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 clippy_utils::{get_parent_expr, path_to_local};
   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         if let Some(id) = path_to_local(cast_expr)
  79             && let Some(span) = cx.tcx.hir().opt_span(id)
  80             && span.ctxt() != cast_expr.span.ctxt()
  81         {
  82             // Binding context is different than the identifiers context.
  83             // Weird macro wizardry could be involved here.
  84             return false;
  85         }
  86
  87         span_lint_and_sugg(
  88             cx,
  89             UNNECESSARY_CAST,
  90             expr.span,
  91             &format!("casting to the same type is unnecessary (`{cast_from}` -> `{cast_to}`)"),
  92             "try",
  93             cast_str,
  94             Applicability::MachineApplicable,
  95         );
  96         return true;
  97     }
  98
  99     false
 100 }
 101
 102 fn lint_unnecessary_cast(
 103     cx: &LateContext<'_>,
 104     expr: &Expr<'_>,
 105     raw_literal_str: &str,
 106     cast_from: Ty<'_>,
 107     cast_to: Ty<'_>,
 108 ) {
 109     let literal_kind_name = if cast_from.is_integral() { "integer" } else { "float" };
 110     // first we remove all matches so `-(1)` become `-1`, and remove trailing dots, so `1.` become `1`
 111     let literal_str = raw_literal_str
 112         .replace(['(', ')'], "")
 113         .trim_end_matches('.')
 114         .to_string();
 115     // we know need to check if the parent is a method call, to add parenthesis accordingly (eg:
 116     // (-1).foo() instead of -1.foo())
 117     let sugg = if let Some(parent_expr) = get_parent_expr(cx, expr)
 118         && let ExprKind::MethodCall(..) = parent_expr.kind
 119         && literal_str.starts_with('-')
 120         {
 121             format!("({literal_str}_{cast_to})")
 122
 123         } else {
 124             format!("{literal_str}_{cast_to}")
 125     };
 126
 127     span_lint_and_sugg(
 128         cx,
 129         UNNECESSARY_CAST,
 130         expr.span,
 131         &format!("casting {literal_kind_name} literal to `{cast_to}` is unnecessary"),
 132         "try",
 133         sugg,
 134         Applicability::MachineApplicable,
 135     );
 136 }
 137
 138 fn get_numeric_literal<'e>(expr: &'e Expr<'e>) -> Option<&'e Lit> {
 139     match expr.kind {
 140         ExprKind::Lit(ref lit) => Some(lit),
 141         ExprKind::Unary(UnOp::Neg, e) => {
 142             if let ExprKind::Lit(ref lit) = e.kind {
 143                 Some(lit)
 144             } else {
 145                 None
 146             }
 147         },
 148         _ => None,
 149     }
 150 }
 151
 152 /// Returns the mantissa bits wide of a fp type.
 153 /// Will return 0 if the type is not a fp
 154 fn fp_ty_mantissa_nbits(typ: Ty<'_>) -> u32 {
 155     match typ.kind() {
 156         ty::Float(FloatTy::F32) => 23,
 157         ty::Float(FloatTy::F64) | ty::Infer(InferTy::FloatVar(_)) => 52,
 158         _ => 0,
 159     }
 160 }