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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::is_trait_method;
use clippy_utils::source::snippet;
use clippy_utils::ty::is_type_diagnostic_item;
use rustc_errors::Applicability;
use rustc_hir as hir;
use rustc_lint::LateContext;
use rustc_middle::ty;
use rustc_span::symbol::sym;
use super::MAP_FLATTEN;
/// lint use of `map().flatten()` for `Iterators` and 'Options'
pub(super) fn check<'tcx>(
cx: &LateContext<'tcx>,
expr: &'tcx hir::Expr<'_>,
recv: &'tcx hir::Expr<'_>,
map_arg: &'tcx hir::Expr<'_>,
) {
// lint if caller of `.map().flatten()` is an Iterator
if is_trait_method(cx, expr, sym::Iterator) {
let map_closure_ty = cx.typeck_results().expr_ty(map_arg);
let is_map_to_option = match map_closure_ty.kind() {
ty::Closure(_, _) | ty::FnDef(_, _) | ty::FnPtr(_) => {
let map_closure_sig = match map_closure_ty.kind() {
ty::Closure(_, substs) => substs.as_closure().sig(),
_ => map_closure_ty.fn_sig(cx.tcx),
};
let map_closure_return_ty = cx.tcx.erase_late_bound_regions(map_closure_sig.output());
is_type_diagnostic_item(cx, map_closure_return_ty, sym::Option)
},
_ => false,
};
let method_to_use = if is_map_to_option {
// `(...).map(...)` has type `impl Iterator<Item=Option<...>>
"filter_map"
} else {
// `(...).map(...)` has type `impl Iterator<Item=impl Iterator<...>>
"flat_map"
};
let func_snippet = snippet(cx, map_arg.span, "..");
let hint = format!(".{0}({1})", method_to_use, func_snippet);
span_lint_and_sugg(
cx,
MAP_FLATTEN,
expr.span.with_lo(recv.span.hi()),
"called `map(..).flatten()` on an `Iterator`",
&format!("try using `{}` instead", method_to_use),
hint,
Applicability::MachineApplicable,
);
}
// lint if caller of `.map().flatten()` is an Option or Result
let caller_type = match cx.typeck_results().expr_ty(recv).kind() {
ty::Adt(adt, _) => {
if cx.tcx.is_diagnostic_item(sym::Option, adt.did) {
"Option"
} else if cx.tcx.is_diagnostic_item(sym::Result, adt.did) {
"Result"
} else {
return;
}
},
_ => {
return;
},
};
let func_snippet = snippet(cx, map_arg.span, "..");
let hint = format!(".and_then({})", func_snippet);
let lint_info = format!("called `map(..).flatten()` on an `{}`", caller_type);
span_lint_and_sugg(
cx,
MAP_FLATTEN,
expr.span.with_lo(recv.span.hi()),
&lint_info,
"try using `and_then` instead",
hint,
Applicability::MachineApplicable,
);
}
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