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|
use crate::consts::{constant, Constant};
use crate::utils::{sext, span_lint_and_then};
use if_chain::if_chain;
use rustc::ty::{self};
use rustc_hir::*;
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use std::fmt::Display;
declare_clippy_lint! {
/// **What it does:** Checks for modulo arithemtic.
///
/// **Why is this bad?** The results of modulo (%) operation might differ
/// depending on the language, when negative numbers are involved.
/// If you interop with different languages it might be beneficial
/// to double check all places that use modulo arithmetic.
///
/// For example, in Rust `17 % -3 = 2`, but in Python `17 % -3 = -1`.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// let x = -17 % 3;
/// ```
pub MODULO_ARITHMETIC,
restriction,
"any modulo arithmetic statement"
}
declare_lint_pass!(ModuloArithmetic => [MODULO_ARITHMETIC]);
struct OperandInfo {
string_representation: Option<String>,
is_negative: bool,
is_integral: bool,
}
fn analyze_operand(operand: &Expr<'_>, cx: &LateContext<'_, '_>, expr: &Expr<'_>) -> Option<OperandInfo> {
match constant(cx, cx.tables, operand) {
Some((Constant::Int(v), _)) => match cx.tables.expr_ty(expr).kind {
ty::Int(ity) => {
let value = sext(cx.tcx, v, ity);
return Some(OperandInfo {
string_representation: Some(value.to_string()),
is_negative: value < 0,
is_integral: true,
});
},
ty::Uint(_) => {
return Some(OperandInfo {
string_representation: None,
is_negative: false,
is_integral: true,
});
},
_ => {},
},
Some((Constant::F32(f), _)) => {
return Some(floating_point_operand_info(&f));
},
Some((Constant::F64(f), _)) => {
return Some(floating_point_operand_info(&f));
},
_ => {},
}
None
}
fn floating_point_operand_info<T: Display + PartialOrd + From<f32>>(f: &T) -> OperandInfo {
OperandInfo {
string_representation: Some(format!("{:.3}", *f)),
is_negative: *f < 0.0.into(),
is_integral: false,
}
}
fn might_have_negative_value(t: &ty::TyS<'_>) -> bool {
t.is_signed() || t.is_floating_point()
}
fn check_const_operands<'a, 'tcx>(
cx: &LateContext<'a, 'tcx>,
expr: &'tcx Expr<'_>,
lhs_operand: &OperandInfo,
rhs_operand: &OperandInfo,
) {
if lhs_operand.is_negative ^ rhs_operand.is_negative {
span_lint_and_then(
cx,
MODULO_ARITHMETIC,
expr.span,
&format!(
"you are using modulo operator on constants with different signs: `{} % {}`",
lhs_operand.string_representation.as_ref().unwrap(),
rhs_operand.string_representation.as_ref().unwrap()
),
|db| {
db.note("double check for expected result especially when interoperating with different languages");
if lhs_operand.is_integral {
db.note("or consider using `rem_euclid` or similar function");
}
},
);
}
}
fn check_non_const_operands<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>, operand: &Expr<'_>) {
let operand_type = cx.tables.expr_ty(operand);
if might_have_negative_value(operand_type) {
span_lint_and_then(
cx,
MODULO_ARITHMETIC,
expr.span,
"you are using modulo operator on types that might have different signs",
|db| {
db.note("double check for expected result especially when interoperating with different languages");
if operand_type.is_integral() {
db.note("or consider using `rem_euclid` or similar function");
}
},
);
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ModuloArithmetic {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
match &expr.kind {
ExprKind::Binary(op, lhs, rhs) | ExprKind::AssignOp(op, lhs, rhs) => {
if let BinOpKind::Rem = op.node {
let lhs_operand = analyze_operand(lhs, cx, expr);
let rhs_operand = analyze_operand(rhs, cx, expr);
if_chain! {
if let Some(lhs_operand) = lhs_operand;
if let Some(rhs_operand) = rhs_operand;
then {
check_const_operands(cx, expr, &lhs_operand, &rhs_operand);
}
else {
check_non_const_operands(cx, expr, lhs);
}
}
};
},
_ => {},
}
}
}
|
