clippy_lints/src/casts/unnecessary_cast.rs

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