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
31 /// i32::try_from(foo).is_ok()
34 pub CHECKED_CONVERSIONS,
36 "`try_from` could replace manual bounds checking when casting"
39 declare_lint_pass!(CheckedConversions => [CHECKED_CONVERSIONS]);
41 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for CheckedConversions {
42 fn check_expr(&mut self, cx: &LateContext<'_, '_>, item: &Expr) {
43 let result = if_chain! {
44 if !in_external_macro(cx.sess(), item.span);
45 if let ExprKind::Binary(op, ref left, ref right) = &item.node;
49 BinOpKind::Ge | BinOpKind::Le => single_check(item),
50 BinOpKind::And => double_check(cx, left, right),
59 if let Some(cv) = result;
60 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
70 "Checked cast can be simplified.",
72 format!("{}::try_from({}).is_ok()",
82 /// Searches for a single check from unsigned to _ is done
83 /// todo: check for case signed -> larger unsigned == only x >= 0
84 fn single_check(expr: &Expr) -> Option<Conversion<'_>> {
85 check_upper_bound(expr).filter(|cv| cv.cvt == ConversionType::FromUnsigned)
88 /// Searches for a combination of upper & lower bound checks
89 fn double_check<'a>(cx: &LateContext<'_, '_>, left: &'a Expr, right: &'a Expr) -> Option<Conversion<'a>> {
90 let upper_lower = |l, r| {
91 let upper = check_upper_bound(l);
92 let lower = check_lower_bound(r);
94 transpose(upper, lower).and_then(|(l, r)| l.combine(r, cx))
97 upper_lower(left, right).or_else(|| upper_lower(right, left))
100 /// Contains the result of a tried conversion check
101 #[derive(Clone, Debug)]
102 struct Conversion<'a> {
104 expr_to_cast: &'a Expr,
105 to_type: Option<&'a str>,
108 /// The kind of conversion that is checked
109 #[derive(Copy, Clone, Debug, PartialEq)]
110 enum ConversionType {
116 impl<'a> Conversion<'a> {
117 /// Combine multiple conversions if the are compatible
118 pub fn combine(self, other: Self, cx: &LateContext<'_, '_>) -> Option<Conversion<'a>> {
119 if self.is_compatible(&other, cx) {
120 // Prefer a Conversion that contains a type-constraint
121 Some(if self.to_type.is_some() { self } else { other })
127 /// Checks if two conversions are compatible
128 /// same type of conversion, same 'castee' and same 'to type'
129 pub fn is_compatible(&self, other: &Self, cx: &LateContext<'_, '_>) -> bool {
130 (self.cvt == other.cvt)
131 && (SpanlessEq::new(cx).eq_expr(self.expr_to_cast, other.expr_to_cast))
132 && (self.has_compatible_to_type(other))
135 /// Checks if the to-type is the same (if there is a type constraint)
136 fn has_compatible_to_type(&self, other: &Self) -> bool {
137 transpose(self.to_type.as_ref(), other.to_type.as_ref()).map_or(true, |(l, 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
161 fn try_new(from: &str, to: &str) -> Option<Self> {
162 if UINTS.contains(&from) {
163 Some(ConversionType::FromUnsigned)
164 } else if SINTS.contains(&from) {
165 if UINTS.contains(&to) {
166 Some(ConversionType::SignedToUnsigned)
167 } else if SINTS.contains(&to) {
168 Some(ConversionType::SignedToSigned)
178 /// Check for `expr <= (to_type::max_value() as from_type)`
179 fn check_upper_bound(expr: &Expr) -> Option<Conversion<'_>> {
181 if let ExprKind::Binary(ref op, ref left, ref right) = &expr.node;
182 if let Some((candidate, check)) = normalize_le_ge(op, left, right);
183 if let Some((from, to)) = get_types_from_cast(check, MAX_VALUE, INTS);
186 Conversion::try_new(candidate, from, to)
193 /// Check for `expr >= 0|(to_type::min_value() as from_type)`
194 fn check_lower_bound(expr: &Expr) -> Option<Conversion<'_>> {
195 fn check_function<'a>(candidate: &'a Expr, check: &'a Expr) -> Option<Conversion<'a>> {
