Fix diff xmit of metatables

luprex/core/cpp/world-difftab.cpp

@@ -290,7 +290,11 @@ static void patch_table(LuaStack &LS0, LuaSlot tangibles, LuaSlot ntmap, LuaSlot
     for (int i = 0; i < ndiffs; i++) {
         set_transmitted_value(LS, tangibles, ntmap, key, sb);
         set_transmitted_value(LS, tangibles, ntmap, val, sb);
-        LS.rawset(tab, key, val);
+        if (LS.isnil(key)) {
+            LS.setmetatable(tab, val);
+        } else {
+            LS.rawset(tab, key, val);
+        }
     }
     LS.result();
 }

luprex/core/lua/ut-tablecmp.lua

@@ -8,6 +8,7 @@ local tdc = table.diffcompare
 local tda = table.diffapply
 
 function unittests.diffcompare()
+    local mtab = nil
     local rtab = nil
 
     -- No differences in these simple-valued tables.
@@ -73,6 +74,15 @@ function unittests.diffcompare()
     assert(tdc(mtnmap, {a={}}, stnmap, {}) == "")
     assert(tdc(mtnmap, {a={}}, stnmap, {a=3}) == "a=nil;")
 
+    -- transmit a correction to the metatable.
+    mtab={}
+    stab={}
+    setmetatable(mtab, mtab10)
+    setmetatable(stab, stab10)
+    assert(tdc(mtnmap, mtab, stnmap, {}) == "nil=table 10;")
+    assert(tdc(mtnmap, mtab, stnmap, stab) == "")
+    assert(tdc(mtnmap, {}, stnmap, stab) == "nil=nil;")
+
     -- we're not going to test tangibles
     -- creating tangibles here is too difficult.
 end
@@ -83,6 +93,8 @@ function unittests.diffapply()
     local tnmap={}
     tnmap[tab10] = 10
     tnmap[tab11] = 11
+    local mtab=nil
+    local stab=nil
 
     -- verify some simple values.
     assert(tda(tnmap, {a=1}, {}))
@@ -114,6 +126,20 @@ function unittests.diffapply()
     assert(not tda({}, {a={}}, rtab))
     assert(rtab.a == nil)
 
+    -- transmit a correction to the metatable
+    mtab={}
+    rtab={}
+    setmetatable(mtab, tab10)
+    assert(tda(tnmap, mtab, rtab))
+    assert(getmetatable(rtab) == tab10)
+
+    -- transmit a clearing of the metatable
+    mtab={}
+    rtab={}
+    setmetatable(rtab, tab10)
+    assert(tda(tnmap, mtab, rtab))
+    assert(getmetatable(rtab) == nil)
+
     -- don't test tangibles.
 end