Allow ruleset tables to be passed to legacy functions.

VM/include/llruleset_builder.h

@@ -65,6 +65,13 @@ void ruleset_builder_def_add_flags(
 // Flag boolean properties are merged into their backing integer field before emission.
 void slua_ruleset_serialize(lua_State* L, int params_idx, const RulesetBuilderDef* def);
 
+// Coerce a dict-style params table to a flat rules list in-place.
+// If the value at params_idx is a dict (table with no integer key 1), serializes it
+// using slua_ruleset_serialize and replaces the stack slot with the result.
+// If the value is already a sequential list, nil, or non-table, leaves it unchanged.
+// Returns true if coercion was performed, false otherwise.
+bool slua_ruleset_coerce(lua_State* L, int params_idx, const RulesetBuilderDef* def);
+
 // Register fn as module_name.fn_name in L's globals, with def stored as upvalue 1.
 // Creates the module table if it does not yet exist; adds to it if it does.
 // Sets the module table readonly after each call.

VM/src/llruleset_builder.cpp

@@ -296,6 +296,40 @@ void slua_ruleset_serialize(lua_State* L, int params_idx, const RulesetBuilderDe
     }
 }
 
+bool slua_ruleset_coerce(lua_State* L, int params_idx, const RulesetBuilderDef* def)
+{
+    // Convert relative index to absolute
+    if (params_idx < 0 && params_idx > LUA_REGISTRYINDEX)
+        params_idx = lua_gettop(L) + params_idx + 1;
+
+    // Not a table? Leave unchanged.
+    if (!lua_istable(L, params_idx))
+        return false;
+
+    // Check if this is a dict (no integer key 1) vs sequential list (has key 1).
+    lua_rawgeti(L, params_idx, 1);
+    bool has_first = !lua_isnil(L, -1);
+    lua_pop(L, 1);
+
+    if (has_first)
+        return false;  // Sequential list, leave unchanged
+
+    // Check if table has any keys at all.
+    lua_pushnil(L);
+    bool has_keys = (lua_next(L, params_idx) != 0);
+    if (!has_keys)
+        return false;  // Empty table, already a valid empty list
+    lua_pop(L, 2);  // Pop key and value
+
+    // Serialize dict to flat list (pushes new table on stack)
+    slua_ruleset_serialize(L, params_idx, def);
+
+    // Replace original table with serialized list
+    lua_replace(L, params_idx);
+
+    return true;
+}
+
 void slua_register_ruleset_fn(
     lua_State*               L,
     const char*              module_name,

tests/SLConformance.test.cpp

@@ -1566,4 +1566,32 @@ TEST_CASE("ruleset_builder_collection")
     });
 }
 
+TEST_CASE("slua_ruleset_coerce")
+{
+    // Simple descriptor table for testing coercion.
+    static const RulesetParamDescriptor kDescs[] = {
+        {"alpha", 'f', 1},
+        {"name",  's', 2},
+        {"count", 'i', 3},
+    };
+    static RulesetBuilderDef* s_def = []() {
+        return ruleset_builder_def_build(kDescs, std::size(kDescs));
+    }();
+
+    runConformance("ruleset_coerce.lua", nullptr, [](lua_State* L) {
+        // Test function: coerces input, returns (did_coerce, result).
+        auto coerce_test = [](lua_State* L) -> int {
+            const auto* def = (const RulesetBuilderDef*)lua_tolightuserdata(L, lua_upvalueindex(1));
+            lua_settop(L, 1);  // Ensure exactly one argument
+            bool did_coerce = slua_ruleset_coerce(L, 1, def);
+            lua_pushboolean(L, did_coerce);
+            lua_insert(L, 1);  // [did_coerce, coerced_or_original]
+            return 2;
+        };
+        lua_pushlightuserdata(L, (void*)s_def);
+        lua_pushcclosure(L, coerce_test, nullptr, 1);
+        lua_setglobal(L, "test_coerce");
+    });
+}
+
 TEST_SUITE_END();

tests/conformance/ruleset_coerce.lua

@@ -0,0 +1,57 @@
+-- Conformance tests for slua_ruleset_coerce().
+--
+-- The C++ harness registers test_coerce(value) which calls slua_ruleset_coerce
+-- on the input and returns (did_coerce, result).
+-- Descriptor table: alpha='f'/1, name='s'/2, count='i'/3
+
+-- ─── Dict tables should be coerced ───────────────────────────────────────────
+
+-- Basic dict with multiple fields
+local did, result = test_coerce({alpha = 0.5, name = "test", count = 42})
+assert(did == true, "dict should be coerced")
+assert(type(result) == "table", "result should be a table")
+-- Verify serialized output: tags in order 1, 2, 3
+assert(result[1] == 1, "first tag should be alpha (1)")
+assert(result[2] == 0.5, "alpha value")
+assert(result[3] == 2, "second tag should be name (2)")
+assert(result[4] == "test", "name value")
+assert(result[5] == 3, "third tag should be count (3)")
+assert(result[6] == 42, "count value")
+
+-- Single field dict
+local did2, result2 = test_coerce({name = "solo"})
+assert(did2 == true, "single-field dict should be coerced")
+assert(result2[1] == 2 and result2[2] == "solo", "single field serialized correctly")
+
+-- ─── Sequential lists should pass through unchanged ──────────────────────────
+
+-- Flat rules list (has integer key 1)
+local did3, result3 = test_coerce({1, 0.5, 2, "test"})
+assert(did3 == false, "sequential list should not be coerced")
+assert(result3[1] == 1, "list unchanged")
+assert(result3[2] == 0.5, "list unchanged")
+assert(result3[3] == 2, "list unchanged")
+assert(result3[4] == "test", "list unchanged")
+
+-- ─── Empty table should pass through unchanged ───────────────────────────────
+
+local did4, result4 = test_coerce({})
+assert(did4 == false, "empty table should not be coerced")
+assert(type(result4) == "table", "empty table passed through")
+assert(next(result4) == nil, "table is still empty")
+
+-- ─── Non-table values should pass through unchanged ──────────────────────────
+
+local did5, result5 = test_coerce(nil)
+assert(did5 == false, "nil should not be coerced")
+assert(result5 == nil, "nil passed through")
+
+local did6, result6 = test_coerce(123)
+assert(did6 == false, "number should not be coerced")
+assert(result6 == 123, "number passed through")
+
+local did7, result7 = test_coerce("hello")
+assert(did7 == false, "string should not be coerced")
+assert(result7 == "hello", "string passed through")
+
+return "OK"