src/tools/clippy/clippy_lints/src/match_result_ok.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::higher;
   3 use clippy_utils::method_chain_args;
   4 use clippy_utils::source::snippet_with_applicability;
   5 use clippy_utils::ty::is_type_diagnostic_item;
   6 use if_chain::if_chain;
   7 use rustc_errors::Applicability;
   8 use rustc_hir::{Expr, ExprKind, PatKind, QPath};
   9 use rustc_lint::{LateContext, LateLintPass};
  10 use rustc_session::{declare_lint_pass, declare_tool_lint};
  11 use rustc_span::sym;
  12
  13 declare_clippy_lint! {
  14     /// ### What it does
  15     /// Checks for unnecessary `ok()` in `while let`.
  16     ///
  17     /// ### Why is this bad?
  18     /// Calling `ok()` in `while let` is unnecessary, instead match
  19     /// on `Ok(pat)`
  20     ///
  21     /// ### Example
  22     /// ```ignore
  23     /// while let Some(value) = iter.next().ok() {
  24     ///     vec.push(value)
  25     /// }
  26     ///
  27     /// if let Some(valie) = iter.next().ok() {
  28     ///     vec.push(value)
  29     /// }
  30     /// ```
  31     /// Use instead:
  32     /// ```ignore
  33     /// while let Ok(value) = iter.next() {
  34     ///     vec.push(value)
  35     /// }
  36     ///
  37     /// if let Ok(value) = iter.next() {
  38     ///        vec.push_value)
  39     /// }
  40     /// ```
  41     pub MATCH_RESULT_OK,
  42     style,
  43     "usage of `ok()` in `let Some(pat)` statements is unnecessary, match on `Ok(pat)` instead"
  44 }
  45
  46 declare_lint_pass!(MatchResultOk => [MATCH_RESULT_OK]);
  47
  48 impl<'tcx> LateLintPass<'tcx> for MatchResultOk {
  49     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  50         let (let_pat, let_expr, ifwhile) =
  51             if let Some(higher::IfLet { let_pat, let_expr, .. }) = higher::IfLet::hir(cx, expr) {
  52                 (let_pat, let_expr, "if")
  53             } else if let Some(higher::WhileLet { let_pat, let_expr, .. }) = higher::WhileLet::hir(expr) {
  54                 (let_pat, let_expr, "while")
  55             } else {
  56                 return;
  57             };
  58
  59         if_chain! {
  60             if let ExprKind::MethodCall(_, ok_span, [ref result_types_0, ..], _) = let_expr.kind; //check is expr.ok() has type Result<T,E>.ok(, _)
  61             if let PatKind::TupleStruct(QPath::Resolved(_, x), y, _)  = let_pat.kind; //get operation
  62             if method_chain_args(let_expr, &["ok"]).is_some(); //test to see if using ok() methoduse std::marker::Sized;
  63             if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(result_types_0), sym::Result);
  64             if rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| s.print_path(x, false)) == "Some";
  65
  66             then {
  67
  68                 let mut applicability = Applicability::MachineApplicable;
  69                 let some_expr_string = snippet_with_applicability(cx, y[0].span, "", &mut applicability);
  70                 let trimmed_ok = snippet_with_applicability(cx, let_expr.span.until(ok_span), "", &mut applicability);
  71                 let sugg = format!(
  72                     "{} let Ok({}) = {}",
  73                     ifwhile,
  74                     some_expr_string,
  75                     trimmed_ok.trim().trim_end_matches('.'),
  76                 );
  77                 span_lint_and_sugg(
  78                     cx,
  79                     MATCH_RESULT_OK,
  80                     expr.span.with_hi(let_expr.span.hi()),
  81                     "matching on `Some` with `ok()` is redundant",
  82                     &format!("consider matching on `Ok({})` and removing the call to `ok` instead", some_expr_string),
  83                     sugg,
  84                     applicability,
  85                 );
  86             }
  87         }
  88     }
  89 }