clippy_lints/src/if_let_some_result.rs

   1 use crate::utils::{is_type_diagnostic_item, method_chain_args, snippet_with_applicability, span_lint_and_sugg};
   2 use if_chain::if_chain;
   3 use rustc_errors::Applicability;
   4 use rustc_hir::{Expr, ExprKind, MatchSource, PatKind, QPath};
   5 use rustc_lint::{LateContext, LateLintPass};
   6 use rustc_session::{declare_lint_pass, declare_tool_lint};
   7 use rustc_span::sym;
   8
   9 declare_clippy_lint! {
  10     /// **What it does:*** Checks for unnecessary `ok()` in if let.
  11     ///
  12     /// **Why is this bad?** Calling `ok()` in if let is unnecessary, instead match
  13     /// on `Ok(pat)`
  14     ///
  15     /// **Known problems:** None.
  16     ///
  17     /// **Example:**
  18     /// ```ignore
  19     /// for i in iter {
  20     ///     if let Some(value) = i.parse().ok() {
  21     ///         vec.push(value)
  22     ///     }
  23     /// }
  24     /// ```
  25     /// Could be written:
  26     ///
  27     /// ```ignore
  28     /// for i in iter {
  29     ///     if let Ok(value) = i.parse() {
  30     ///         vec.push(value)
  31     ///     }
  32     /// }
  33     /// ```
  34     pub IF_LET_SOME_RESULT,
  35     style,
  36     "usage of `ok()` in `if let Some(pat)` statements is unnecessary, match on `Ok(pat)` instead"
  37 }
  38
  39 declare_lint_pass!(OkIfLet => [IF_LET_SOME_RESULT]);
  40
  41 impl<'tcx> LateLintPass<'tcx> for OkIfLet {
  42     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  43         if_chain! { //begin checking variables
  44             if let ExprKind::Match(ref op, ref body, MatchSource::IfLetDesugar { .. }) = expr.kind; //test if expr is 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             if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&result_types[0]), sym::result_type);
  49             if rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| s.print_path(x, false)) == "Some";
  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 }