src/librustc_lint/types.rs

   1 #![allow(non_snake_case)]
   2
   3 use rustc::hir::Node;
   4 use rustc::ty::subst::Substs;
   5 use rustc::ty::{self, AdtKind, ParamEnv, Ty, TyCtxt};
   6 use rustc::ty::layout::{self, IntegerExt, LayoutOf, VariantIdx};
   7 use rustc_data_structures::indexed_vec::Idx;
   8 use util::nodemap::FxHashSet;
   9 use lint::{LateContext, LintContext, LintArray};
  10 use lint::{LintPass, LateLintPass};
  11
  12 use std::cmp;
  13 use std::{i8, i16, i32, i64, u8, u16, u32, u64, f32, f64};
  14
  15 use syntax::{ast, attr};
  16 use syntax::errors::Applicability;
  17 use rustc_target::spec::abi::Abi;
  18 use syntax_pos::Span;
  19 use syntax::source_map;
  20
  21 use rustc::hir;
  22
  23 declare_lint! {
  24     UNUSED_COMPARISONS,
  25     Warn,
  26     "comparisons made useless by limits of the types involved"
  27 }
  28
  29 declare_lint! {
  30     OVERFLOWING_LITERALS,
  31     Deny,
  32     "literal out of range for its type"
  33 }
  34
  35 declare_lint! {
  36     VARIANT_SIZE_DIFFERENCES,
  37     Allow,
  38     "detects enums with widely varying variant sizes"
  39 }
  40
  41 #[derive(Copy, Clone)]
  42 pub struct TypeLimits {
  43     /// Id of the last visited negated expression
  44     negated_expr_id: ast::NodeId,
  45 }
  46
  47 impl TypeLimits {
  48     pub fn new() -> TypeLimits {
  49         TypeLimits { negated_expr_id: ast::DUMMY_NODE_ID }
  50     }
  51 }
  52
  53 impl LintPass for TypeLimits {
  54     fn get_lints(&self) -> LintArray {
  55         lint_array!(UNUSED_COMPARISONS,
  56                     OVERFLOWING_LITERALS)
  57     }
  58 }
  59
  60 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TypeLimits {
  61     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx hir::Expr) {
  62         match e.node {
  63             hir::ExprKind::Unary(hir::UnNeg, ref expr) => {
  64                 // propagate negation, if the negation itself isn't negated
  65                 if self.negated_expr_id != e.id {
  66                     self.negated_expr_id = expr.id;
  67                 }
  68             }
  69             hir::ExprKind::Binary(binop, ref l, ref r) => {
  70                 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
  71                     cx.span_lint(UNUSED_COMPARISONS,
  72                                  e.span,
  73                                  "comparison is useless due to type limits");
  74                 }
  75             }
  76             hir::ExprKind::Lit(ref lit) => {
  77                 match cx.tables.node_id_to_type(e.hir_id).sty {
  78                     ty::Int(t) => {
  79                         match lit.node {
  80                             ast::LitKind::Int(v, ast::LitIntType::Signed(_)) |
  81                             ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => {
  82                                 let int_type = if let ast::IntTy::Isize = t {
  83                                     cx.sess().target.isize_ty
  84                                 } else {
  85                                     t
  86                                 };
  87                                 let (_, max) = int_ty_range(int_type);
  88                                 let max = max as u128;
  89                                 let negative = self.negated_expr_id == e.id;
  90
  91                                 // Detect literal value out of range [min, max] inclusive
  92                                 // avoiding use of -min to prevent overflow/panic
  93                                 if (negative && v > max + 1) || (!negative && v > max) {
  94                                     if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
  95                                         report_bin_hex_error(
  96                                             cx,
  97                                             e,
  98                                             ty::Int(t),
  99                                             repr_str,
 100                                             v,
 101                                             negative,
 102                                         );
 103                                         return;
 104                                     }
 105                                     cx.span_lint(
 106                                         OVERFLOWING_LITERALS,
 107                                         e.span,
 108                                         &format!("literal out of range for {:?}", t),
 109                                     );
 110                                     return;
 111                                 }
 112                             }
 113                             _ => bug!(),
 114                         };
 115                     }
 116                     ty::Uint(t) => {
 117                         let uint_type = if let ast::UintTy::Usize = t {
