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_semver::RustcVersion;
10 use rustc_session::{declare_tool_lint, impl_lint_pass};
12 use crate::utils::{meets_msrv, snippet_with_applicability, span_lint_and_sugg, SpanlessEq};
14 const CHECKED_CONVERSIONS_MSRV: RustcVersion = RustcVersion::new(1, 34, 0);
16 declare_clippy_lint! {
17 /// **What it does:** Checks for explicit bounds checking when casting.
19 /// **Why is this bad?** Reduces the readability of statements & is error prone.
21 /// **Known problems:** None.
25 /// # let foo: u32 = 5;
27 /// foo <= i32::MAX as u32
34 /// # use std::convert::TryFrom;
37 /// i32::try_from(foo).is_ok()
40 pub CHECKED_CONVERSIONS,
42 "`try_from` could replace manual bounds checking when casting"
45 pub struct CheckedConversions {
46 msrv: Option<RustcVersion>,
49 impl CheckedConversions {
51 pub fn new(msrv: Option<RustcVersion>) -> Self {
56 impl_lint_pass!(CheckedConversions => [CHECKED_CONVERSIONS]);
58 impl<'tcx> LateLintPass<'tcx> for CheckedConversions {
59 fn check_expr(&mut self, cx: &LateContext<'_>, item: &Expr<'_>) {
60 if !meets_msrv(self.msrv.as_ref(), &CHECKED_CONVERSIONS_MSRV) {
64 let result = if_chain! {
65 if !in_external_macro(cx.sess(), item.span);
66 if let ExprKind::Binary(op, ref left, ref right) = &item.kind;
70 BinOpKind::Ge | BinOpKind::Le => single_check(item),
71 BinOpKind::And => double_check(cx, left, right),
79 if let Some(cv) = result {
80 if let Some(to_type) = cv.to_type {
81 let mut applicability = Applicability::MachineApplicable;
82 let snippet = snippet_with_applicability(cx, cv.expr_to_cast.span, "_", &mut applicability);
87 "checked cast can be simplified",
89 format!("{}::try_from({}).is_ok()", to_type, snippet),
96 extract_msrv_attr!(LateContext);
99 /// Searches for a single check from unsigned to _ is done
100 /// todo: check for case signed -> larger unsigned == only x >= 0
101 fn single_check<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<Conversion<'tcx>> {
102 check_upper_bound(expr).filter(|cv| cv.cvt == ConversionType::FromUnsigned)
105 /// Searches for a combination of upper & lower bound checks
106 fn double_check<'a>(cx: &LateContext<'_>, left: &'a Expr<'_>, right: &'a Expr<'_>) -> Option<Conversion<'a>> {
107 let upper_lower = |l, r| {
108 let upper = check_upper_bound(l);
109 let lower = check_lower_bound(r);
111 upper.zip(lower).and_then(|(l, r)| l.combine(r, cx))
114 upper_lower(left, right).or_else(|| upper_lower(right, left))
117 /// Contains the result of a tried conversion check
118 #[derive(Clone, Debug)]
119 struct Conversion<'a> {
121 expr_to_cast: &'a Expr<'a>,
122 to_type: Option<&'a str>,
125 /// The kind of conversion that is checked
126 #[derive(Copy, Clone, Debug, PartialEq)]
127 enum ConversionType {
133 impl<'a> Conversion<'a> {
134 /// Combine multiple conversions if the are compatible
135 pub fn combine(self, other: Self, cx: &LateContext<'_>) -> Option<Conversion<'a>> {
136 if self.is_compatible(&other, cx) {
137 // Prefer a Conversion that contains a type-constraint
138 Some(if self.to_type.is_some() { self } else { other })
144 /// Checks if two conversions are compatible
145 /// same type of conversion, same 'castee' and same 'to type'
146 pub fn is_compatible(&self, other: &Self, cx: &LateContext<'_>) -> bool {
147 (self.cvt == other.cvt)
148 && (SpanlessEq::new(cx).eq_expr(self.expr_to_cast, other.expr_to_cast))
149 && (self.has_compatible_to_type(other))
152 /// Checks if the to-type is the same (if there is a type constraint)
153 fn has_compatible_to_type(&self, other: &Self) -> bool {
154 match (self.to_type, other.to_type) {
155 (Some(l), Some(r)) => l == r,
160 /// Try to construct a new conversion if the conversion type is valid
161 fn try_new(expr_to_cast: &'a Expr<'_>, from_type: &str, to_type: &'a str) -> Option<Conversion<'a>> {
162 ConversionType::try_new(from_type, to_type).map(|cvt| Conversion {
165 to_type: Some(to_type),
169 /// Construct a new conversion without type constraint
170 fn new_any(expr_to_cast: &'a Expr<'_>) -> Conversion<'a> {
172 cvt: ConversionType::SignedToUnsigned,
179 impl ConversionType {
180 /// Creates a conversion type if the type is allowed & conversion is valid
182 fn try_new(from: &str, to: &str) -> Option<Self> {
183 if UINTS.contains(&from) {
184 Some(Self::FromUnsigned)
185 } else if SINTS.contains(&from) {
186 if UINTS.contains(&to) {
