# Duplicate Function Argument
# Detects duplicate parameter names
id: duplicate-function-arg
name: Function Argument Names Should Be Unique
severity: error
category: reliability
defect_class: correctness
inline_tier: blocking
language: typescript

message: "Duplicate parameter name '{{NAME}}'"

description: |
  Duplicate parameter names cause the last one to shadow earlier
  ones, leading to confusing behavior. Use unique names.

  ✅ FIX: Use unique parameter names

  ```typescript
  function add(a: number, b: number) { }  // GOOD
  ```

query: |
  (function_declaration
    parameters: (formal_parameters
      (identifier) @PARAM1
      (identifier) @PARAM2))
  (arrow_function
    parameters: (formal_parameters
      (identifier) @PARAM1
      (identifier) @PARAM2))

metavars:
  - PARAM1
  - PARAM2

post_filter: same_param_name

tags:
  - reliability
  - typescript
  - bugs

examples:
  bad: |
    function add(a, a) { }  // BAD - duplicate

  good: |
    function add(a, b) { }  // GOOD - unique

has_fix: false