src/tools/clippy/clippy_lints/src/checked_conversions.rs

   1 //! lint on manually implemented checked conversions that could be transformed into `try_from`
   2
   3 use clippy_config::msrvs::{self, Msrv};
   4 use clippy_utils::diagnostics::span_lint_and_sugg;
   5 use clippy_utils::source::snippet_with_applicability;
   6 use clippy_utils::{in_constant, is_integer_literal, SpanlessEq};
   7 use rustc_errors::Applicability;
   8 use rustc_hir::{BinOp, BinOpKind, Expr, ExprKind, QPath, TyKind};
   9 use rustc_lint::{LateContext, LateLintPass, LintContext};
  10 use rustc_middle::lint::in_external_macro;
  11 use rustc_session::impl_lint_pass;
  12
  13 declare_clippy_lint! {
  14     /// ### What it does
  15     /// Checks for explicit bounds checking when casting.
  16     ///
  17     /// ### Why is this bad?
  18     /// Reduces the readability of statements & is error prone.
  19     ///
  20     /// ### Example
  21     /// ```no_run
  22     /// # let foo: u32 = 5;
  23     /// foo <= i32::MAX as u32;
  24     /// ```
  25     ///
  26     /// Use instead:
  27     /// ```no_run
  28     /// # let foo = 1;
  29     /// # #[allow(unused)]
  30     /// i32::try_from(foo).is_ok();
  31     /// ```
  32     #[clippy::version = "1.37.0"]
  33     pub CHECKED_CONVERSIONS,
  34     pedantic,
  35     "`try_from` could replace manual bounds checking when casting"
  36 }
  37
  38 pub struct CheckedConversions {
  39     msrv: Msrv,
  40 }
  41
  42 impl CheckedConversions {
  43     #[must_use]
  44     pub fn new(msrv: Msrv) -> Self {
  45         Self { msrv }
  46     }
  47 }
  48
  49 impl_lint_pass!(CheckedConversions => [CHECKED_CONVERSIONS]);
  50
  51 impl<'tcx> LateLintPass<'tcx> for CheckedConversions {
  52     fn check_expr(&mut self, cx: &LateContext<'_>, item: &Expr<'_>) {
  53         if !self.msrv.meets(msrvs::TRY_FROM) {
  54             return;
  55         }
  56
  57         let result = if !in_constant(cx, item.hir_id)
  58             && !in_external_macro(cx.sess(), item.span)
  59             && let ExprKind::Binary(op, left, right) = &item.kind
  60         {
  61             match op.node {
  62                 BinOpKind::Ge | BinOpKind::Le => single_check(item),
  63                 BinOpKind::And => double_check(cx, left, right),
  64                 _ => None,
  65             }
  66         } else {
  67             None
  68         };
  69
  70         if let Some(cv) = result {
  71             if let Some(to_type) = cv.to_type {
  72                 let mut applicability = Applicability::MachineApplicable;
  73                 let snippet = snippet_with_applicability(cx, cv.expr_to_cast.span, "_", &mut applicability);
  74                 span_lint_and_sugg(
  75                     cx,
  76                     CHECKED_CONVERSIONS,
  77                     item.span,
  78                     "checked cast can be simplified",
  79                     "try",
  80                     format!("{to_type}::try_from({snippet}).is_ok()"),
  81                     applicability,
  82                 );
  83             }
  84         }
  85     }
  86
  87     extract_msrv_attr!(LateContext);
  88 }
  89
  90 /// Searches for a single check from unsigned to _ is done
  91 /// todo: check for case signed -> larger unsigned == only x >= 0
  92 fn single_check<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<Conversion<'tcx>> {
  93     check_upper_bound(expr).filter(|cv| cv.cvt == ConversionType::FromUnsigned)
  94 }
  95
  96 /// Searches for a combination of upper & lower bound checks
  97 fn double_check<'a>(cx: &LateContext<'_>, left: &'a Expr<'_>, right: &'a Expr<'_>) -> Option<Conversion<'a>> {
  98     let upper_lower = |l, r| {
  99         let upper = check_upper_bound(l);
 100         let lower = check_lower_bound(r);
 101
 102         upper.zip(lower).and_then(|(l, r)| l.combine(r, cx))
 103     };
 104
 105     upper_lower(left, right).or_else(|| upper_lower(right, left))
 106 }
 107
 108 /// Contains the result of a tried conversion check
 109 #[derive(Clone, Debug)]
 110 struct Conversion<'a> {
 111     cvt: ConversionType,
