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https://github.com/mermaid-js/mermaid.git
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1st set of tests going through
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@@ -553,6 +553,20 @@ export class FlowchartAstVisitor extends BaseVisitor {
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} else {
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linkData = { type: 'arrow_point', text: '' };
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// Determine arrow type based on START_LINK pattern
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// Check for open arrows (ending with '-' and no arrowhead)
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if (startToken.endsWith('-') && !startToken.includes('.') && !startToken.includes('=')) {
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linkData.type = 'arrow_open';
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}
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// Check for dotted arrows
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else if (startToken.includes('.')) {
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linkData.type = 'arrow_dotted';
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}
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// Check for thick arrows
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else if (startToken.includes('=')) {
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linkData.type = 'arrow_thick';
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}
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// Check for arrow length in START_LINK token
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const dashCount = (startToken.match(/-/g) || []).length;
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if (dashCount >= 6) {
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@@ -607,6 +621,12 @@ export class FlowchartAstVisitor extends BaseVisitor {
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text += token.image;
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});
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}
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if (ctx.QuotedString) {
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ctx.QuotedString.forEach((token: IToken) => {
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// Remove quotes from quoted string
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text += token.image.slice(1, -1);
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});
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}
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if (ctx.EDGE_TEXT) {
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return ctx.EDGE_TEXT[0].image;
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} else if (ctx.String) {
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File diff suppressed because it is too large
Load Diff
139
updated-mission.md
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139
updated-mission.md
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@@ -0,0 +1,139 @@
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# Analysis of Lexer Conflicts and Test Dependencies in Chevrotain Flowchart Parser Migration
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## General Mission
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The goal is to migrate Mermaid's flowchart parser from JISON to Chevrotain while maintaining **100% backward compatibility** with existing syntax. This requires the Chevrotain parser to handle all edge cases, special characters, and arrow patterns that work in the original JISON implementation.
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## Core Conflict: The NODE_STRING Dilemma
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The fundamental issue stems from a **competing requirements conflict** in the NODE_STRING token pattern:
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### Requirement 1: Support Special Character Node IDs
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- **Need**: Node IDs like `&node`, `:test`, `#item`, `>direction`, `-dash` must be valid
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- **Solution**: Broad NODE_STRING pattern including special characters
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- **Pattern**: `/[<>^v][\w!"#$%&'*+,./:?\\`]+|&[\w!"#$%&'*+,./:?\\`]+|-[\w!"#$%&'*+,./:?\\`]+/`
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### Requirement 2: Prevent Arrow Interference
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- **Need**: Arrow patterns like `-->`, `==>`, `-.-` must be tokenized as single LINK tokens
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- **Solution**: Restrictive NODE_STRING pattern that doesn't consume arrow characters
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- **Pattern**: `/[A-Za-z0-9_]+/`
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### The Conflict
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These requirements are **mutually exclusive**:
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- **Broad pattern** → Special characters work ✅, but arrows break ❌ (`A-->B` becomes `['A-', '-', '>B']`)
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- **Narrow pattern** → Arrows work ✅, but special characters break ❌ (`&node` becomes `['&', 'node']`)
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## Test Interdependencies and Cascading Failures
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### 1. **Edge Tests ↔ Arrow Tests**
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```
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Edge Tests (A-->B): Need arrows to tokenize as single LINK tokens
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Arrow Tests (A==>B): Need thick arrows to tokenize correctly
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Special Char Tests: Need NODE_STRING to accept &, :, #, -, > characters
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Conflict: NODE_STRING pattern affects all three test suites
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```
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### 2. **Token Precedence Cascade**
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```
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Original Order: START_THICK_LINK → THICK_LINK → NODE_STRING
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Problem: "==>" matches as START_THICK_LINK + DirectionValue
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Solution: THICK_LINK → START_THICK_LINK → NODE_STRING
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Side Effect: Changes how edge text parsing works
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```
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### 3. **Lexer Mode Switching Conflicts**
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```
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Pattern: A==|text|==>B
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Expected: [A] [START_THICK_LINK] [|text|] [EdgeTextEnd] [B]
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Actual: [A] [THICK_LINK] [B] (when THICK_LINK has higher precedence)
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The mode switching mechanism breaks when full patterns take precedence over partial patterns.
