src/librustc_lint/types.rs

   1 #![allow(non_snake_case)]
   2
   3 use crate::{LateContext, LateLintPass, LintContext};
   4 use rustc::mir::interpret::{sign_extend, truncate};
   5 use rustc::ty::layout::{self, IntegerExt, LayoutOf, SizeSkeleton, VariantIdx};
   6 use rustc::ty::subst::SubstsRef;
   7 use rustc::ty::{self, AdtKind, ParamEnv, Ty, TyCtxt};
   8 use rustc_attr as attr;
   9 use rustc_data_structures::fx::FxHashSet;
  10 use rustc_errors::Applicability;
  11 use rustc_hir as hir;
  12 use rustc_hir::def_id::DefId;
  13 use rustc_hir::{is_range_literal, ExprKind, Node};
  14 use rustc_index::vec::Idx;
  15 use rustc_span::source_map;
  16 use rustc_span::symbol::sym;
  17 use rustc_span::Span;
  18 use rustc_target::spec::abi::Abi;
  19 use syntax::ast;
  20
  21 use log::debug;
  22 use std::cmp;
  23 use std::{f32, f64, i16, i32, i64, i8, u16, u32, u64, u8};
  24
  25 declare_lint! {
  26     UNUSED_COMPARISONS,
  27     Warn,
  28     "comparisons made useless by limits of the types involved"
  29 }
  30
  31 declare_lint! {
  32     OVERFLOWING_LITERALS,
  33     Deny,
  34     "literal out of range for its type"
  35 }
  36
  37 declare_lint! {
  38     VARIANT_SIZE_DIFFERENCES,
  39     Allow,
  40     "detects enums with widely varying variant sizes"
  41 }
  42
  43 #[derive(Copy, Clone)]
  44 pub struct TypeLimits {
  45     /// Id of the last visited negated expression
  46     negated_expr_id: hir::HirId,
  47 }
  48
  49 impl_lint_pass!(TypeLimits => [UNUSED_COMPARISONS, OVERFLOWING_LITERALS]);
  50
  51 impl TypeLimits {
  52     pub fn new() -> TypeLimits {
  53         TypeLimits { negated_expr_id: hir::DUMMY_HIR_ID }
  54     }
  55 }
  56
  57 /// Attempts to special-case the overflowing literal lint when it occurs as a range endpoint.
  58 /// Returns `true` iff the lint was overridden.
  59 fn lint_overflowing_range_endpoint<'a, 'tcx>(
  60     cx: &LateContext<'a, 'tcx>,
  61     lit: &hir::Lit,
  62     lit_val: u128,
  63     max: u128,
  64     expr: &'tcx hir::Expr<'tcx>,
  65     parent_expr: &'tcx hir::Expr<'tcx>,
  66     ty: &str,
  67 ) -> bool {
  68     // We only want to handle exclusive (`..`) ranges,
  69     // which are represented as `ExprKind::Struct`.
  70     if let ExprKind::Struct(_, eps, _) = &parent_expr.kind {
  71         if eps.len() != 2 {
  72             return false;
  73         }
  74         // We can suggest using an inclusive range
  75         // (`..=`) instead only if it is the `end` that is
  76         // overflowing and only by 1.
  77         if eps[1].expr.hir_id == expr.hir_id && lit_val - 1 == max {
  78             let mut err = cx.struct_span_lint(
  79                 OVERFLOWING_LITERALS,
  80                 parent_expr.span,
  81                 &format!("range endpoint is out of range for `{}`", ty),
  82             );
  83             if let Ok(start) = cx.sess().source_map().span_to_snippet(eps[0].span) {
  84                 use ast::{LitIntType, LitKind};
  85                 // We need to preserve the literal's suffix,
  86                 // as it may determine typing information.
  87                 let suffix = match lit.node {
  88                     LitKind::Int(_, LitIntType::Signed(s)) => format!("{}", s.name_str()),
  89                     LitKind::Int(_, LitIntType::Unsigned(s)) => format!("{}", s.name_str()),
  90                     LitKind::Int(_, LitIntType::Unsuffixed) => "".to_owned(),
  91                     _ => bug!(),
  92                 };
  93                 let suggestion = format!("{}..={}{}", start, lit_val - 1, suffix);
  94                 err.span_suggestion(
  95                     parent_expr.span,
  96                     &"use an inclusive range instead",
  97                     suggestion,
  98                     Applicability::MachineApplicable,
  99                 );
 100                 err.emit();
 101                 return true;
 102             }
 103         }
 104     }
 105
 106     false
 107 }
 108
 109 // For `isize` & `usize`, be conservative with the warnings, so that the
 110 // warnings are consistent between 32- and 64-bit platforms.
