fix: Sequence diagram loop rendering

packages/mermaid/src/diagrams/sequence/sequenceRenderer.ts

@@ -1421,6 +1421,13 @@ const buildMessageModel = function (msg, actors, diagObj) {
     return isArrowToRight ? -value : value;
   };
 
+  // 3 is max difference for +/- 1
+  if (Math.abs(startx - stopx) <= 3) {
+    // This is a self reference, so we need to make sure the arrow is drawn correctly
+    // There are many checks in the downstream rendering that checks for equality.
+    // The lines on loops will be off by few pixels, but that's fine for now.
+    stopx = startx;
+  } else {
     /**
      * This is an edge case for the first activation.
      * Proper fix would require significant changes.
@@ -1439,6 +1446,7 @@ const buildMessageModel = function (msg, actors, diagObj) {
     if (![diagObj.db.LINETYPE.SOLID_OPEN, diagObj.db.LINETYPE.DOTTED_OPEN].includes(msg.type)) {
       stopx += adjustValue(3);
     }
+  }
 
   const allBounds = [fromLeft, fromRight, toLeft, toRight];
   const boundedWidth = Math.abs(startx - stopx);