 112     expr_to_cast: &'a Expr<'a>,
 113     to_type: Option<&'a str>,
 114 }
 115
 116 /// The kind of conversion that is checked
 117 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 118 enum ConversionType {
 119     SignedToUnsigned,
 120     SignedToSigned,
 121     FromUnsigned,
 122 }
 123
 124 impl<'a> Conversion<'a> {
 125     /// Combine multiple conversions if the are compatible
 126     pub fn combine(self, other: Self, cx: &LateContext<'_>) -> Option<Conversion<'a>> {
 127         if self.is_compatible(&other, cx) {
 128             // Prefer a Conversion that contains a type-constraint
 129             Some(if self.to_type.is_some() { self } else { other })
 130         } else {
 131             None
 132         }
 133     }
 134
 135     /// Checks if two conversions are compatible
 136     /// same type of conversion, same 'castee' and same 'to type'
 137     pub fn is_compatible(&self, other: &Self, cx: &LateContext<'_>) -> bool {
 138         (self.cvt == other.cvt)
 139             && (SpanlessEq::new(cx).eq_expr(self.expr_to_cast, other.expr_to_cast))
 140             && (self.has_compatible_to_type(other))
 141     }
 142
 143     /// Checks if the to-type is the same (if there is a type constraint)
 144     fn has_compatible_to_type(&self, other: &Self) -> bool {
 145         match (self.to_type, other.to_type) {
 146             (Some(l), Some(r)) => l == r,
 147             _ => true,
 148         }
 149     }
 150
 151     /// Try to construct a new conversion if the conversion type is valid
 152     fn try_new(expr_to_cast: &'a Expr<'_>, from_type: &str, to_type: &'a str) -> Option<Conversion<'a>> {
 153         ConversionType::try_new(from_type, to_type).map(|cvt| Conversion {
 154             cvt,
 155             expr_to_cast,
 156             to_type: Some(to_type),
 157         })
 158     }
 159
 160     /// Construct a new conversion without type constraint
 161     fn new_any(expr_to_cast: &'a Expr<'_>) -> Conversion<'a> {
 162         Conversion {
 163             cvt: ConversionType::SignedToUnsigned,
 164             expr_to_cast,
 165             to_type: None,
 166         }
 167     }
 168 }
 169
 170 impl ConversionType {
 171     /// Creates a conversion type if the type is allowed & conversion is valid
 172     #[must_use]
 173     fn try_new(from: &str, to: &str) -> Option<Self> {
 174         if UINTS.contains(&from) {
 175             Some(Self::FromUnsigned)
 176         } else if SINTS.contains(&from) {
 177             if UINTS.contains(&to) {
 178                 Some(Self::SignedToUnsigned)
 179             } else if SINTS.contains(&to) {
 180                 Some(Self::SignedToSigned)
 181             } else {
 182                 None
 183             }
 184         } else {
 185             None
 186         }
 187     }
 188 }
 189
 190 /// Check for `expr <= (to_type::MAX as from_type)`
 191 fn check_upper_bound<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<Conversion<'tcx>> {
 192     if let ExprKind::Binary(ref op, left, right) = &expr.kind
 193         && let Some((candidate, check)) = normalize_le_ge(op, left, right)
 194         && let Some((from, to)) = get_types_from_cast(check, INTS, "max_value", "MAX")
 195     {
 196         Conversion::try_new(candidate, from, to)
 197     } else {
 198         None
 199     }
 200 }
 201
 202 /// Check for `expr >= 0|(to_type::MIN as from_type)`
 203 fn check_lower_bound<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<Conversion<'tcx>> {
 204     fn check_function<'a>(candidate: &'a Expr<'a>, check: &'a Expr<'a>) -> Option<Conversion<'a>> {
 205         (check_lower_bound_zero(candidate, check)).or_else(|| (check_lower_bound_min(candidate, check)))
 206     }
 207
 208     // First of we need a binary containing the expression & the cast
 209     if let ExprKind::Binary(ref op, left, right) = &expr.kind {
 210         normalize_le_ge(op, right, left).and_then(|(l, r)| check_function(l, r))
 211     } else {
 212         None
 213     }
 214 }
 215
 216 /// Check for `expr >= 0`
 217 fn check_lower_bound_zero<'a>(candidate: &'a Expr<'_>, check: &'a Expr<'_>) -> Option<Conversion<'a>> {
