From 6bd08196351eef39c6728ea1e9b67b14be56306d Mon Sep 17 00:00:00 2001
From: lethosor <lethosor@gmail.com>
Date: Fri, 11 Aug 2023 02:31:54 -0400
Subject: [PATCH 1/2] Fix crash in df.global:_field() when global address is
 unknown

and add a test
---
 library/LuaTypes.cpp        |  3 +++
 test/structures/globals.lua | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+)
 create mode 100644 test/structures/globals.lua

diff --git a/library/LuaTypes.cpp b/library/LuaTypes.cpp
index ef69958e0..ddc166abc 100644
--- a/library/LuaTypes.cpp
+++ b/library/LuaTypes.cpp
@@ -664,6 +664,9 @@ static int meta_global_field_reference(lua_State *state)
     auto field = (struct_field_info*)find_field(state, 2, "reference");
     if (!field)
         field_error(state, 2, "builtin property or method", "reference");
+    void *ptr = *(void**)field->offset;
+    if (!ptr)
+        field_error(state, 2, "global address not known", "reference");
     field_reference(state, field, *(void**)field->offset);
     return 1;
 }
diff --git a/test/structures/globals.lua b/test/structures/globals.lua
new file mode 100644
index 000000000..6b278af96
--- /dev/null
+++ b/test/structures/globals.lua
@@ -0,0 +1,33 @@
+config.mode = 'title'
+config.target = 'core'
+
+local function with_temp_global_address(name, addr, callback, ...)
+    dfhack.call_with_finalizer(2, true,
+        dfhack.internal.setAddress, name, dfhack.internal.getAddress(name),
+        function(...)
+            dfhack.internal.setAddress(name, addr)
+            callback(...)
+        end, ...)
+end
+
+function test.unknown_global_address()
+    expect.ne(dfhack.internal.getAddress('army_next_id'), 0)
+    local old_id = df.global.army_next_id
+
+    with_temp_global_address('army_next_id', 0, function()
+        expect.error_match('Cannot read field global.army_next_id: global address not known.', function()
+            local _ = df.global.army_next_id
+        end)
+
+        expect.error_match('Cannot write field global.army_next_id: global address not known.', function()
+            df.global.army_next_id = old_id
+        end)
+
+        expect.error_match('Cannot reference field global.army_next_id: global address not known.', function()
+            local _ = df.global:_field('army_next_id')
+        end)
+    end)
+
+    expect.gt(dfhack.internal.getAddress('army_next_id'), 0)
+    expect.eq(df.global.army_next_id, old_id)
+end

From 9aee332fbda8f17866bda63b2c5f88711451117a Mon Sep 17 00:00:00 2001
From: lethosor <lethosor@gmail.com>
Date: Fri, 11 Aug 2023 12:52:28 -0400
Subject: [PATCH 2/2] Widen and clarify structures test mode restrictions

---
 test/structures/find.lua    | 2 +-
 test/structures/globals.lua | 1 -
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/test/structures/find.lua b/test/structures/find.lua
index e93b2cc7f..590df8971 100644
--- a/test/structures/find.lua
+++ b/test/structures/find.lua
@@ -1,4 +1,4 @@
-config.mode = 'title'
+config.mode = 'title' -- not safe to run when a world is loaded
 config.target = 'core'
 
 local function clean_vec(vec)
diff --git a/test/structures/globals.lua b/test/structures/globals.lua
index 6b278af96..81d77f8c7 100644
--- a/test/structures/globals.lua
+++ b/test/structures/globals.lua
@@ -1,4 +1,3 @@
-config.mode = 'title'
 config.target = 'core'
 
 local function with_temp_global_address(name, addr, callback, ...)