src/tools/clippy/clippy_lints/src/methods/map_flatten.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg_for_edges;
   2 use clippy_utils::is_trait_method;
   3 use clippy_utils::source::snippet_with_applicability;
   4 use clippy_utils::ty::is_type_diagnostic_item;
   5 use rustc_errors::Applicability;
   6 use rustc_hir::Expr;
   7 use rustc_lint::LateContext;
   8 use rustc_middle::ty;
   9 use rustc_span::{symbol::sym, Span};
  10
  11 use super::MAP_FLATTEN;
  12
  13 /// lint use of `map().flatten()` for `Iterators` and 'Options'
  14 pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, recv: &Expr<'_>, map_arg: &Expr<'_>, map_span: Span) {
  15     if let Some((caller_ty_name, method_to_use)) = try_get_caller_ty_name_and_method_name(cx, expr, recv, map_arg) {
  16         let mut applicability = Applicability::MachineApplicable;
  17         let help_msgs = [
  18             &format!("try replacing `map` with `{}`", method_to_use),
  19             "and remove the `.flatten()`",
  20         ];
  21         let closure_snippet = snippet_with_applicability(cx, map_arg.span, "..", &mut applicability);
  22         span_lint_and_sugg_for_edges(
  23             cx,
  24             MAP_FLATTEN,
  25             expr.span.with_lo(map_span.lo()),
  26             &format!("called `map(..).flatten()` on `{}`", caller_ty_name),
  27             &help_msgs,
  28             format!("{}({})", method_to_use, closure_snippet),
  29             applicability,
  30         );
  31     }
  32 }
  33
  34 fn try_get_caller_ty_name_and_method_name(
  35     cx: &LateContext<'_>,
  36     expr: &Expr<'_>,
  37     caller_expr: &Expr<'_>,
  38     map_arg: &Expr<'_>,
  39 ) -> Option<(&'static str, &'static str)> {
  40     if is_trait_method(cx, expr, sym::Iterator) {
  41         if is_map_to_option(cx, map_arg) {
  42             // `(...).map(...)` has type `impl Iterator<Item=Option<...>>
  43             Some(("Iterator", "filter_map"))
  44         } else {
  45             // `(...).map(...)` has type `impl Iterator<Item=impl Iterator<...>>
  46             Some(("Iterator", "flat_map"))
  47         }
  48     } else {
  49         if let ty::Adt(adt, _) = cx.typeck_results().expr_ty(caller_expr).kind() {
  50             if cx.tcx.is_diagnostic_item(sym::Option, adt.did()) {
  51                 return Some(("Option", "and_then"));
  52             } else if cx.tcx.is_diagnostic_item(sym::Result, adt.did()) {
  53                 return Some(("Result", "and_then"));
  54             }
  55         }
  56         None
  57     }
  58 }
  59
  60 fn is_map_to_option(cx: &LateContext<'_>, map_arg: &Expr<'_>) -> bool {
  61     let map_closure_ty = cx.typeck_results().expr_ty(map_arg);
  62     match map_closure_ty.kind() {
  63         ty::Closure(_, _) | ty::FnDef(_, _) | ty::FnPtr(_) => {
  64             let map_closure_sig = match map_closure_ty.kind() {
  65                 ty::Closure(_, substs) => substs.as_closure().sig(),
  66                 _ => map_closure_ty.fn_sig(cx.tcx),
  67             };
  68             let map_closure_return_ty = cx.tcx.erase_late_bound_regions(map_closure_sig.output());
  69             is_type_diagnostic_item(cx, map_closure_return_ty, sym::Option)
  70         },
  71         _ => false,
  72     }
  73 }