# Loose equality in for-loop termination
# Detects ==/!= used as a for-loop's exit test, which is fragile.
id: no-equality-in-for-condition
name: Loose equality in for-loop condition
severity: warning
category: bug
defect_class: correctness
inline_tier: warning
language: typescript

message: "for-loop uses ==/!= for termination — prefer </<=/>/>= so stepping past the bound still exits"

description: |
  Using == or != as a for-loop's termination test is fragile: if the counter
  steps past the target value (e.g. i += 2, or it is mutated in the body), the
  equality never holds and the loop runs forever. Use a relational operator
  (<, <=, >, >=) so the loop still terminates when the counter overshoots.

  ❌  for (let i = 0; i != n; i += 2)   // infinite if n is odd
  ✅  for (let i = 0; i < n;  i += 2)

query: |
  (for_statement
    (expression_statement
      (binary_expression
        ["==" "!="] @OP)))

metavars:
  - OP

has_fix: false

tags:
  - bug
  - loop

examples:
  bad: |
    for (let i = 0; i != items.length; i += 2) { /* ... */ }
  good: |
    for (let i = 0; i < items.length; i += 2) { /* ... */ }