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