pi-lens/rules/tree-sitter-queries/rust/rust-expect.yml

Real-time code feedback for pi — LSP, linters, formatters, type-checking, structural analysis & booboo

id: rust-expect
name: Expect Instead of Proper Error Handling
severity: warning
category: error-handling
defect_class: correctness
inline_tier: warning
language: rust

message: "expect() panics with a message — use ? or match for recoverable error handling"

description: |
  expect() is slightly better than unwrap() (gives a message) but still panics
  on None/Err. In library or server code this crashes the process.

  ✅ FIX: use ? to propagate, or match/if let to handle the case.

  ❌ NEVER:
    let cfg = std::env::var("PORT").expect("PORT must be set");

  ✅ SAFE:
    let cfg = std::env::var("PORT").map_err(|_| AppError::MissingEnvVar("PORT"))?;

query: |
  (call_expression
    function: (field_expression
      field: (field_identifier) @METHOD)
    (#eq? @METHOD "expect"))

metavars:
  - METHOD

has_fix: false

tags:
  - rust
  - panic
  - error-handling
  - reliability

examples:
  bad: |
    let port = std::env::var("PORT").expect("PORT must be set");
    let conn = pool.get().expect("failed to get connection");

  good: |
    let port = std::env::var("PORT")?;
    let conn = pool.get().map_err(|e| AppError::Pool(e))?;