 118                             cx.sess().target.usize_ty
 119                         } else {
 120                             t
 121                         };
 122                         let (min, max) = uint_ty_range(uint_type);
 123                         let lit_val: u128 = match lit.node {
 124                             // _v is u8, within range by definition
 125                             ast::LitKind::Byte(_v) => return,
 126                             ast::LitKind::Int(v, _) => v,
 127                             _ => bug!(),
 128                         };
 129                         if lit_val < min || lit_val > max {
 130                             let parent_id = cx.tcx.hir().get_parent_node(e.id);
 131                             if let Node::Expr(parent_expr) = cx.tcx.hir().get(parent_id) {
 132                                 if let hir::ExprKind::Cast(..) = parent_expr.node {
 133                                     if let ty::Char = cx.tables.expr_ty(parent_expr).sty {
 134                                         let mut err = cx.struct_span_lint(
 135                                                              OVERFLOWING_LITERALS,
 136                                                              parent_expr.span,
 137                                                              "only u8 can be cast into char");
 138                                         err.span_suggestion_with_applicability(
 139                                             parent_expr.span,
 140                                             &"use a char literal instead",
 141                                             format!("'\\u{{{:X}}}'", lit_val),
 142                                             Applicability::MachineApplicable
 143                                         );
 144                                         err.emit();
 145                                         return
 146                                     }
 147                                 }
 148                             }
 149                             if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 150                                 report_bin_hex_error(
 151                                     cx,
 152                                     e,
 153                                     ty::Uint(t),
 154                                     repr_str,
 155                                     lit_val,
 156                                     false,
 157                                 );
 158                                 return;
 159                             }
 160                             cx.span_lint(
 161                                 OVERFLOWING_LITERALS,
 162                                 e.span,
 163                                 &format!("literal out of range for {:?}", t),
 164                             );
 165                         }
 166                     }
 167                     ty::Float(t) => {
 168                         let is_infinite = match lit.node {
 169                             ast::LitKind::Float(v, _) |
 170                             ast::LitKind::FloatUnsuffixed(v) => {
 171                                 match t {
 172                                     ast::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
 173                                     ast::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
 174                                 }
 175                             }
 176                             _ => bug!(),
 177                         };
 178                         if is_infinite == Ok(true) {
 179                             cx.span_lint(OVERFLOWING_LITERALS,
 180                                          e.span,
 181                                          &format!("literal out of range for {:?}", t));
 182                         }
 183                     }
 184                     _ => (),
 185                 };
 186             }
 187             _ => (),
 188         };
 189
 190         fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
 191             match binop.node {
 192                 hir::BinOpKind::Lt => v > min && v <= max,
 193                 hir::BinOpKind::Le => v >= min && v < max,
 194                 hir::BinOpKind::Gt => v >= min && v < max,
 195                 hir::BinOpKind::Ge => v > min && v <= max,
 196                 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
 197                 _ => bug!(),
 198             }
 199         }
 200
 201         fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
 202             source_map::respan(binop.span,
 203                             match binop.node {
 204                                 hir::BinOpKind::Lt => hir::BinOpKind::Gt,
 205                                 hir::BinOpKind::Le => hir::BinOpKind::Ge,
 206                                 hir::BinOpKind::Gt => hir::BinOpKind::Lt,
 207                                 hir::BinOpKind::Ge => hir::BinOpKind::Le,
