1 //! lint on manually implemented checked conversions that could be transformed into `try_from`
3 use clippy_utils::diagnostics::span_lint_and_sugg;
4 use clippy_utils::source::snippet_with_applicability;
5 use clippy_utils::{in_constant, meets_msrv, msrvs, SpanlessEq};
6 use if_chain::if_chain;
7 use rustc_ast::ast::LitKind;
8 use rustc_errors::Applicability;
9 use rustc_hir::{BinOp, BinOpKind, Expr, ExprKind, QPath, TyKind};
10 use rustc_lint::{LateContext, LateLintPass, LintContext};
11 use rustc_middle::lint::in_external_macro;
12 use rustc_semver::RustcVersion;
13 use rustc_session::{declare_tool_lint, impl_lint_pass};
15 declare_clippy_lint! {
17 /// Checks for explicit bounds checking when casting.
19 /// ### Why is this bad?
20 /// Reduces the readability of statements & is error prone.
24 /// # let foo: u32 = 5;
25 /// foo <= i32::MAX as u32;
31 /// # #[allow(unused)]
32 /// i32::try_from(foo).is_ok();
34 #[clippy::version = "1.37.0"]
35 pub CHECKED_CONVERSIONS,
37 "`try_from` could replace manual bounds checking when casting"
40 pub struct CheckedConversions {
41 msrv: Option<RustcVersion>,
44 impl CheckedConversions {
46 pub fn new(msrv: Option<RustcVersion>) -> Self {
51 impl_lint_pass!(CheckedConversions => [CHECKED_CONVERSIONS]);
53 impl<'tcx> LateLintPass<'tcx> for CheckedConversions {
54 fn check_expr(&mut self, cx: &LateContext<'_>, item: &Expr<'_>) {
55 if !meets_msrv(self.msrv, msrvs::TRY_FROM) {
59 let result = if_chain! {
60 if !in_constant(cx, item.hir_id);
61 if !in_external_macro(cx.sess(), item.span);
62 if let ExprKind::Binary(op, left, right) = &item.kind;
66 BinOpKind::Ge | BinOpKind::Le => single_check(item),
67 BinOpKind::And => double_check(cx, left, right),
75 if let Some(cv) = result {
76 if let Some(to_type) = cv.to_type {
77 let mut applicability = Applicability::MachineApplicable;
78 let snippet = snippet_with_applicability(cx, cv.expr_to_cast.span, "_", &mut applicability);
83 "checked cast can be simplified",
85 format!("{}::try_from({}).is_ok()", to_type, snippet),
92 extract_msrv_attr!(LateContext);
95 /// Searches for a single check from unsigned to _ is done
96 /// todo: check for case signed -> larger unsigned == only x >= 0
97 fn single_check<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<Conversion<'tcx>> {
98 check_upper_bound(expr).filter(|cv| cv.cvt == ConversionType::FromUnsigned)
101 /// Searches for a combination of upper & lower bound checks
102 fn double_check<'a>(cx: &LateContext<'_>, left: &'a Expr<'_>, right: &'a Expr<'_>) -> Option<Conversion<'a>> {
103 let upper_lower = |l, r| {
104 let upper = check_upper_bound(l);
105 let lower = check_lower_bound(r);
107 upper.zip(lower).and_then(|(l, r)| l.combine(r, cx))
110 upper_lower(left, right).or_else(|| upper_lower(right, left))
113 /// Contains the result of a tried conversion check
114 #[derive(Clone, Debug)]
115 struct Conversion<'a> {
117 expr_to_cast: &'a Expr<'a>,
118 to_type: Option<&'a str>,
121 /// The kind of conversion that is checked
122 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
123 enum ConversionType {
129 impl<'a> Conversion<'a> {
130 /// Combine multiple conversions if the are compatible
131 pub fn combine(self, other: Self, cx: &LateContext<'_>) -> Option<Conversion<'a>> {
132 if self.is_compatible(&other, cx) {
133 // Prefer a Conversion that contains a type-constraint
134 Some(if self.to_type.is_some() { self } else { other })
140 /// Checks if two conversions are compatible
141 /// same type of conversion, same 'castee' and same 'to type'
142 pub fn is_compatible(&self, other: &Self, cx: &LateContext<'_>) -> bool {
143 (self.cvt == other.cvt)
144 && (SpanlessEq::new(cx).eq_expr(self.expr_to_cast, other.expr_to_cast))
145 && (self.has_compatible_to_type(other))
148 /// Checks if the to-type is the same (if there is a type constraint)
149 fn has_compatible_to_type(&self, other: &Self) -> bool {
150 match (self.to_type, other.to_type) {
151 (Some(l), Some(r)) => l == r,
156 /// Try to construct a new conversion if the conversion type is valid
157 fn try_new(expr_to_cast: &'a Expr<'_>, from_type: &str, to_type: &'a str) -> Option<Conversion<'a>> {
158 ConversionType::try_new(from_type, to_type).map(|cvt| Conversion {
161 to_type: Some(to_type),
165 /// Construct a new conversion without type constraint
166 fn new_any(expr_to_cast: &'a Expr<'_>) -> Conversion<'a> {
168 cvt: ConversionType::SignedToUnsigned,
175 impl ConversionType {
176 /// Creates a conversion type if the type is allowed & conversion is valid
