|
| 1 | +use rustc_errors::Applicability; |
| 2 | +use rustc_hir::def::{DefKind,Res}; |
| 3 | +use rustc_hir::def_id::LocalDefId; |
| 4 | +use rustc_hir::{selfas hir}; |
| 5 | +use rustc_macros::LintDiagnostic; |
| 6 | +use rustc_middle::ty::{self,Ty}; |
| 7 | +use rustc_session::{declare_lint, impl_lint_pass}; |
| 8 | +use rustc_span::sym; |
| 9 | + |
| 10 | +usecrate::{LateContext,LateLintPass}; |
| 11 | + |
| 12 | +declare_lint!{ |
| 13 | +/// The `ptr_to_integer_transmute_in_consts` lint detects pointer to integer |
| 14 | +/// transmute in const functions and associated constants. |
| 15 | +/// |
| 16 | +/// ### Example |
| 17 | +/// |
| 18 | +/// ```rust |
| 19 | +/// const fn foo(ptr: *const u8) -> usize { |
| 20 | +/// unsafe { |
| 21 | +/// std::mem::transmute::<*const u8, usize>(ptr) |
| 22 | +/// } |
| 23 | +/// } |
| 24 | +/// ``` |
| 25 | +/// |
| 26 | +/// {{produces}} |
| 27 | +/// |
| 28 | +/// ### Explanation |
| 29 | +/// |
| 30 | +/// Transmuting pointers to integers in a `const` context is undefined behavior. |
| 31 | +/// Any attempt to use the resulting integer will abort const-evaluation. |
| 32 | +/// |
| 33 | +/// But sometimes the compiler might not emit an error for pointer to integer transmutes |
| 34 | +/// inside const functions and associated consts because they are evaluated only when referenced. |
| 35 | +/// Therefore, this lint serves as an extra layer of defense to prevent any undefined behavior |
| 36 | +/// from compiling without any warnings or errors. |
| 37 | +/// |
| 38 | +/// See [std::mem::transmute] in the reference for more details. |
| 39 | +/// |
| 40 | +/// [std::mem::transmute]: https://doc.rust-lang.org/std/mem/fn.transmute.html |
| 41 | +pubPTR_TO_INTEGER_TRANSMUTE_IN_CONSTS, |
| 42 | +Warn, |
| 43 | +"detects pointer to integer transmutes in const functions and associated constants", |
| 44 | +} |
| 45 | + |
| 46 | +declare_lint!{ |
| 47 | +/// The `unnecessary_transmutes` lint detects transmutations that have safer alternatives. |
| 48 | +/// |
| 49 | +/// ### Example |
| 50 | +/// |
| 51 | +/// ```rust |
| 52 | +/// fn bytes_at_home(x: [u8; 4]) -> u32 { |
| 53 | +/// unsafe { std::mem::transmute(x) } |
| 54 | +/// } |
| 55 | +/// ``` |
| 56 | +/// |
| 57 | +/// {{produces}} |
| 58 | +/// |
| 59 | +/// ### Explanation |
| 60 | +/// |
| 61 | +/// Using an explicit method is preferable over calls to |
| 62 | +/// [`transmute`](https://doc.rust-lang.org/std/mem/fn.transmute.html) as |
| 63 | +/// they more clearly communicate the intent, are easier to review, and |
| 64 | +/// are less likely to accidentally result in unsoundness. |
| 65 | +pubUNNECESSARY_TRANSMUTES, |
| 66 | +Warn, |
| 67 | +"detects transmutes that can also be achieved by other operations" |
| 68 | +} |
| 69 | + |
| 70 | +pub(crate)structCheckTransmutes; |