 111 fn int_ty_range(int_ty: ast::IntTy) -> (i128, i128) {
 112     match int_ty {
 113         ast::IntTy::Isize => (i64::min_value() as i128, i64::max_value() as i128),
 114         ast::IntTy::I8 => (i8::min_value() as i64 as i128, i8::max_value() as i128),
 115         ast::IntTy::I16 => (i16::min_value() as i64 as i128, i16::max_value() as i128),
 116         ast::IntTy::I32 => (i32::min_value() as i64 as i128, i32::max_value() as i128),
 117         ast::IntTy::I64 => (i64::min_value() as i128, i64::max_value() as i128),
 118         ast::IntTy::I128 => (i128::min_value() as i128, i128::max_value()),
 119     }
 120 }
 121
 122 fn uint_ty_range(uint_ty: ast::UintTy) -> (u128, u128) {
 123     match uint_ty {
 124         ast::UintTy::Usize => (u64::min_value() as u128, u64::max_value() as u128),
 125         ast::UintTy::U8 => (u8::min_value() as u128, u8::max_value() as u128),
 126         ast::UintTy::U16 => (u16::min_value() as u128, u16::max_value() as u128),
 127         ast::UintTy::U32 => (u32::min_value() as u128, u32::max_value() as u128),
 128         ast::UintTy::U64 => (u64::min_value() as u128, u64::max_value() as u128),
 129         ast::UintTy::U128 => (u128::min_value(), u128::max_value()),
 130     }
 131 }
 132
 133 fn get_bin_hex_repr(cx: &LateContext<'_, '_>, lit: &hir::Lit) -> Option<String> {
 134     let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?;
 135     let firstch = src.chars().next()?;
 136
 137     if firstch == '0' {
 138         match src.chars().nth(1) {
 139             Some('x') | Some('b') => return Some(src),
 140             _ => return None,
 141         }
 142     }
 143
 144     None
 145 }
 146
 147 fn report_bin_hex_error(
 148     cx: &LateContext<'_, '_>,
 149     expr: &hir::Expr<'_>,
 150     ty: attr::IntType,
 151     repr_str: String,
 152     val: u128,
 153     negative: bool,
 154 ) {
 155     let size = layout::Integer::from_attr(&cx.tcx, ty).size();
 156     let (t, actually) = match ty {
 157         attr::IntType::SignedInt(t) => {
 158             let actually = sign_extend(val, size) as i128;
 159             (t.name_str(), actually.to_string())
 160         }
 161         attr::IntType::UnsignedInt(t) => {
 162             let actually = truncate(val, size);
 163             (t.name_str(), actually.to_string())
 164         }
 165     };
 166     let mut err = cx.struct_span_lint(
 167         OVERFLOWING_LITERALS,
 168         expr.span,
 169         &format!("literal out of range for {}", t),
 170     );
 171     err.note(&format!(
 172         "the literal `{}` (decimal `{}`) does not fit into \
 173             an `{}` and will become `{}{}`",
 174         repr_str, val, t, actually, t
 175     ));
 176     if let Some(sugg_ty) = get_type_suggestion(&cx.tables.node_type(expr.hir_id), val, negative) {
 177         if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') {
 178             let (sans_suffix, _) = repr_str.split_at(pos);
 179             err.span_suggestion(
 180                 expr.span,
 181                 &format!("consider using `{}` instead", sugg_ty),
 182                 format!("{}{}", sans_suffix, sugg_ty),
 183                 Applicability::MachineApplicable,
 184             );
 185         } else {
 186             err.help(&format!("consider using `{}` instead", sugg_ty));
 187         }
 188     }
 189
 190     err.emit();
 191 }
 192
 193 // This function finds the next fitting type and generates a suggestion string.
 194 // It searches for fitting types in the following way (`X < Y`):
 195 //  - `iX`: if literal fits in `uX` => `uX`, else => `iY`
 196 //  - `-iX` => `iY`
 197 //  - `uX` => `uY`
 198 //
 199 // No suggestion for: `isize`, `usize`.
 200 fn get_type_suggestion(t: Ty<'_>, val: u128, negative: bool) -> Option<&'static str> {
 201     use syntax::ast::IntTy::*;
 202     use syntax::ast::UintTy::*;
 203     macro_rules! find_fit {
 204         ($ty:expr, $val:expr, $negative:expr,
 205          $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => {
 206             {
 207                 let _neg = if negative { 1 } else { 0 };
 208                 match $ty {
 209                     $($type => {
 210                         $(if !negative && val <= uint_ty_range($utypes).1 {
 211                             return Some($utypes.name_str())
 212                         })*
 213                         $(if val <= int_ty_range($itypes).1 as u128 + _neg {
 214                             return Some($itypes.name_str())
 215                         })*
 216                         None
 217                     },)+
 218                     _ => None
 219                 }
 220             }
 221         }
 222     }
 223     match t.kind {
 224         ty::Int(i) => find_fit!(i, val, negative,
 225                       I8 => [U8] => [I16, I32, I64, I128],
 226                       I16 => [U16] => [I32, I64, I128],
 227                       I32 => [U32] => [I64, I128],
 228                       I64 => [U64] => [I128],
 229                       I128 => [U128] => []),
 230         ty::Uint(u) => find_fit!(u, val, negative,
 231                       U8 => [U8, U16, U32, U64, U128] => [],
 232                       U16 => [U16, U32, U64, U128] => [],
 233                       U32 => [U32, U64, U128] => [],
 234                       U64 => [U64, U128] => [],
 235                       U128 => [U128] => []),
 236         _ => None,
 237     }
 238 }
 239
 240 fn lint_int_literal<'a, 'tcx>(
 241     cx: &LateContext<'a, 'tcx>,
 242     type_limits: &TypeLimits,
 243     e: &'tcx hir::Expr<'tcx>,
 244     lit: &hir::Lit,
 245     t: ast::IntTy,
 246     v: u128,
 247 ) {
 248     let int_type = t.normalize(cx.sess().target.ptr_width);
 249     let (_, max) = int_ty_range(int_type);
 250     let max = max as u128;
 251     let negative = type_limits.negated_expr_id == e.hir_id;
 252
 253     // Detect literal value out of range [min, max] inclusive
 254     // avoiding use of -min to prevent overflow/panic
 255     if (negative && v > max + 1) || (!negative && v > max) {
 256         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 257             report_bin_hex_error(cx, e, attr::IntType::SignedInt(t), repr_str, v, negative);
 258             return;
 259         }
 260
 261         let par_id = cx.tcx.hir().get_parent_node(e.hir_id);
 262         if let Node::Expr(par_e) = cx.tcx.hir().get(par_id) {
 263             if let hir::ExprKind::Struct(..) = par_e.kind {
 264                 if is_range_literal(cx.sess().source_map(), par_e)
 265                     && lint_overflowing_range_endpoint(cx, lit, v, max, e, par_e, t.name_str())
 266                 {
 267                     // The overflowing literal lint was overridden.