 208                                 _ => return binop,
 209                             })
 210         }
 211
 212         // for isize & usize, be conservative with the warnings, so that the
 213         // warnings are consistent between 32- and 64-bit platforms
 214         fn int_ty_range(int_ty: ast::IntTy) -> (i128, i128) {
 215             match int_ty {
 216                 ast::IntTy::Isize => (i64::min_value() as i128, i64::max_value() as i128),
 217                 ast::IntTy::I8 => (i8::min_value() as i64 as i128, i8::max_value() as i128),
 218                 ast::IntTy::I16 => (i16::min_value() as i64 as i128, i16::max_value() as i128),
 219                 ast::IntTy::I32 => (i32::min_value() as i64 as i128, i32::max_value() as i128),
 220                 ast::IntTy::I64 => (i64::min_value() as i128, i64::max_value() as i128),
 221                 ast::IntTy::I128 =>(i128::min_value() as i128, i128::max_value()),
 222             }
 223         }
 224
 225         fn uint_ty_range(uint_ty: ast::UintTy) -> (u128, u128) {
 226             match uint_ty {
 227                 ast::UintTy::Usize => (u64::min_value() as u128, u64::max_value() as u128),
 228                 ast::UintTy::U8 => (u8::min_value() as u128, u8::max_value() as u128),
 229                 ast::UintTy::U16 => (u16::min_value() as u128, u16::max_value() as u128),
 230                 ast::UintTy::U32 => (u32::min_value() as u128, u32::max_value() as u128),
 231                 ast::UintTy::U64 => (u64::min_value() as u128, u64::max_value() as u128),
 232                 ast::UintTy::U128 => (u128::min_value(), u128::max_value()),
 233             }
 234         }
 235
 236         fn check_limits(cx: &LateContext,
 237                         binop: hir::BinOp,
 238                         l: &hir::Expr,
 239                         r: &hir::Expr)
 240                         -> bool {
 241             let (lit, expr, swap) = match (&l.node, &r.node) {
 242                 (&hir::ExprKind::Lit(_), _) => (l, r, true),
 243                 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
 244                 _ => return true,
 245             };
 246             // Normalize the binop so that the literal is always on the RHS in
 247             // the comparison
 248             let norm_binop = if swap { rev_binop(binop) } else { binop };
 249             match cx.tables.node_id_to_type(expr.hir_id).sty {
 250                 ty::Int(int_ty) => {
 251                     let (min, max) = int_ty_range(int_ty);
 252                     let lit_val: i128 = match lit.node {
 253                         hir::ExprKind::Lit(ref li) => {
 254                             match li.node {
 255                                 ast::LitKind::Int(v, ast::LitIntType::Signed(_)) |
 256                                 ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => v as i128,
 257                                 _ => return true
 258                             }
 259                         },
 260                         _ => bug!()
 261                     };
 262                     is_valid(norm_binop, lit_val, min, max)
 263                 }
 264                 ty::Uint(uint_ty) => {
 265                     let (min, max) :(u128, u128) = uint_ty_range(uint_ty);
 266                     let lit_val: u128 = match lit.node {
 267                         hir::ExprKind::Lit(ref li) => {
 268                             match li.node {
 269                                 ast::LitKind::Int(v, _) => v,
 270                                 _ => return true
 271                             }
 272                         },
 273                         _ => bug!()
 274                     };
 275                     is_valid(norm_binop, lit_val, min, max)
 276                 }
 277                 _ => true,
 278             }
 279         }
 280
 281         fn is_comparison(binop: hir::BinOp) -> bool {
 282             match binop.node {
 283                 hir::BinOpKind::Eq |
 284                 hir::BinOpKind::Lt |
 285                 hir::BinOpKind::Le |
 286                 hir::BinOpKind::Ne |
 287                 hir::BinOpKind::Ge |
 288                 hir::BinOpKind::Gt => true,
 289                 _ => false,
 290             }
 291         }
 292
 293         fn get_bin_hex_repr(cx: &LateContext, lit: &ast::Lit) -> Option<String> {
 294             let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?;
 295             let firstch = src.chars().next()?;
 296
 297             if firstch == '0' {
 298                 match src.chars().nth(1) {
 299                     Some('x') | Some('b') => return Some(src),
 300                     _ => return None,
 301                 }
 302             }
 303
 304             None
 305         }
 306
 307         // This function finds the next fitting type and generates a suggestion string.