| 71 | + |
| 72 | +impl_lint_pass!(CheckTransmutes => [PTR_TO_INTEGER_TRANSMUTE_IN_CONSTS,UNNECESSARY_TRANSMUTES]); |
| 73 | + |
| 74 | +impl<'tcx>LateLintPass<'tcx>forCheckTransmutes{ |
| 75 | +fncheck_expr(&mutself,cx:&LateContext<'tcx>,expr:&'tcx hir::Expr<'tcx>){ |
| 76 | +let hir::ExprKind::Call(callee,[arg]) = expr.kindelse{ |
| 77 | +return; |
| 78 | +}; |
| 79 | +let hir::ExprKind::Path(qpath) = callee.kindelse{ |
| 80 | +return; |
| 81 | +}; |
| 82 | +letRes::Def(DefKind::Fn, def_id) = cx.qpath_res(&qpath, callee.hir_id)else{ |
| 83 | +return; |
| 84 | +}; |
| 85 | +if !cx.tcx.is_intrinsic(def_id, sym::transmute){ |
| 86 | +return; |
| 87 | +}; |
| 88 | +let body_owner_def_id = cx.tcx.hir_enclosing_body_owner(expr.hir_id); |
| 89 | +let const_context = cx.tcx.hir_body_const_context(body_owner_def_id); |
| 90 | +let args = cx.typeck_results().node_args(callee.hir_id); |
| 91 | + |
| 92 | +let src = args.type_at(0); |
| 93 | +let dst = args.type_at(1); |
| 94 | + |
| 95 | +check_ptr_transmute_in_const(cx, expr, body_owner_def_id, const_context, src, dst); |
| 96 | +check_unnecessary_transmute(cx, expr, callee, arg, const_context, src, dst); |
| 97 | +} |
| 98 | +} |
| 99 | + |
| 100 | +/// Check for transmutes that exhibit undefined behavior. |
| 101 | +/// For example, transmuting pointers to integers in a const context. |
| 102 | +/// |
| 103 | +/// Why do we consider const functions and associated constants only? |
| 104 | +/// |
| 105 | +/// Generally, undefined behavior in const items are handled by the evaluator. |
| 106 | +/// But, const functions and associated constants are evaluated only when referenced. |
| 107 | +/// This can result in undefined behavior in a library going unnoticed until |
| 108 | +/// the function or constant is actually used. |
| 109 | +/// |
| 110 | +/// Therefore, we only consider const functions and associated constants here and leave |
| 111 | +/// other const items to be handled by the evaluator. |
| 112 | +fncheck_ptr_transmute_in_const<'tcx>( |
| 113 | +cx:&LateContext<'tcx>, |
| 114 | +expr:&'tcx hir::Expr<'tcx>, |
| 115 | +body_owner_def_id:LocalDefId, |
| 116 | +const_context:Option<hir::ConstContext>, |
| 117 | +src:Ty<'tcx>, |
| 118 | +dst:Ty<'tcx>, |
| 119 | +){ |
| 120 | +ifmatches!(const_context,Some(hir::ConstContext::ConstFn)) |
| 121 | + || matches!(cx.tcx.def_kind(body_owner_def_id),DefKind::AssocConst) |
| 122 | +{ |
| 123 | +if src.is_raw_ptr() && dst.is_integral(){ |
| 124 | + cx.tcx.emit_node_span_lint( |
| 125 | +PTR_TO_INTEGER_TRANSMUTE_IN_CONSTS, |
| 126 | + expr.hir_id, |
| 127 | + expr.span, |
| 128 | +UndefinedTransmuteLint, |
| 129 | +); |
| 130 | +} |
| 131 | +} |
| 132 | +} |
| 133 | + |
| 134 | +/// Check for transmutes that overlap with stdlib methods. |