 268                     return;
 269                 }
 270             }
 271         }
 272
 273         cx.span_lint(
 274             OVERFLOWING_LITERALS,
 275             e.span,
 276             &format!("literal out of range for `{}`", t.name_str()),
 277         );
 278     }
 279 }
 280
 281 fn lint_uint_literal<'a, 'tcx>(
 282     cx: &LateContext<'a, 'tcx>,
 283     e: &'tcx hir::Expr<'tcx>,
 284     lit: &hir::Lit,
 285     t: ast::UintTy,
 286 ) {
 287     let uint_type = t.normalize(cx.sess().target.ptr_width);
 288     let (min, max) = uint_ty_range(uint_type);
 289     let lit_val: u128 = match lit.node {
 290         // _v is u8, within range by definition
 291         ast::LitKind::Byte(_v) => return,
 292         ast::LitKind::Int(v, _) => v,
 293         _ => bug!(),
 294     };
 295     if lit_val < min || lit_val > max {
 296         let parent_id = cx.tcx.hir().get_parent_node(e.hir_id);
 297         if let Node::Expr(par_e) = cx.tcx.hir().get(parent_id) {
 298             match par_e.kind {
 299                 hir::ExprKind::Cast(..) => {
 300                     if let ty::Char = cx.tables.expr_ty(par_e).kind {
 301                         let mut err = cx.struct_span_lint(
 302                             OVERFLOWING_LITERALS,
 303                             par_e.span,
 304                             "only `u8` can be cast into `char`",
 305                         );
 306                         err.span_suggestion(
 307                             par_e.span,
 308                             &"use a `char` literal instead",
 309                             format!("'\\u{{{:X}}}'", lit_val),
 310                             Applicability::MachineApplicable,
 311                         );
 312                         err.emit();
 313                         return;
 314                     }
 315                 }
 316                 hir::ExprKind::Struct(..) if is_range_literal(cx.sess().source_map(), par_e) => {
 317                     let t = t.name_str();
 318                     if lint_overflowing_range_endpoint(cx, lit, lit_val, max, e, par_e, t) {
 319                         // The overflowing literal lint was overridden.
 320                         return;
 321                     }
 322                 }
 323                 _ => {}
 324             }
 325         }
 326         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 327             report_bin_hex_error(cx, e, attr::IntType::UnsignedInt(t), repr_str, lit_val, false);
 328             return;
 329         }
 330         cx.span_lint(
 331             OVERFLOWING_LITERALS,
 332             e.span,
 333             &format!("literal out of range for `{}`", t.name_str()),
 334         );
 335     }
 336 }
 337
 338 fn lint_literal<'a, 'tcx>(
 339     cx: &LateContext<'a, 'tcx>,
 340     type_limits: &TypeLimits,
 341     e: &'tcx hir::Expr<'tcx>,
 342     lit: &hir::Lit,
 343 ) {
 344     match cx.tables.node_type(e.hir_id).kind {
 345         ty::Int(t) => {
 346             match lit.node {
 347                 ast::LitKind::Int(v, ast::LitIntType::Signed(_))
 348                 | ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => {
 349                     lint_int_literal(cx, type_limits, e, lit, t, v)
 350                 }
 351                 _ => bug!(),
 352             };
 353         }
 354         ty::Uint(t) => lint_uint_literal(cx, e, lit, t),
 355         ty::Float(t) => {
 356             let is_infinite = match lit.node {
 357                 ast::LitKind::Float(v, _) => match t {
 358                     ast::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
 359                     ast::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
 360                 },
 361                 _ => bug!(),
 362             };
 363             if is_infinite == Ok(true) {
 364                 cx.span_lint(
 365                     OVERFLOWING_LITERALS,
 366                     e.span,
 367                     &format!("literal out of range for `{}`", t.name_str()),
 368                 );
 369             }
 370         }
 371         _ => {}
 372     }
 373 }
 374
 375 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TypeLimits {
 376     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx hir::Expr<'tcx>) {
 377         match e.kind {
 378             hir::ExprKind::Unary(hir::UnOp::UnNeg, ref expr) => {
 379                 // propagate negation, if the negation itself isn't negated
 380                 if self.negated_expr_id != e.hir_id {
 381                     self.negated_expr_id = expr.hir_id;
 382                 }
 383             }
 384             hir::ExprKind::Binary(binop, ref l, ref r) => {
 385                 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
 386                     cx.span_lint(
 387                         UNUSED_COMPARISONS,
 388                         e.span,
 389                         "comparison is useless due to type limits",
 390                     );
 391                 }
 392             }
 393             hir::ExprKind::Lit(ref lit) => lint_literal(cx, self, e, lit),
 394             _ => {}
 395         };
 396
 397         fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
 398             match binop.node {
 399                 hir::BinOpKind::Lt => v > min && v <= max,
