clippy_lints/src/if_let_some_result.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::method_chain_args;
   3 use clippy_utils::source::snippet_with_applicability;
   4 use clippy_utils::ty::is_type_diagnostic_item;
   5 use if_chain::if_chain;
   6 use rustc_errors::Applicability;
   7 use rustc_hir::{Expr, ExprKind, MatchSource, PatKind, QPath};
   8 use rustc_lint::{LateContext, LateLintPass};
   9 use rustc_session::{declare_lint_pass, declare_tool_lint};
  10 use rustc_span::sym;
  11
  12 declare_clippy_lint! {
  13     /// **What it does:*** Checks for unnecessary `ok()` in if let.
  14     ///
  15     /// **Why is this bad?** Calling `ok()` in if let is unnecessary, instead match
  16     /// on `Ok(pat)`
  17     ///
  18     /// **Known problems:** None.
  19     ///
  20     /// **Example:**
  21     /// ```ignore
  22     /// for i in iter {
  23     ///     if let Some(value) = i.parse().ok() {
  24     ///         vec.push(value)
  25     ///     }
  26     /// }
  27     /// ```
  28     /// Could be written:
  29     ///
  30     /// ```ignore
  31     /// for i in iter {
  32     ///     if let Ok(value) = i.parse() {
  33     ///         vec.push(value)
  34     ///     }
  35     /// }
  36     /// ```
  37     pub IF_LET_SOME_RESULT,
  38     style,
  39     "usage of `ok()` in `if let Some(pat)` statements is unnecessary, match on `Ok(pat)` instead"
  40 }
  41
  42 declare_lint_pass!(OkIfLet => [IF_LET_SOME_RESULT]);
  43
  44 impl<'tcx> LateLintPass<'tcx> for OkIfLet {
  45     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  46         if_chain! { //begin checking variables
  47             if let ExprKind::Match(op, body, MatchSource::IfLetDesugar { .. }) = expr.kind; //test if expr is if let
  48             if let ExprKind::MethodCall(_, ok_span, result_types, _) = op.kind; //check is expr.ok() has type Result<T,E>.ok(, _)
  49             if let PatKind::TupleStruct(QPath::Resolved(_, x), y, _)  = body[0].pat.kind; //get operation
  50             if method_chain_args(op, &["ok"]).is_some(); //test to see if using ok() methoduse std::marker::Sized;
  51             if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&result_types[0]), sym::result_type);
  52             if rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| s.print_path(x, false)) == "Some";
  53
  54             then {
  55                 let mut applicability = Applicability::MachineApplicable;
  56                 let some_expr_string = snippet_with_applicability(cx, y[0].span, "", &mut applicability);
  57                 let trimmed_ok = snippet_with_applicability(cx, op.span.until(ok_span), "", &mut applicability);
  58                 let sugg = format!(
  59                     "if let Ok({}) = {}",
  60                     some_expr_string,
  61                     trimmed_ok.trim().trim_end_matches('.'),
  62                 );
  63                 span_lint_and_sugg(
  64                     cx,
  65                     IF_LET_SOME_RESULT,
  66                     expr.span.with_hi(op.span.hi()),
  67                     "matching on `Some` with `ok()` is redundant",
  68                     &format!("consider matching on `Ok({})` and removing the call to `ok` instead", some_expr_string),
  69                     sugg,
  70                     applicability,
  71                 );
  72             }
  73         }
  74     }
  75 }