clippy_lints/src/methods/unnecessary_lazy_eval.rs

   1 use crate::utils::{eager_or_lazy, usage};
   2 use crate::utils::{is_type_diagnostic_item, snippet, span_lint_and_sugg};
   3 use rustc_errors::Applicability;
   4 use rustc_hir as hir;
   5 use rustc_lint::LateContext;
   6 use rustc_span::sym;
   7
   8 use super::UNNECESSARY_LAZY_EVALUATIONS;
   9
  10 /// lint use of `<fn>_else(simple closure)` for `Option`s and `Result`s that can be
  11 /// replaced with `<fn>(return value of simple closure)`
  12 pub(super) fn lint<'tcx>(
  13     cx: &LateContext<'tcx>,
  14     expr: &'tcx hir::Expr<'_>,
  15     args: &'tcx [hir::Expr<'_>],
  16     simplify_using: &str,
  17 ) {
  18     let is_option = is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&args[0]), sym::option_type);
  19     let is_result = is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&args[0]), sym::result_type);
  20
  21     if is_option || is_result {
  22         if let hir::ExprKind::Closure(_, _, eid, _, _) = args[1].kind {
  23             let body = cx.tcx.hir().body(eid);
  24             let body_expr = &body.value;
  25
  26             if usage::BindingUsageFinder::are_params_used(cx, body) {
  27                 return;
  28             }
  29
  30             if eager_or_lazy::is_eagerness_candidate(cx, body_expr) {
  31                 let msg = if is_option {
  32                     "unnecessary closure used to substitute value for `Option::None`"
  33                 } else {
  34                     "unnecessary closure used to substitute value for `Result::Err`"
  35                 };
  36                 let applicability = if body
  37                     .params
  38                     .iter()
  39                     // bindings are checked to be unused above
  40                     .all(|param| matches!(param.pat.kind, hir::PatKind::Binding(..) | hir::PatKind::Wild))
  41                 {
  42                     Applicability::MachineApplicable
  43                 } else {
  44                     // replacing the lambda may break type inference
  45                     Applicability::MaybeIncorrect
  46                 };
  47
  48                 span_lint_and_sugg(
  49                     cx,
  50                     UNNECESSARY_LAZY_EVALUATIONS,
  51                     expr.span,
  52                     msg,
  53                     &format!("use `{}` instead", simplify_using),
  54                     format!(
  55                         "{0}.{1}({2})",
  56                         snippet(cx, args[0].span, ".."),
  57                         simplify_using,
  58                         snippet(cx, body_expr.span, ".."),
  59                     ),
  60                     applicability,
  61                 );
  62             }
  63         }
  64     }
  65 }