clippy_lints/src/methods/flat_map_identity.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::{is_expr_path_def_path, is_trait_method, paths};
   3 use if_chain::if_chain;
   4 use rustc_errors::Applicability;
   5 use rustc_hir as hir;
   6 use rustc_lint::LateContext;
   7 use rustc_span::{source_map::Span, sym};
   8
   9 use super::FLAT_MAP_IDENTITY;
  10
  11 /// lint use of `flat_map` for `Iterators` where `flatten` would be sufficient
  12 pub(super) fn check<'tcx>(
  13     cx: &LateContext<'tcx>,
  14     expr: &'tcx hir::Expr<'_>,
  15     flat_map_arg: &'tcx hir::Expr<'_>,
  16     flat_map_span: Span,
  17 ) {
  18     if is_trait_method(cx, expr, sym::Iterator) {
  19         let apply_lint = |message: &str| {
  20             span_lint_and_sugg(
  21                 cx,
  22                 FLAT_MAP_IDENTITY,
  23                 flat_map_span.with_hi(expr.span.hi()),
  24                 message,
  25                 "try",
  26                 "flatten()".to_string(),
  27                 Applicability::MachineApplicable,
  28             );
  29         };
  30
  31         if_chain! {
  32             if let hir::ExprKind::Closure(_, _, body_id, _, _) = flat_map_arg.kind;
  33             let body = cx.tcx.hir().body(body_id);
  34
  35             if let hir::PatKind::Binding(_, _, binding_ident, _) = body.params[0].pat.kind;
  36             if let hir::ExprKind::Path(hir::QPath::Resolved(_, path)) = body.value.kind;
  37
  38             if path.segments.len() == 1;
  39             if path.segments[0].ident.name == binding_ident.name;
  40
  41             then {
  42                 apply_lint("called `flat_map(|x| x)` on an `Iterator`");
  43             }
  44         }
  45
  46         if is_expr_path_def_path(cx, flat_map_arg, &paths::CONVERT_IDENTITY) {
  47             apply_lint("called `flat_map(std::convert::identity)` on an `Iterator`");
  48         }
  49     }
  50 }