1 //! lint on manually implemented checked conversions that could be transformed into `try_from`
3 use if_chain::if_chain;
5 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
6 use rustc::{declare_lint_pass, declare_tool_lint};
7 use rustc_errors::Applicability;
8 use syntax::ast::LitKind;
10 use crate::utils::{snippet_with_applicability, span_lint_and_sugg, SpanlessEq};
12 declare_clippy_lint! {
13 /// **What it does:** Checks for explicit bounds checking when casting.
15 /// **Why is this bad?** Reduces the readability of statements & is error prone.
17 /// **Known problems:** None.
21 /// # let foo: u32 = 5;
23 /// foo <= i32::max_value() as u32
30 /// # use std::convert::TryFrom;
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<&'a str>,
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: &str, to_type: &'a str) -> 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: &str, to: &str) -> Option<Self> {
164 if UINTS.contains(&from) {
165 Some(Self::FromUnsigned)
166 } else if SINTS.contains(&from) {
167 if UINTS.contains(&to) {
168 Some(Self::SignedToUnsigned)
169 } else if SINTS.contains(&to) {
170 Some(Self::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, 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, 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<'a>(expr: &'a Expr, func: &'a str, types: &'a [&str]) -> Option<(&'a str, &'a str)> {
234 // `to_type::maxmin_value() as from_type`
235 let call_from_cast: Option<(&Expr, &str)> = 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, &str)> = 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, 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<'a>(path: &QPath, candidates: &'a [&str], function: &str) -> Option<&'a str> {
290 if let QPath::TypeRelative(ref ty, ref path) = &path;
291 if path.ident.name.as_str() == 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.as_str();
297 candidates.iter().find(|c| name == *c).cloned()
304 /// Gets the type as a string, if it is a supported integer
305 fn int_ty_to_sym(path: &QPath) -> Option<&str> {
307 if let QPath::Resolved(_, ref path) = *path;
308 if let [ty] = &*path.segments;
309 let name = &ty.ident.name.as_str();
312 INTS.iter().find(|c| name == *c).cloned()
319 /// (Option<T>, Option<U>) -> Option<(T, U)>
320 fn transpose<T, U>(lhs: Option<T>, rhs: Option<U>) -> Option<(T, U)> {
322 (Some(l), Some(r)) => Some((l, r)),
327 /// Will return the expressions as if they were expr1 <= expr2
328 fn normalize_le_ge<'a>(op: &BinOp, left: &'a Expr, right: &'a Expr) -> Option<(&'a Expr, &'a Expr)> {
330 BinOpKind::Le => Some((left, right)),
331 BinOpKind::Ge => Some((right, left)),
337 const FROM: &str = "from";
338 const MAX_VALUE: &str = "max_value";
339 const MIN_VALUE: &str = "min_value";
341 const UINTS: &[&str] = &["u8", "u16", "u32", "u64", "usize"];
342 const SINTS: &[&str] = &["i8", "i16", "i32", "i64", "isize"];
343 const INTS: &[&str] = &["u8", "u16", "u32", "u64", "usize", "i8", "i16", "i32", "i64", "isize"];