abstract type Any
+      body: mutable struct Array{T, N} <: DenseArray{T, N}
   cache: SimpleVector
     ...
 

test/show.jl

@@ -703,7 +703,7 @@ let oldout = stdout, olderr = stderr
         redirect_stderr(olderr)
         close(wrout)
         close(wrerr)
-        @test fetch(out) == "Int64 <: Signed\nTESTA\nTESTB\nΑ1Β2\"A\"\nA\n123\"C\"\n"
+        @test fetch(out) == "primitive type Int64 <: Signed\nTESTA\nTESTB\nΑ1Β2\"A\"\nA\n123\"C\"\n"
         @test fetch(err) == "TESTA\nTESTB\nΑ1Β2\"A\"\n"
     finally
         redirect_stdout(oldout)
@@ -1259,64 +1259,64 @@ end
     close(s2)
 end
 
-let repr = sprint(dump, :(x = 1))
-    @test repr == "Expr\n  head: Symbol =\n  args: Array{Any}((2,))\n    1: Symbol x\n    2: $Int 1\n"
-end
-let repr = sprint(dump, Pair{String,Int64})
-    @test repr == "Pair{String, Int64} <: Any\n  first::String\n  second::Int64\n"
-end
-let repr = sprint(dump, Tuple)
-    @test repr == "Tuple <: Any\n"
-end
-let repr = sprint(dump, Int64)
-    @test repr == "Int64 <: Signed\n"
-end
-let repr = sprint(dump, Any)
-    @test length(repr) == 4
-    @test occursin(r"^Any\n", repr)
-    @test endswith(repr, '\n')
-end
-let repr = sprint(dump, Integer)
-    @test occursin("Integer <: Real", repr)
-    @test !occursin("Any", repr)
-end
-let repr = sprint(dump, Union{Integer, Float32})
-    @test repr == "Union{Integer, Float32}\n" || repr == "Union{Float32, Integer}\n"
-end
 module M30442
     struct T end
 end
-let repr = sprint(show, Union{String, M30442.T})
-    @test repr == "Union{$(curmod_prefix)M30442.T, String}" ||
-          repr == "Union{String, $(curmod_prefix)M30442.T}"
-end
-let repr = sprint(dump, Ptr{UInt8}(UInt(1)))
-    @test repr == "Ptr{UInt8} @$(Base.repr(UInt(1)))\n"
-end
-let repr = sprint(dump, Core.svec())
-    @test repr == "empty SimpleVector\n"
-end
-let repr = sprint(dump, sin)
-    @test repr == "sin (function of type typeof(sin))\n"
-end
-let repr = sprint(dump, Test)
-    @test repr == "Module Test\n"
-end
-let repr = sprint(dump, nothing)
-    @test repr == "Nothing nothing\n"
-end
-let a = Vector{Any}(undef, 10000)
-    a[2] = "elemA"
-    a[4] = "elemB"
-    a[11] = "elemC"
-    repr = sprint(dump, a; context=(:limit => true), sizehint=0)
-    @test repr == "Array{Any}((10000,))\n  1: #undef\n  2: String \"elemA\"\n  3: #undef\n  4: String \"elemB\"\n  5: #undef\n  ...\n  9996: #undef\n  9997: #undef\n  9998: #undef\n  9999: #undef\n  10000: #undef\n"
-end
-@test occursin("NamedTuple", sprint(dump, NamedTuple))
+@testset "Dump types" begin
+    let repr = sprint(dump, :(x = 1))
+        @test repr == "Expr\n  head: Symbol =\n  args: Array{Any}((2,))\n    1: Symbol x\n    2: $Int 1\n"
+    end
+    let repr = sprint(dump, Pair{String,Int64})
+        @test repr == "struct Pair{String, Int64} <: Any\n  first::String\n  second::Int64\n"
+    end
+    let repr = sprint(dump, Tuple)
+        @test repr == "Tuple <: Any\n"
+    end
+    let repr = sprint(dump, Int64)
+        @test repr == "primitive type Int64 <: Signed\n"
+    end
+    let repr = sprint(dump, Any)
+        @test repr == "abstract type Any\n"
+    end
+    let repr = sprint(dump, Integer)
+        @test occursin("abstract type Integer <: Real", repr)
+        @test !occursin("Any", repr)
+    end
+    let repr = sprint(dump, Union{Integer, Float32})
+        @test repr == "Union{Integer, Float32}\n" || repr == "Union{Float32, Integer}\n"
+    end
 
-# issue 36495, dumping a partial NamedTupled shouldn't error
-@test occursin("NamedTuple", sprint(dump, NamedTuple{(:foo,:bar)}))
+    let repr = sprint(show, Union{String, M30442.T})
+        @test repr == "Union{$(curmod_prefix)M30442.T, String}" ||
+              repr == "Union{String, $(curmod_prefix)M30442.T}"
+    end
+    let repr = sprint(dump, Ptr{UInt8}(UInt(1)))
+        @test repr == "Ptr{UInt8} @$(Base.repr(UInt(1)))\n"
+    end
+    let repr = sprint(dump, Core.svec())
+        @test repr == "empty SimpleVector\n"
+    end
+    let repr = sprint(dump, sin)
+        @test repr == "sin (function of type typeof(sin))\n"
+    end
+    let repr = sprint(dump, Test)
+        @test repr == "Module Test\n"
+    end
+    let repr = sprint(dump, nothing)
+        @test repr == "Nothing nothing\n"
+    end
+    let a = Vector{Any}(undef, 10000)
+        a[2] = "elemA"
+        a[4] = "elemB"
+        a[11] = "elemC"
+        repr = sprint(dump, a; context=(:limit => true), sizehint=0)
+        @test repr == "Array{Any}((10000,))\n  1: #undef\n  2: String \"elemA\"\n  3: #undef\n  4: String \"elemB\"\n  5: #undef\n  ...\n  9996: #undef\n  9997: #undef\n  9998: #undef\n  9999: #undef\n  10000: #undef\n"
+    end
+    @test occursin("NamedTuple", sprint(dump, NamedTuple))
 
+    # issue 36495, dumping a partial NamedTupled shouldn't error
+    @test occursin("NamedTuple", sprint(dump, NamedTuple{(:foo,:bar)}))
+end
 # issue #17338
 @test repr(Core.svec(1, 2)) == "svec(1, 2)"