310 lines
10 KiB
Rust
310 lines
10 KiB
Rust
use clippy_config::Conf;
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use clippy_config::msrvs::{self, Msrv};
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use clippy_utils::diagnostics::span_lint_and_sugg;
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use clippy_utils::source::snippet_with_applicability;
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use clippy_utils::{SpanlessEq, is_in_const_context, is_integer_literal};
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use rustc_errors::Applicability;
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use rustc_hir::{BinOpKind, Expr, ExprKind, QPath, TyKind};
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use rustc_lint::{LateContext, LateLintPass, LintContext};
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use rustc_middle::lint::in_external_macro;
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use rustc_session::impl_lint_pass;
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for explicit bounds checking when casting.
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///
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/// ### Why is this bad?
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/// Reduces the readability of statements & is error prone.
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///
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/// ### Example
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/// ```no_run
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/// # let foo: u32 = 5;
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/// foo <= i32::MAX as u32;
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/// ```
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///
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/// Use instead:
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/// ```no_run
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/// # let foo = 1;
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/// # #[allow(unused)]
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/// i32::try_from(foo).is_ok();
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/// ```
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#[clippy::version = "1.37.0"]
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pub CHECKED_CONVERSIONS,
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pedantic,
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"`try_from` could replace manual bounds checking when casting"
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}
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pub struct CheckedConversions {
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msrv: Msrv,
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}
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impl CheckedConversions {
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pub fn new(conf: &'static Conf) -> Self {
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Self {
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msrv: conf.msrv.clone(),
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}
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}
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}
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impl_lint_pass!(CheckedConversions => [CHECKED_CONVERSIONS]);
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impl LateLintPass<'_> for CheckedConversions {
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fn check_expr(&mut self, cx: &LateContext<'_>, item: &Expr<'_>) {
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if let ExprKind::Binary(op, lhs, rhs) = item.kind
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&& let (lt1, gt1, op2) = match op.node {
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BinOpKind::Le => (lhs, rhs, None),
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BinOpKind::Ge => (rhs, lhs, None),
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BinOpKind::And
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if let ExprKind::Binary(op1, lhs1, rhs1) = lhs.kind
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&& let ExprKind::Binary(op2, lhs2, rhs2) = rhs.kind
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&& let Some((lt1, gt1)) = read_le_ge(op1.node, lhs1, rhs1)
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&& let Some((lt2, gt2)) = read_le_ge(op2.node, lhs2, rhs2) =>
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{
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(lt1, gt1, Some((lt2, gt2)))
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},
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_ => return,
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}
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&& !in_external_macro(cx.sess(), item.span)
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&& !is_in_const_context(cx)
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&& self.msrv.meets(msrvs::TRY_FROM)
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&& let Some(cv) = match op2 {
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// todo: check for case signed -> larger unsigned == only x >= 0
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None => check_upper_bound(lt1, gt1).filter(|cv| cv.cvt == ConversionType::FromUnsigned),
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Some((lt2, gt2)) => {
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let upper_lower = |lt1, gt1, lt2, gt2| {
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check_upper_bound(lt1, gt1)
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.zip(check_lower_bound(lt2, gt2))
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.and_then(|(l, r)| l.combine(r, cx))
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};
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upper_lower(lt1, gt1, lt2, gt2).or_else(|| upper_lower(lt2, gt2, lt1, gt1))
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},
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}
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&& let Some(to_type) = cv.to_type
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{
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let mut applicability = Applicability::MachineApplicable;
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let snippet = snippet_with_applicability(cx, cv.expr_to_cast.span, "_", &mut applicability);
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span_lint_and_sugg(
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cx,
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CHECKED_CONVERSIONS,
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item.span,
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"checked cast can be simplified",
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"try",
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format!("{to_type}::try_from({snippet}).is_ok()"),
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applicability,
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);
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}
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}
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extract_msrv_attr!(LateContext);
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}
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/// Contains the result of a tried conversion check
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#[derive(Clone, Debug)]
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struct Conversion<'a> {
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cvt: ConversionType,
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expr_to_cast: &'a Expr<'a>,
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to_type: Option<&'a str>,
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}
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/// The kind of conversion that is checked
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#[derive(Copy, Clone, Debug, PartialEq, Eq)]
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enum ConversionType {
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SignedToUnsigned,
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SignedToSigned,
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FromUnsigned,
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}
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/// Attempts to read either `<=` or `>=` with a normalized operand order.
