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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::{is_trait_method, match_qpath, paths};
use if_chain::if_chain;
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) {
let arg_node = &flat_map_arg.kind;
let apply_lint = |message: &str| {
span_lint_and_sugg(
cx,
FLAT_MAP_IDENTITY,
flat_map_span.with_hi(expr.span.hi()),
message,
"try",
"flatten()".to_string(),
Applicability::MachineApplicable,
);
};
if_chain! {
if let hir::ExprKind::Closure(_, _, body_id, _, _) = arg_node;
let body = cx.tcx.hir().body(*body_id);
if let hir::PatKind::Binding(_, _, binding_ident, _) = body.params[0].pat.kind;
if let hir::ExprKind::Path(hir::QPath::Resolved(_, path)) = body.value.kind;
if path.segments.len() == 1;
if path.segments[0].ident.name == binding_ident.name;
then {
apply_lint("called `flat_map(|x| x)` on an `Iterator`");
}
}
if_chain! {
if let hir::ExprKind::Path(ref qpath) = arg_node;
if match_qpath(qpath, &paths::STD_CONVERT_IDENTITY);
then {
apply_lint("called `flat_map(std::convert::identity)` on an `Iterator`");
}
}
}
}
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