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::{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! {
16 /// **What it does:** Checks for explicit bounds checking when casting.
18 /// **Why is this bad?** Reduces the readability of statements & is error prone.
20 /// **Known problems:** None.
24 /// # let foo: u32 = 5;
26 /// foo <= i32::MAX as u32
33 /// # use std::convert::TryFrom;
36 /// i32::try_from(foo).is_ok()
39 pub CHECKED_CONVERSIONS,
41 "`try_from` could replace manual bounds checking when casting"
44 pub struct CheckedConversions {
45 msrv: Option<RustcVersion>,
48 impl CheckedConversions {
50 pub fn new(msrv: Option<RustcVersion>) -> Self {
55 impl_lint_pass!(CheckedConversions => [CHECKED_CONVERSIONS]);
57 impl<'tcx> LateLintPass<'tcx> for CheckedConversions {
58 fn check_expr(&mut self, cx: &LateContext<'_>, item: &Expr<'_>) {
59 if !meets_msrv(self.msrv.as_ref(), &msrvs::TRY_FROM) {
63 let result = if_chain! {
64 if !in_external_macro(cx.sess(), item.span);
65 if let ExprKind::Binary(op, left, right) = &item.kind;
69 BinOpKind::Ge | BinOpKind::Le => single_check(item),
70 BinOpKind::And => double_check(cx, left, right),
78 if let Some(cv) = result {
79 if let Some(to_type) = cv.to_type {
80 let mut applicability = Applicability::MachineApplicable;
81 let snippet = snippet_with_applicability(cx, cv.expr_to_cast.span, "_", &mut applicability);
86 "checked cast can be simplified",
88 format!("{}::try_from({}).is_ok()", to_type, snippet),
95 extract_msrv_attr!(LateContext);
98 /// Searches for a single check from unsigned to _ is done
99 /// todo: check for case signed -> larger unsigned == only x >= 0
100 fn single_check<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<Conversion<'tcx>> {
101 check_upper_bound(expr).filter(|cv| cv.cvt == ConversionType::FromUnsigned)
104 /// Searches for a combination of upper & lower bound checks
105 fn double_check<'a>(cx: &LateContext<'_>, left: &'a Expr<'_>, right: &'a Expr<'_>) -> Option<Conversion<'a>> {
106 let upper_lower = |l, r| {
107 let upper = check_upper_bound(l);
108 let lower = check_lower_bound(r);
110 upper.zip(lower).and_then(|(l, r)| l.combine(r, cx))
113 upper_lower(left, right).or_else(|| upper_lower(right, left))
116 /// Contains the result of a tried conversion check
117 #[derive(Clone, Debug)]
118 struct Conversion<'a> {
120 expr_to_cast: &'a Expr<'a>,
121 to_type: Option<&'a str>,
124 /// The kind of conversion that is checked
125 #[derive(Copy, Clone, Debug, PartialEq)]
126 enum ConversionType {
132 impl<'a> Conversion<'a> {
133 /// Combine multiple conversions if the are compatible
134 pub fn combine(self, other: Self, cx: &LateContext<'_>) -> Option<Conversion<'a>> {
135 if self.is_compatible(&other, cx) {
136 // Prefer a Conversion that contains a type-constraint
137 Some(if self.to_type.is_some() { self } else { other })
143 /// Checks if two conversions are compatible
144 /// same type of conversion, same 'castee' and same 'to type'
145 pub fn is_compatible(&self, other: &Self, cx: &LateContext<'_>) -> bool {
146 (self.cvt == other.cvt)
147 && (SpanlessEq::new(cx).eq_expr(self.expr_to_cast, other.expr_to_cast))
148 && (self.has_compatible_to_type(other))
151 /// Checks if the to-type is the same (if there is a type constraint)
152 fn has_compatible_to_type(&self, other: &Self) -> bool {
153 match (self.to_type, other.to_type) {
154 (Some(l), Some(r)) => l == r,
159 /// Try to construct a new conversion if the conversion type is valid
160 fn try_new(expr_to_cast: &'a Expr<'_>, from_type: &str, to_type: &'a str) -> Option<Conversion<'a>> {
161 ConversionType::try_new(from_type, to_type).map(|cvt| Conversion {
164 to_type: Some(to_type),
168 /// Construct a new conversion without type constraint
169 fn new_any(expr_to_cast: &'a Expr<'_>) -> Conversion<'a> {
171 cvt: ConversionType::SignedToUnsigned,
178 impl ConversionType {
179 /// Creates a conversion type if the type is allowed & conversion is valid
181 fn try_new(from: &str, to: &str) -> Option<Self> {
182 if UINTS.contains(&from) {
183 Some(Self::FromUnsigned)
184 } else if SINTS.contains(&from) {
185 if UINTS.contains(&to) {
186 Some(Self::SignedToUnsigned)
187 } else if SINTS.contains(&to) {
188 Some(Self::SignedToSigned)
