From a3c32862fc5c2757cc34ab1690d3f95bf94a0be1 Mon Sep 17 00:00:00 2001
From: Jameson Nash <vtjnash@gmail.com>
Date: Thu, 18 Feb 2021 01:59:49 -0500
Subject: [PATCH] ensure to show the whole type, even if the proper subset
 matched an alias

This code should only have been active for make_typealiases, but #38099
already fixed that better, so we can just remove this now.

Fixes #39723

(cherry picked from commit b72966751e13f6e4c7571b33d3675d225d29d940)
---
 base/show.jl | 22 +++++-----------------
 test/show.jl |  7 ++++++-
 2 files changed, 11 insertions(+), 18 deletions(-)

diff --git a/base/show.jl b/base/show.jl
index 2fbc8f50ee7374..79ac682f9e22dd 100644
--- a/base/show.jl
+++ b/base/show.jl
@@ -522,26 +522,12 @@ function makeproper(io::IO, x::Type)
             end
         end
     end
-    if x isa Union
-        y = []
-        normal = true
-        for typ in uniontypes(x)
-            if isa(typ, TypeVar)
-                normal = false
-            else
-                push!(y, typ)
-            end
-        end
-        if !normal
-            properx = rewrap_unionall(Union{y...}, properx)
-        end
-    end
     has_free_typevars(properx) && return Any
     return properx
 end
 
 function make_typealias(@nospecialize(x::Type))
-    Any <: x && return
+    Any === x && return
     x <: Tuple && return
     mods = modulesof!(Set{Module}(), x)
     Core in mods && push!(mods, Base)
@@ -681,7 +667,7 @@ function show_typealias(io::IO, x::Type)
 end
 
 function make_typealiases(@nospecialize(x::Type))
-    Any <: x && return Core.svec(), Union{}
+    Any === x && return Core.svec(), Union{}
     x <: Tuple && return Core.svec(), Union{}
     mods = modulesof!(Set{Module}(), x)
     Core in mods && push!(mods, Base)
@@ -701,7 +687,9 @@ function make_typealiases(@nospecialize(x::Type))
                 if alias isa Type && !has_free_typevars(alias) && !isvarargtype(alias) && !print_without_params(alias) && !(alias <: Tuple)
                     (ti, env) = ccall(:jl_type_intersection_with_env, Any, (Any, Any), x, alias)::SimpleVector
                     ti === Union{} && continue
-                    mod in modulesof!(Set{Module}(), alias) || continue # make sure this alias wasn't from an unrelated part of the Union
+                    # make sure this alias wasn't from an unrelated part of the Union
+                    mod2 = modulesof!(Set{Module}(), alias)
+                    mod in mod2 || (mod === Base && Core in mods) || continue
                     env = env::SimpleVector
                     applied = alias
                     if !isempty(env)
diff --git a/test/show.jl b/test/show.jl
index b0bc4455d990a2..83cee001257022 100644
--- a/test/show.jl
+++ b/test/show.jl
@@ -2070,12 +2070,13 @@ end
 end
 
 module M37012
-export AValue, B2
+export AValue, B2, SimpleU
 struct AnInteger{S<:Integer} end
 struct AStruct{N} end
 const AValue{S} = Union{AStruct{S}, AnInteger{S}}
 struct BStruct{T,S} end
 const B2{S,T} = BStruct{T,S}
+const SimpleU = Union{AnInteger, AStruct, BStruct}
 end
 @test Base.make_typealias(M37012.AStruct{1}) === nothing
 @test isempty(Base.make_typealiases(M37012.AStruct{1})[1])
@@ -2085,6 +2086,10 @@ end
 @test string(M37012.BStruct{T, T} where T) == "$(curmod_prefix)M37012.B2{T, T} where T"
 @test string(M37012.BStruct{T, S} where {T<:Unsigned, S<:Signed}) == "$(curmod_prefix)M37012.B2{S, T} where {T<:Unsigned, S<:Signed}"
 @test string(M37012.BStruct{T, S} where {T<:Signed, S<:T}) == "$(curmod_prefix)M37012.B2{S, T} where {T<:Signed, S<:T}"
+@test string(Union{M37012.SimpleU, Nothing}) == "Union{Nothing, $(curmod_prefix)M37012.SimpleU}"
+@test string(Union{M37012.SimpleU, Nothing, T} where T) == "Union{Nothing, T, $(curmod_prefix)M37012.SimpleU} where T"
+@test string(Union{AbstractVector{T}, T} where T) == "Union{AbstractVector{T}, T} where T"
+@test string(Union{AbstractVector, T} where T) == "Union{T, AbstractVector{T} where T} where T"
 
 @test sprint(show, :(./)) == ":((./))"
 @test sprint(show, :((.|).(.&, b))) == ":((.|).((.&), b))"