clippy_lints/src/casts/cast_sign_loss.rs

   1 use rustc_hir::{Expr, ExprKind};
   2 use rustc_lint::LateContext;
   3 use rustc_middle::ty::{self, Ty};
   4
   5 use if_chain::if_chain;
   6
   7 use crate::consts::{constant, Constant};
   8 use crate::utils::{method_chain_args, sext, span_lint};
   9
  10 use super::CAST_SIGN_LOSS;
  11
  12 pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_op: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
  13     if should_lint(cx, cast_op, cast_from, cast_to) {
  14         span_lint(
  15             cx,
  16             CAST_SIGN_LOSS,
  17             expr.span,
  18             &format!(
  19                 "casting `{}` to `{}` may lose the sign of the value",
  20                 cast_from, cast_to
  21             ),
  22         );
  23     }
  24 }
  25
  26 fn should_lint(cx: &LateContext<'_>, cast_op: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) -> bool {
  27     match (cast_from.is_integral(), cast_to.is_integral()) {
  28         (true, true) => {
  29             if !cast_from.is_signed() || cast_to.is_signed() {
  30                 return false;
  31             }
  32
  33             // Don't lint for positive constants.
  34             let const_val = constant(cx, &cx.typeck_results(), cast_op);
  35             if_chain! {
  36                 if let Some((Constant::Int(n), _)) = const_val;
  37                 if let ty::Int(ity) = *cast_from.kind();
  38                 if sext(cx.tcx, n, ity) >= 0;
  39                 then {
  40                     return false;
  41                 }
  42             }
  43
  44             // Don't lint for the result of methods that always return non-negative values.
  45             if let ExprKind::MethodCall(ref path, _, _, _) = cast_op.kind {
  46                 let mut method_name = path.ident.name.as_str();
  47                 let allowed_methods = ["abs", "checked_abs", "rem_euclid", "checked_rem_euclid"];
  48
  49                 if_chain! {
  50                     if method_name == "unwrap";
  51                     if let Some(arglist) = method_chain_args(cast_op, &["unwrap"]);
  52                     if let ExprKind::MethodCall(ref inner_path, _, _, _) = &arglist[0][0].kind;
  53                     then {
  54                         method_name = inner_path.ident.name.as_str();
  55                     }
  56                 }
  57
  58                 if allowed_methods.iter().any(|&name| method_name == name) {
  59                     return false;
  60                 }
  61             }
  62
  63             true
  64         },
  65
  66         (false, true) => !cast_to.is_signed(),
  67
  68         (_, _) => false,
  69     }
  70 }