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|
use clippy_utils::consts::{constant, Constant};
use clippy_utils::diagnostics::span_lint;
use clippy_utils::expr_or_init;
use clippy_utils::ty::{get_discriminant_value, is_isize_or_usize};
use rustc_hir::def::{DefKind, Res};
use rustc_hir::{BinOpKind, Expr, ExprKind};
use rustc_lint::LateContext;
use rustc_middle::ty::{self, FloatTy, Ty};
use rustc_target::abi::IntegerType;
use super::{utils, CAST_ENUM_TRUNCATION, CAST_POSSIBLE_TRUNCATION};
fn constant_int(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<u128> {
if let Some((Constant::Int(c), _)) = constant(cx, cx.typeck_results(), expr) {
Some(c)
} else {
None
}
}
fn get_constant_bits(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<u64> {
constant_int(cx, expr).map(|c| u64::from(128 - c.leading_zeros()))
}
fn apply_reductions(cx: &LateContext<'_>, nbits: u64, expr: &Expr<'_>, signed: bool) -> u64 {
match expr_or_init(cx, expr).kind {
ExprKind::Cast(inner, _) => apply_reductions(cx, nbits, inner, signed),
ExprKind::Block(block, _) => block.expr.map_or(nbits, |e| apply_reductions(cx, nbits, e, signed)),
ExprKind::Binary(op, left, right) => match op.node {
BinOpKind::Div => {
apply_reductions(cx, nbits, left, signed).saturating_sub(if signed {
// let's be conservative here
0
} else {
// by dividing by 1, we remove 0 bits, etc.
get_constant_bits(cx, right).map_or(0, |b| b.saturating_sub(1))
})
},
BinOpKind::Rem | BinOpKind::BitAnd => get_constant_bits(cx, right)
.unwrap_or(u64::max_value())
.min(apply_reductions(cx, nbits, left, signed)),
BinOpKind::Shr => apply_reductions(cx, nbits, left, signed)
.saturating_sub(constant_int(cx, right).map_or(0, |s| u64::try_from(s).expect("shift too high"))),
_ => nbits,
},
ExprKind::MethodCall(method, left, [right], _) => {
if signed {
return nbits;
}
let max_bits = if method.ident.as_str() == "min" {
get_constant_bits(cx, right)
} else {
None
};
apply_reductions(cx, nbits, left, signed).min(max_bits.unwrap_or(u64::max_value()))
},
ExprKind::MethodCall(method, _, [lo, hi], _) => {
if method.ident.as_str() == "clamp" {
//FIXME: make this a diagnostic item
if let (Some(lo_bits), Some(hi_bits)) = (get_constant_bits(cx, lo), get_constant_bits(cx, hi)) {
return lo_bits.max(hi_bits);
}
}
nbits
},
ExprKind::MethodCall(method, _value, [], _) => {
if method.ident.name.as_str() == "signum" {
0 // do not lint if cast comes from a `signum` function
} else {
nbits
}
},
_ => nbits,
}
}
pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
let msg = match (cast_from.kind(), cast_to.is_integral()) {
(ty::Int(_) | ty::Uint(_), true) => {
let from_nbits = apply_reductions(
cx,
utils::int_ty_to_nbits(cast_from, cx.tcx),
cast_expr,
cast_from.is_signed(),
);
let to_nbits = utils::int_ty_to_nbits(cast_to, cx.tcx);
let (should_lint, suffix) = match (is_isize_or_usize(cast_from), is_isize_or_usize(cast_to)) {
(true, true) | (false, false) => (to_nbits < from_nbits, ""),
(true, false) => (
to_nbits <= 32,
if to_nbits == 32 {
" on targets with 64-bit wide pointers"
} else {
""
},
),
(false, true) => (from_nbits == 64, " on targets with 32-bit wide pointers"),
};
if !should_lint {
return;
}
format!("casting `{cast_from}` to `{cast_to}` may truncate the value{suffix}",)
},
(ty::Adt(def, _), true) if def.is_enum() => {
let (from_nbits, variant) = if let ExprKind::Path(p) = &cast_expr.kind
&& let Res::Def(DefKind::Ctor(..), id) = cx.qpath_res(p, cast_expr.hir_id)
{
let i = def.variant_index_with_ctor_id(id);
let variant = def.variant(i);
let nbits = utils::enum_value_nbits(get_discriminant_value(cx.tcx, *def, i));
(nbits, Some(variant))
} else {
(utils::enum_ty_to_nbits(*def, cx.tcx), None)
};
let to_nbits = utils::int_ty_to_nbits(cast_to, cx.tcx);
let cast_from_ptr_size = def.repr().int.map_or(true, |ty| matches!(ty, IntegerType::Pointer(_),));
let suffix = match (cast_from_ptr_size, is_isize_or_usize(cast_to)) {
(false, false) if from_nbits > to_nbits => "",
(true, false) if from_nbits > to_nbits => "",
(false, true) if from_nbits > 64 => "",
(false, true) if from_nbits > 32 => " on targets with 32-bit wide pointers",
_ => return,
};
if let Some(variant) = variant {
span_lint(
cx,
CAST_ENUM_TRUNCATION,
expr.span,
&format!(
"casting `{cast_from}::{}` to `{cast_to}` will truncate the value{suffix}",
variant.name,
),
);
return;
}
format!("casting `{cast_from}` to `{cast_to}` may truncate the value{suffix}",)
},
(ty::Float(_), true) => {
format!("casting `{cast_from}` to `{cast_to}` may truncate the value")
},
(ty::Float(FloatTy::F64), false) if matches!(cast_to.kind(), &ty::Float(FloatTy::F32)) => {
"casting `f64` to `f32` may truncate the value".to_string()
},
_ => return,
};
span_lint(cx, CAST_POSSIBLE_TRUNCATION, expr.span, &msg);
}
|