198 /// Check for `expr <= (to_type::MAX as from_type)`
199 fn check_upper_bound<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<Conversion<'tcx>> {
201 if let ExprKind::Binary(ref op, left, right) = &expr.kind;
202 if let Some((candidate, check)) = normalize_le_ge(op, left, right);
203 if let Some((from, to)) = get_types_from_cast(check, INTS, "max_value", "MAX");
206 Conversion::try_new(candidate, from, to)
213 /// Check for `expr >= 0|(to_type::MIN as from_type)`
214 fn check_lower_bound<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<Conversion<'tcx>> {
215 fn check_function<'a>(candidate: &'a Expr<'a>, check: &'a Expr<'a>) -> Option<Conversion<'a>> {
216 (check_lower_bound_zero(candidate, check)).or_else(|| (check_lower_bound_min(candidate, check)))
219 // First of we need a binary containing the expression & the cast
220 if let ExprKind::Binary(ref op, left, right) = &expr.kind {
221 normalize_le_ge(op, right, left).and_then(|(l, r)| check_function(l, r))
227 /// Check for `expr >= 0`
228 fn check_lower_bound_zero<'a>(candidate: &'a Expr<'_>, check: &'a Expr<'_>) -> Option<Conversion<'a>> {
230 if let ExprKind::Lit(ref lit) = &check.kind;
231 if let LitKind::Int(0, _) = &lit.node;
234 Some(Conversion::new_any(candidate))
241 /// Check for `expr >= (to_type::MIN as from_type)`
242 fn check_lower_bound_min<'a>(candidate: &'a Expr<'_>, check: &'a Expr<'_>) -> Option<Conversion<'a>> {
243 if let Some((from, to)) = get_types_from_cast(check, SINTS, "min_value", "MIN") {
244 Conversion::try_new(candidate, from, to)
250 /// Tries to extract the from- and to-type from a cast expression
251 fn get_types_from_cast<'a>(
255 assoc_const: &'a str,
256 ) -> Option<(&'a str, &'a str)> {
257 // `to_type::max_value() as from_type`
258 // or `to_type::MAX as from_type`
259 let call_from_cast: Option<(&Expr<'_>, &str)> = if_chain! {
260 // to_type::max_value(), from_type
261 if let ExprKind::Cast(limit, from_type) = &expr.kind;
262 if let TyKind::Path(ref from_type_path) = &from_type.kind;
263 if let Some(from_sym) = int_ty_to_sym(from_type_path);
266 Some((limit, from_sym))
272 // `from_type::from(to_type::max_value())`
273 let limit_from: Option<(&Expr<'_>, &str)> = call_from_cast.or_else(|| {
275 // `from_type::from, to_type::max_value()`
276 if let ExprKind::Call(from_func, args) = &expr.kind;
277 // `to_type::max_value()`
279 if let limit = &args[0];
281 if let ExprKind::Path(ref path) = &from_func.kind;
282 if let Some(from_sym) = get_implementing_type(path, INTS, "from");
285 Some((limit, from_sym))
292 if let Some((limit, from_type)) = limit_from {
294 // `from_type::from(_)`
295 ExprKind::Call(path, _) => {
296 if let ExprKind::Path(ref path) = path.kind {
298 if let Some(to_type) = get_implementing_type(path, types, func) {
299 return Some((from_type, to_type));
304 ExprKind::Path(ref path) => {
305 if let Some(to_type) = get_implementing_type(path, types, assoc_const) {
306 return Some((from_type, to_type));
315 /// Gets the type which implements the called function
316 fn get_implementing_type<'a>(path: &QPath<'_>, candidates: &'a [&str], function: &str) -> Option<&'a str> {
318 if let QPath::TypeRelative(ty, path) = &path;
319 if path.ident.name.as_str() == function;
320 if let TyKind::Path(QPath::Resolved(None, tp)) = &ty.kind;
321 if let [int] = &*tp.segments;
323 let name = &int.ident.name.as_str();
324 candidates.iter().find(|c| name == *c).copied()
331 /// Gets the type as a string, if it is a supported integer
332 fn int_ty_to_sym<'tcx>(path: &QPath<'_>) -> Option<&'tcx str> {
334 if let QPath::Resolved(_, path) = *path;
335 if let [ty] = &*path.segments;
337 let name = &ty.ident.name.as_str();
338 INTS.iter().find(|c| name == *c).copied()
345 /// Will return the expressions as if they were expr1 <= expr2
346 fn normalize_le_ge<'a>(op: &BinOp, left: &'a Expr<'a>, right: &'a Expr<'a>) -> Option<(&'a Expr<'a>, &'a Expr<'a>)> {
348 BinOpKind::Le => Some((left, right)),
349 BinOpKind::Ge => Some((right, left)),
355 const UINTS: &[&str] = &["u8", "u16", "u32", "u64", "usize"];
356 const SINTS: &[&str] = &["i8", "i16", "i32", "i64", "isize"];
357 const INTS: &[&str] = &["u8", "u16", "u32", "u64", "usize", "i8", "i16", "i32", "i64", "isize"];