clippy_lints/src/if_let_some_result.rs

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