 308         // It searches for fitting types in the following way (`X < Y`):
 309         //  - `iX`: if literal fits in `uX` => `uX`, else => `iY`
 310         //  - `-iX` => `iY`
 311         //  - `uX` => `uY`
 312         //
 313         // No suggestion for: `isize`, `usize`.
 314         fn get_type_suggestion<'a>(
 315             t: &ty::TyKind,
 316             val: u128,
 317             negative: bool,
 318         ) -> Option<String> {
 319             use syntax::ast::IntTy::*;
 320             use syntax::ast::UintTy::*;
 321             macro_rules! find_fit {
 322                 ($ty:expr, $val:expr, $negative:expr,
 323                  $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => {
 324                     {
 325                         let _neg = if negative { 1 } else { 0 };
 326                         match $ty {
 327                             $($type => {
 328                                 $(if !negative && val <= uint_ty_range($utypes).1 {
 329                                     return Some(format!("{:?}", $utypes))
 330                                 })*
 331                                 $(if val <= int_ty_range($itypes).1 as u128 + _neg {
 332                                     return Some(format!("{:?}", $itypes))
 333                                 })*
 334                                 None
 335                             },)*
 336                             _ => None
 337                         }
 338                     }
 339                 }
 340             }
 341             match t {
 342                 &ty::Int(i) => find_fit!(i, val, negative,
 343                               I8 => [U8] => [I16, I32, I64, I128],
 344                               I16 => [U16] => [I32, I64, I128],
 345                               I32 => [U32] => [I64, I128],
 346                               I64 => [U64] => [I128],
 347                               I128 => [U128] => []),
 348                 &ty::Uint(u) => find_fit!(u, val, negative,
 349                               U8 => [U8, U16, U32, U64, U128] => [],
 350                               U16 => [U16, U32, U64, U128] => [],
 351                               U32 => [U32, U64, U128] => [],
 352                               U64 => [U64, U128] => [],
 353                               U128 => [U128] => []),
 354                 _ => None,
 355             }
 356         }
 357
 358         fn report_bin_hex_error(
 359             cx: &LateContext,
 360             expr: &hir::Expr,
 361             ty: ty::TyKind,
 362             repr_str: String,
 363             val: u128,
 364             negative: bool,
 365         ) {
 366             let (t, actually) = match ty {
 367                 ty::Int(t) => {
 368                     let ity = attr::IntType::SignedInt(t);
 369                     let bits = layout::Integer::from_attr(&cx.tcx, ity).size().bits();
 370                     let actually = (val << (128 - bits)) as i128 >> (128 - bits);
 371                     (format!("{:?}", t), actually.to_string())
 372                 }
 373                 ty::Uint(t) => {
 374                     let ity = attr::IntType::UnsignedInt(t);
 375                     let bits = layout::Integer::from_attr(&cx.tcx, ity).size().bits();
 376                     let actually = (val << (128 - bits)) >> (128 - bits);
 377                     (format!("{:?}", t), actually.to_string())
 378                 }
 379                 _ => bug!(),
 380             };
 381             let mut err = cx.struct_span_lint(
 382                 OVERFLOWING_LITERALS,
 383                 expr.span,
 384                 &format!("literal out of range for {}", t),
 385             );
 386             err.note(&format!(
 387                 "the literal `{}` (decimal `{}`) does not fit into \
 388                  an `{}` and will become `{}{}`",
 389                 repr_str, val, t, actually, t
 390             ));
 391             if let Some(sugg_ty) =
 392                 get_type_suggestion(&cx.tables.node_id_to_type(expr.hir_id).sty, val, negative)
 393             {
 394                 if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') {
 395                     let (sans_suffix, _) = repr_str.split_at(pos);
 396                     err.span_suggestion_with_applicability(
 397                         expr.span,