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fn read_le_ge<'tcx>(
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op: BinOpKind,
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lhs: &'tcx Expr<'tcx>,
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rhs: &'tcx Expr<'tcx>,
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) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
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match op {
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BinOpKind::Le => Some((lhs, rhs)),
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BinOpKind::Ge => Some((rhs, lhs)),
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_ => None,
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}
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}
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impl<'a> Conversion<'a> {
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/// Combine multiple conversions if the are compatible
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pub fn combine(self, other: Self, cx: &LateContext<'_>) -> Option<Conversion<'a>> {
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if self.is_compatible(&other, cx) {
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// Prefer a Conversion that contains a type-constraint
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Some(if self.to_type.is_some() { self } else { other })
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} else {
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None
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}
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}
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/// Checks if two conversions are compatible
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/// same type of conversion, same 'castee' and same 'to type'
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pub fn is_compatible(&self, other: &Self, cx: &LateContext<'_>) -> bool {
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(self.cvt == other.cvt)
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&& (SpanlessEq::new(cx).eq_expr(self.expr_to_cast, other.expr_to_cast))
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&& (self.has_compatible_to_type(other))
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}
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/// Checks if the to-type is the same (if there is a type constraint)
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fn has_compatible_to_type(&self, other: &Self) -> bool {
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match (self.to_type, other.to_type) {
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(Some(l), Some(r)) => l == r,
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_ => true,
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}
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}
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/// Try to construct a new conversion if the conversion type is valid
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fn try_new(expr_to_cast: &'a Expr<'_>, from_type: &str, to_type: &'a str) -> Option<Conversion<'a>> {
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ConversionType::try_new(from_type, to_type).map(|cvt| Conversion {
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cvt,
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expr_to_cast,
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to_type: Some(to_type),
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})
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}
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/// Construct a new conversion without type constraint
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fn new_any(expr_to_cast: &'a Expr<'_>) -> Conversion<'a> {
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Conversion {
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cvt: ConversionType::SignedToUnsigned,
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expr_to_cast,
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to_type: None,
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}
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}
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}
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impl ConversionType {
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/// Creates a conversion type if the type is allowed & conversion is valid
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#[must_use]
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fn try_new(from: &str, to: &str) -> Option<Self> {
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if UINTS.contains(&from) {
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Some(Self::FromUnsigned)
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} else if SINTS.contains(&from) {
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if UINTS.contains(&to) {
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Some(Self::SignedToUnsigned)
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} else if SINTS.contains(&to) {
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Some(Self::SignedToSigned)
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} else {
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None
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}
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} else {
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None
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}
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}
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}
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/// Check for `expr <= (to_type::MAX as from_type)`
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fn check_upper_bound<'tcx>(lt: &'tcx Expr<'tcx>, gt: &'tcx Expr<'tcx>) -> Option<Conversion<'tcx>> {
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if let Some((from, to)) = get_types_from_cast(gt, INTS, "max_value", "MAX") {
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Conversion::try_new(lt, from, to)
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} else {
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None
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}
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}
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/// Check for `expr >= 0|(to_type::MIN as from_type)`
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fn check_lower_bound<'tcx>(lt: &'tcx Expr<'tcx>, gt: &'tcx Expr<'tcx>) -> Option<Conversion<'tcx>> {
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check_lower_bound_zero(gt, lt).or_else(|| check_lower_bound_min(gt, lt))
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}
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/// Check for `expr >= 0`
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fn check_lower_bound_zero<'a>(candidate: &'a Expr<'_>, check: &'a Expr<'_>) -> Option<Conversion<'a>> {
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is_integer_literal(check, 0).then(|| Conversion::new_any(candidate))
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}
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/// Check for `expr >= (to_type::MIN as from_type)`