196 (check_lower_bound_zero(candidate, check)).or_else(|| (check_lower_bound_min(candidate, check)))
199 // First of we need a binary containing the expression & the cast
200 if let ExprKind::Binary(ref op, ref left, ref right) = &expr.node {
201 normalize_le_ge(op, right, left).and_then(|(l, r)| check_function(l, r))
207 /// Check for `expr >= 0`
208 fn check_lower_bound_zero<'a>(candidate: &'a Expr, check: &'a Expr) -> Option<Conversion<'a>> {
210 if let ExprKind::Lit(ref lit) = &check.node;
211 if let LitKind::Int(0, _) = &lit.node;
214 Some(Conversion::new_any(candidate))
221 /// Check for `expr >= (to_type::min_value() as from_type)`
222 fn check_lower_bound_min<'a>(candidate: &'a Expr, check: &'a Expr) -> Option<Conversion<'a>> {
223 if let Some((from, to)) = get_types_from_cast(check, MIN_VALUE, SINTS) {
224 Conversion::try_new(candidate, from, to)
230 /// Tries to extract the from- and to-type from a cast expression
231 fn get_types_from_cast<'a>(expr: &'a Expr, func: &'a str, types: &'a [&str]) -> Option<(&'a str, &'a str)> {
232 // `to_type::maxmin_value() as from_type`
233 let call_from_cast: Option<(&Expr, &str)> = if_chain! {
234 // to_type::maxmin_value(), from_type
235 if let ExprKind::Cast(ref limit, ref from_type) = &expr.node;
236 if let TyKind::Path(ref from_type_path) = &from_type.node;
237 if let Some(from_sym) = int_ty_to_sym(from_type_path);
240 Some((limit, from_sym))
246 // `from_type::from(to_type::maxmin_value())`
247 let limit_from: Option<(&Expr, &str)> = call_from_cast.or_else(|| {
249 // `from_type::from, to_type::maxmin_value()`
250 if let ExprKind::Call(ref from_func, ref args) = &expr.node;
251 // `to_type::maxmin_value()`
253 if let limit = &args[0];
255 if let ExprKind::Path(ref path) = &from_func.node;
256 if let Some(from_sym) = get_implementing_type(path, INTS, FROM);
259 Some((limit, from_sym))
266 if let Some((limit, from_type)) = limit_from {
268 if let ExprKind::Call(ref fun_name, _) = &limit.node;
269 // `to_type, maxmin_value`
270 if let ExprKind::Path(ref path) = &fun_name.node;
272 if let Some(to_type) = get_implementing_type(path, types, func);
275 Some((from_type, to_type))
285 /// Gets the type which implements the called function
286 fn get_implementing_type<'a>(path: &QPath, candidates: &'a [&str], function: &str) -> Option<&'a str> {
288 if let QPath::TypeRelative(ref ty, ref path) = &path;
289 if path.ident.name.as_str() == function;
290 if let TyKind::Path(QPath::Resolved(None, ref tp)) = &ty.node;
291 if let [int] = &*tp.segments;
292 let name = &int.ident.name.as_str();
295 candidates.iter().find(|c| name == *c).cloned()
302 /// Gets the type as a string, if it is a supported integer
303 fn int_ty_to_sym(path: &QPath) -> Option<&str> {
305 if let QPath::Resolved(_, ref path) = *path;
306 if let [ty] = &*path.segments;
307 let name = &ty.ident.name.as_str();
310 INTS.iter().find(|c| name == *c).cloned()
317 /// (Option<T>, Option<U>) -> Option<(T, U)>
318 fn transpose<T, U>(lhs: Option<T>, rhs: Option<U>) -> Option<(T, U)> {
320 (Some(l), Some(r)) => Some((l, r)),
325 /// Will return the expressions as if they were expr1 <= expr2
326 fn normalize_le_ge<'a>(op: &BinOp, left: &'a Expr, right: &'a Expr) -> Option<(&'a Expr, &'a Expr)> {
328 BinOpKind::Le => Some((left, right)),
329 BinOpKind::Ge => Some((right, left)),
335 const FROM: &str = "from";
336 const MAX_VALUE: &str = "max_value";
337 const MIN_VALUE: &str = "min_value";
339 const UINTS: &[&str] = &["u8", "u16", "u32", "u64", "usize"];
340 const SINTS: &[&str] = &["i8", "i16", "i32", "i64", "isize"];
341 const INTS: &[&str] = &["u8", "u16", "u32", "u64", "usize", "i8", "i16", "i32", "i64", "isize"];