 400                 hir::BinOpKind::Le => v >= min && v < max,
 401                 hir::BinOpKind::Gt => v >= min && v < max,
 402                 hir::BinOpKind::Ge => v > min && v <= max,
 403                 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
 404                 _ => bug!(),
 405             }
 406         }
 407
 408         fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
 409             source_map::respan(
 410                 binop.span,
 411                 match binop.node {
 412                     hir::BinOpKind::Lt => hir::BinOpKind::Gt,
 413                     hir::BinOpKind::Le => hir::BinOpKind::Ge,
 414                     hir::BinOpKind::Gt => hir::BinOpKind::Lt,
 415                     hir::BinOpKind::Ge => hir::BinOpKind::Le,
 416                     _ => return binop,
 417                 },
 418             )
 419         }
 420
 421         fn check_limits(
 422             cx: &LateContext<'_, '_>,
 423             binop: hir::BinOp,
 424             l: &hir::Expr<'_>,
 425             r: &hir::Expr<'_>,
 426         ) -> bool {
 427             let (lit, expr, swap) = match (&l.kind, &r.kind) {
 428                 (&hir::ExprKind::Lit(_), _) => (l, r, true),
 429                 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
 430                 _ => return true,
 431             };
 432             // Normalize the binop so that the literal is always on the RHS in
 433             // the comparison
 434             let norm_binop = if swap { rev_binop(binop) } else { binop };
 435             match cx.tables.node_type(expr.hir_id).kind {
 436                 ty::Int(int_ty) => {
 437                     let (min, max) = int_ty_range(int_ty);
 438                     let lit_val: i128 = match lit.kind {
 439                         hir::ExprKind::Lit(ref li) => match li.node {
 440                             ast::LitKind::Int(v, ast::LitIntType::Signed(_))
 441                             | ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => v as i128,
 442                             _ => return true,
 443                         },
 444                         _ => bug!(),
 445                     };
 446                     is_valid(norm_binop, lit_val, min, max)
 447                 }
 448                 ty::Uint(uint_ty) => {
 449                     let (min, max): (u128, u128) = uint_ty_range(uint_ty);
 450                     let lit_val: u128 = match lit.kind {
 451                         hir::ExprKind::Lit(ref li) => match li.node {
 452                             ast::LitKind::Int(v, _) => v,
 453                             _ => return true,
 454                         },
 455                         _ => bug!(),
 456                     };
 457                     is_valid(norm_binop, lit_val, min, max)
 458                 }
 459                 _ => true,
 460             }
 461         }
 462
 463         fn is_comparison(binop: hir::BinOp) -> bool {
 464             match binop.node {
 465                 hir::BinOpKind::Eq
 466                 | hir::BinOpKind::Lt
 467                 | hir::BinOpKind::Le
 468                 | hir::BinOpKind::Ne
 469                 | hir::BinOpKind::Ge
 470                 | hir::BinOpKind::Gt => true,
 471                 _ => false,
 472             }
 473         }
 474     }
 475 }
 476
 477 declare_lint! {
 478     IMPROPER_CTYPES,
 479     Warn,
 480     "proper use of libc types in foreign modules"
 481 }
 482
 483 declare_lint_pass!(ImproperCTypes => [IMPROPER_CTYPES]);
 484
 485 struct ImproperCTypesVisitor<'a, 'tcx> {
 486     cx: &'a LateContext<'a, 'tcx>,
 487 }
 488
 489 enum FfiResult<'tcx> {
 490     FfiSafe,
 491     FfiPhantom(Ty<'tcx>),
 492     FfiUnsafe { ty: Ty<'tcx>, reason: &'static str, help: Option<&'static str> },
 493 }
 494
 495 fn is_zst<'tcx>(tcx: TyCtxt<'tcx>, did: DefId, ty: Ty<'tcx>) -> bool {
 496     tcx.layout_of(tcx.param_env(did).and(ty)).map(|layout| layout.is_zst()).unwrap_or(false)
 497 }
 498
 499 fn ty_is_known_nonnull<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool {
 500     match ty.kind {
 501         ty::FnPtr(_) => true,
 502         ty::Ref(..) => true,
 503         ty::Adt(field_def, substs) if field_def.repr.transparent() && !field_def.is_union() => {
 504             for field in field_def.all_fields() {
 505                 let field_ty =
 506                     tcx.normalize_erasing_regions(ParamEnv::reveal_all(), field.ty(tcx, substs));
 507                 if is_zst(tcx, field.did, field_ty) {
 508                     continue;
 509                 }
 510
 511                 let attrs = tcx.get_attrs(field_def.did);
 512                 if attrs.iter().any(|a| a.check_name(sym::rustc_nonnull_optimization_guaranteed))
 513                     || ty_is_known_nonnull(tcx, field_ty)
 514                 {
 515                     return true;
 516                 }
 517             }
 518
 519             false
 520         }
 521         _ => false,
 522     }
 523 }
 524
 525 /// Check if this enum can be safely exported based on the
 526 /// "nullable pointer optimization". Currently restricted
 527 /// to function pointers, references, core::num::NonZero*,
 528 /// core::ptr::NonNull, and #[repr(transparent)] newtypes.
