clippy_lints/src/methods/unnecessary_fold.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::source::snippet_with_applicability;
   3 use clippy_utils::{is_trait_method, path_to_local_id, remove_blocks, strip_pat_refs};
   4 use if_chain::if_chain;
   5 use rustc_ast::ast;
   6 use rustc_errors::Applicability;
   7 use rustc_hir as hir;
   8 use rustc_hir::PatKind;
   9 use rustc_lint::LateContext;
  10 use rustc_span::{source_map::Span, sym};
  11
  12 use super::UNNECESSARY_FOLD;
  13
  14 pub(super) fn check(cx: &LateContext<'_>, expr: &hir::Expr<'_>, fold_args: &[hir::Expr<'_>], fold_span: Span) {
  15     fn check_fold_with_op(
  16         cx: &LateContext<'_>,
  17         expr: &hir::Expr<'_>,
  18         fold_args: &[hir::Expr<'_>],
  19         fold_span: Span,
  20         op: hir::BinOpKind,
  21         replacement_method_name: &str,
  22         replacement_has_args: bool,
  23     ) {
  24         if_chain! {
  25             // Extract the body of the closure passed to fold
  26             if let hir::ExprKind::Closure(_, _, body_id, _, _) = fold_args[2].kind;
  27             let closure_body = cx.tcx.hir().body(body_id);
  28             let closure_expr = remove_blocks(&closure_body.value);
  29
  30             // Check if the closure body is of the form `acc <op> some_expr(x)`
  31             if let hir::ExprKind::Binary(ref bin_op, ref left_expr, ref right_expr) = closure_expr.kind;
  32             if bin_op.node == op;
  33
  34             // Extract the names of the two arguments to the closure
  35             if let [param_a, param_b] = closure_body.params;
  36             if let PatKind::Binding(_, first_arg_id, ..) = strip_pat_refs(&param_a.pat).kind;
  37             if let PatKind::Binding(_, second_arg_id, second_arg_ident, _) = strip_pat_refs(&param_b.pat).kind;
  38
  39             if path_to_local_id(left_expr, first_arg_id);
  40             if replacement_has_args || path_to_local_id(right_expr, second_arg_id);
  41
  42             then {
  43                 let mut applicability = Applicability::MachineApplicable;
  44                 let sugg = if replacement_has_args {
  45                     format!(
  46                         "{replacement}(|{s}| {r})",
  47                         replacement = replacement_method_name,
  48                         s = second_arg_ident,
  49                         r = snippet_with_applicability(cx, right_expr.span, "EXPR", &mut applicability),
  50                     )
  51                 } else {
  52                     format!(
  53                         "{replacement}()",
  54                         replacement = replacement_method_name,
  55                     )
  56                 };
  57
  58                 span_lint_and_sugg(
  59                     cx,
  60                     UNNECESSARY_FOLD,
  61                     fold_span.with_hi(expr.span.hi()),
  62                     // TODO #2371 don't suggest e.g., .any(|x| f(x)) if we can suggest .any(f)
  63                     "this `.fold` can be written more succinctly using another method",
  64                     "try",
  65                     sugg,
  66                     applicability,
  67                 );
  68             }
  69         }
  70     }
  71
  72     // Check that this is a call to Iterator::fold rather than just some function called fold
  73     if !is_trait_method(cx, expr, sym::Iterator) {
  74         return;
  75     }
  76
  77     assert!(
  78         fold_args.len() == 3,
  79         "Expected fold_args to have three entries - the receiver, the initial value and the closure"
  80     );
  81
  82     // Check if the first argument to .fold is a suitable literal
  83     if let hir::ExprKind::Lit(ref lit) = fold_args[1].kind {
  84         match lit.node {
  85             ast::LitKind::Bool(false) => {
  86                 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::Or, "any", true)
  87             },
  88             ast::LitKind::Bool(true) => {
  89                 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::And, "all", true)
  90             },
  91             ast::LitKind::Int(0, _) => {
  92                 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::Add, "sum", false)
  93             },
  94             ast::LitKind::Int(1, _) => {
  95                 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::Mul, "product", false)
  96             },
  97             _ => (),
  98         }
  99     }
 100 }