# TypeScript/React Slop Detection
# Detects common React anti-patterns that cause bugs or unnecessary re-renders.
id: ts-react-antipatterns
name: React Anti-Pattern
severity: warning
category: correctness
defect_class: logic-error
inline_tier: warning
language: typescript

message: "React anti-pattern: setState inside a loop causes multiple re-renders — batch with a single state update"

description: |
  Calling a state setter inside a loop triggers a re-render on every iteration.
  Batch the updates into a single setState call outside the loop.

  ✅ FIX: compute the new state value in the loop, then call setState once after.

query: |
  [
    (for_statement
      (statement_block) @BODY
      (#match? @BODY "set[A-Z]")
      (#not-match? @BODY "set(Timeout|Interval|Immediate)"))
    (for_in_statement
      (statement_block) @BODY
      (#match? @BODY "set[A-Z]")
      (#not-match? @BODY "set(Timeout|Interval|Immediate)"))
    (while_statement
      (statement_block) @BODY
      (#match? @BODY "set[A-Z]")
      (#not-match? @BODY "set(Timeout|Interval|Immediate)"))
  ]

metavars:
  - BODY

has_fix: false

tags:
  - typescript
  - react
  - correctness
  - performance
  - slop
  - ai-generated

examples:
  bad: |
    for (const item of items) {
      setCount(count + 1)
    }

  good: |
    setCount(count + items.length)