Merge pull request #6886 from mermaid-js/6721/Bidirectional-arrows--render-incorrectly-with-autonumber-in-sequence-diagrams

6721: Correct rendering of bidirectional arrows with auto number

.changeset/crazy-loops-matter.md

@@ -0,0 +1,5 @@
+---
+'mermaid': patch
+---
+
+fix: Handle arrows correctly when auto number is enabled

cypress/integration/rendering/sequencediagram.spec.js

@@ -893,6 +893,17 @@ describe('Sequence diagram', () => {
         }
       );
     });
+
+    it('should handle bidirectional arrows with autonumber', () => {
+      imgSnapshotTest(`
+       sequenceDiagram
+       autonumber
+       participant A
+       participant B
+       A<<->>B: This is a bidirectional message
+       A->B: This is a normal message`);
+    });
+
     it('should support actor links and properties when not mirrored EXPERIMENTAL: USE WITH CAUTION', () => {
       //Be aware that the syntax for "properties" is likely to be changed.
       imgSnapshotTest(

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

@@ -476,7 +476,29 @@ const drawMessage = async function (diagram, msgModel, lineStartY: number, diagO
 
   // add node number
   if (sequenceVisible || conf.showSequenceNumbers) {
-    line.attr('marker-start', 'url(' + url + '#sequencenumber)');
+    const isBidirectional =
+      type === diagObj.db.LINETYPE.BIDIRECTIONAL_SOLID ||
+      type === diagObj.db.LINETYPE.BIDIRECTIONAL_DOTTED;
+
+    if (isBidirectional) {
+      const SEQUENCE_NUMBER_RADIUS = 6;
+
+      if (startx < stopx) {
+        line.attr('x1', startx + 2 * SEQUENCE_NUMBER_RADIUS);
+      } else {
+        line.attr('x1', startx + SEQUENCE_NUMBER_RADIUS);
+      }
+    }
+
+    diagram
+      .append('line')
+      .attr('x1', startx)
+      .attr('y1', lineStartY)
+      .attr('x2', startx)
+      .attr('y2', lineStartY)
+      .attr('stroke-width', 0)
+      .attr('marker-start', 'url(' + url + '#sequencenumber)');
+
     diagram
       .append('text')
       .attr('x', startx)