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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::{is_expr_identity_function, is_trait_method};
use rustc_errors::Applicability;
use rustc_hir as hir;
use rustc_lint::LateContext;
use rustc_span::{source_map::Span, sym};
use super::FLAT_MAP_IDENTITY;
/// lint use of `flat_map` for `Iterators` where `flatten` would be sufficient
pub(super) fn check<'tcx>(
cx: &LateContext<'tcx>,
expr: &'tcx hir::Expr<'_>,
flat_map_arg: &'tcx hir::Expr<'_>,
flat_map_span: Span,
) {
if is_trait_method(cx, expr, sym::Iterator) && is_expr_identity_function(cx, flat_map_arg) {
span_lint_and_sugg(
cx,
FLAT_MAP_IDENTITY,
flat_map_span.with_hi(expr.span.hi()),
"use of `flat_map` with an identity function",
"try",
"flatten()".to_string(),
Applicability::MachineApplicable,
);
}
}
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