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https://github.com/rust-lang/rust-clippy
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avoid linting possible_truncation
on bit-reducing operations
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df65291edd
commit
00ea73e162
3 changed files with 101 additions and 9 deletions
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@ -1,23 +1,88 @@
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use clippy_utils::consts::{constant, Constant};
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use clippy_utils::diagnostics::span_lint;
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use clippy_utils::expr_or_init;
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use clippy_utils::ty::is_isize_or_usize;
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use rustc_hir::{Expr, ExprKind};
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use rustc_hir::{BinOpKind, Expr, ExprKind};
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use rustc_lint::LateContext;
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use rustc_middle::ty::{self, FloatTy, Ty};
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use super::{utils, CAST_POSSIBLE_TRUNCATION};
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pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
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// do not lint if cast comes from a `signum` function
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if let ExprKind::MethodCall(path, ..) = expr_or_init(cx, cast_expr).kind {
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if path.ident.name.as_str() == "signum" {
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return;
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}
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fn constant_int(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<u128> {
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if let Some((Constant::Int(c), _)) = constant(cx, cx.typeck_results(), expr) {
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Some(c)
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} else {
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None
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}
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}
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fn get_constant_bits(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<u64> {
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constant_int(cx, expr).map(|c| u64::from(128 - c.leading_zeros()))
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}
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fn apply_reductions(cx: &LateContext<'_>, nbits: u64, expr: &Expr<'_>, signed: bool) -> u64 {
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match expr_or_init(cx, expr).kind {
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ExprKind::Cast(inner, _) => apply_reductions(cx, nbits, inner, signed),
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ExprKind::Block(block, _) => block.expr.map_or(nbits, |e| apply_reductions(cx, nbits, e, signed)),
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ExprKind::Binary(op, left, right) => match op.node {
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BinOpKind::Div => {
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apply_reductions(cx, nbits, left, signed)
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- (if signed {
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0 // let's be conservative here
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} else {
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// by dividing by 1, we remove 0 bits, etc.
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get_constant_bits(cx, right).map_or(0, |b| b.saturating_sub(1))
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})
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},
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BinOpKind::Rem | BinOpKind::BitAnd => get_constant_bits(cx, right)
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.unwrap_or(u64::max_value())
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.min(apply_reductions(cx, nbits, left, signed)),
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BinOpKind::Shr => {
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apply_reductions(cx, nbits, left, signed)
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- constant_int(cx, right).map_or(0, |s| u64::try_from(s).expect("shift too high"))
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},
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_ => nbits,
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},
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ExprKind::MethodCall(method, _, [left, right], _) => {
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if signed {
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return nbits;
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}
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let max_bits = if method.ident.as_str() == "min" {
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get_constant_bits(cx, right)
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} else {
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None
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};
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apply_reductions(cx, nbits, left, signed).min(max_bits.unwrap_or(u64::max_value()))
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},
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ExprKind::MethodCall(method, _, [_, lo, hi], _) => {
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if method.ident.as_str() == "clamp" {
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//FIXME: make this a diagnostic item
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if let (Some(lo_bits), Some(hi_bits)) = (get_constant_bits(cx, lo), get_constant_bits(cx, hi)) {
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return lo_bits.max(hi_bits);
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}
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}
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nbits
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},
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ExprKind::MethodCall(method, _, [_value], _) => {
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if method.ident.name.as_str() == "signum" {
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0 // do not lint if cast comes from a `signum` function
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} else {
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nbits
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}
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},
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_ => nbits,
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}
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}
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pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
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let msg = match (cast_from.is_integral(), cast_to.is_integral()) {
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(true, true) => {
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let from_nbits = utils::int_ty_to_nbits(cast_from, cx.tcx);
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let from_nbits = apply_reductions(
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cx,
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utils::int_ty_to_nbits(cast_from, cx.tcx),
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cast_expr,
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cast_from.is_signed(),
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);
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let to_nbits = utils::int_ty_to_nbits(cast_to, cx.tcx);
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let (should_lint, suffix) = match (is_isize_or_usize(cast_from), is_isize_or_usize(cast_to)) {
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@ -100,4 +100,19 @@ fn main() {
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let s = x.signum();
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let _ = s as i32;
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// Test for signed min
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(-99999999999i64).min(1) as i8; // should be linted because signed
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// Test for various operations that remove enough bits for the result to fit
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(999999u64 & 1) as u8;
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(999999u64 % 15) as u8;
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(999999u64 / 0x1_0000_0000_0000) as u16;
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({ 999999u64 >> 56 }) as u8;
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({
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let x = 999999u64;
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x.min(1)
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}) as u8;
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999999u64.clamp(0, 255) as u8;
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999999u64.clamp(0, 256) as u8; // should still be linted
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}
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@ -138,5 +138,17 @@ error: casting `isize` to `usize` may lose the sign of the value
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LL | -1isize as usize;
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| ^^^^^^^^^^^^^^^^
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error: aborting due to 22 previous errors
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error: casting `i64` to `i8` may truncate the value
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--> $DIR/cast.rs:105:5
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LL | (-99999999999i64).min(1) as i8; // should be linted because signed
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: casting `u64` to `u8` may truncate the value
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--> $DIR/cast.rs:117:5
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LL | 999999u64.clamp(0, 256) as u8; // should still be linted
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: aborting due to 24 previous errors
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