 529 /// FIXME: This duplicates code in codegen.
 530 fn is_repr_nullable_ptr<'tcx>(
 531     tcx: TyCtxt<'tcx>,
 532     ty: Ty<'tcx>,
 533     ty_def: &'tcx ty::AdtDef,
 534     substs: SubstsRef<'tcx>,
 535 ) -> bool {
 536     if ty_def.variants.len() != 2 {
 537         return false;
 538     }
 539
 540     let get_variant_fields = |index| &ty_def.variants[VariantIdx::new(index)].fields;
 541     let variant_fields = [get_variant_fields(0), get_variant_fields(1)];
 542     let fields = if variant_fields[0].is_empty() {
 543         &variant_fields[1]
 544     } else if variant_fields[1].is_empty() {
 545         &variant_fields[0]
 546     } else {
 547         return false;
 548     };
 549
 550     if fields.len() != 1 {
 551         return false;
 552     }
 553
 554     let field_ty = fields[0].ty(tcx, substs);
 555     if !ty_is_known_nonnull(tcx, field_ty) {
 556         return false;
 557     }
 558
 559     // At this point, the field's type is known to be nonnull and the parent enum is Option-like.
 560     // If the computed size for the field and the enum are different, the nonnull optimization isn't
 561     // being applied (and we've got a problem somewhere).
 562     let compute_size_skeleton = |t| SizeSkeleton::compute(t, tcx, ParamEnv::reveal_all()).unwrap();
 563     if !compute_size_skeleton(ty).same_size(compute_size_skeleton(field_ty)) {
 564         bug!("improper_ctypes: Option nonnull optimization not applied?");
 565     }
 566
 567     true
 568 }
 569
 570 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
 571     /// Check if the type is array and emit an unsafe type lint.
 572     fn check_for_array_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
 573         if let ty::Array(..) = ty.kind {
 574             self.emit_ffi_unsafe_type_lint(
 575                 ty,
 576                 sp,
 577                 "passing raw arrays by value is not FFI-safe",
 578                 Some("consider passing a pointer to the array"),
 579             );
 580             true
 581         } else {
 582             false
 583         }
 584     }
 585
 586     /// Checks if the given type is "ffi-safe" (has a stable, well-defined
 587     /// representation which can be exported to C code).
 588     fn check_type_for_ffi(&self, cache: &mut FxHashSet<Ty<'tcx>>, ty: Ty<'tcx>) -> FfiResult<'tcx> {
 589         use FfiResult::*;
 590
 591         let cx = self.cx.tcx;
 592
 593         // Protect against infinite recursion, for example
 594         // `struct S(*mut S);`.
 595         // FIXME: A recursion limit is necessary as well, for irregular
 596         // recursive types.
 597         if !cache.insert(ty) {
 598             return FfiSafe;
 599         }
 600
 601         match ty.kind {
 602             ty::Adt(def, substs) => {
 603                 if def.is_phantom_data() {
 604                     return FfiPhantom(ty);
 605                 }
 606                 match def.adt_kind() {
 607                     AdtKind::Struct => {
 608                         if !def.repr.c() && !def.repr.transparent() {
 609                             return FfiUnsafe {
 610                                 ty,
 611                                 reason: "this struct has unspecified layout",
 612                                 help: Some(
 613                                     "consider adding a `#[repr(C)]` or \
 614                                             `#[repr(transparent)]` attribute to this struct",
 615                                 ),
 616                             };
 617                         }
 618
 619                         let is_non_exhaustive =
 620                             def.non_enum_variant().is_field_list_non_exhaustive();
 621                         if is_non_exhaustive && !def.did.is_local() {
 622                             return FfiUnsafe {
 623                                 ty,
 624                                 reason: "this struct is non-exhaustive",
 625                                 help: None,
 626                             };
 627                         }
 628
 629                         if def.non_enum_variant().fields.is_empty() {
 630                             return FfiUnsafe {
 631                                 ty,
 632                                 reason: "this struct has no fields",
 633                                 help: Some("consider adding a member to this struct"),
 634                             };
 635                         }
 636
 637                         // We can't completely trust repr(C) and repr(transparent) markings;
 638                         // make sure the fields are actually safe.