 398                         &format!("consider using `{}` instead", sugg_ty),
 399                         format!("{}{}", sans_suffix, sugg_ty),
 400                         Applicability::MachineApplicable
 401                     );
 402                 } else {
 403                     err.help(&format!("consider using `{}` instead", sugg_ty));
 404                 }
 405             }
 406
 407             err.emit();
 408         }
 409     }
 410 }
 411
 412 declare_lint! {
 413     IMPROPER_CTYPES,
 414     Warn,
 415     "proper use of libc types in foreign modules"
 416 }
 417
 418 struct ImproperCTypesVisitor<'a, 'tcx: 'a> {
 419     cx: &'a LateContext<'a, 'tcx>,
 420 }
 421
 422 enum FfiResult<'tcx> {
 423     FfiSafe,
 424     FfiPhantom(Ty<'tcx>),
 425     FfiUnsafe {
 426         ty: Ty<'tcx>,
 427         reason: &'static str,
 428         help: Option<&'static str>,
 429     },
 430 }
 431
 432 /// Check if this enum can be safely exported based on the
 433 /// "nullable pointer optimization". Currently restricted
 434 /// to function pointers and references, but could be
 435 /// expanded to cover NonZero raw pointers and newtypes.
 436 /// FIXME: This duplicates code in codegen.
 437 fn is_repr_nullable_ptr<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 438                                   def: &'tcx ty::AdtDef,
 439                                   substs: &Substs<'tcx>)
 440                                   -> bool {
 441     if def.variants.len() == 2 {
 442         let data_idx;
 443
 444         let zero = VariantIdx::new(0);
 445         let one = VariantIdx::new(1);
 446
 447         if def.variants[zero].fields.is_empty() {
 448             data_idx = one;
 449         } else if def.variants[one].fields.is_empty() {
 450             data_idx = zero;
 451         } else {
 452             return false;
 453         }
 454
 455         if def.variants[data_idx].fields.len() == 1 {
 456             match def.variants[data_idx].fields[0].ty(tcx, substs).sty {
 457                 ty::FnPtr(_) => {
 458                     return true;
 459                 }
 460                 ty::Ref(..) => {
 461                     return true;
 462                 }
 463                 _ => {}
 464             }
 465         }
 466     }
 467     false
 468 }
 469
 470 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
 471     /// Check if the given type is "ffi-safe" (has a stable, well-defined
 472     /// representation which can be exported to C code).
 473     fn check_type_for_ffi(&self,
 474                           cache: &mut FxHashSet<Ty<'tcx>>,
 475                           ty: Ty<'tcx>) -> FfiResult<'tcx> {
 476         use self::FfiResult::*;
 477
 478         let cx = self.cx.tcx;
 479
 480         // Protect against infinite recursion, for example
 481         // `struct S(*mut S);`.
 482         // FIXME: A recursion limit is necessary as well, for irregular
 483         // recursive types.
 484         if !cache.insert(ty) {
 485             return FfiSafe;
 486         }
 487
 488         match ty.sty {
 489             ty::Adt(def, substs) => {
 490                 if def.is_phantom_data() {
 491                     return FfiPhantom(ty);
 492                 }
 493                 match def.adt_kind() {
 494                     AdtKind::Struct => {
 495                         if !def.repr.c() && !def.repr.transparent() {
 496                             return FfiUnsafe {
 497                                 ty: ty,
 498                                 reason: "this struct has unspecified layout",
 499                                 help: Some("consider adding a #[repr(C)] or #[repr(transparent)] \
 500                                             attribute to this struct"),
 501                             };
 502                         }
 503
 504                         if def.non_enum_variant().fields.is_empty() {
 505                             return FfiUnsafe {
 506                                 ty: ty,
 507                                 reason: "this struct has no fields",
 508                                 help: Some("consider adding a member to this struct"),
 509                             };
 510                         }
 511
 512                         // We can't completely trust repr(C) and repr(transparent) markings;
 513                         // make sure the fields are actually safe.
