clippy_lints/src/casts/unnecessary_cast.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::get_parent_expr;
   3 use clippy_utils::numeric_literal::NumericLiteral;
   4 use clippy_utils::source::snippet_opt;
   5 use if_chain::if_chain;
   6 use rustc_ast::{LitFloatType, LitIntType, LitKind};
   7 use rustc_errors::Applicability;
   8 use rustc_hir::def::Res;
   9 use rustc_hir::{Expr, ExprKind, Lit, QPath, TyKind, UnOp};
  10 use rustc_lint::{LateContext, LintContext};
  11 use rustc_middle::lint::in_external_macro;
  12 use rustc_middle::ty::{self, FloatTy, InferTy, Ty};
  13
  14 use super::UNNECESSARY_CAST;
  15
  16 pub(super) fn check<'tcx>(
  17     cx: &LateContext<'tcx>,
  18     expr: &Expr<'tcx>,
  19     cast_expr: &Expr<'tcx>,
  20     cast_from: Ty<'tcx>,
  21     cast_to: Ty<'tcx>,
  22 ) -> bool {
  23     // skip non-primitive type cast
  24     if_chain! {
  25         if let ExprKind::Cast(_, cast_to) = expr.kind;
  26         if let TyKind::Path(QPath::Resolved(_, path)) = &cast_to.kind;
  27         if let Res::PrimTy(_) = path.res;
  28         then {}
  29         else {
  30             return false
  31         }
  32     }
  33
  34     let cast_str = snippet_opt(cx, cast_expr.span).unwrap_or_default();
  35
  36     if let Some(lit) = get_numeric_literal(cast_expr) {
  37         let literal_str = &cast_str;
  38
  39         if_chain! {
  40             if let LitKind::Int(n, _) = lit.node;
  41             if let Some(src) = snippet_opt(cx, cast_expr.span);
  42             if cast_to.is_floating_point();
  43             if let Some(num_lit) = NumericLiteral::from_lit_kind(&src, &lit.node);
  44             let from_nbits = 128 - n.leading_zeros();
  45             let to_nbits = fp_ty_mantissa_nbits(cast_to);
  46             if from_nbits != 0 && to_nbits != 0 && from_nbits <= to_nbits && num_lit.is_decimal();
  47             then {
  48                 lint_unnecessary_cast(cx, expr, num_lit.integer, cast_from, cast_to);
  49                 return true
  50             }
  51         }
  52
  53         match lit.node {
  54             LitKind::Int(_, LitIntType::Unsuffixed) if cast_to.is_integral() => {
  55                 lint_unnecessary_cast(cx, expr, literal_str, cast_from, cast_to);
  56                 return true;
  57             },
  58             LitKind::Float(_, LitFloatType::Unsuffixed) if cast_to.is_floating_point() => {
  59                 lint_unnecessary_cast(cx, expr, literal_str, cast_from, cast_to);
  60                 return true;
  61             },
  62             LitKind::Int(_, LitIntType::Unsuffixed) | LitKind::Float(_, LitFloatType::Unsuffixed) => {},
  63             LitKind::Int(_, LitIntType::Signed(_) | LitIntType::Unsigned(_))
  64             | LitKind::Float(_, LitFloatType::Suffixed(_))
  65                 if cast_from.kind() == cast_to.kind() =>
  66             {
  67                 if let Some(src) = snippet_opt(cx, cast_expr.span) {
  68                     if let Some(num_lit) = NumericLiteral::from_lit_kind(&src, &lit.node) {
  69                         lint_unnecessary_cast(cx, expr, num_lit.integer, cast_from, cast_to);
  70                         return true;
  71                     }
  72                 }
  73             },
  74             _ => {},
  75         }
  76     }
  77
  78     if cast_from.kind() == cast_to.kind() && !in_external_macro(cx.sess(), expr.span) {
  79         span_lint_and_sugg(
  80             cx,
  81             UNNECESSARY_CAST,
  82             expr.span,
  83             &format!("casting to the same type is unnecessary (`{cast_from}` -> `{cast_to}`)"),
  84             "try",
  85             cast_str,
  86             Applicability::MachineApplicable,
  87         );
  88         return true;
  89     }
  90
  91     false
  92 }
  93
  94 fn lint_unnecessary_cast(
  95     cx: &LateContext<'_>,
  96     expr: &Expr<'_>,
  97     raw_literal_str: &str,
  98     cast_from: Ty<'_>,
  99     cast_to: Ty<'_>,
 100 ) {
 101     let literal_kind_name = if cast_from.is_integral() { "integer" } else { "float" };
 102     // first we remove all matches so `-(1)` become `-1`, and remove trailing dots, so `1.` become `1`
 103     let literal_str = raw_literal_str
 104         .replace(['(', ')'], "")
 105         .trim_end_matches('.')
 106         .to_string();
 107     // we know need to check if the parent is a method call, to add parenthesis accordingly (eg:
 108     // (-1).foo() instead of -1.foo())
 109     let sugg = if let Some(parent_expr) = get_parent_expr(cx, expr)
 110         && let ExprKind::MethodCall(..) = parent_expr.kind
 111         && literal_str.starts_with('-')
 112         {
 113             format!("({literal_str}_{cast_to})")
 114
 115         } else {
 116             format!("{literal_str}_{cast_to}")
 117     };
 118
 119     span_lint_and_sugg(
 120         cx,
 121         UNNECESSARY_CAST,
 122         expr.span,
 123         &format!("casting {literal_kind_name} literal to `{cast_to}` is unnecessary"),
 124         "try",
 125         sugg,
 126         Applicability::MachineApplicable,
 127     );
 128 }
 129
 130 fn get_numeric_literal<'e>(expr: &'e Expr<'e>) -> Option<&'e Lit> {
 131     match expr.kind {
 132         ExprKind::Lit(ref lit) => Some(lit),
 133         ExprKind::Unary(UnOp::Neg, e) => {
 134             if let ExprKind::Lit(ref lit) = e.kind {
 135                 Some(lit)
 136             } else {
 137                 None
 138             }
 139         },
 140         _ => None,
 141     }
 142 }
 143
 144 /// Returns the mantissa bits wide of a fp type.
 145 /// Will return 0 if the type is not a fp
 146 fn fp_ty_mantissa_nbits(typ: Ty<'_>) -> u32 {
 147     match typ.kind() {
 148         ty::Float(FloatTy::F32) => 23,
 149         ty::Float(FloatTy::F64) | ty::Infer(InferTy::FloatVar(_)) => 52,
 150         _ => 0,
 151     }
 152 }