 639                         let mut all_phantom = true;
 640                         for field in &def.non_enum_variant().fields {
 641                             let field_ty = cx.normalize_erasing_regions(
 642                                 ParamEnv::reveal_all(),
 643                                 field.ty(cx, substs),
 644                             );
 645                             // repr(transparent) types are allowed to have arbitrary ZSTs, not just
 646                             // PhantomData -- skip checking all ZST fields
 647                             if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 648                                 continue;
 649                             }
 650                             let r = self.check_type_for_ffi(cache, field_ty);
 651                             match r {
 652                                 FfiSafe => {
 653                                     all_phantom = false;
 654                                 }
 655                                 FfiPhantom(..) => {}
 656                                 FfiUnsafe { .. } => {
 657                                     return r;
 658                                 }
 659                             }
 660                         }
 661
 662                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 663                     }
 664                     AdtKind::Union => {
 665                         if !def.repr.c() && !def.repr.transparent() {
 666                             return FfiUnsafe {
 667                                 ty,
 668                                 reason: "this union has unspecified layout",
 669                                 help: Some(
 670                                     "consider adding a `#[repr(C)]` or \
 671                                             `#[repr(transparent)]` attribute to this union",
 672                                 ),
 673                             };
 674                         }
 675
 676                         if def.non_enum_variant().fields.is_empty() {
 677                             return FfiUnsafe {
 678                                 ty,
 679                                 reason: "this union has no fields",
 680                                 help: Some("consider adding a field to this union"),
 681                             };
 682                         }
 683
 684                         let mut all_phantom = true;
 685                         for field in &def.non_enum_variant().fields {
 686                             let field_ty = cx.normalize_erasing_regions(
 687                                 ParamEnv::reveal_all(),
 688                                 field.ty(cx, substs),
 689                             );
 690                             // repr(transparent) types are allowed to have arbitrary ZSTs, not just
 691                             // PhantomData -- skip checking all ZST fields.
 692                             if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 693                                 continue;
 694                             }
 695                             let r = self.check_type_for_ffi(cache, field_ty);
 696                             match r {
 697                                 FfiSafe => {
 698                                     all_phantom = false;
 699                                 }
 700                                 FfiPhantom(..) => {}
 701                                 FfiUnsafe { .. } => {
 702                                     return r;
 703                                 }
 704                             }
 705                         }
 706
 707                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 708                     }
 709                     AdtKind::Enum => {
 710                         if def.variants.is_empty() {
 711                             // Empty enums are okay... although sort of useless.
 712                             return FfiSafe;
 713                         }
 714
 715                         // Check for a repr() attribute to specify the size of the
 716                         // discriminant.
 717                         if !def.repr.c() && !def.repr.transparent() && def.repr.int.is_none() {
 718                             // Special-case types like `Option<extern fn()>`.
 719                             if !is_repr_nullable_ptr(cx, ty, def, substs) {
 720                                 return FfiUnsafe {
 721                                     ty,
 722                                     reason: "enum has no representation hint",
 723                                     help: Some(
 724                                         "consider adding a `#[repr(C)]`, \
 725                                                 `#[repr(transparent)]`, or integer `#[repr(...)]` \
 726                                                 attribute to this enum",
 727                                     ),
 728                                 };
 729                             }
 730                         }
 731
 732                         if def.is_variant_list_non_exhaustive() && !def.did.is_local() {
 733                             return FfiUnsafe {
 734                                 ty,
 735                                 reason: "this enum is non-exhaustive",
 736                                 help: None,
 737                             };
 738                         }
 739
 740                         // Check the contained variants.
 741                         for variant in &def.variants {
 742                             let is_non_exhaustive = variant.is_field_list_non_exhaustive();
 743                             if is_non_exhaustive && !variant.def_id.is_local() {
 744                                 return FfiUnsafe {
 745                                     ty,
 746                                     reason: "this enum has non-exhaustive variants",
 747                                     help: None,
 748                                 };
 749                             }
 750
 751                             for field in &variant.fields {
 752                                 let field_ty = cx.normalize_erasing_regions(
 753                                     ParamEnv::reveal_all(),
 754                                     field.ty(cx, substs),
 755                                 );
 756                                 // repr(transparent) types are allowed to have arbitrary ZSTs, not
 757                                 // just PhantomData -- skip checking all ZST fields.
 758                                 if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 759                                     continue;
 760                                 }
 761                                 let r = self.check_type_for_ffi(cache, field_ty);
 762                                 match r {
 763                                     FfiSafe => {}
 764                                     FfiUnsafe { .. } => {
 765                                         return r;
 766                                     }
 767                                     FfiPhantom(..) => {
 768                                         return FfiUnsafe {
 769                                             ty,
 770                                             reason: "this enum contains a PhantomData field",
 771                                             help: None,
 772                                         };
 773                                     }
 774                                 }
 775                             }
 776                         }
 777                         FfiSafe
 778                     }
 779                 }
 780             }
 781
 782             ty::Char => FfiUnsafe {
 783                 ty,
 784                 reason: "the `char` type has no C equivalent",
 785                 help: Some("consider using `u32` or `libc::wchar_t` instead"),
 786             },
 787
 788             ty::Int(ast::IntTy::I128) | ty::Uint(ast::UintTy::U128) => FfiUnsafe {
 789                 ty,
 790                 reason: "128-bit integers don't currently have a known stable ABI",
 791                 help: None,
 792             },
 793
 794             // Primitive types with a stable representation.
