From a4f298056ed8147711601f2070014467288f9452 Mon Sep 17 00:00:00 2001
From: JonasIsensee <jonas.isensee@web.de>
Date: Sat, 10 Sep 2022 09:28:48 +0200
Subject: [PATCH] const fields in mutable structs (#414)

* testing const fields in mutable structs

* support const fields in mutable structs

* bump version

Co-authored-by: Jonas Isensee <jonas.isensee@ds.mpg.de>
---
 CHANGELOG.md                         |  3 +++
 Project.toml                         |  2 +-
 src/data/reconstructing_datatypes.jl |  9 +++++++--
 test/loadsave.jl                     | 27 +++++++++++++++++++++++++++
 4 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 85791692..9fcaaa4e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,6 @@
+## 0.4.23
+ - Support for `const` fields in mutable structs
+ 
 ## 0.4.22
  - Fix reconstruction of partially intialized structs
 
diff --git a/Project.toml b/Project.toml
index e923e72d..0f1f7e15 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,6 +1,6 @@
 name = "JLD2"
 uuid = "033835bb-8acc-5ee8-8aae-3f567f8a3819"
-version = "0.4.22"
+version = "0.4.23"
 
 [deps]
 FileIO = "5789e2e9-d7fb-5bc7-8068-2c6fae9b9549"
diff --git a/src/data/reconstructing_datatypes.jl b/src/data/reconstructing_datatypes.jl
index 6449f023..9165547e 100644
--- a/src/data/reconstructing_datatypes.jl
+++ b/src/data/reconstructing_datatypes.jl
@@ -540,9 +540,14 @@ jlconvert(::ReadRepresentation{Core.TypeofBottom,nothing}, f::JLDFile, ptr::Ptr,
             if odr === nothing
                 # Type is not stored or single instance
                 newi = Expr(:new, ttype)
-                push!(args, :(setfield!(obj, $fni, $newi)))                    
+                # use jl_set_nth_field instead of setfield! since the former also works for const fields
+                # in mutable structs.
+                push!(args, :(ccall(:jl_set_nth_field, Nothing, (Any, Csize_t, Any), obj, ($i)-1, $newi)))
             else
-                loadfield = :(setfield!(obj, $fni, rconvert($ttype, jlconvert($rr, f, ptr+$offset, NULL_REFERENCE)::$rtype)::$ttype))
+                loadfield = quote
+                    fieldval = rconvert($ttype, jlconvert($rr, f, ptr+$offset, NULL_REFERENCE)::$rtype)::$ttype
+                    ccall(:jl_set_nth_field, Nothing, (Any, Csize_t, Any), obj, ($i)-1, fieldval)
+                end
                 if jlconvert_canbeuninitialized(rr)
                     push!(args, :(jlconvert_isinitialized($rr, ptr+$offset) && $(loadfield)))
                 else
diff --git a/test/loadsave.jl b/test/loadsave.jl
index 681f5e7b..d7e3a430 100644
--- a/test/loadsave.jl
+++ b/test/loadsave.jl
@@ -513,4 +513,31 @@ end
         @test_throws UndefRefError fu.x
 
     end
+end
+
+if VERSION ≥ v"1.8"
+
+    struct SingletonStruct end
+
+    # This is a workaround since for old julia versions this syntax is not allowed and the parser
+    # is eager and attempts to parse this piece of code anyway
+    eval(Meta.parse("""mutable struct WrappedSingleton
+                  x::Int
+                  const y::Vector{Int}
+                  const z::SingletonStruct
+              end
+              """))
+
+    @testset "Constant fields in mutable structs (>v1.8) - Issue #410" begin
+        mktempdir() do folder
+            # The real test here is that it doesn't fail in v1.8
+            b = WrappedSingleton(1, [2,3], SingletonStruct())
+            save("test.jld2", "b", b)
+            bloaded = load("test.jld2", "b")
+            @test b.x == bloaded.x
+            @test b.y == bloaded.y
+            @test b.z == bloaded.z
+        end
+    end
+
 end
\ No newline at end of file