 218     is_integer_literal(check, 0).then(|| Conversion::new_any(candidate))
 219 }
 220
 221 /// Check for `expr >= (to_type::MIN 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, SINTS, "min_value", "MIN") {
 224         Conversion::try_new(candidate, from, to)
 225     } else {
 226         None
 227     }
 228 }
 229
 230 /// Tries to extract the from- and to-type from a cast expression
 231 fn get_types_from_cast<'a>(
 232     expr: &'a Expr<'_>,
 233     types: &'a [&str],
 234     func: &'a str,
 235     assoc_const: &'a str,
 236 ) -> Option<(&'a str, &'a str)> {
 237     // `to_type::max_value() as from_type`
 238     // or `to_type::MAX as from_type`
 239     let call_from_cast: Option<(&Expr<'_>, &str)> = if let ExprKind::Cast(limit, from_type) = &expr.kind
 240         // to_type::max_value(), from_type
 241         && let TyKind::Path(ref from_type_path) = &from_type.kind
 242         && let Some(from_sym) = int_ty_to_sym(from_type_path)
 243     {
 244         Some((limit, from_sym))
 245     } else {
 246         None
 247     };
 248
 249     // `from_type::from(to_type::max_value())`
 250     let limit_from: Option<(&Expr<'_>, &str)> = call_from_cast.or_else(|| {
 251         if let ExprKind::Call(from_func, [limit]) = &expr.kind
 252             // `from_type::from, to_type::max_value()`
 253             // `from_type::from`
 254             && let ExprKind::Path(ref path) = &from_func.kind
 255             && let Some(from_sym) = get_implementing_type(path, INTS, "from")
 256         {
 257             Some((limit, from_sym))
 258         } else {
 259             None
 260         }
 261     });
 262
 263     if let Some((limit, from_type)) = limit_from {
 264         match limit.kind {
 265             // `from_type::from(_)`
 266             ExprKind::Call(path, _) => {
 267                 if let ExprKind::Path(ref path) = path.kind {
 268                     // `to_type`
 269                     if let Some(to_type) = get_implementing_type(path, types, func) {
 270                         return Some((from_type, to_type));
 271                     }
 272                 }
 273             },
 274             // `to_type::MAX`
 275             ExprKind::Path(ref path) => {
 276                 if let Some(to_type) = get_implementing_type(path, types, assoc_const) {
 277                     return Some((from_type, to_type));
 278                 }
 279             },
 280             _ => {},
 281         }
 282     };
 283     None
 284 }
 285
 286 /// Gets the type which implements the called function
 287 fn get_implementing_type<'a>(path: &QPath<'_>, candidates: &'a [&str], function: &str) -> Option<&'a str> {
 288     if let QPath::TypeRelative(ty, path) = &path
 289         && path.ident.name.as_str() == function
 290         && let TyKind::Path(QPath::Resolved(None, tp)) = &ty.kind
 291         && let [int] = tp.segments
 292     {
 293         let name = int.ident.name.as_str();
 294         candidates.iter().find(|c| &name == *c).copied()
 295     } else {
 296         None
 297     }
 298 }
 299
 300 /// Gets the type as a string, if it is a supported integer
 301 fn int_ty_to_sym<'tcx>(path: &QPath<'_>) -> Option<&'tcx str> {
 302     if let QPath::Resolved(_, path) = *path
 303         && let [ty] = path.segments
 304     {
 305         let name = ty.ident.name.as_str();
 306         INTS.iter().find(|c| &name == *c).copied()
 307     } else {
 308         None
 309     }
 310 }
 311
 312 /// Will return the expressions as if they were expr1 <= expr2
 313 fn normalize_le_ge<'a>(op: &BinOp, left: &'a Expr<'a>, right: &'a Expr<'a>) -> Option<(&'a Expr<'a>, &'a Expr<'a>)> {
 314     match op.node {
 315         BinOpKind::Le => Some((left, right)),
 316         BinOpKind::Ge => Some((right, left)),
 317         _ => None,
 318     }
 319 }
 320
 321 // Constants
 322 const UINTS: &[&str] = &["u8", "u16", "u32", "u64", "usize"];
 323 const SINTS: &[&str] = &["i8", "i16", "i32", "i64", "isize"];
 324 const INTS: &[&str] = &["u8", "u16", "u32", "u64", "usize", "i8", "i16", "i32", "i64", "isize"];