Code Anti-patterns Analysis

Expert knowledge for systematic detection and analysis of anti-patterns, code smells, and quality issues across codebases using ast-grep and parallel agent delegation.

Analysis Philosophy

This skill emphasizes parallel delegation for comprehensive analysis. Rather than sequentially scanning for issues, launch multiple specialized agents to examine different categories simultaneously, then consolidate findings.

Analysis Categories

1. JavaScript/TypeScript Anti-patterns

Callback Hell & Async Issues

# Nested callbacks (3+ levels)
ast-grep -p '$FUNC($$$, function($$$) { $FUNC2($$$, function($$$) { $$$ }) })' --lang js

# Missing error handling in async
ast-grep -p 'async function $NAME($$$) { $$$ }' --lang js
# Then check if try-catch is present

# Unhandled promise rejection
ast-grep -p '$PROMISE.then($$$)' --lang js
# Without .catch() - use composite rule

Magic Values

# Magic numbers in comparisons
ast-grep -p 'if ($VAR > 100)' --lang js
ast-grep -p 'if ($VAR < 50)' --lang js
ast-grep -p 'if ($VAR === 42)' --lang js

# Magic strings
ast-grep -p "if ($VAR === 'admin')" --lang js

Empty Catch Blocks

ast-grep -p 'try { $$$ } catch ($E) { }' --lang js

Console Statements (Debug Leftovers)

ast-grep -p 'console.log($$$)' --lang js
ast-grep -p 'console.debug($$$)' --lang js
ast-grep -p 'console.warn($$$)' --lang js

Use let/const for Variable Declarations

ast-grep -p 'var $VAR = $$$' --lang js

2. Vue 3 Anti-patterns

Props Mutation

# YAML rule for props mutation detection
id: vue-props-mutation
language: JavaScript
message: Use computed properties or emit events to update props
rule:
  pattern: props.$PROP = $VALUE

# Direct prop assignment
ast-grep -p 'props.$PROP = $VALUE' --lang js

Missing Keys in v-for

# Search in Vue templates
ast-grep -p 'v-for="$ITEM in $LIST"' --lang html
# Check if :key is present nearby

Options API in Composition API Codebase

# Find Options API usage
ast-grep -p 'export default { data() { $$$ } }' --lang js
ast-grep -p 'export default { methods: { $$$ } }' --lang js
ast-grep -p 'export default { computed: { $$$ } }' --lang js

# vs Composition API
ast-grep -p 'defineComponent({ setup($$$) { $$$ } })' --lang js

Reactive State Issues

# Destructuring reactive state (loses reactivity)
ast-grep -p 'const { $$$PROPS } = $REACTIVE' --lang js

# Should use toRefs
ast-grep -p 'const { $$$PROPS } = toRefs($REACTIVE)' --lang js

3. TypeScript Quality Issues

Excessive any Usage

ast-grep -p ': any' --lang ts
ast-grep -p 'as any' --lang ts
ast-grep -p '<any>' --lang ts

Non-null Assertions

ast-grep -p '$VAR!' --lang ts
ast-grep -p '$VAR!.$PROP' --lang ts

Type Assertions Instead of Guards

ast-grep -p '$VAR as $TYPE' --lang ts

Missing Return Types

# Functions without return type annotations
ast-grep -p 'function $NAME($$$) { $$$ }' --lang ts
# Check if return type is present

4. Async/Promise Patterns

Unhandled Promises

# Promise without await or .then/.catch
ast-grep -p '$ASYNC_FUNC($$$)' --lang js
# Context: check if result is used

# Floating promises (no await)
ast-grep -p '$PROMISE_RETURNING()' --lang ts

Nested Callbacks (Pyramid of Doom)

ast-grep -p '$F1($$$, function($$$) { $F2($$$, function($$$) { $F3($$$, function($$$) { $$$ }) }) })' --lang js

Promise Constructor Anti-pattern

# Wrapping already-async code in new Promise
ast-grep -p 'new Promise(($RESOLVE, $REJECT) => { $ASYNC_FUNC($$$).then($$$) })' --lang js

5. Code Complexity

Long Functions (Manual Review)

# Find function definitions, then count lines
ast-grep -p 'function $NAME($$$) { $$$ }' --lang js --json | jq '.[] | select(.range.end.line - .range.start.line > 50)'

Deep Nesting

# Nested if statements (4+ levels)
ast-grep -p 'if ($A) { if ($B) { if ($C) { if ($D) { $$$ } } } }' --lang js

Large Parameter Lists

ast-grep -p 'function $NAME($A, $B, $C, $D, $E, $$$)' --lang js

Cyclomatic Complexity Indicators

# Multiple conditionals in single function
ast-grep -p 'if ($$$) { $$$ } else if ($$$) { $$$ } else if ($$$) { $$$ }' --lang js

6. React/Pinia Store Patterns

Direct State Mutation (Pinia)

# Direct store state mutation outside actions
ast-grep -p '$STORE.$STATE = $VALUE' --lang js

Missing Dependencies in useEffect

ast-grep -p 'useEffect(() => { $$$ }, [])' --lang jsx
# Check if variables used inside are in dependency array

Inline Functions in JSX

ast-grep -p '<$COMPONENT onClick={() => $$$} />' --lang jsx
ast-grep -p '<$COMPONENT onChange={() => $$$} />' --lang jsx

