1 //! lint on manually implemented checked conversions that could be transformed into `try_from`
3 use if_chain::if_chain;
4 use lazy_static::lazy_static;
6 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
7 use rustc::{declare_lint_pass, declare_tool_lint};
8 use rustc_errors::Applicability;
9 use syntax::ast::LitKind;
10 use syntax::symbol::Symbol;
12 use crate::utils::{snippet_with_applicability, span_lint_and_sugg, sym, SpanlessEq};
14 declare_clippy_lint! {
15 /// **What it does:** Checks for explicit bounds checking when casting.
17 /// **Why is this bad?** Reduces the readability of statements & is error prone.
19 /// **Known problems:** None.
23 /// # let foo: u32 = 5;
25 /// foo <= i32::max_value() as u32
33 /// i32::try_from(foo).is_ok()
36 pub CHECKED_CONVERSIONS,
38 "`try_from` could replace manual bounds checking when casting"
41 declare_lint_pass!(CheckedConversions => [CHECKED_CONVERSIONS]);
43 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for CheckedConversions {
44 fn check_expr(&mut self, cx: &LateContext<'_, '_>, item: &Expr) {
45 let result = if_chain! {
46 if !in_external_macro(cx.sess(), item.span);
47 if let ExprKind::Binary(op, ref left, ref right) = &item.node;
51 BinOpKind::Ge | BinOpKind::Le => single_check(item),
52 BinOpKind::And => double_check(cx, left, right),
61 if let Some(cv) = result;
62 if let Some(to_type) = cv.to_type;
65 let mut applicability = Applicability::MachineApplicable;
66 let snippet = snippet_with_applicability(cx, cv.expr_to_cast.span, "_", &mut
72 "Checked cast can be simplified.",
74 format!("{}::try_from({}).is_ok()",
84 /// Searches for a single check from unsigned to _ is done
85 /// todo: check for case signed -> larger unsigned == only x >= 0
86 fn single_check(expr: &Expr) -> Option<Conversion<'_>> {
87 check_upper_bound(expr).filter(|cv| cv.cvt == ConversionType::FromUnsigned)
90 /// Searches for a combination of upper & lower bound checks
91 fn double_check<'a>(cx: &LateContext<'_, '_>, left: &'a Expr, right: &'a Expr) -> Option<Conversion<'a>> {
92 let upper_lower = |l, r| {
93 let upper = check_upper_bound(l);
94 let lower = check_lower_bound(r);
96 transpose(upper, lower).and_then(|(l, r)| l.combine(r, cx))
99 upper_lower(left, right).or_else(|| upper_lower(right, left))
102 /// Contains the result of a tried conversion check
103 #[derive(Clone, Debug)]
104 struct Conversion<'a> {
106 expr_to_cast: &'a Expr,
107 to_type: Option<Symbol>,
110 /// The kind of conversion that is checked
111 #[derive(Copy, Clone, Debug, PartialEq)]
112 enum ConversionType {
118 impl<'a> Conversion<'a> {
119 /// Combine multiple conversions if the are compatible
120 pub fn combine(self, other: Self, cx: &LateContext<'_, '_>) -> Option<Conversion<'a>> {
121 if self.is_compatible(&other, cx) {
122 // Prefer a Conversion that contains a type-constraint
123 Some(if self.to_type.is_some() { self } else { other })
129 /// Checks if two conversions are compatible
130 /// same type of conversion, same 'castee' and same 'to type'
131 pub fn is_compatible(&self, other: &Self, cx: &LateContext<'_, '_>) -> bool {
132 (self.cvt == other.cvt)
133 && (SpanlessEq::new(cx).eq_expr(self.expr_to_cast, other.expr_to_cast))
134 && (self.has_compatible_to_type(other))
137 /// Checks if the to-type is the same (if there is a type constraint)
138 fn has_compatible_to_type(&self, other: &Self) -> bool {
139 transpose(self.to_type.as_ref(), other.to_type.as_ref()).map_or(true, |(l, r)| l == r)
142 /// Try to construct a new conversion if the conversion type is valid
143 fn try_new(expr_to_cast: &'a Expr, from_type: Symbol, to_type: Symbol) -> Option<Conversion<'a>> {
144 ConversionType::try_new(from_type, to_type).map(|cvt| Conversion {
147 to_type: Some(to_type),
151 /// Construct a new conversion without type constraint
152 fn new_any(expr_to_cast: &'a Expr) -> Conversion<'a> {
154 cvt: ConversionType::SignedToUnsigned,
161 impl ConversionType {
162 /// Creates a conversion type if the type is allowed & conversion is valid
163 fn try_new(from: Symbol, to: Symbol) -> Option<Self> {
164 if UINTS.contains(&from) {
165 Some(ConversionType::FromUnsigned)
166 } else if SINTS.contains(&from) {
167 if UINTS.contains(&to) {
