6784: Fix edge ID styling mismatch with linkStyle color

.changeset/four-eyes-wish.md

@@ -0,0 +1,5 @@
+---
+'mermaid': patch
+---
+
+fix: Ensure edge label color is applied when using classDef with edge IDs

cypress/integration/rendering/flowchart-v2.spec.js

@@ -1186,4 +1186,17 @@ end
       imgSnapshotTest(graph, { htmlLabels: false });
     });
   });
+
+  it('V2 - 17: should apply class def colour to edge label', () => {
+    imgSnapshotTest(
+      ` graph LR
+    id1(Start) link@-- "Label" -->id2(Stop)
+    style id1 fill:#f9f,stroke:#333,stroke-width:4px
+
+class id2 myClass
+classDef myClass fill:#bbf,stroke:#f66,stroke-width:2px,color:white,stroke-dasharray: 5 5
+class link myClass
+`
+    );
+  });
 });

packages/mermaid/src/rendering-util/rendering-elements/edges.js

@@ -25,7 +25,7 @@ import {
 import rough from 'roughjs';
 import createLabel from './createLabel.js';
 import { addEdgeMarkers } from './edgeMarker.ts';
-import { isLabelStyle } from './shapes/handDrawnShapeStyles.js';
+import { isLabelStyle, styles2String } from './shapes/handDrawnShapeStyles.js';
 
 const edgeLabels = new Map();
 const terminalLabels = new Map();
@@ -43,8 +43,10 @@ export const getLabelStyles = (styleArray) => {
 export const insertEdgeLabel = async (elem, edge) => {
   let useHtmlLabels = evaluate(getConfig().flowchart.htmlLabels);
 
+  const { labelStyles } = styles2String(edge);
+  edge.labelStyle = labelStyles;
   const labelElement = await createText(elem, edge.label, {
-    style: getLabelStyles(edge.labelStyle),
+    style: edge.labelStyle,
     useHtmlLabels,
     addSvgBackground: true,
     isNode: false,

packages/mermaid/src/rendering-util/rendering-elements/shapes/handDrawnShapeStyles.ts

@@ -20,7 +20,11 @@ export const compileStyles = (node: Node) => {
   // the array is the styles of node from the classes it is using
   // node.cssStyles is an array of styles directly set on the node
   // concat the arrays and remove duplicates such that the values from node.cssStyles are used if there are duplicates
-  const stylesMap = styles2Map([...(node.cssCompiledStyles || []), ...(node.cssStyles || [])]);
+  const stylesMap = styles2Map([
+    ...(node.cssCompiledStyles || []),
+    ...(node.cssStyles || []),
+    ...(node.labelStyle || []),
+  ]);
   return { stylesMap, stylesArray: [...stylesMap] };
 };