From 6d0650918f6825d0ff09f15940dd300cc5198c7c Mon Sep 17 00:00:00 2001
From: darshanr0107 <darshan@mermaidchart.com>
Date: Wed, 8 Oct 2025 13:09:30 +0530
Subject: [PATCH] fix: handle participant names with spaces correctly in
 sequenceDiagram

on-behalf-of: @Mermaid-Chart <hello@mermaidchart.com>
---
 .../diagrams/sequence/parser/sequenceDiagram.jison   |  8 +++++---
 .../src/diagrams/sequence/sequenceDiagram.spec.js    | 12 ++++++++++++
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/packages/mermaid/src/diagrams/sequence/parser/sequenceDiagram.jison b/packages/mermaid/src/diagrams/sequence/parser/sequenceDiagram.jison
index f1364895b..e932f604f 100644
--- a/packages/mermaid/src/diagrams/sequence/parser/sequenceDiagram.jison
+++ b/packages/mermaid/src/diagrams/sequence/parser/sequenceDiagram.jison
@@ -32,13 +32,14 @@
 <CONFIG>[^\}]+                                                  { return 'CONFIG_CONTENT'; }
 <CONFIG>\}                                                      { this.popState(); this.popState(); return 'CONFIG_END'; }
 <ID>[^\<->\->:\n,;@\s]+(?=\@\{)                                 { yytext = yytext.trim(); return 'ACTOR'; }
-<ID>[^\<->\->:\n,;@]+?([\-]*[^\<->\->:\n,;@]+?)*?(?=((?!\n)\s)+"as"(?!\n)\s|[#\n;]|$) { yytext = yytext.trim(); this.begin('ALIAS'); return 'ACTOR'; }
+<ID>[^<>:\n,;@]+(?=\s+as\s) { yytext = yytext.trim(); this.begin('ALIAS'); return 'ACTOR'; }
+<ID>[^<>:\n,;@]+(?=\s*[\n;#]|$) { yytext = yytext.trim(); this.popState(); return 'ACTOR'; }
+<ID>[^<>:\n,;@]*\<[^\n]* { this.popState(); return 'INVALID'; }
 "box"															{ this.begin('LINE'); return 'box'; }
 "participant"                                                   { this.begin('ID'); return 'participant'; }
 "actor"                                                   		{ this.begin('ID'); return 'participant_actor'; }
 "create"                                                        return 'create';
 "destroy"                                                       { this.begin('ID'); return 'destroy'; }
-<ID>[^<\->\->:\n,;]+?([\-]*[^<\->\->:\n,;]+?)*?(?=((?!\n)\s)+"as"(?!\n)\s|[#\n;]|$)     { yytext = yytext.trim(); this.begin('ALIAS'); return 'ACTOR'; }
 <ALIAS>"as"                                                     { this.popState(); this.popState(); this.begin('LINE'); return 'AS'; }
 <ALIAS>(?:)                                                     { this.popState(); this.popState(); return 'NEWLINE'; }
 "loop"                                                          { this.begin('LINE'); return 'loop'; }
@@ -145,6 +146,7 @@ line
 	: SPACE statement { $$ = $2 }
 	| statement { $$ = $1 }
 	| NEWLINE { $$=[]; }
+	| INVALID { $$=[]; }
 	;
 
 box_section
@@ -411,4 +413,4 @@ text2
   : TXT {$$ = yy.parseMessage($1.trim().substring(1)) }
   ;
 
-%%
+%%
\ No newline at end of file
diff --git a/packages/mermaid/src/diagrams/sequence/sequenceDiagram.spec.js b/packages/mermaid/src/diagrams/sequence/sequenceDiagram.spec.js
index 5f4e06dcd..cabcd7db5 100644
--- a/packages/mermaid/src/diagrams/sequence/sequenceDiagram.spec.js
+++ b/packages/mermaid/src/diagrams/sequence/sequenceDiagram.spec.js
@@ -2609,5 +2609,17 @@ Bob->>Alice:Got it!
       expect(actors.get('E').type).toBe('entity');
       expect(actors.get('E').description).toBe('E');
     });
+    it('should handle fail parsing when alias token causes conflicts in participant definition', async () => {
+      let error = false;
+      try {
+        await Diagram.fromText(`
+        sequenceDiagram
+        participant SAS MyServiceWithMoreThan20Chars <br> service decription
+       `);
+      } catch (e) {
+        error = true;
+      }
+      expect(error).toBe(true);
+    });
   });
 });