187 Some(Self::SignedToUnsigned)
188 } else if SINTS.contains(&to) {
189 Some(Self::SignedToSigned)
199 /// Check for `expr <= (to_type::MAX as from_type)`
200 fn check_upper_bound<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<Conversion<'tcx>> {
202 if let ExprKind::Binary(ref op, ref left, ref right) = &expr.kind;
203 if let Some((candidate, check)) = normalize_le_ge(op, left, right);
204 if let Some((from, to)) = get_types_from_cast(check, INTS, "max_value", "MAX");
207 Conversion::try_new(candidate, from, to)
214 /// Check for `expr >= 0|(to_type::MIN as from_type)`
215 fn check_lower_bound<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<Conversion<'tcx>> {
216 fn check_function<'a>(candidate: &'a Expr<'a>, check: &'a Expr<'a>) -> Option<Conversion<'a>> {
217 (check_lower_bound_zero(candidate, check)).or_else(|| (check_lower_bound_min(candidate, check)))
220 // First of we need a binary containing the expression & the cast
221 if let ExprKind::Binary(ref op, ref left, ref right) = &expr.kind {
222 normalize_le_ge(op, right, left).and_then(|(l, r)| check_function(l, r))
228 /// Check for `expr >= 0`
229 fn check_lower_bound_zero<'a>(candidate: &'a Expr<'_>, check: &'a Expr<'_>) -> Option<Conversion<'a>> {
231 if let ExprKind::Lit(ref lit) = &check.kind;
232 if let LitKind::Int(0, _) = &lit.node;
235 Some(Conversion::new_any(candidate))
242 /// Check for `expr >= (to_type::MIN as from_type)`
243 fn check_lower_bound_min<'a>(candidate: &'a Expr<'_>, check: &'a Expr<'_>) -> Option<Conversion<'a>> {
244 if let Some((from, to)) = get_types_from_cast(check, SINTS, "min_value", "MIN") {
245 Conversion::try_new(candidate, from, to)
251 /// Tries to extract the from- and to-type from a cast expression
252 fn get_types_from_cast<'a>(
256 assoc_const: &'a str,
257 ) -> Option<(&'a str, &'a str)> {
258 // `to_type::max_value() as from_type`
259 // or `to_type::MAX as from_type`
260 let call_from_cast: Option<(&Expr<'_>, &str)> = if_chain! {
261 // to_type::max_value(), from_type
262 if let ExprKind::Cast(ref limit, ref from_type) = &expr.kind;
263 if let TyKind::Path(ref from_type_path) = &from_type.kind;
264 if let Some(from_sym) = int_ty_to_sym(from_type_path);
267 Some((limit, from_sym))
273 // `from_type::from(to_type::max_value())`
274 let limit_from: Option<(&Expr<'_>, &str)> = call_from_cast.or_else(|| {
276 // `from_type::from, to_type::max_value()`
277 if let ExprKind::Call(ref from_func, ref args) = &expr.kind;
278 // `to_type::max_value()`
280 if let limit = &args[0];
282 if let ExprKind::Path(ref path) = &from_func.kind;
283 if let Some(from_sym) = get_implementing_type(path, INTS, "from");
286 Some((limit, from_sym))
293 if let Some((limit, from_type)) = limit_from {
295 // `from_type::from(_)`
296 ExprKind::Call(path, _) => {
297 if let ExprKind::Path(ref path) = path.kind {
299 if let Some(to_type) = get_implementing_type(path, types, func) {
300 return Some((from_type, to_type));
305 ExprKind::Path(ref path) => {
306 if let Some(to_type) = get_implementing_type(path, types, assoc_const) {
307 return Some((from_type, to_type));
316 /// Gets the type which implements the called function
317 fn get_implementing_type<'a>(path: &QPath<'_>, candidates: &'a [&str], function: &str) -> Option<&'a str> {
319 if let QPath::TypeRelative(ref ty, ref path) = &path;
320 if path.ident.name.as_str() == function;
321 if let TyKind::Path(QPath::Resolved(None, ref tp)) = &ty.kind;
322 if let [int] = &*tp.segments;
323 let name = &int.ident.name.as_str();
326 candidates.iter().find(|c| name == *c).cloned()
333 /// Gets the type as a string, if it is a supported integer
334 fn int_ty_to_sym<'tcx>(path: &QPath<'_>) -> Option<&'tcx str> {
336 if let QPath::Resolved(_, ref path) = *path;
337 if let [ty] = &*path.segments;
338 let name = &ty.ident.name.as_str();
341 INTS.iter().find(|c| name == *c).cloned()
348 /// Will return the expressions as if they were expr1 <= expr2
349 fn normalize_le_ge<'a>(op: &BinOp, left: &'a Expr<'a>, right: &'a Expr<'a>) -> Option<(&'a Expr<'a>, &'a Expr<'a>)> {
351 BinOpKind::Le => Some((left, right)),
352 BinOpKind::Ge => Some((right, left)),
358 const UINTS: &[&str] = &["u8", "u16", "u32", "u64", "usize"];
359 const SINTS: &[&str] = &["i8", "i16", "i32", "i64", "isize"];
360 const INTS: &[&str] = &["u8", "u16", "u32", "u64", "usize", "i8", "i16", "i32", "i64", "isize"];