src/tools/clippy/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 false;
  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 false;
  61             },
  62             LitKind::Int(_, LitIntType::Signed(_) | LitIntType::Unsigned(_))
  63             | LitKind::Float(_, LitFloatType::Suffixed(_))
  64                 if cast_from.kind() == cast_to.kind() =>
  65             {
  66                 if let Some(src) = snippet_opt(cx, cast_expr.span) {
  67                     if let Some(num_lit) = NumericLiteral::from_lit_kind(&src, &lit.node) {
  68                         lint_unnecessary_cast(cx, expr, num_lit.integer, cast_from, cast_to);
  69                         return true;
  70                     }
  71                 }
  72             },
  73             _ => {},
  74         }
  75     }
  76
  77     if cast_from.kind() == cast_to.kind() && !in_external_macro(cx.sess(), expr.span) {
  78         span_lint_and_sugg(
  79             cx,
  80             UNNECESSARY_CAST,
  81             expr.span,
  82             &format!("casting to the same type is unnecessary (`{cast_from}` -> `{cast_to}`)"),
  83             "try",
  84             cast_str,
  85             Applicability::MachineApplicable,
  86         );
  87         return true;
  88     }
  89
  90     false
  91 }
  92
  93 fn lint_unnecessary_cast(
  94     cx: &LateContext<'_>,
  95     expr: &Expr<'_>,
  96     raw_literal_str: &str,
  97     cast_from: Ty<'_>,
  98     cast_to: Ty<'_>,
  99 ) {
 100     let literal_kind_name = if cast_from.is_integral() { "integer" } else { "float" };
 101     // first we remove all matches so `-(1)` become `-1`, and remove trailing dots, so `1.` become `1`
 102     let literal_str = raw_literal_str
 103         .replace(['(', ')'], "")
 104         .trim_end_matches('.')
 105         .to_string();
 106     // we know need to check if the parent is a method call, to add parenthesis accordingly (eg:
 107     // (-1).foo() instead of -1.foo())
 108     let sugg = if let Some(parent_expr) = get_parent_expr(cx, expr)
 109         && let ExprKind::MethodCall(..) = parent_expr.kind
 110         && literal_str.starts_with('-')
 111         {
 112             format!("({literal_str}_{cast_to})")
 113
 114         } else {
 115             format!("{literal_str}_{cast_to}")
 116     };
 117
 118     span_lint_and_sugg(
 119         cx,
 120         UNNECESSARY_CAST,
 121         expr.span,
 122         &format!("casting {literal_kind_name} literal to `{cast_to}` is unnecessary"),
 123         "try",
 124         sugg,
 125         Applicability::MachineApplicable,
 126     );
 127 }
 128
 129 fn get_numeric_literal<'e>(expr: &'e Expr<'e>) -> Option<&'e Lit> {
 130     match expr.kind {
 131         ExprKind::Lit(ref lit) => Some(lit),
 132         ExprKind::Unary(UnOp::Neg, e) => {
 133             if let ExprKind::Lit(ref lit) = e.kind {
 134                 Some(lit)
 135             } else {
 136                 None
 137             }
 138         },
 139         _ => None,
 140     }
 141 }
 142
 143 /// Returns the mantissa bits wide of a fp type.
 144 /// Will return 0 if the type is not a fp
 145 fn fp_ty_mantissa_nbits(typ: Ty<'_>) -> u32 {
 146     match typ.kind() {
 147         ty::Float(FloatTy::F32) => 23,
 148         ty::Float(FloatTy::F64) | ty::Infer(InferTy::FloatVar(_)) => 52,
 149         _ => 0,
 150     }
 151 }