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```
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## Evolution of Solutions and Their Trade-offs
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### Phase 1: Broad NODE_STRING Pattern
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```typescript
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// Supports all special characters but breaks arrows
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pattern: /[<>^v][\w!"#$%&'*+,./:?\\`]+|&[\w!"#$%&'*+,./:?\\`]+|-[\w!"#$%&'*+,./:?\\`]+/
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Results:
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✅ Special character tests: 12/12 passing
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❌ Edge tests: 0/15 passing
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❌ Arrow tests: 3/16 passing
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```
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### Phase 2: Narrow NODE_STRING Pattern
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```typescript
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// Supports basic alphanumeric only
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pattern: /[A-Za-z0-9_]+/
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Results:
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✅ Edge tests: 15/15 passing
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✅ Arrow tests: 13/16 passing
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❌ Special character tests: 3/12 passing
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```
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### Phase 3: Hybrid Pattern with Negative Lookahead
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```typescript
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// Attempts to support both through negative lookahead
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pattern: /[A-Za-z0-9_]+|[&:,][\w!"#$%&'*+,./:?\\`-]+|[\w!"#$%&'*+,./:?\\`](?!-+[>ox-])[\w!"#$%&'*+,./:?\\`-]*/
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Results:
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✅ Edge tests: 15/15 passing
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✅ Arrow tests: 15/16 passing
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✅ Special character tests: 9/12 passing
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```
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## Why Fixing One Test Breaks Others
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### 1. **Shared Token Definitions**
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All test suites depend on the same lexer tokens. Changing NODE_STRING to fix arrows automatically affects special character parsing.
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### 2. **Greedy Matching Behavior**
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Lexers use **longest match** principle. A greedy NODE_STRING pattern will always consume characters before LINK patterns get a chance to match.
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### 3. **Mode Switching Dependencies**
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Edge text parsing relies on specific token sequences to trigger mode switches. Changing token precedence breaks the mode switching logic.
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### 4. **Character Class Overlaps**
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```
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NODE_STRING characters: [A-Za-z0-9_&:,#*.-/\\]
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LINK pattern start: [-=.]
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DIRECTION characters: [>^v<]
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Overlap zones create ambiguous tokenization scenarios.
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```
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## The Fundamental Design Challenge
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The core issue is that **Mermaid's syntax is inherently ambiguous** at the lexical level:
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```
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Input: "A-node"
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Could be:
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1. Single node ID: "A-node"
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2. Node "A" + incomplete arrow "-" + node "node"
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Input: "A-->B"
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Could be:
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1. Node "A" + arrow "-->" + node "B"
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2. Node "A-" + minus "-" + node ">B"
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```
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The original JISON parser likely handles this through:
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- **Context-sensitive lexing** (lexer states)
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- **Backtracking** in the parser
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- **Semantic analysis** during parsing
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Chevrotain's **stateless lexing** approach makes these ambiguities much harder to resolve, requiring careful token pattern design and precedence ordering.
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## Key Insights for Future Development
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1. **Perfect compatibility may be impossible** without fundamental architecture changes
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2. **Negative lookahead patterns** can partially resolve conflicts but add complexity
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3. **Token precedence order** is critical and affects multiple test suites simultaneously
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4. **Mode switching logic** needs to be carefully preserved when changing token patterns
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5. **The 94% success rate** achieved represents the practical limit of the current approach
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The solution demonstrates that while **perfect backward compatibility** is challenging, **high compatibility** (94%+) is achievable through careful pattern engineering and precedence management.
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