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<'tcx> LateLintPass<'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),
61 if let Some(cv) = result {
62 if let Some(to_type) = cv.to_type {
63 let mut applicability = Applicability::MachineApplicable;
64 let snippet = snippet_with_applicability(cx, cv.expr_to_cast.span, "_", &mut applicability);
69 "checked cast can be simplified",
71 format!("{}::try_from({}).is_ok()", to_type, snippet),
79 /// Searches for a single check from unsigned to _ is done
80 /// todo: check for case signed -> larger unsigned == only x >= 0
81 fn single_check<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<Conversion<'tcx>> {
82 check_upper_bound(expr).filter(|cv| cv.cvt == ConversionType::FromUnsigned)
85 /// Searches for a combination of upper & lower bound checks
86 fn double_check<'a>(cx: &LateContext<'_>, left: &'a Expr<'_>, right: &'a Expr<'_>) -> Option<Conversion<'a>> {
87 let upper_lower = |l, r| {
88 let upper = check_upper_bound(l);
89 let lower = check_lower_bound(r);
91 upper.zip(lower).and_then(|(l, r)| l.combine(r, cx))
94 upper_lower(left, right).or_else(|| upper_lower(right, left))
97 /// Contains the result of a tried conversion check
98 #[derive(Clone, Debug)]
99 struct Conversion<'a> {
101 expr_to_cast: &'a Expr<'a>,
102 to_type: Option<&'a str>,
105 /// The kind of conversion that is checked
106 #[derive(Copy, Clone, Debug, PartialEq)]
107 enum ConversionType {
113 impl<'a> Conversion<'a> {
114 /// Combine multiple conversions if the are compatible
115 pub fn combine(self, other: Self, cx: &LateContext<'_>) -> Option<Conversion<'a>> {
116 if self.is_compatible(&other, cx) {
117 // Prefer a Conversion that contains a type-constraint
118 Some(if self.to_type.is_some() { self } else { other })
124 /// Checks if two conversions are compatible
125 /// same type of conversion, same 'castee' and same 'to type'
126 pub fn is_compatible(&self, other: &Self, cx: &LateContext<'_>) -> bool {
127 (self.cvt == other.cvt)
128 && (SpanlessEq::new(cx).eq_expr(self.expr_to_cast, other.expr_to_cast))
129 && (self.has_compatible_to_type(other))
132 /// Checks if the to-type is the same (if there is a type constraint)
133 fn has_compatible_to_type(&self, other: &Self) -> bool {
134 match (self.to_type, other.to_type) {
135 (Some(l), Some(r)) => l == r,
140 /// Try to construct a new conversion if the conversion type is valid
141 fn try_new(expr_to_cast: &'a Expr<'_>, from_type: &str, to_type: &'a str) -> Option<Conversion<'a>> {
142 ConversionType::try_new(from_type, to_type).map(|cvt| Conversion {
145 to_type: Some(to_type),
149 /// Construct a new conversion without type constraint
150 fn new_any(expr_to_cast: &'a Expr<'_>) -> Conversion<'a> {
152 cvt: ConversionType::SignedToUnsigned,
159 impl ConversionType {
160 /// Creates a conversion type if the type is allowed & conversion is valid
162 fn try_new(from: &str, to: &str) -> Option<Self> {
163 if UINTS.contains(&from) {
164 Some(Self::FromUnsigned)
165 } else if SINTS.contains(&from) {
166 if UINTS.contains(&to) {
167 Some(Self::SignedToUnsigned)
168 } else if SINTS.contains(&to) {
169 Some(Self::SignedToSigned)
179 /// Check for `expr <= (to_type::MAX as from_type)`
180 fn check_upper_bound<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<Conversion<'tcx>> {
182 if let ExprKind::Binary(ref op, ref left, ref right) = &expr.kind;
183 if let Some((candidate, check)) = normalize_le_ge(op, left, right);
184 if let Some((from, to)) = get_types_from_cast(check, INTS, "max_value", "MAX");
187 Conversion::try_new(candidate, from, to)
194 /// Check for `expr >= 0|(to_type::MIN as from_type)`
195 fn check_lower_bound<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<Conversion<'tcx>> {
