src/tools/clippy/clippy_lints/src/if_let_some_result.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 if let.
  16     ///
  17     /// ### Why is this bad?
  18     /// Calling `ok()` in if let is unnecessary, instead match
  19     /// on `Ok(pat)`
  20     ///
  21     /// ### Example
  22     /// ```ignore
  23     /// for i in iter {
  24     ///     if let Some(value) = i.parse().ok() {
  25     ///         vec.push(value)
  26     ///     }
  27     /// }
  28     /// ```
  29     /// Could be written:
  30     ///
  31     /// ```ignore
  32     /// for i in iter {
  33     ///     if let Ok(value) = i.parse() {
  34     ///         vec.push(value)
  35     ///     }
  36     /// }
  37     /// ```
  38     pub IF_LET_SOME_RESULT,
  39     style,
  40     "usage of `ok()` in `if let Some(pat)` statements is unnecessary, match on `Ok(pat)` instead"
  41 }
  42
  43 declare_lint_pass!(OkIfLet => [IF_LET_SOME_RESULT]);
  44
  45 impl<'tcx> LateLintPass<'tcx> for OkIfLet {
  46     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  47         if_chain! { //begin checking variables
  48             if let Some(higher::IfLet { let_pat, let_expr, .. }) = higher::IfLet::hir(cx, expr);
  49             if let ExprKind::MethodCall(_, ok_span, ref result_types, _) = let_expr.kind; //check is expr.ok() has type Result<T,E>.ok(, _)
  50             if let PatKind::TupleStruct(QPath::Resolved(_, ref x), ref y, _)  = let_pat.kind; //get operation
  51             if method_chain_args(let_expr, &["ok"]).is_some(); //test to see if using ok() methoduse std::marker::Sized;
  52             if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&result_types[0]), sym::result_type);
  53             if rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| s.print_path(x, false)) == "Some";
  54
  55             then {
  56                 let mut applicability = Applicability::MachineApplicable;
  57                 let some_expr_string = snippet_with_applicability(cx, y[0].span, "", &mut applicability);
  58                 let trimmed_ok = snippet_with_applicability(cx, let_expr.span.until(ok_span), "", &mut applicability);
  59                 let sugg = format!(
  60                     "if let Ok({}) = {}",
  61                     some_expr_string,
  62                     trimmed_ok.trim().trim_end_matches('.'),
  63                 );
  64                 span_lint_and_sugg(
  65                     cx,
  66                     IF_LET_SOME_RESULT,
  67                     expr.span.with_hi(let_expr.span.hi()),
  68                     "matching on `Some` with `ok()` is redundant",
  69                     &format!("consider matching on `Ok({})` and removing the call to `ok` instead", some_expr_string),
  70                     sugg,
  71                     applicability,
  72                 );
  73             }
  74         }
  75     }
  76 }