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