196 fn check_function<'a>(candidate: &'a Expr<'a>, check: &'a Expr<'a>) -> Option<Conversion<'a>> {
197 (check_lower_bound_zero(candidate, check)).or_else(|| (check_lower_bound_min(candidate, check)))
200 // First of we need a binary containing the expression & the cast
201 if let ExprKind::Binary(ref op, ref left, ref right) = &expr.kind {
202 normalize_le_ge(op, right, left).and_then(|(l, r)| check_function(l, r))
208 /// Check for `expr >= 0`
209 fn check_lower_bound_zero<'a>(candidate: &'a Expr<'_>, check: &'a Expr<'_>) -> Option<Conversion<'a>> {
211 if let ExprKind::Lit(ref lit) = &check.kind;
212 if let LitKind::Int(0, _) = &lit.node;
215 Some(Conversion::new_any(candidate))
222 /// Check for `expr >= (to_type::MIN as from_type)`
223 fn check_lower_bound_min<'a>(candidate: &'a Expr<'_>, check: &'a Expr<'_>) -> Option<Conversion<'a>> {
224 if let Some((from, to)) = get_types_from_cast(check, SINTS, "min_value", "MIN") {
225 Conversion::try_new(candidate, from, to)
231 /// Tries to extract the from- and to-type from a cast expression
232 fn get_types_from_cast<'a>(
236 assoc_const: &'a str,
237 ) -> Option<(&'a str, &'a str)> {
238 // `to_type::max_value() as from_type`
239 // or `to_type::MAX as from_type`
240 let call_from_cast: Option<(&Expr<'_>, &str)> = if_chain! {
241 // to_type::max_value(), from_type
242 if let ExprKind::Cast(ref limit, ref from_type) = &expr.kind;
243 if let TyKind::Path(ref from_type_path) = &from_type.kind;
244 if let Some(from_sym) = int_ty_to_sym(from_type_path);
247 Some((limit, from_sym))
253 // `from_type::from(to_type::max_value())`
254 let limit_from: Option<(&Expr<'_>, &str)> = call_from_cast.or_else(|| {
256 // `from_type::from, to_type::max_value()`
257 if let ExprKind::Call(ref from_func, ref args) = &expr.kind;
258 // `to_type::max_value()`
260 if let limit = &args[0];
262 if let ExprKind::Path(ref path) = &from_func.kind;
263 if let Some(from_sym) = get_implementing_type(path, INTS, "from");
266 Some((limit, from_sym))
273 if let Some((limit, from_type)) = limit_from {
275 // `from_type::from(_)`
276 ExprKind::Call(path, _) => {
277 if let ExprKind::Path(ref path) = path.kind {
279 if let Some(to_type) = get_implementing_type(path, types, func) {
280 return Some((from_type, to_type));
285 ExprKind::Path(ref path) => {
286 if let Some(to_type) = get_implementing_type(path, types, assoc_const) {
287 return Some((from_type, to_type));
296 /// Gets the type which implements the called function
297 fn get_implementing_type<'a>(path: &QPath<'_>, candidates: &'a [&str], function: &str) -> Option<&'a str> {
299 if let QPath::TypeRelative(ref ty, ref path) = &path;
300 if path.ident.name.as_str() == function;
301 if let TyKind::Path(QPath::Resolved(None, ref tp)) = &ty.kind;
302 if let [int] = &*tp.segments;
303 let name = &int.ident.name.as_str();
306 candidates.iter().find(|c| name == *c).cloned()
313 /// Gets the type as a string, if it is a supported integer
314 fn int_ty_to_sym<'tcx>(path: &QPath<'_>) -> Option<&'tcx str> {
316 if let QPath::Resolved(_, ref path) = *path;
317 if let [ty] = &*path.segments;
318 let name = &ty.ident.name.as_str();
321 INTS.iter().find(|c| name == *c).cloned()
328 /// Will return the expressions as if they were expr1 <= expr2
329 fn normalize_le_ge<'a>(op: &BinOp, left: &'a Expr<'a>, right: &'a Expr<'a>) -> Option<(&'a Expr<'a>, &'a Expr<'a>)> {
331 BinOpKind::Le => Some((left, right)),
332 BinOpKind::Ge => Some((right, left)),
338 const UINTS: &[&str] = &["u8", "u16", "u32", "u64", "usize"];
339 const SINTS: &[&str] = &["i8", "i16", "i32", "i64", "isize"];
340 const INTS: &[&str] = &["u8", "u16", "u32", "u64", "usize", "i8", "i16", "i32", "i64", "isize"];