178 fn try_new(from: &str, to: &str) -> Option<Self> {
179 if UINTS.contains(&from) {
180 Some(Self::FromUnsigned)
181 } else if SINTS.contains(&from) {
182 if UINTS.contains(&to) {
183 Some(Self::SignedToUnsigned)
184 } else if SINTS.contains(&to) {
185 Some(Self::SignedToSigned)
195 /// Check for `expr <= (to_type::MAX as from_type)`
196 fn check_upper_bound<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<Conversion<'tcx>> {
198 if let ExprKind::Binary(ref op, left, right) = &expr.kind;
199 if let Some((candidate, check)) = normalize_le_ge(op, left, right);
200 if let Some((from, to)) = get_types_from_cast(check, INTS, "max_value", "MAX");
203 Conversion::try_new(candidate, from, to)
210 /// Check for `expr >= 0|(to_type::MIN as from_type)`
211 fn check_lower_bound<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<Conversion<'tcx>> {
212 fn check_function<'a>(candidate: &'a Expr<'a>, check: &'a Expr<'a>) -> Option<Conversion<'a>> {
213 (check_lower_bound_zero(candidate, check)).or_else(|| (check_lower_bound_min(candidate, check)))
216 // First of we need a binary containing the expression & the cast
217 if let ExprKind::Binary(ref op, left, right) = &expr.kind {
218 normalize_le_ge(op, right, left).and_then(|(l, r)| check_function(l, r))
224 /// Check for `expr >= 0`
225 fn check_lower_bound_zero<'a>(candidate: &'a Expr<'_>, check: &'a Expr<'_>) -> Option<Conversion<'a>> {
227 if let ExprKind::Lit(ref lit) = &check.kind;
228 if let LitKind::Int(0, _) = &lit.node;
231 Some(Conversion::new_any(candidate))
238 /// Check for `expr >= (to_type::MIN as from_type)`
239 fn check_lower_bound_min<'a>(candidate: &'a Expr<'_>, check: &'a Expr<'_>) -> Option<Conversion<'a>> {
240 if let Some((from, to)) = get_types_from_cast(check, SINTS, "min_value", "MIN") {
241 Conversion::try_new(candidate, from, to)
247 /// Tries to extract the from- and to-type from a cast expression
248 fn get_types_from_cast<'a>(
252 assoc_const: &'a str,
253 ) -> Option<(&'a str, &'a str)> {
254 // `to_type::max_value() as from_type`
255 // or `to_type::MAX as from_type`
256 let call_from_cast: Option<(&Expr<'_>, &str)> = if_chain! {
257 // to_type::max_value(), from_type
258 if let ExprKind::Cast(limit, from_type) = &expr.kind;
259 if let TyKind::Path(ref from_type_path) = &from_type.kind;
260 if let Some(from_sym) = int_ty_to_sym(from_type_path);
263 Some((limit, from_sym))
269 // `from_type::from(to_type::max_value())`
270 let limit_from: Option<(&Expr<'_>, &str)> = call_from_cast.or_else(|| {
272 // `from_type::from, to_type::max_value()`
273 if let ExprKind::Call(from_func, [limit]) = &expr.kind;
275 if let ExprKind::Path(ref path) = &from_func.kind;
276 if let Some(from_sym) = get_implementing_type(path, INTS, "from");
279 Some((limit, from_sym))
286 if let Some((limit, from_type)) = limit_from {
288 // `from_type::from(_)`
289 ExprKind::Call(path, _) => {
290 if let ExprKind::Path(ref path) = path.kind {
292 if let Some(to_type) = get_implementing_type(path, types, func) {
293 return Some((from_type, to_type));
298 ExprKind::Path(ref path) => {
299 if let Some(to_type) = get_implementing_type(path, types, assoc_const) {
300 return Some((from_type, to_type));
309 /// Gets the type which implements the called function
310 fn get_implementing_type<'a>(path: &QPath<'_>, candidates: &'a [&str], function: &str) -> Option<&'a str> {
312 if let QPath::TypeRelative(ty, path) = &path;
313 if path.ident.name.as_str() == function;
314 if let TyKind::Path(QPath::Resolved(None, tp)) = &ty.kind;
315 if let [int] = tp.segments;
317 let name = int.ident.name.as_str();
318 candidates.iter().find(|c| &name == *c).copied()
325 /// Gets the type as a string, if it is a supported integer
326 fn int_ty_to_sym<'tcx>(path: &QPath<'_>) -> Option<&'tcx str> {
328 if let QPath::Resolved(_, path) = *path;
329 if let [ty] = path.segments;
331 let name = ty.ident.name.as_str();
332 INTS.iter().find(|c| &name == *c).copied()
339 /// Will return the expressions as if they were expr1 <= expr2
340 fn normalize_le_ge<'a>(op: &BinOp, left: &'a Expr<'a>, right: &'a Expr<'a>) -> Option<(&'a Expr<'a>, &'a Expr<'a>)> {
342 BinOpKind::Le => Some((left, right)),
343 BinOpKind::Ge => Some((right, left)),
349 const UINTS: &[&str] = &["u8", "u16", "u32", "u64", "usize"];
350 const SINTS: &[&str] = &["i8", "i16", "i32", "i64", "isize"];
351 const INTS: &[&str] = &["u8", "u16", "u32", "u64", "usize", "i8", "i16", "i32", "i64", "isize"];