1 //! lint on manually implemented checked conversions that could be transformed into `try_from`
3 use if_chain::if_chain;
4 use rustc_ast::ast::LitKind;
5 use rustc_errors::Applicability;
6 use rustc_hir::{BinOp, BinOpKind, Expr, ExprKind, QPath, TyKind};
7 use rustc_lint::{LateContext, LateLintPass, LintContext};
8 use rustc_middle::lint::in_external_macro;
9 use rustc_session::{declare_lint_pass, declare_tool_lint};
11 use crate::utils::{snippet_with_applicability, span_lint_and_sugg, SpanlessEq};
13 declare_clippy_lint! {
14 /// **What it does:** Checks for explicit bounds checking when casting.
16 /// **Why is this bad?** Reduces the readability of statements & is error prone.
18 /// **Known problems:** None.
22 /// # let foo: u32 = 5;
24 /// foo <= i32::MAX as u32
31 /// # use std::convert::TryFrom;
34 /// i32::try_from(foo).is_ok()
37 pub CHECKED_CONVERSIONS,
39 "`try_from` could replace manual bounds checking when casting"
42 declare_lint_pass!(CheckedConversions => [CHECKED_CONVERSIONS]);
44 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for CheckedConversions {
45 fn check_expr(&mut self, cx: &LateContext<'_, '_>, item: &Expr<'_>) {
46 let result = if_chain! {
47 if !in_external_macro(cx.sess(), item.span);
48 if let ExprKind::Binary(op, ref left, ref right) = &item.kind;
52 BinOpKind::Ge | BinOpKind::Le => single_check(item),
53 BinOpKind::And => double_check(cx, left, right),
62 if let Some(cv) = result;
63 if let Some(to_type) = cv.to_type;
66 let mut applicability = Applicability::MachineApplicable;
67 let snippet = snippet_with_applicability(cx, cv.expr_to_cast.span, "_", &mut
73 "Checked cast can be simplified.",
75 format!("{}::try_from({}).is_ok()",
85 /// Searches for a single check from unsigned to _ is done
86 /// todo: check for case signed -> larger unsigned == only x >= 0
87 fn single_check<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<Conversion<'tcx>> {
88 check_upper_bound(expr).filter(|cv| cv.cvt == ConversionType::FromUnsigned)
91 /// Searches for a combination of upper & lower bound checks
92 fn double_check<'a>(cx: &LateContext<'_, '_>, left: &'a Expr<'_>, right: &'a Expr<'_>) -> Option<Conversion<'a>> {
93 let upper_lower = |l, r| {
94 let upper = check_upper_bound(l);
95 let lower = check_lower_bound(r);
97 transpose(upper, lower).and_then(|(l, r)| l.combine(r, cx))
100 upper_lower(left, right).or_else(|| upper_lower(right, left))
103 /// Contains the result of a tried conversion check
104 #[derive(Clone, Debug)]
105 struct Conversion<'a> {
107 expr_to_cast: &'a Expr<'a>,
108 to_type: Option<&'a str>,
111 /// The kind of conversion that is checked
112 #[derive(Copy, Clone, Debug, PartialEq)]
113 enum ConversionType {
119 impl<'a> Conversion<'a> {
120 /// Combine multiple conversions if the are compatible
121 pub fn combine(self, other: Self, cx: &LateContext<'_, '_>) -> Option<Conversion<'a>> {
122 if self.is_compatible(&other, cx) {
123 // Prefer a Conversion that contains a type-constraint
124 Some(if self.to_type.is_some() { self } else { other })
130 /// Checks if two conversions are compatible
131 /// same type of conversion, same 'castee' and same 'to type'
132 pub fn is_compatible(&self, other: &Self, cx: &LateContext<'_, '_>) -> bool {
133 (self.cvt == other.cvt)
134 && (SpanlessEq::new(cx).eq_expr(self.expr_to_cast, other.expr_to_cast))
135 && (self.has_compatible_to_type(other))
138 /// Checks if the to-type is the same (if there is a type constraint)
139 fn has_compatible_to_type(&self, other: &Self) -> bool {
140 transpose(self.to_type.as_ref(), other.to_type.as_ref()).map_or(true, |(l, r)| l == r)
143 /// Try to construct a new conversion if the conversion type is valid
144 fn try_new(expr_to_cast: &'a Expr<'_>, from_type: &str, to_type: &'a str) -> Option<Conversion<'a>> {
145 ConversionType::try_new(from_type, to_type).map(|cvt| Conversion {
148 to_type: Some(to_type),
152 /// Construct a new conversion without type constraint
153 fn new_any(expr_to_cast: &'a Expr<'_>) -> Conversion<'a> {
155 cvt: ConversionType::SignedToUnsigned,
162 impl ConversionType {
163 /// Creates a conversion type if the type is allowed & conversion is valid
165 fn try_new(from: &str, to: &str) -> Option<Self> {
166 if UINTS.contains(&from) {
167 Some(Self::FromUnsigned)
168 } else if SINTS.contains(&from) {
169 if UINTS.contains(&to) {
170 Some(Self::SignedToUnsigned)
171 } else if SINTS.contains(&to) {