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fn check_lower_bound_min<'a>(candidate: &'a Expr<'_>, check: &'a Expr<'_>) -> Option<Conversion<'a>> {
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if let Some((from, to)) = get_types_from_cast(check, SINTS, "min_value", "MIN") {
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Conversion::try_new(candidate, from, to)
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} else {
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None
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}
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}
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/// Tries to extract the from- and to-type from a cast expression
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fn get_types_from_cast<'a>(
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expr: &'a Expr<'_>,
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types: &'a [&str],
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func: &'a str,
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assoc_const: &'a str,
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) -> Option<(&'a str, &'a str)> {
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// `to_type::max_value() as from_type`
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// or `to_type::MAX as from_type`
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let call_from_cast: Option<(&Expr<'_>, &str)> = if let ExprKind::Cast(limit, from_type) = &expr.kind
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// to_type::max_value(), from_type
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&& let TyKind::Path(ref from_type_path) = &from_type.kind
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&& let Some(from_sym) = int_ty_to_sym(from_type_path)
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{
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Some((limit, from_sym))
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} else {
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None
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};
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// `from_type::from(to_type::max_value())`
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let limit_from: Option<(&Expr<'_>, &str)> = call_from_cast.or_else(|| {
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if let ExprKind::Call(from_func, [limit]) = &expr.kind
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// `from_type::from, to_type::max_value()`
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// `from_type::from`
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&& let ExprKind::Path(ref path) = &from_func.kind
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&& let Some(from_sym) = get_implementing_type(path, INTS, "from")
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{
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Some((limit, from_sym))
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} else {
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None
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}
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});
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if let Some((limit, from_type)) = limit_from {
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match limit.kind {
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// `from_type::from(_)`
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ExprKind::Call(path, _) => {
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if let ExprKind::Path(ref path) = path.kind {
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// `to_type`
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if let Some(to_type) = get_implementing_type(path, types, func) {
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return Some((from_type, to_type));
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}
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}
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},
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// `to_type::MAX`
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ExprKind::Path(ref path) => {
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if let Some(to_type) = get_implementing_type(path, types, assoc_const) {
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return Some((from_type, to_type));
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}
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},
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_ => {},
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}
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};
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None
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}
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/// Gets the type which implements the called function
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fn get_implementing_type<'a>(path: &QPath<'_>, candidates: &'a [&str], function: &str) -> Option<&'a str> {
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if let QPath::TypeRelative(ty, path) = &path
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&& path.ident.name.as_str() == function
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&& let TyKind::Path(QPath::Resolved(None, tp)) = &ty.kind
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&& let [int] = tp.segments
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{
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let name = int.ident.name.as_str();
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candidates.iter().find(|c| &name == *c).copied()
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} else {
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None
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}
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}
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/// Gets the type as a string, if it is a supported integer
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fn int_ty_to_sym<'tcx>(path: &QPath<'_>) -> Option<&'tcx str> {
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if let QPath::Resolved(_, path) = *path
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&& let [ty] = path.segments
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{
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let name = ty.ident.name.as_str();
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INTS.iter().find(|c| &name == *c).copied()
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} else {
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None
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}
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}
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// Constants
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const UINTS: &[&str] = &["u8", "u16", "u32", "u64", "usize"];
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const SINTS: &[&str] = &["i8", "i16", "i32", "i64", "isize"];
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const INTS: &[&str] = &["u8", "u16", "u32", "u64", "usize", "i8", "i16", "i32", "i64", "isize"];
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