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, is_from_proc_macro, usage};
5 use rustc_errors::Applicability;
7 use rustc_lint::LateContext;
10 use super::UNNECESSARY_LAZY_EVALUATIONS;
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<'_>,
21 if is_from_proc_macro(cx, expr) {
25 let is_option = is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(recv), sym::Option);
26 let is_result = is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(recv), sym::Result);
27 let is_bool = cx.typeck_results().expr_ty(recv).is_bool();
29 if is_option || is_result || is_bool {
30 if let hir::ExprKind::Closure(&hir::Closure { body, .. }) = arg.kind {
31 let body = cx.tcx.hir().body(body);
32 let body_expr = &body.value;
34 if usage::BindingUsageFinder::are_params_used(cx, body) {
38 if eager_or_lazy::switch_to_eager_eval(cx, body_expr) {
39 let msg = if is_option {
40 "unnecessary closure used to substitute value for `Option::None`"
42 "unnecessary closure used to substitute value for `Result::Err`"
44 "unnecessary closure used with `bool::then`"
46 let applicability = if body
49 // bindings are checked to be unused above
50 .all(|param| matches!(param.pat.kind, hir::PatKind::Binding(..) | hir::PatKind::Wild))
52 Applicability::MachineApplicable
54 // replacing the lambda may break type inference
55 Applicability::MaybeIncorrect
58 // This is a duplicate of what's happening in clippy_lints::methods::method_call,
59 // which isn't ideal, We want to get the method call span,
60 // but prefer to avoid changing the signature of the function itself.
61 if let hir::ExprKind::MethodCall(.., span) = expr.kind {
62 span_lint_and_then(cx, UNNECESSARY_LAZY_EVALUATIONS, expr.span, msg, |diag| {
65 &format!("use `{simplify_using}(..)` instead"),
66 format!("{simplify_using}({})", snippet(cx, body_expr.span, "..")),