switch tie-breaker to site_id

This is to allow us to preserve transactionality of mutations.

In conjunction with #386, this'll allow fields to be all set together or all reverted together.

Useful for cases where `x` & `y` coordinates are supposed to be updated together or not at all or some such thing.

core/rs/core/src/changes_vtab_write.rs

@@ -28,12 +28,13 @@ use crate::util::slab_rowid;
  */
 fn did_cid_win(
     db: *mut sqlite3,
+    ext_data: *mut crsql_ExtData,
     insert_tbl: &str,
     tbl_info: &TableInfo,
     unpacked_pks: &Vec<ColumnValue>,
     key: sqlite::int64,
+    insert_site_id: &[u8],
     col_name: &str,
-    insert_val: *mut sqlite::value,
     col_version: sqlite::int64,
     errmsg: *mut *mut c_char,
 ) -> Result<bool, ResultCode> {
@@ -76,38 +77,12 @@ fn did_cid_win(
     }
 
     // versions are equal
-    // need to pull the current value and compare
-    // we could compare on site_id if we can guarantee site_id is always provided.
-    // would be slightly more performant..
-    let col_val_stmt_ref = tbl_info.get_col_value_stmt(db, col_name)?;
-    let col_val_stmt = col_val_stmt_ref.as_ref().ok_or(ResultCode::ERROR)?;
-
-    let bind_result = bind_package_to_stmt(col_val_stmt.stmt, &unpacked_pks, 0);
-    if let Err(rc) = bind_result {
-        reset_cached_stmt(col_val_stmt.stmt)?;
-        return Err(rc);
-    }
-
-    let step_result = col_val_stmt.step();
-    match step_result {
-        Ok(ResultCode::ROW) => {
-            let local_value = col_val_stmt.column_value(0)?;
-            let ret = crsql_compare_sqlite_values(insert_val, local_value);
-            reset_cached_stmt(col_val_stmt.stmt)?;
-            return Ok(ret > 0);
-        }
-        _ => {
-            // ResultCode::DONE would happen if clock values exist but actual values are missing.
-            // should we just allow the insert anyway?
-            reset_cached_stmt(col_val_stmt.stmt)?;
-            let err = CString::new(format!(
-                "could not find row to merge with for tbl {}",
-                insert_tbl
-            ))?;
-            unsafe { *errmsg = err.into_raw() };
-            return Err(ResultCode::ERROR);
-        }
-    }
+    // need to compare site ids
+    let ret = unsafe {
+        let my_site_id = core::slice::from_raw_parts((*ext_data).siteId, 16);
+        insert_site_id.cmp(my_site_id) as c_int
+    };
+    return Ok(ret > 0);
 }
 
 fn set_winner_clock(
@@ -585,12 +560,13 @@ unsafe fn merge_insert(
         || !row_exists_locally
         || did_cid_win(
             db,
+            (*tab).pExtData,
             insert_tbl,
             &tbl_info,
             &unpacked_pks,
             key,
+            insert_site_id,
             insert_col,
-            insert_val,
             insert_col_vrsn,
             errmsg,
         )?;