168 Some(ConversionType::SignedToUnsigned)
169 } else if SINTS.contains(&to) {
170 Some(ConversionType::SignedToSigned)
180 /// Check for `expr <= (to_type::max_value() as from_type)`
181 fn check_upper_bound(expr: &Expr) -> Option<Conversion<'_>> {
183 if let ExprKind::Binary(ref op, ref left, ref right) = &expr.node;
184 if let Some((candidate, check)) = normalize_le_ge(op, left, right);
185 if let Some((from, to)) = get_types_from_cast(check, *sym::max_value, &*INTS);
188 Conversion::try_new(candidate, from, to)
195 /// Check for `expr >= 0|(to_type::min_value() as from_type)`
196 fn check_lower_bound(expr: &Expr) -> Option<Conversion<'_>> {
197 fn check_function<'a>(candidate: &'a Expr, check: &'a Expr) -> Option<Conversion<'a>> {
198 (check_lower_bound_zero(candidate, check)).or_else(|| (check_lower_bound_min(candidate, check)))
201 // First of we need a binary containing the expression & the cast
202 if let ExprKind::Binary(ref op, ref left, ref right) = &expr.node {
203 normalize_le_ge(op, right, left).and_then(|(l, r)| check_function(l, r))
209 /// Check for `expr >= 0`
210 fn check_lower_bound_zero<'a>(candidate: &'a Expr, check: &'a Expr) -> Option<Conversion<'a>> {
212 if let ExprKind::Lit(ref lit) = &check.node;
213 if let LitKind::Int(0, _) = &lit.node;
216 Some(Conversion::new_any(candidate))
223 /// Check for `expr >= (to_type::min_value() as from_type)`
224 fn check_lower_bound_min<'a>(candidate: &'a Expr, check: &'a Expr) -> Option<Conversion<'a>> {
225 if let Some((from, to)) = get_types_from_cast(check, *sym::min_value, &*SINTS) {
226 Conversion::try_new(candidate, from, to)
232 /// Tries to extract the from- and to-type from a cast expression
233 fn get_types_from_cast(expr: &Expr, func: Symbol, types: &[Symbol]) -> Option<(Symbol, Symbol)> {
234 // `to_type::maxmin_value() as from_type`
235 let call_from_cast: Option<(&Expr, Symbol)> = if_chain! {
236 // to_type::maxmin_value(), from_type
237 if let ExprKind::Cast(ref limit, ref from_type) = &expr.node;
238 if let TyKind::Path(ref from_type_path) = &from_type.node;
239 if let Some(from_sym) = int_ty_to_sym(from_type_path);
242 Some((limit, from_sym))
248 // `from_type::from(to_type::maxmin_value())`
249 let limit_from: Option<(&Expr, Symbol)> = call_from_cast.or_else(|| {
251 // `from_type::from, to_type::maxmin_value()`
252 if let ExprKind::Call(ref from_func, ref args) = &expr.node;
253 // `to_type::maxmin_value()`
255 if let limit = &args[0];
257 if let ExprKind::Path(ref path) = &from_func.node;
258 if let Some(from_sym) = get_implementing_type(path, &*INTS, *sym::from);
261 Some((limit, from_sym))
268 if let Some((limit, from_type)) = limit_from {
270 if let ExprKind::Call(ref fun_name, _) = &limit.node;
271 // `to_type, maxmin_value`
272 if let ExprKind::Path(ref path) = &fun_name.node;
274 if let Some(to_type) = get_implementing_type(path, types, func);
277 Some((from_type, to_type))
287 /// Gets the type which implements the called function
288 fn get_implementing_type(path: &QPath, candidates: &[Symbol], function: Symbol) -> Option<Symbol> {
290 if let QPath::TypeRelative(ref ty, ref path) = &path;
291 if path.ident.name == function;
292 if let TyKind::Path(QPath::Resolved(None, ref tp)) = &ty.node;
293 if let [int] = &*tp.segments;
294 let name = int.ident.name;
295 if candidates.contains(&name);
305 /// Gets the type as a string, if it is a supported integer
306 fn int_ty_to_sym(path: &QPath) -> Option<Symbol> {
308 if let QPath::Resolved(_, ref path) = *path;
309 if let [ty] = &*path.segments;
314 .find(|c| ty.ident.name == **c)
322 /// (Option<T>, Option<U>) -> Option<(T, U)>
323 fn transpose<T, U>(lhs: Option<T>, rhs: Option<U>) -> Option<(T, U)> {
325 (Some(l), Some(r)) => Some((l, r)),
330 /// Will return the expressions as if they were expr1 <= expr2
331 fn normalize_le_ge<'a>(op: &'a BinOp, left: &'a Expr, right: &'a Expr) -> Option<(&'a Expr, &'a Expr)> {
333 BinOpKind::Le => Some((left, right)),
334 BinOpKind::Ge => Some((right, left)),
340 static ref UINTS: [Symbol; 5] = [*sym::u8, *sym::u16, *sym::u32, *sym::u64, *sym::usize];
341 static ref SINTS: [Symbol; 5] = [*sym::i8, *sym::i16, *sym::i32, *sym::i64, *sym::isize];
342 static ref INTS: [Symbol; 10] = [