src/tools/clippy/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::source::{indent_of, snippet_with_applicability};
   4 use if_chain::if_chain;
   5 use rustc_errors::Applicability;
   6 use rustc_hir::{BorrowKind, Expr, ExprKind, Pat};
   7 use rustc_lint::LateContext;
   8
   9 pub(super) fn check<'tcx>(
  10     cx: &LateContext<'tcx>,
  11     pat: &'tcx Pat<'_>,
  12     arg: &'tcx Expr<'_>,
  13     body: &'tcx Expr<'_>,
  14     expr: &'tcx Expr<'_>,
  15 ) {
  16     let arg_expr = match arg.kind {
  17         ExprKind::AddrOf(BorrowKind::Ref, _, ref_arg) => ref_arg,
  18         ExprKind::MethodCall(method, [arg], _) if method.ident.name == rustc_span::sym::iter => arg,
  19         _ => return,
  20     };
  21     if_chain! {
  22         if let ExprKind::Array([arg_expression]) = arg_expr.kind;
  23         if let ExprKind::Block(block, _) = body.kind;
  24         if !block.stmts.is_empty();
  25         then {
  26             let mut applicability = Applicability::MachineApplicable;
  27             let pat_snip = snippet_with_applicability(cx, pat.span, "..", &mut applicability);
  28             let arg_snip = snippet_with_applicability(cx, arg_expression.span, "..", &mut applicability);
  29             let mut block_str = snippet_with_applicability(cx, block.span, "..", &mut applicability).into_owned();
  30             block_str.remove(0);
  31             block_str.pop();
  32             let indent = " ".repeat(indent_of(cx, block.stmts[0].span).unwrap_or(0));
  33
  34             span_lint_and_sugg(
  35                 cx,
  36                 SINGLE_ELEMENT_LOOP,
  37                 expr.span,
  38                 "for loop over a single element",
  39                 "try",
  40                 format!("{{\n{}let {} = &{};{}}}", indent, pat_snip, arg_snip, block_str),
  41                 applicability,
  42             )
  43         }
  44     }
  45 }