From f7d7fe42aa83974432f65d2dd4c40bd97a1724f1 Mon Sep 17 00:00:00 2001
From: darshanr0107 <darshan@mermaidchart.com>
Date: Mon, 27 Oct 2025 13:33:48 +0530
Subject: [PATCH] fix: prevent edge direction tokens L,R,T,B from breaking ID
 parsing on-behalf-of: @Mermaid-Chart <hello@mermaidchart.com>

---
 .changeset/lucky-cases-switch.md              |  5 ++
 .../architecture/architecture.langium         |  5 +-
 packages/parser/tests/architecture.test.ts    | 58 +++++++++++++++++++
 3 files changed, 65 insertions(+), 3 deletions(-)
 create mode 100644 .changeset/lucky-cases-switch.md

diff --git a/.changeset/lucky-cases-switch.md b/.changeset/lucky-cases-switch.md
new file mode 100644
index 000000000..dac42549b
--- /dev/null
+++ b/.changeset/lucky-cases-switch.md
@@ -0,0 +1,5 @@
+---
+'mermaid': patch
+---
+
+fix: Allow IDs starting with L, R, T, or B in parser
diff --git a/packages/parser/src/language/architecture/architecture.langium b/packages/parser/src/language/architecture/architecture.langium
index 2e97372bd..b7d38e50d 100644
--- a/packages/parser/src/language/architecture/architecture.langium
+++ b/packages/parser/src/language/architecture/architecture.langium
@@ -20,11 +20,11 @@ fragment Statement:
 ;
 
 fragment LeftPort:
-    ':'lhsDir=ARROW_DIRECTION
+    ':' lhsDir=ID
 ;
 
 fragment RightPort:
-    rhsDir=ARROW_DIRECTION':'
+    rhsDir=ID ':'
 ;
 
 fragment Arrow:
@@ -47,6 +47,5 @@ Edge:
     lhsId=ID lhsGroup?=ARROW_GROUP? Arrow rhsId=ID rhsGroup?=ARROW_GROUP? EOL
 ;
 
-terminal ARROW_DIRECTION: 'L' | 'R' | 'T' | 'B';
 terminal ARROW_GROUP: /\{group\}/;
 terminal ARROW_INTO: /<|>/;
diff --git a/packages/parser/tests/architecture.test.ts b/packages/parser/tests/architecture.test.ts
index 4dcce17d3..58f49dd99 100644
--- a/packages/parser/tests/architecture.test.ts
+++ b/packages/parser/tests/architecture.test.ts
@@ -19,6 +19,64 @@ describe('architecture', () => {
     });
   });
 
+  describe('should handle services', () => {
+    it('should handle service with icon', () => {
+      const context = `architecture-beta
+        service TH(disk)
+      `;
+      const result = parse(context);
+      expectNoErrorsOrAlternatives(result);
+      expect(result.value.$type).toBe(Architecture);
+      expect(result.value.services).toHaveLength(1);
+      expect(result.value.services?.[0].id).toBe('TH');
+      expect(result.value.services?.[0].icon).toBe('disk');
+    });
+
+    it('should handle service with icon starting with arrow direction letters', () => {
+      const context = `architecture-beta
+        service T(disk)
+        service TH(database)
+        service L(server)
+        service R(cloud)
+        service B(internet)
+        service TOP(disk)
+        service LEFT(disk)
+        service RIGHT(disk)
+        service BOTTOM(disk)
+      `;
+      const result = parse(context);
+      expectNoErrorsOrAlternatives(result);
+      expect(result.value.$type).toBe(Architecture);
+      expect(result.value.services).toHaveLength(9);
+    });
+
+    it('should handle service with icon and title', () => {
+      const context = `architecture-beta
+        service db(database)[Database]
+      `;
+      const result = parse(context);
+      expectNoErrorsOrAlternatives(result);
+      expect(result.value.$type).toBe(Architecture);
+      expect(result.value.services).toHaveLength(1);
+      expect(result.value.services?.[0].id).toBe('db');
+      expect(result.value.services?.[0].icon).toBe('database');
+      expect(result.value.services?.[0].title).toBe('Database');
+    });
+
+    it('should handle service in a group', () => {
+      const context = `architecture-beta
+        group api(cloud)[API]
+        service db(database)[Database] in api
+      `;
+      const result = parse(context);
+      expectNoErrorsOrAlternatives(result);
+      expect(result.value.$type).toBe(Architecture);
+      expect(result.value.services).toHaveLength(1);
+      expect(result.value.services?.[0].id).toBe('db');
+      expect(result.value.services?.[0].in).toBe('api');
+    });
+  });
+
   describe('should handle TitleAndAccessibilities', () => {
     it.each([
       `architecture-beta title sample title`,