fix Math.atan2 emitting math.atan2 instead of math.atan for Lua 5.4+

RealColdFry · RealColdFry · commit 9935e8d6e308 · 2026-03-29T20:23:26.000+01:00
math.atan2 was removed in Lua 5.3 (replaced by two-arg math.atan).
The codegen only special-cased 5.3 but not 5.4 or 5.5, which also
lack math.atan2 (5.4 has it behind a compat flag, 5.5 drops it).
diff --git a/src/transformation/builtins/math.ts b/src/transformation/builtins/math.ts
@@ -42,14 +42,18 @@ export function transformMathCall(
 
     const expressionName = calledMethod.name.text;
     switch (expressionName) {
-        // Lua 5.3: math.atan(y, x)
+        // Lua 5.3+: math.atan(y, x)
         // Otherwise: math.atan2(y, x)
         case "atan2": {
             if (context.luaTarget === LuaTarget.Universal) {
                 return transformLuaLibFunction(context, LuaLibFeature.MathAtan2, node, ...params);
             }
 
-            const method = lua.createStringLiteral(context.luaTarget === LuaTarget.Lua53 ? "atan" : "atan2");
+            const useAtan =
+                context.luaTarget === LuaTarget.Lua53 ||
+                context.luaTarget === LuaTarget.Lua54 ||
+                context.luaTarget === LuaTarget.Lua55;
+            const method = lua.createStringLiteral(useAtan ? "atan" : "atan2");
             return lua.createCallExpression(lua.createTableIndexExpression(math, method), params, node);
         }
 
diff --git a/test/unit/builtins/math.spec.ts b/test/unit/builtins/math.spec.ts
@@ -95,8 +95,8 @@ util.testEachVersion("Math.atan2", () => util.testExpression`Math.atan2(4, 5)`,
     [tstl.LuaTarget.Lua51]: builder => builder.tap(expectMathAtan2),
     [tstl.LuaTarget.Lua52]: builder => builder.tap(expectMathAtan2),
     [tstl.LuaTarget.Lua53]: builder => builder.tap(expectMathAtan),
-    [tstl.LuaTarget.Lua54]: builder => builder.tap(expectMathAtan2),
-    [tstl.LuaTarget.Lua55]: builder => builder.tap(expectMathAtan2),
+    [tstl.LuaTarget.Lua54]: builder => builder.tap(expectMathAtan),
+    [tstl.LuaTarget.Lua55]: builder => builder.tap(expectMathAtan),
     [tstl.LuaTarget.Luau]: builder => builder.tap(expectMathAtan2),
 });
 