| 135 | +/// For example, transmuting `[u8; 4]` to `u32`. |
| 136 | +/// |
| 137 | +/// We chose not to lint u8 -> bool transmutes, see #140431. |
| 138 | +fncheck_unnecessary_transmute<'tcx>( |
| 139 | +cx:&LateContext<'tcx>, |
| 140 | +expr:&'tcx hir::Expr<'tcx>, |
| 141 | +callee:&'tcx hir::Expr<'tcx>, |
| 142 | +arg:&'tcx hir::Expr<'tcx>, |
| 143 | +const_context:Option<hir::ConstContext>, |
| 144 | +src:Ty<'tcx>, |
| 145 | +dst:Ty<'tcx>, |
| 146 | +){ |
| 147 | +let callee_span = callee.span.find_ancestor_inside(expr.span).unwrap_or(callee.span); |
| 148 | +let(sugg, help) = match(src.kind(), dst.kind()){ |
| 149 | +// dont check the length; transmute does that for us. |
| 150 | +// [u8; _] => primitive |
| 151 | +(ty::Array(t, _), ty::Uint(_) | ty::Float(_) | ty::Int(_)) |
| 152 | +if*t.kind() == ty::Uint(ty::UintTy::U8) => |
| 153 | +{ |
| 154 | +( |
| 155 | +Some(vec![(callee_span, format!("{dst}::from_ne_bytes"))]), |
| 156 | +Some( |
| 157 | +"there's also `from_le_bytes` and `from_be_bytes` if you expect a particular byte order", |
| 158 | +), |
| 159 | +) |
| 160 | +} |
| 161 | +// primitive => [u8; _] |
| 162 | +(ty::Uint(_) | ty::Float(_) | ty::Int(_), ty::Array(t, _)) |
| 163 | +if*t.kind() == ty::Uint(ty::UintTy::U8) => |
| 164 | +{ |
| 165 | +( |
| 166 | +Some(vec![(callee_span, format!("{src}::to_ne_bytes"))]), |
| 167 | +Some( |
| 168 | +"there's also `to_le_bytes` and `to_be_bytes` if you expect a particular byte order", |
| 169 | +), |
| 170 | +) |
| 171 | +} |
| 172 | +// char → u32 |
| 173 | +(ty::Char, ty::Uint(ty::UintTy::U32)) => { |
| 174 | +(Some(vec![(callee_span,"u32::from".to_string())]),None) |
| 175 | +} |
| 176 | +// char (→ u32) → i32 |
| 177 | +(ty::Char, ty::Int(ty::IntTy::I32)) => ( |
| 178 | +Some(vec![ |
| 179 | +(callee_span,"u32::from".to_string()), |
| 180 | +(expr.span.shrink_to_hi(),".cast_signed()".to_string()), |
| 181 | +]), |
| 182 | +None, |
| 183 | +), |
| 184 | +// u32 → char |
| 185 | +(ty::Uint(ty::UintTy::U32), ty::Char) => ( |
| 186 | +Some(vec![(callee_span,"char::from_u32_unchecked".to_string())]), |
| 187 | +Some("consider using `char::from_u32(…).unwrap()`"), |
| 188 | +), |
| 189 | +// i32 → char |
| 190 | +(ty::Int(ty::IntTy::I32), ty::Char) => ( |
| 191 | +Some(vec![ |
| 192 | +(callee_span,"char::from_u32_unchecked(i32::cast_unsigned".to_string()), |
| 193 | +(expr.span.shrink_to_hi(),")".to_string()), |
| 194 | +]), |
| 195 | +Some("consider using `char::from_u32(i32::cast_unsigned(…)).unwrap()`"), |
| 196 | +), |
| 197 | +// uNN → iNN |
| 198 | +(ty::Uint(_), ty::Int(_)) => { |
| 199 | +(Some(vec![(callee_span, format!("{src}::cast_signed"))]),None) |
| 200 | +} |
| 201 | +// iNN → uNN |
| 202 | +(ty::Int(_), ty::Uint(_)) => { |
| 203 | +(Some(vec![(callee_span, format!("{src}::cast_unsigned"))]),None) |
| 204 | +} |
