fix: Allow C4 Dynamic multiple interactions

.changeset/salty-wombats-sin.md

@@ -0,0 +1,5 @@
+---
+'mermaid': patch
+---
+
+fix: Allow multiple interactions between the same components in C4 Dynamic diagrams

packages/mermaid/src/diagrams/c4/c4Db.js

@@ -54,12 +54,7 @@ export const addRel = function (type, from, to, label, techn, descr, sprite, tag
   }
 
   let rel = {};
-  const old = rels.find((rel) => rel.from === from && rel.to === to);
-  if (old) {
-    rel = old;
-  } else {
-    rels.push(rel);
-  }
+  rels.push(rel);
 
   rel.type = type;
   rel.from = from;

packages/mermaid/src/diagrams/c4/parser/c4Dynamic.spec.js

@@ -0,0 +1,30 @@
+import c4Db from '../c4Db.js';
+import c4 from './c4Diagram.jison';
+import { setConfig } from '../../../config.js';
+
+setConfig({
+  securityLevel: 'strict',
+});
+
+describe('parsing a C4 dynamic diagram', function () {
+  beforeEach(function () {
+    c4.parser.yy = c4Db;
+    c4.parser.yy.clear();
+  });
+
+  it('should allow multiple interactions between components', function () {
+    c4.parser.parse(`C4Dynamic
+System(a, "A")
+System(b, "B")
+Rel(a, b, "Interaction 1")
+Rel(a, b, "Interaction 2")`);
+
+    const yy = c4.parser.yy;
+
+    expect(yy.getC4Type()).toBe('C4Dynamic');
+    const rels = yy.getRels();
+    expect(rels.length).toBe(2);
+    expect(rels[0].label.text).toBe('Interaction 1');
+    expect(rels[1].label.text).toBe('Interaction 2');
+  });
+});