clippy_lints/src/if_let_some_result.rs

   1 use crate::utils::{match_type, method_chain_args, paths, snippet_with_applicability, span_lint_and_sugg};
   2 use if_chain::if_chain;
   3 use rustc_errors::Applicability;
   4 use rustc_hir::*;
   5 use rustc_lint::{LateContext, LateLintPass};
   6 use rustc_session::{declare_lint_pass, declare_tool_lint};
   7
   8 declare_clippy_lint! {
   9     /// **What it does:*** Checks for unnecessary `ok()` in if let.
  10     ///
  11     /// **Why is this bad?** Calling `ok()` in if let is unnecessary, instead match
  12     /// on `Ok(pat)`
  13     ///
  14     /// **Known problems:** None.
  15     ///
  16     /// **Example:**
  17     /// ```ignore
  18     /// for i in iter {
  19     ///     if let Some(value) = i.parse().ok() {
  20     ///         vec.push(value)
  21     ///     }
  22     /// }
  23     /// ```
  24     /// Could be written:
  25     ///
  26     /// ```ignore
  27     /// for i in iter {
  28     ///     if let Ok(value) = i.parse() {
  29     ///         vec.push(value)
  30     ///     }
  31     /// }
  32     /// ```
  33     pub IF_LET_SOME_RESULT,
  34     style,
  35     "usage of `ok()` in `if let Some(pat)` statements is unnecessary, match on `Ok(pat)` instead"
  36 }
  37
  38 declare_lint_pass!(OkIfLet => [IF_LET_SOME_RESULT]);
  39
  40 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for OkIfLet {
  41     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
  42         if_chain! { //begin checking variables
  43             if let ExprKind::Match(ref op, ref body, source) = expr.kind; //test if expr is a match
  44             if let MatchSource::IfLetDesugar { .. } = source; //test if it is an If Let
  45             if let ExprKind::MethodCall(_, ok_span, ref result_types) = op.kind; //check is expr.ok() has type Result<T,E>.ok()
  46             if let PatKind::TupleStruct(QPath::Resolved(_, ref x), ref y, _)  = body[0].pat.kind; //get operation
  47             if method_chain_args(op, &["ok"]).is_some(); //test to see if using ok() methoduse std::marker::Sized;
  48             let is_result_type = match_type(cx, cx.tables.expr_ty(&result_types[0]), &paths::RESULT);
  49             if print::to_string(print::NO_ANN, |s| s.print_path(x, false)) == "Some" && is_result_type;
  50
  51             then {
  52                 let mut applicability = Applicability::MachineApplicable;
  53                 let some_expr_string = snippet_with_applicability(cx, y[0].span, "", &mut applicability);
  54                 let trimmed_ok = snippet_with_applicability(cx, op.span.until(ok_span), "", &mut applicability);
  55                 let sugg = format!(
  56                     "if let Ok({}) = {}",
  57                     some_expr_string,
  58                     trimmed_ok.trim().trim_end_matches('.'),
  59                 );
  60                 span_lint_and_sugg(
  61                     cx,
  62                     IF_LET_SOME_RESULT,
  63                     expr.span.with_hi(op.span.hi()),
  64                     "Matching on `Some` with `ok()` is redundant",
  65                     &format!("Consider matching on `Ok({})` and removing the call to `ok` instead", some_expr_string),
  66                     sugg,
  67                     applicability,
  68                 );
  69             }
  70         }
  71     }
  72 }