clippy_lints/src/loops/single_element_loop.rs

   1 use super::SINGLE_ELEMENT_LOOP;
   2 use clippy_utils::diagnostics::span_lint_and_sugg;
   3 use clippy_utils::single_segment_path;
   4 use clippy_utils::source::{indent_of, snippet};
   5 use if_chain::if_chain;
   6 use rustc_errors::Applicability;
   7 use rustc_hir::{BorrowKind, Expr, ExprKind, Pat, PatKind};
   8 use rustc_lint::LateContext;
   9
  10 pub(super) fn check<'tcx>(
  11     cx: &LateContext<'tcx>,
  12     pat: &'tcx Pat<'_>,
  13     arg: &'tcx Expr<'_>,
  14     body: &'tcx Expr<'_>,
  15     expr: &'tcx Expr<'_>,
  16 ) {
  17     let arg_expr = match arg.kind {
  18         ExprKind::AddrOf(BorrowKind::Ref, _, ref_arg) => ref_arg,
  19         ExprKind::MethodCall(method, args, _) if args.len() == 1 && method.ident.name == rustc_span::sym::iter => {
  20             &args[0]
  21         },
  22         _ => return,
  23     };
  24     if_chain! {
  25         if let PatKind::Binding(.., target, _) = pat.kind;
  26         if let ExprKind::Array([arg_expression]) = arg_expr.kind;
  27         if let ExprKind::Path(ref list_item) = arg_expression.kind;
  28         if let Some(list_item_name) = single_segment_path(list_item).map(|ps| ps.ident.name);
  29         if let ExprKind::Block(block, _) = body.kind;
  30         if !block.stmts.is_empty();
  31
  32         then {
  33             let mut block_str = snippet(cx, block.span, "..").into_owned();
  34             block_str.remove(0);
  35             block_str.pop();
  36
  37
  38             span_lint_and_sugg(
  39                 cx,
  40                 SINGLE_ELEMENT_LOOP,
  41                 expr.span,
  42                 "for loop over a single element",
  43                 "try",
  44                 format!("{{\n{}let {} = &{};{}}}", " ".repeat(indent_of(cx, block.stmts[0].span).unwrap_or(0)), target.name, list_item_name, block_str),
  45                 Applicability::MachineApplicable
  46             )
  47         }
  48     }
  49 }