program: make it easier for jit fills

CHANGELOG.md

@@ -11,6 +11,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixes
 
+- program: enable jit maker to fill same slot as taker placed ([#835](https://github.com/drift-labs/protocol-v2/pull/835))
+
 ### Breaking
 
 ## [2.55.0] - 2023-01-18

programs/drift/src/math/matching.rs

@@ -18,7 +18,7 @@ pub fn is_maker_for_taker(
     slot: u64,
 ) -> DriftResult<bool> {
     // Maker and taker order not allowed to match if both were placed in the current slot
-    if slot == maker_order.slot && slot == taker_order.slot {
+    if slot == maker_order.slot && slot == taker_order.slot && !maker_order.is_jit_maker() {
         return Ok(false);
     };
 

programs/drift/src/validation/order.rs

@@ -220,6 +220,11 @@ fn validate_post_only_order(
     valid_oracle_price: Option<i64>,
     slot: u64,
 ) -> DriftResult {
+    // jit maker can fill against amm
+    if order.is_jit_maker() {
+        return Ok(());
+    }
+
     let limit_price =
         order.force_get_limit_price(valid_oracle_price, None, slot, market.amm.order_tick_size)?;