172 Some(Self::SignedToSigned)
182 /// Check for `expr <= (to_type::MAX as from_type)`
183 fn check_upper_bound<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<Conversion<'tcx>> {
185 if let ExprKind::Binary(ref op, ref left, ref right) = &expr.kind;
186 if let Some((candidate, check)) = normalize_le_ge(op, left, right);
187 if let Some((from, to)) = get_types_from_cast(check, MAX_VALUE, INTS);
190 Conversion::try_new(candidate, from, to)
197 /// Check for `expr >= 0|(to_type::MIN as from_type)`
198 fn check_lower_bound<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<Conversion<'tcx>> {
199 fn check_function<'a>(candidate: &'a Expr<'a>, check: &'a Expr<'a>) -> Option<Conversion<'a>> {
200 (check_lower_bound_zero(candidate, check)).or_else(|| (check_lower_bound_min(candidate, check)))
203 // First of we need a binary containing the expression & the cast
204 if let ExprKind::Binary(ref op, ref left, ref right) = &expr.kind {
205 normalize_le_ge(op, right, left).and_then(|(l, r)| check_function(l, r))
211 /// Check for `expr >= 0`
212 fn check_lower_bound_zero<'a>(candidate: &'a Expr<'_>, check: &'a Expr<'_>) -> Option<Conversion<'a>> {
214 if let ExprKind::Lit(ref lit) = &check.kind;
215 if let LitKind::Int(0, _) = &lit.node;
218 Some(Conversion::new_any(candidate))
225 /// Check for `expr >= (to_type::MIN as from_type)`
226 fn check_lower_bound_min<'a>(candidate: &'a Expr<'_>, check: &'a Expr<'_>) -> Option<Conversion<'a>> {
227 if let Some((from, to)) = get_types_from_cast(check, MIN_VALUE, SINTS) {
228 Conversion::try_new(candidate, from, to)
234 /// Tries to extract the from- and to-type from a cast expression
235 fn get_types_from_cast<'a>(expr: &'a Expr<'_>, func: &'a str, types: &'a [&str]) -> Option<(&'a str, &'a str)> {
236 // `to_type::maxmin_value() as from_type`
237 let call_from_cast: Option<(&Expr<'_>, &str)> = if_chain! {
238 // to_type::maxmin_value(), from_type
239 if let ExprKind::Cast(ref limit, ref from_type) = &expr.kind;
240 if let TyKind::Path(ref from_type_path) = &from_type.kind;
241 if let Some(from_sym) = int_ty_to_sym(from_type_path);
244 Some((limit, from_sym))
250 // `from_type::from(to_type::maxmin_value())`
251 let limit_from: Option<(&Expr<'_>, &str)> = call_from_cast.or_else(|| {
253 // `from_type::from, to_type::maxmin_value()`
254 if let ExprKind::Call(ref from_func, ref args) = &expr.kind;
255 // `to_type::maxmin_value()`
257 if let limit = &args[0];
259 if let ExprKind::Path(ref path) = &from_func.kind;
260 if let Some(from_sym) = get_implementing_type(path, INTS, FROM);
263 Some((limit, from_sym))
270 if let Some((limit, from_type)) = limit_from {
272 if let ExprKind::Call(ref fun_name, _) = &limit.kind;
273 // `to_type, maxmin_value`
274 if let ExprKind::Path(ref path) = &fun_name.kind;
276 if let Some(to_type) = get_implementing_type(path, types, func);
279 Some((from_type, to_type))
289 /// Gets the type which implements the called function
290 fn get_implementing_type<'a>(path: &QPath<'_>, candidates: &'a [&str], function: &str) -> Option<&'a str> {
292 if let QPath::TypeRelative(ref ty, ref path) = &path;
293 if path.ident.name.as_str() == function;
294 if let TyKind::Path(QPath::Resolved(None, ref tp)) = &ty.kind;
295 if let [int] = &*tp.segments;
296 let name = &int.ident.name.as_str();
299 candidates.iter().find(|c| name == *c).cloned()
306 /// Gets the type as a string, if it is a supported integer
307 fn int_ty_to_sym<'tcx>(path: &QPath<'_>) -> Option<&'tcx str> {
309 if let QPath::Resolved(_, ref path) = *path;
310 if let [ty] = &*path.segments;
311 let name = &ty.ident.name.as_str();
314 INTS.iter().find(|c| name == *c).cloned()
321 /// (Option<T>, Option<U>) -> Option<(T, U)>
322 fn transpose<T, U>(lhs: Option<T>, rhs: Option<U>) -> Option<(T, U)> {
324 (Some(l), Some(r)) => Some((l, r)),
329 /// Will return the expressions as if they were expr1 <= expr2
330 fn normalize_le_ge<'a>(op: &BinOp, left: &'a Expr<'a>, right: &'a Expr<'a>) -> Option<(&'a Expr<'a>, &'a Expr<'a>)> {
332 BinOpKind::Le => Some((left, right)),
333 BinOpKind::Ge => Some((right, left)),
339 const FROM: &str = "from";
340 const MAX_VALUE: &str = "max_value";
341 const MIN_VALUE: &str = "min_value";
343 const UINTS: &[&str] = &["u8", "u16", "u32", "u64", "usize"];
344 const SINTS: &[&str] = &["i8", "i16", "i32", "i64", "isize"];
345 const INTS: &[&str] = &["u8", "u16", "u32", "u64", "usize", "i8", "i16", "i32", "i64", "isize"];