7. Memory & Performance

Event Listeners Without Cleanup

ast-grep -p 'addEventListener($EVENT, $HANDLER)' --lang js
# Check for corresponding removeEventListener

setInterval Without Cleanup

ast-grep -p 'setInterval($$$)' --lang js
# Check for clearInterval

Large Arrays in Computed/Memos

ast-grep -p 'computed(() => $ARRAY.filter($$$))' --lang js
ast-grep -p 'useMemo(() => $ARRAY.filter($$$), [$$$])' --lang jsx

8. Security Concerns

eval Usage

ast-grep -p 'eval($$$)' --lang js
ast-grep -p 'new Function($$$)' --lang js

innerHTML Assignment (XSS Risk)

ast-grep -p '$ELEM.innerHTML = $$$' --lang js
ast-grep -p 'dangerouslySetInnerHTML={{ __html: $$$ }}' --lang jsx

Hardcoded Secrets

ast-grep -p "apiKey: '$$$'" --lang js
ast-grep -p "password = '$$$'" --lang js
ast-grep -p "secret: '$$$'" --lang js

SQL String Concatenation

ast-grep -p '"SELECT * FROM " + $VAR' --lang js
ast-grep -p '`SELECT * FROM ${$VAR}`' --lang js

9. Python Anti-patterns

Bare Except

ast-grep -p 'except: $$$' --lang py

Mutable Default Arguments

ast-grep -p 'def $FUNC($ARG=[])' --lang py
ast-grep -p 'def $FUNC($ARG={})' --lang py

Global Variable Usage

ast-grep -p 'global $VAR' --lang py

Type: ignore Without Reason

# Search in comments via grep
grep -r "# type: ignore$" --include="*.py"

Parallel Analysis Strategy

When analyzing a codebase, launch multiple agents in parallel to maximize efficiency:

Agent Delegation Pattern

1. **Language Detection Agent** (Explore)
   - Detect project languages and frameworks
   - Identify relevant file patterns

2. **JavaScript/TypeScript Agent** (code-analysis or Explore)
   - JS anti-patterns
   - TypeScript quality issues
   - Async/Promise patterns

3. **Framework-Specific Agent** (code-analysis or Explore)
   - Vue 3 anti-patterns (if Vue detected)
   - React anti-patterns (if React detected)
   - Pinia/Redux patterns (if detected)

4. **Security Agent** (security-audit)
   - Security concerns
   - Hardcoded values
   - Injection risks

5. **Complexity Agent** (code-analysis or Explore)
   - Code complexity metrics
   - Long functions
   - Deep nesting

6. **Python Agent** (if Python detected)
   - Python anti-patterns
   - Type annotation issues

Consolidation

After parallel analysis completes:

1. Aggregate findings by severity (critical, high, medium, low)
2. Group by category (security, performance, maintainability)
3. Provide actionable remediation suggestions
4. Prioritize fixes based on impact

YAML Rule Examples

Complete Anti-pattern Rule

id: no-empty-catch
language: JavaScript
severity: warning
message: Empty catch block suppresses errors silently
note: |
  Empty catch blocks hide errors and make debugging difficult.
  Either log the error, handle it specifically, or re-throw.

rule:
  pattern: try { $$$ } catch ($E) { }

fix: |
  try { $$$ } catch ($E) {
    console.error('Error:', $E);
    throw $E;
  }

files:
  - 'src/**/*.js'
  - 'src/**/*.ts'
ignores:
  - '**/*.test.js'
  - '**/node_modules/**'

Vue Props Mutation Rule

id: no-props-mutation
language: JavaScript
severity: error
message: Never mutate props directly - use emit or local copy

rule:
  all:
    - pattern: props.$PROP = $VALUE
    - inside:
        kind: function_declaration

note: |
  Props should be treated as immutable. To modify data:
  1. Emit an event to parent: emit('update:propName', newValue)
  2. Create a local ref: const local = ref(props.propName)

Integration with Commands

This skill is designed to work with the /code:antipatterns command, which:

1. Detects project language stack
2. Launches parallel specialized agents
3. Consolidates findings into prioritized report
4. Suggests automated fixes where possible

Best Practices for Analysis

1. Start with language detection - Run appropriate patterns for detected languages
2. Use parallel agents - Don't sequentially analyze; delegate to specialized agents
3. Prioritize by severity - Security issues first, then correctness, then style
4. Provide fixes - Don't just identify problems; suggest solutions
5. Consider context - Some "anti-patterns" are acceptable in specific contexts
6. Check test files separately - Different standards may apply to test code

Severity Levels

Severity	Description	Examples
Critical	Security vulnerabilities, data loss risk	eval(), SQL injection, hardcoded secrets
High	Bugs, incorrect behavior	Props mutation, unhandled promises, empty catch
Medium	Maintainability issues	Magic numbers, deep nesting, large functions
Low	Style/preference	var usage, console.log, inline functions

Resources

• ast-grep Documentation: https://ast-grep.github.io/
• ast-grep Playground: https://ast-grep.github.io/playground.html
• OWASP Top 10: https://owasp.org/www-project-top-ten/
• Clean Code Principles: https://clean-code-developer.com/