 795             ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
 796
 797             ty::Slice(_) => FfiUnsafe {
 798                 ty,
 799                 reason: "slices have no C equivalent",
 800                 help: Some("consider using a raw pointer instead"),
 801             },
 802
 803             ty::Dynamic(..) => {
 804                 FfiUnsafe { ty, reason: "trait objects have no C equivalent", help: None }
 805             }
 806
 807             ty::Str => FfiUnsafe {
 808                 ty,
 809                 reason: "string slices have no C equivalent",
 810                 help: Some("consider using `*const u8` and a length instead"),
 811             },
 812
 813             ty::Tuple(..) => FfiUnsafe {
 814                 ty,
 815                 reason: "tuples have unspecified layout",
 816                 help: Some("consider using a struct instead"),
 817             },
 818
 819             ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _) => {
 820                 self.check_type_for_ffi(cache, ty)
 821             }
 822
 823             ty::Array(inner_ty, _) => self.check_type_for_ffi(cache, inner_ty),
 824
 825             ty::FnPtr(sig) => {
 826                 match sig.abi() {
 827                     Abi::Rust | Abi::RustIntrinsic | Abi::PlatformIntrinsic | Abi::RustCall => {
 828                         return FfiUnsafe {
 829                             ty,
 830                             reason: "this function pointer has Rust-specific calling convention",
 831                             help: Some(
 832                                 "consider using an `extern fn(...) -> ...` \
 833                                         function pointer instead",
 834                             ),
 835                         };
 836                     }
 837                     _ => {}
 838                 }
 839
 840                 let sig = cx.erase_late_bound_regions(&sig);
 841                 if !sig.output().is_unit() {
 842                     let r = self.check_type_for_ffi(cache, sig.output());
 843                     match r {
 844                         FfiSafe => {}
 845                         _ => {
 846                             return r;
 847                         }
 848                     }
 849                 }
 850                 for arg in sig.inputs() {
 851                     let r = self.check_type_for_ffi(cache, arg);
 852                     match r {
 853                         FfiSafe => {}
 854                         _ => {
 855                             return r;
 856                         }
 857                     }
 858                 }
 859                 FfiSafe
 860             }
 861
 862             ty::Foreign(..) => FfiSafe,
 863
 864             ty::Param(..)
 865             | ty::Infer(..)
 866             | ty::Bound(..)
 867             | ty::Error
 868             | ty::Closure(..)
 869             | ty::Generator(..)
 870             | ty::GeneratorWitness(..)
 871             | ty::Placeholder(..)
 872             | ty::UnnormalizedProjection(..)
 873             | ty::Projection(..)
 874             | ty::Opaque(..)
 875             | ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty),
 876         }
 877     }
 878
 879     fn emit_ffi_unsafe_type_lint(
 880         &mut self,
 881         ty: Ty<'tcx>,
 882         sp: Span,
 883         note: &str,
 884         help: Option<&str>,
 885     ) {
 886         let mut diag = self.cx.struct_span_lint(
 887             IMPROPER_CTYPES,
 888             sp,
 889             &format!("`extern` block uses type `{}`, which is not FFI-safe", ty),
 890         );
 891         diag.span_label(sp, "not FFI-safe");
 892         if let Some(help) = help {
 893             diag.help(help);
 894         }
 895         diag.note(note);
 896         if let ty::Adt(def, _) = ty.kind {
 897             if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did) {
 898                 diag.span_note(sp, "the type is defined here");
 899             }
 900         }
 901         diag.emit();
 902     }
 903
 904     fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
 905         use crate::rustc::ty::TypeFoldable;
 906
 907         struct ProhibitOpaqueTypes<'tcx> {
 908             ty: Option<Ty<'tcx>>,
 909         };
 910
 911         impl<'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'tcx> {
 912             fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
 913                 if let ty::Opaque(..) = ty.kind {
 914                     self.ty = Some(ty);
 915                     true
 916                 } else {
 917                     ty.super_visit_with(self)
 918                 }
 919             }
 920         }
 921
 922         let mut visitor = ProhibitOpaqueTypes { ty: None };
 923         ty.visit_with(&mut visitor);
 924         if let Some(ty) = visitor.ty {
 925             self.emit_ffi_unsafe_type_lint(ty, sp, "opaque types have no C equivalent", None);
 926             true
 927         } else {
 928             false
 929         }
 930     }
 931
 932     fn check_type_for_ffi_and_report_errors(&mut self, sp: Span, ty: Ty<'tcx>, is_static: bool) {
 933         // We have to check for opaque types before `normalize_erasing_regions`,
 934         // which will replace opaque types with their underlying concrete type.
 935         if self.check_for_opaque_ty(sp, ty) {
 936             // We've already emitted an error due to an opaque type.
 937             return;
 938         }
 939
 940         // it is only OK to use this function because extern fns cannot have
 941         // any generic types right now:
 942         let ty = self.cx.tcx.normalize_erasing_regions(ParamEnv::reveal_all(), ty);
 943         // C doesn't really support passing arrays by value.
