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use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::source::snippet;
use clippy_utils::ty::is_type_diagnostic_item;
use clippy_utils::{eager_or_lazy, is_from_proc_macro, usage};
use rustc_errors::Applicability;
use rustc_hir as hir;
use rustc_lint::LateContext;
use rustc_span::sym;
use super::UNNECESSARY_LAZY_EVALUATIONS;
/// lint use of `<fn>_else(simple closure)` for `Option`s and `Result`s that can be
/// replaced with `<fn>(return value of simple closure)`
pub(super) fn check<'tcx>(
cx: &LateContext<'tcx>,
expr: &'tcx hir::Expr<'_>,
recv: &'tcx hir::Expr<'_>,
arg: &'tcx hir::Expr<'_>,
simplify_using: &str,
) {
if is_from_proc_macro(cx, expr) {
return;
}
let is_option = is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(recv), sym::Option);
let is_result = is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(recv), sym::Result);
let is_bool = cx.typeck_results().expr_ty(recv).is_bool();
if is_option || is_result || is_bool {
if let hir::ExprKind::Closure(&hir::Closure { body, .. }) = arg.kind {
let body = cx.tcx.hir().body(body);
let body_expr = &body.value;
if usage::BindingUsageFinder::are_params_used(cx, body) {
return;
}
if eager_or_lazy::switch_to_eager_eval(cx, body_expr) {
let msg = if is_option {
"unnecessary closure used to substitute value for `Option::None`"
} else if is_result {
"unnecessary closure used to substitute value for `Result::Err`"
} else {
"unnecessary closure used with `bool::then`"
};
let applicability = if body
.params
.iter()
// bindings are checked to be unused above
.all(|param| matches!(param.pat.kind, hir::PatKind::Binding(..) | hir::PatKind::Wild))
{
Applicability::MachineApplicable
} else {
// replacing the lambda may break type inference
Applicability::MaybeIncorrect
};
// This is a duplicate of what's happening in clippy_lints::methods::method_call,
// which isn't ideal, We want to get the method call span,
// but prefer to avoid changing the signature of the function itself.
if let hir::ExprKind::MethodCall(.., span) = expr.kind {
span_lint_and_then(cx, UNNECESSARY_LAZY_EVALUATIONS, expr.span, msg, |diag| {
diag.span_suggestion(
span,
format!("use `{simplify_using}(..)` instead"),
format!("{simplify_using}({})", snippet(cx, body_expr.span, "..")),
applicability,
);
});
}
}
}
}
}
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