clippy_lints/src/methods/unnecessary_lazy_eval.rs

   1 use clippy_utils::diagnostics::span_lint_and_then;
   2 use clippy_utils::source::snippet;
   3 use clippy_utils::ty::is_type_diagnostic_item;
   4 use clippy_utils::{eager_or_lazy, usage};
   5 use rustc_errors::Applicability;
   6 use rustc_hir as hir;
   7 use rustc_lint::LateContext;
   8 use rustc_span::sym;
   9
  10 use super::UNNECESSARY_LAZY_EVALUATIONS;
  11
  12 /// lint use of `<fn>_else(simple closure)` for `Option`s and `Result`s that can be
  13 /// replaced with `<fn>(return value of simple closure)`
  14 pub(super) fn check<'tcx>(
  15     cx: &LateContext<'tcx>,
  16     expr: &'tcx hir::Expr<'_>,
  17     recv: &'tcx hir::Expr<'_>,
  18     arg: &'tcx hir::Expr<'_>,
  19     simplify_using: &str,
  20 ) {
  21     let is_option = is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(recv), sym::Option);
  22     let is_result = is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(recv), sym::Result);
  23
  24     if is_option || is_result {
  25         if let hir::ExprKind::Closure(_, _, eid, _, _) = arg.kind {
  26             let body = cx.tcx.hir().body(eid);
  27             let body_expr = &body.value;
  28
  29             if usage::BindingUsageFinder::are_params_used(cx, body) {
  30                 return;
  31             }
  32
  33             if eager_or_lazy::switch_to_eager_eval(cx, body_expr) {
  34                 let msg = if is_option {
  35                     "unnecessary closure used to substitute value for `Option::None`"
  36                 } else {
  37                     "unnecessary closure used to substitute value for `Result::Err`"
  38                 };
  39                 let applicability = if body
  40                     .params
  41                     .iter()
  42                     // bindings are checked to be unused above
  43                     .all(|param| matches!(param.pat.kind, hir::PatKind::Binding(..) | hir::PatKind::Wild))
  44                 {
  45                     Applicability::MachineApplicable
  46                 } else {
  47                     // replacing the lambda may break type inference
  48                     Applicability::MaybeIncorrect
  49                 };
  50
  51                 // This is a duplicate of what's happening in clippy_lints::methods::method_call,
  52                 // which isn't ideal, We want to get the method call span,
  53                 // but prefer to avoid changing the signature of the function itself.
  54                 if let hir::ExprKind::MethodCall(_, _, span) = expr.kind {
  55                     span_lint_and_then(cx, UNNECESSARY_LAZY_EVALUATIONS, expr.span, msg, |diag| {
  56                         diag.span_suggestion(
  57                             span,
  58                             &format!("use `{}(..)` instead", simplify_using),
  59                             format!("{}({})", simplify_using, snippet(cx, body_expr.span, "..")),
  60                             applicability,
  61                         );
  62                     });
  63                 }
  64             }
  65         }
  66     }
  67 }