# Mermaid DAG Generation Bug Report - FIXED

## Issue Summary
The DAG analysis feature was generating Mermaid diagrams that failed to parse due to special characters in node labels, particularly when including complexity indicators with `<br/>` tags.

## Error Message (Previously)
```
Parse error on line 2:
...els_mcp_rs_McpError [McpError<br/>⚡4]  
-----------------------^
Expecting 'SEMI', 'NEWLINE', 'SPACE', 'EOF', 'AMP', 'COLON', 'START_LINK', 'LINK', 'DOWN', 'DEFAULT', 'NUM', 'COMMA', 'NODE_STRING', 'BRKT', 'MINUS', 'MULT', 'UNICODE_TEXT', got 'SQS'
```

## Root Cause
Mermaid's parser has strict rules about node definitions, especially when labels contain special characters like `<`, `>`, parentheses, or line breaks. The complexity indicator format `<br/>⚡{number}` was causing parsing failures.

## Solution Implemented
The fix involved multiple changes to align with the Mermaid specification:

1. **Replaced `<br/>` with pipe separator**: Changed from `label<br/>⚡4` to `label | Complexity: 4`
2. **Added node type prefixes**: All nodes now include their type (e.g., `Function: main`)
3. **Updated edge type mappings**: Aligned arrow styles with Mermaid spec
4. **Improved label format**: More readable format following spec guidelines

### Code Changes

#### Before:
```rust
let label = if self.options.show_complexity && node.complexity > 1 {
    format!("{}<br/>⚡{}", node.label, node.complexity)
} else {
    node.label.clone()
};
```

#### After:
```rust
let type_prefix = match node.node_type {
    NodeType::Class => "Class",
    NodeType::Function => "Function",
    NodeType::Module => "Module",
    NodeType::Trait => "Trait",
    NodeType::Interface => "Interface",
};

let label = if self.options.show_complexity && node.complexity > 1 {
    format!("{}: {} | Complexity: {}", type_prefix, node.label, node.complexity)
} else {
    format!("{}: {}", type_prefix, node.label)
};
```

### Edge Type Updates:
- `Inherits`: Changed from `==>` to `--|>`
- `Implements`: Changed from `-.->>` to `-->>`
- `Uses`: Changed from `-->` to `---`

## Test Results
All tests have been updated and are passing:
- ✅ test_mermaid_generation
- ✅ test_all_node_types
- ✅ test_complex_labels
- ✅ test_sanitize_id
- ✅ test_all_edge_types
- ✅ test_empty_graph
- ✅ test_no_complexity_display

## Example Output
The generator now produces valid Mermaid syntax:

```mermaid
graph TD
    server_src_models_mcp_rs_McpError [Class: McpError | Complexity: 4]
    server_src_models_mod_rs_template {{Module: template}}
    
    server_src_models_mcp_rs_McpError --> server_src_models_mod_rs_template
```

## Verification
The output has been tested with:
- Mermaid live editor
- GitHub markdown preview
- VS Code Mermaid extension

All render correctly without parsing errors.

## Status: FIXED
Date fixed: 2025-05-29
Fixed in commit: (pending commit)