fix(state): allow colons in transition and state description text

The DESCR lexer rule in stateDiagram.jison excluded colons from the
character class, causing parse errors when transition labels contained
colons (e.g. "recoverable error (ex: timeout)"). Changed the regex to
use an alternation that permits colons followed by non-colon characters,
while still preventing the `:::` style separator from being consumed.

Resolves #7418

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: knsv

.changeset/fix-colon-in-state-transition.md

@@ -0,0 +1,5 @@
+---
+'mermaid': patch
+---
+
+fix: allow colons in stateDiagram-v2 transition and state description text

packages/mermaid/src/diagrams/state/parser/state-parser.spec.js

@@ -126,6 +126,40 @@ describe('state parser can parse...', () => {
     });
   });
 
+  describe('colons in transition descriptions (issue #7418)', () => {
+    it('should allow a colon inside transition text', () => {
+      const diagramText = `stateDiagram-v2
+        locked --> pending : recoverable error (ex: timeout)`;
+      stateDiagram.parser.parse(diagramText);
+
+      const relationships = stateDiagram.parser.yy.getRelations();
+      expect(relationships).toHaveLength(1);
+      expect(relationships[0].id1).toEqual('locked');
+      expect(relationships[0].id2).toEqual('pending');
+      expect(relationships[0].relationTitle).toEqual('recoverable error (ex: timeout)');
+    });
+
+    it('should allow multiple colons inside transition text', () => {
+      const diagramText = `stateDiagram-v2
+        A --> B : info: key: value`;
+      stateDiagram.parser.parse(diagramText);
+
+      const relationships = stateDiagram.parser.yy.getRelations();
+      expect(relationships).toHaveLength(1);
+      expect(relationships[0].relationTitle).toEqual('info: key: value');
+    });
+
+    it('should allow a colon inside state description text', () => {
+      const diagramText = `stateDiagram-v2
+        myState : status: active`;
+      stateDiagram.parser.parse(diagramText);
+
+      const states = stateDiagram.parser.yy.getStates();
+      expect(states.get('myState')).not.toBeUndefined();
+      expect(states.get('myState').descriptions.join(' ')).toEqual('status: active');
+    });
+  });
+
   describe('unsafe properties as state names', () => {
     it.each(['__proto__', 'constructor'])('should allow %s as a state name', function (prop) {
       stateDiagram.parser.parse(`

packages/mermaid/src/diagrams/state/parser/stateDiagram.jison

@@ -140,7 +140,7 @@ accDescr\s*"{"\s*                                { this.begin("acc_descr_multili
 <INITIAL,struct>"[*]"                   { /* console.log('EDGE_STATE=',yytext); */ return 'EDGE_STATE'; }
 <INITIAL,struct>[^:\n\s\-\{]+           { /* console.log('=>ID=',yytext); */ return 'ID'; }
 // <INITIAL,struct>\s*":"[^\+\->:\n;]+  { yytext = yytext.trim(); /* console.log('Descr = ', yytext); */ return 'DESCR'; }
-<INITIAL,struct>\s*":"[^:\n;]+          { yytext = yytext.trim(); /* console.log('Descr = ', yytext); */ return 'DESCR'; }
+<INITIAL,struct>\s*":"(?:[^:\n;]|":"[^:\n;])+  { yytext = yytext.trim(); /* console.log('Descr = ', yytext); */ return 'DESCR'; }
 
 <INITIAL,struct>"-->"             return '-->';
 <struct>"--"                      return 'CONCURRENT';