src/tools/clippy/clippy_lints/src/ok_if_let.rs

   1 use rustc::lint::*;
   2 use rustc::hir::*;
   3 use utils::{match_type, method_chain_args, paths, snippet, span_help_and_lint};
   4
   5 /// **What it does:*** Checks for unnecessary `ok()` in if let.
   6 ///
   7 /// **Why is this bad?** Calling `ok()` in if let is unnecessary, instead match
   8 /// on `Ok(pat)`
   9 ///
  10 /// **Known problems:** None.
  11 ///
  12 /// **Example:**
  13 /// ```rust
  14 /// for result in iter {
  15 ///     if let Some(bench) = try!(result).parse().ok() {
  16 ///         vec.push(bench)
  17 ///     }
  18 /// }
  19 /// ```
  20 /// Could be written:
  21 ///
  22 /// ```rust
  23 /// for result in iter {
  24 ///     if let Ok(bench) = try!(result).parse() {
  25 ///         vec.push(bench)
  26 ///     }
  27 /// }
  28 /// ```
  29 declare_lint! {
  30     pub IF_LET_SOME_RESULT,
  31     Warn,
  32     "usage of `ok()` in `if let Some(pat)` statements is unnecessary, match on `Ok(pat)` instead"
  33 }
  34
  35 #[derive(Copy, Clone)]
  36 pub struct Pass;
  37
  38 impl LintPass for Pass {
  39     fn get_lints(&self) -> LintArray {
  40         lint_array!(IF_LET_SOME_RESULT)
  41     }
  42 }
  43
  44 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
  45     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  46         if_chain! { //begin checking variables
  47             if let ExprMatch(ref op, ref body, ref source) = expr.node; //test if expr is a match
  48             if let MatchSource::IfLetDesugar { .. } = *source; //test if it is an If Let
  49             if let ExprMethodCall(_, _, ref result_types) = op.node; //check is expr.ok() has type Result<T,E>.ok()
  50             if let PatKind::TupleStruct(QPath::Resolved(_, ref x), ref y, _)  = body[0].pats[0].node; //get operation
  51             if method_chain_args(op, &["ok"]).is_some(); //test to see if using ok() methoduse std::marker::Sized;
  52
  53             then {
  54                 let is_result_type = match_type(cx, cx.tables.expr_ty(&result_types[0]), &paths::RESULT);
  55                 let some_expr_string = snippet(cx, y[0].span, "");
  56                 if print::to_string(print::NO_ANN, |s| s.print_path(x, false)) == "Some" && is_result_type {
  57                     span_help_and_lint(cx, IF_LET_SOME_RESULT, expr.span,
  58                     "Matching on `Some` with `ok()` is redundant",
  59                     &format!("Consider matching on `Ok({})` and removing the call to `ok` instead", some_expr_string));
  60                 }
  61             }
  62         }
  63     }
  64 }