fix: test case diagram code

on-behalf-of: @Mermaid-Chart <hello@mermaidchart.com>

.changeset/eager-pigs-help.md

@@ -0,0 +1,5 @@
+---
+'mermaid': patch
+---
+
+fix: Handle backslash parsing in math formulas within new flowchart shape syntax

packages/mermaid/src/diagrams/flowchart/parser/flow-node-data.spec.js

@@ -144,6 +144,18 @@ describe('when parsing directions', function () {
     expect(data4Layout.nodes[0].shape).toEqual('rounded');
     expect(data4Layout.nodes[0].label).toEqual('DD');
   });
+  it('should handle mathematical formulas with backslashes in quoted strings', function () {
+    /* eslint-disable no-useless-escape */
+    const res = flow.parser.parse(`flowchart RL
+    H@{ shape: rect, label: "$$\sin x$$"}`);
+    /* eslint-enable no-useless-escape */
+
+    const data4Layout = flow.parser.yy.getData();
+
+    expect(data4Layout.nodes.length).toBe(1);
+    expect(data4Layout.nodes[0].shape).toEqual('rect');
+    expect(data4Layout.nodes[0].label).toEqual('$$sin x$$');
+  });
   it('should be possible to link to a node with more data', function () {
     const res = flow.parser.parse(`flowchart TB
       A --> D@{

packages/mermaid/src/diagrams/flowchart/parser/flow.jison

@@ -53,6 +53,7 @@ accDescr\s*"{"\s*                               { this.begin("acc_descr_multilin
                                                     // console.log('shapeData', yytext);
                                                     const re = /\n\s*/g;
                                                     yytext = yytext.replace(re,"<br/>");
+                                                    yytext = yytext.replace(/\\/g, "\\\\");
                                                     return 'SHAPE_DATA'}
 <shapeData>[^}^"]+                                {
                                                     // console.log('shapeData', yytext);