 944         // The only way to pass an array by value is through a struct.
 945         // So we first test that the top level isn't an array,
 946         // and then recursively check the types inside.
 947         if !is_static && self.check_for_array_ty(sp, ty) {
 948             return;
 949         }
 950
 951         match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
 952             FfiResult::FfiSafe => {}
 953             FfiResult::FfiPhantom(ty) => {
 954                 self.emit_ffi_unsafe_type_lint(ty, sp, "composed only of `PhantomData`", None);
 955             }
 956             FfiResult::FfiUnsafe { ty, reason, help } => {
 957                 self.emit_ffi_unsafe_type_lint(ty, sp, reason, help);
 958             }
 959         }
 960     }
 961
 962     fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl<'_>) {
 963         let def_id = self.cx.tcx.hir().local_def_id(id);
 964         let sig = self.cx.tcx.fn_sig(def_id);
 965         let sig = self.cx.tcx.erase_late_bound_regions(&sig);
 966
 967         for (input_ty, input_hir) in sig.inputs().iter().zip(decl.inputs) {
 968             self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty, false);
 969         }
 970
 971         if let hir::FunctionRetTy::Return(ref ret_hir) = decl.output {
 972             let ret_ty = sig.output();
 973             if !ret_ty.is_unit() {
 974                 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty, false);
 975             }
 976         }
 977     }
 978
 979     fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
 980         let def_id = self.cx.tcx.hir().local_def_id(id);
 981         let ty = self.cx.tcx.type_of(def_id);
 982         self.check_type_for_ffi_and_report_errors(span, ty, true);
 983     }
 984 }
 985
 986 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImproperCTypes {
 987     fn check_foreign_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::ForeignItem<'_>) {
 988         let mut vis = ImproperCTypesVisitor { cx };
 989         let abi = cx.tcx.hir().get_foreign_abi(it.hir_id);
 990         if let Abi::Rust | Abi::RustCall | Abi::RustIntrinsic | Abi::PlatformIntrinsic = abi {
 991             // Don't worry about types in internal ABIs.
 992         } else {
 993             match it.kind {
 994                 hir::ForeignItemKind::Fn(ref decl, _, _) => {
 995                     vis.check_foreign_fn(it.hir_id, decl);
 996                 }
 997                 hir::ForeignItemKind::Static(ref ty, _) => {
 998                     vis.check_foreign_static(it.hir_id, ty.span);
 999                 }
1000                 hir::ForeignItemKind::Type => (),
1001             }
1002         }
1003     }
1004 }
1005
1006 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
1007
1008 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for VariantSizeDifferences {
1009     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item<'_>) {
1010         if let hir::ItemKind::Enum(ref enum_definition, _) = it.kind {
1011             let item_def_id = cx.tcx.hir().local_def_id(it.hir_id);
1012             let t = cx.tcx.type_of(item_def_id);
1013             let ty = cx.tcx.erase_regions(&t);
1014             let layout = match cx.layout_of(ty) {
1015                 Ok(layout) => layout,
1016                 Err(ty::layout::LayoutError::Unknown(_)) => return,
1017                 Err(err @ ty::layout::LayoutError::SizeOverflow(_)) => {
1018                     bug!("failed to get layout for `{}`: {}", t, err);
1019                 }
1020             };
1021             let (variants, tag) = match layout.variants {
1022                 layout::Variants::Multiple {
1023                     discr_kind: layout::DiscriminantKind::Tag,
1024                     ref discr,
1025                     ref variants,
1026                     ..
1027                 } => (variants, discr),
1028                 _ => return,
1029             };
1030
1031             let discr_size = tag.value.size(&cx.tcx).bytes();
1032
1033             debug!(
1034                 "enum `{}` is {} bytes large with layout:\n{:#?}",
1035                 t,
1036                 layout.size.bytes(),
1037                 layout
1038             );
1039
1040             let (largest, slargest, largest_index) = enum_definition
1041                 .variants
1042                 .iter()
1043                 .zip(variants)
1044                 .map(|(variant, variant_layout)| {
1045                     // Subtract the size of the enum discriminant.
1046                     let bytes = variant_layout.size.bytes().saturating_sub(discr_size);
1047
1048                     debug!("- variant `{}` is {} bytes large", variant.ident, bytes);
1049                     bytes
1050                 })
1051                 .enumerate()
1052                 .fold((0, 0, 0), |(l, s, li), (idx, size)| {
1053                     if size > l {
1054                         (size, l, idx)
1055                     } else if size > s {
1056                         (l, size, li)
1057                     } else {
1058                         (l, s, li)
1059                     }
1060                 });
1061
1062             // We only warn if the largest variant is at least thrice as large as
1063             // the second-largest.
1064             if largest > slargest * 3 && slargest > 0 {
1065                 cx.span_lint(
1066                     VARIANT_SIZE_DIFFERENCES,
1067                     enum_definition.variants[largest_index].span,
1068                     &format!(
1069                         "enum variant is more than three times \
1070                                           larger ({} bytes) than the next largest",
1071                         largest
1072                     ),
1073                 );
1074             }
1075         }
1076     }
1077 }