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

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   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
  18         let closure_snippet = snippet_with_applicability(cx, map_arg.span, "..", &mut applicability);
  19         span_lint_and_sugg(
  20             cx,
  21             MAP_FLATTEN,
  22             expr.span.with_lo(map_span.lo()),
  23             &format!("called `map(..).flatten()` on `{caller_ty_name}`"),
  24             &format!("try replacing `map` with `{method_to_use}` and remove the `.flatten()`"),
  25             format!("{method_to_use}({closure_snippet})"),
  26             applicability,
  27         );
  28     }
  29 }
  30
  31 fn try_get_caller_ty_name_and_method_name(
  32     cx: &LateContext<'_>,
  33     expr: &Expr<'_>,
  34     caller_expr: &Expr<'_>,
  35     map_arg: &Expr<'_>,
  36 ) -> Option<(&'static str, &'static str)> {
  37     if is_trait_method(cx, expr, sym::Iterator) {
  38         if is_map_to_option(cx, map_arg) {
  39             // `(...).map(...)` has type `impl Iterator<Item=Option<...>>
  40             Some(("Iterator", "filter_map"))
  41         } else {
  42             // `(...).map(...)` has type `impl Iterator<Item=impl Iterator<...>>
  43             Some(("Iterator", "flat_map"))
  44         }
  45     } else {
  46         if let ty::Adt(adt, _) = cx.typeck_results().expr_ty(caller_expr).kind() {
  47             if cx.tcx.is_diagnostic_item(sym::Option, adt.did()) {
  48                 return Some(("Option", "and_then"));
  49             } else if cx.tcx.is_diagnostic_item(sym::Result, adt.did()) {
  50                 return Some(("Result", "and_then"));
  51             }
  52         }
  53         None
  54     }
  55 }
  56
  57 fn is_map_to_option(cx: &LateContext<'_>, map_arg: &Expr<'_>) -> bool {
  58     let map_closure_ty = cx.typeck_results().expr_ty(map_arg);
  59     match map_closure_ty.kind() {
  60         ty::Closure(_, _) | ty::FnDef(_, _) | ty::FnPtr(_) => {
  61             let map_closure_sig = match map_closure_ty.kind() {
  62                 ty::Closure(_, substs) => substs.as_closure().sig(),
  63                 _ => map_closure_ty.fn_sig(cx.tcx),
  64             };
  65             let map_closure_return_ty = cx.tcx.erase_late_bound_regions(map_closure_sig.output());
  66             is_type_diagnostic_item(cx, map_closure_return_ty, sym::Option)
  67         },
  68         _ => false,
  69     }
  70 }