From ed4f968a241586d9d7a60a9c40c07268e353f94d Mon Sep 17 00:00:00 2001
From: Jameson Nash <vtjnash@gmail.com>
Date: Fri, 18 Sep 2020 09:41:11 -0400
Subject: [PATCH] fix fields description of Module type

The fields are not accessible, so it is awkward to report they exist.

Fixes #37630
Caused issues starting with #34804
---
 base/boot.jl            | 19 +++++++++++++++++--
 base/compiler/tfuncs.jl |  6 +++---
 src/datatype.c          |  2 +-
 src/jltypes.c           |  5 +++--
 test/misc.jl            |  2 +-
 5 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/base/boot.jl b/base/boot.jl
index e653a82399ba5..7c8d05cc132c4 100644
--- a/base/boot.jl
+++ b/base/boot.jl
@@ -8,7 +8,7 @@
 #abstract type Vararg{T} end
 
 #mutable struct Symbol
-#    #opaque
+## opaque
 #end
 
 #mutable struct TypeName
@@ -53,28 +53,43 @@
 #abstract type DenseArray{T,N} <: AbstractArray{T,N} end
 
 #mutable struct Array{T,N} <: DenseArray{T,N}
+## opaque
 #end
 
 #mutable struct Module
-#    name::Symbol
+## opaque
+#end
+
+#mutable struct SimpleVector
+## opaque
+#end
+
+#mutable struct String
+## opaque
 #end
 
 #mutable struct Method
+#...
 #end
 
 #mutable struct MethodInstance
+#...
 #end
 
 #mutable struct CodeInstance
+#...
 #end
 
 #mutable struct CodeInfo
+#...
 #end
 
 #mutable struct TypeMapLevel
+#...
 #end
 
 #mutable struct TypeMapEntry
+#...
 #end
 
 #abstract type Ref{T} end
diff --git a/base/compiler/tfuncs.jl b/base/compiler/tfuncs.jl
index cbf8e4f0f591d..a938d86f953ae 100644
--- a/base/compiler/tfuncs.jl
+++ b/base/compiler/tfuncs.jl
@@ -951,11 +951,11 @@ function fieldtype_tfunc(@nospecialize(s0), @nospecialize(name))
     if s0 === Any || s0 === Type || DataType ⊑ s0 || UnionAll ⊑ s0
         return Type
     end
-    # fieldtype only accepts Types, errors on `Module`
-    if isa(s0, Const) && (!(isa(s0.val, DataType) || isa(s0.val, UnionAll) || isa(s0.val, Union)) || s0.val === Module)
+    # fieldtype only accepts Types
+    if isa(s0, Const) && !(isa(s0.val, DataType) || isa(s0.val, UnionAll) || isa(s0.val, Union))
         return Bottom
     end
-    if (s0 isa Type && (s0 == Type{Module} || s0 == Type{Union{}})) || isa(s0, Conditional)
+    if (s0 isa Type && s0 == Type{Union{}}) || isa(s0, Conditional)
         return Bottom
     end
 
diff --git a/src/datatype.c b/src/datatype.c
index 269076ef2819b..2fa35f1b5f5f0 100644
--- a/src/datatype.c
+++ b/src/datatype.c
@@ -376,7 +376,7 @@ void jl_compute_field_offsets(jl_datatype_t *st)
             st->layout = &opaque_byte_layout;
             return;
         }
-        else if (st == jl_simplevector_type || st->name == jl_array_typename) {
+        else if (st == jl_simplevector_type || st == jl_module_type || st->name == jl_array_typename) {
             static const jl_datatype_layout_t opaque_ptr_layout = {0, 1, -1, sizeof(void*), 0, 0};
             st->layout = &opaque_ptr_layout;
             return;
diff --git a/src/jltypes.c b/src/jltypes.c
index dd36776f1bac1..27ef5a814411c 100644
--- a/src/jltypes.c
+++ b/src/jltypes.c
@@ -2170,8 +2170,9 @@ void jl_init_types(void) JL_GC_DISABLED
 
     jl_module_type =
         jl_new_datatype(jl_symbol("Module"), core, jl_any_type, jl_emptysvec,
-                        jl_perm_symsvec(2, "name", "parent"),
-                        jl_svec(2, jl_symbol_type, jl_any_type), 0, 1, 2);
+                        jl_emptysvec, jl_emptysvec, 0, 1, 0);
+    jl_module_type->instance = NULL;
+    jl_compute_field_offsets(jl_module_type);
 
     jl_value_t *symornothing[2] = { (jl_value_t*)jl_symbol_type, (jl_value_t*)jl_void_type };
     jl_linenumbernode_type =
diff --git a/test/misc.jl b/test/misc.jl
index e5fc2f461643c..920a03abdb520 100644
--- a/test/misc.jl
+++ b/test/misc.jl
@@ -840,7 +840,7 @@ end
 end
 
 @testset "fieldtypes Module" begin
-    @test fieldtypes(Module) isa Tuple
+    @test fieldtypes(Module) === ()
 end