src/tools/clippy/clippy_lints/src/casts/cast_sign_loss.rs

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