| 205 | +// fNN → usize, isize |
| 206 | +(ty::Float(_), ty::Uint(ty::UintTy::Usize) | ty::Int(ty::IntTy::Isize)) => ( |
| 207 | +Some(vec![ |
| 208 | +(callee_span, format!("{src}::to_bits")), |
| 209 | +(expr.span.shrink_to_hi(), format!(" as {dst}")), |
| 210 | +]), |
| 211 | +None, |
| 212 | +), |
| 213 | +// fNN (→ uNN) → iNN |
| 214 | +(ty::Float(_), ty::Int(..)) => ( |
| 215 | +Some(vec![ |
| 216 | +(callee_span, format!("{src}::to_bits")), |
| 217 | +(expr.span.shrink_to_hi(),".cast_signed()".to_string()), |
| 218 | +]), |
| 219 | +None, |
| 220 | +), |
| 221 | +// fNN → uNN |
| 222 | +(ty::Float(_), ty::Uint(..)) => { |
| 223 | +(Some(vec![(callee_span, format!("{src}::to_bits"))]),None) |
| 224 | +} |
| 225 | +// xsize → fNN |
| 226 | +(ty::Uint(ty::UintTy::Usize) | ty::Int(ty::IntTy::Isize), ty::Float(_)) => ( |
| 227 | +Some(vec![ |
| 228 | +(callee_span, format!("{dst}::from_bits")), |
| 229 | +(arg.span.shrink_to_hi()," as _".to_string()), |
| 230 | +]), |
| 231 | +None, |
| 232 | +), |
| 233 | +// iNN (→ uNN) → fNN |
| 234 | +(ty::Int(_), ty::Float(_)) => ( |
| 235 | +Some(vec![ |
| 236 | +(callee_span, format!("{dst}::from_bits({src}::cast_unsigned")), |
| 237 | +(expr.span.shrink_to_hi(),")".to_string()), |
| 238 | +]), |
| 239 | +None, |
| 240 | +), |
| 241 | +// uNN → fNN |
| 242 | +(ty::Uint(_), ty::Float(_)) => { |
| 243 | +(Some(vec![(callee_span, format!("{dst}::from_bits"))]),None) |
| 244 | +} |
| 245 | +// bool → x8 in const context since `From::from` is not const yet |
| 246 | +// FIXME: Consider arg expr's precedence to avoid parentheses. |
| 247 | +// FIXME(const_traits): Remove this when `From::from` is constified. |
| 248 | +(ty::Bool, ty::Int(..) | ty::Uint(..))if const_context.is_some() => ( |
| 249 | +Some(vec![ |
| 250 | +(callee_span,"".to_string()), |
| 251 | +(expr.span.shrink_to_hi(), format!(" as {dst}")), |
| 252 | +]), |
| 253 | +None, |
| 254 | +), |
| 255 | +// bool → x8 using `x8::from` |
| 256 | +(ty::Bool, ty::Int(..) | ty::Uint(..)) => { |
| 257 | +(Some(vec![(callee_span, format!("{dst}::from"))]),None) |
| 258 | +} |
| 259 | + _ => return, |
| 260 | +}; |
| 261 | + |
| 262 | + cx.tcx.node_span_lint(UNNECESSARY_TRANSMUTES, expr.hir_id, expr.span, |diag| { |
| 263 | + diag.primary_message("unnecessary transmute"); |
| 264 | +ifletSome(sugg) = sugg { |
| 265 | + diag.multipart_suggestion("replace this with", sugg,Applicability::MachineApplicable); |
| 266 | +} |
| 267 | +ifletSome(help) = help { |
| 268 | + diag.help(help); |
| 269 | +} |
| 270 | +}); |
| 271 | +} |
| 272 | + |
| 273 | +#[derive(LintDiagnostic)] |
| 274 | +#[diag(lint_undefined_transmute)] |
| 275 | +#[note] |
| 276 | +#[note(lint_note2)] |
| 277 | +#[help] |
| 278 | +pub(crate)structUndefinedTransmuteLint; |
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