 514                         let mut all_phantom = true;
 515                         for field in &def.non_enum_variant().fields {
 516                             let field_ty = cx.normalize_erasing_regions(
 517                                 ParamEnv::reveal_all(),
 518                                 field.ty(cx, substs),
 519                             );
 520                             // repr(transparent) types are allowed to have arbitrary ZSTs, not just
 521                             // PhantomData -- skip checking all ZST fields
 522                             if def.repr.transparent() {
 523                                 let is_zst = cx
 524                                     .layout_of(cx.param_env(field.did).and(field_ty))
 525                                     .map(|layout| layout.is_zst())
 526                                     .unwrap_or(false);
 527                                 if is_zst {
 528                                     continue;
 529                                 }
 530                             }
 531                             let r = self.check_type_for_ffi(cache, field_ty);
 532                             match r {
 533                                 FfiSafe => {
 534                                     all_phantom = false;
 535                                 }
 536                                 FfiPhantom(..) => {}
 537                                 FfiUnsafe { .. } => {
 538                                     return r;
 539                                 }
 540                             }
 541                         }
 542
 543                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 544                     }
 545                     AdtKind::Union => {
 546                         if !def.repr.c() {
 547                             return FfiUnsafe {
 548                                 ty: ty,
 549                                 reason: "this union has unspecified layout",
 550                                 help: Some("consider adding a #[repr(C)] attribute to this union"),
 551                             };
 552                         }
 553
 554                         if def.non_enum_variant().fields.is_empty() {
 555                             return FfiUnsafe {
 556                                 ty: ty,
 557                                 reason: "this union has no fields",
 558                                 help: Some("consider adding a field to this union"),
 559                             };
 560                         }
 561
 562                         let mut all_phantom = true;
 563                         for field in &def.non_enum_variant().fields {
 564                             let field_ty = cx.normalize_erasing_regions(
 565                                 ParamEnv::reveal_all(),
 566                                 field.ty(cx, substs),
 567                             );
 568                             let r = self.check_type_for_ffi(cache, field_ty);
 569                             match r {
 570                                 FfiSafe => {
 571                                     all_phantom = false;
 572                                 }
 573                                 FfiPhantom(..) => {}
 574                                 FfiUnsafe { .. } => {
 575                                     return r;
 576                                 }
 577                             }
 578                         }
 579
 580                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 581                     }
 582                     AdtKind::Enum => {
 583                         if def.variants.is_empty() {
 584                             // Empty enums are okay... although sort of useless.
 585                             return FfiSafe;
 586                         }
 587
 588                         // Check for a repr() attribute to specify the size of the
 589                         // discriminant.
 590                         if !def.repr.c() && def.repr.int.is_none() {
 591                             // Special-case types like `Option<extern fn()>`.
 592                             if !is_repr_nullable_ptr(cx, def, substs) {
 593                                 return FfiUnsafe {
 594                                     ty: ty,
 595                                     reason: "enum has no representation hint",
 596                                     help: Some("consider adding a #[repr(...)] attribute \
 597                                                 to this enum"),
 598                                 };
 599                             }
 600                         }
 601
 602                         // Check the contained variants.
 603                         for variant in &def.variants {
 604                             for field in &variant.fields {
 605                                 let arg = cx.normalize_erasing_regions(
 606                                     ParamEnv::reveal_all(),
 607                                     field.ty(cx, substs),
 608                                 );
 609                                 let r = self.check_type_for_ffi(cache, arg);
 610                                 match r {
 611                                     FfiSafe => {}
 612                                     FfiUnsafe { .. } => {
 613                                         return r;
 614                                     }
 615                                     FfiPhantom(..) => {
 616                                         return FfiUnsafe {
 617                                             ty: ty,
 618                                             reason: "this enum contains a PhantomData field",
 619                                             help: None,
 620                                         };
 621                                     }
 622                                 }
 623                             }
 624                         }
 625                         FfiSafe
 626                     }
 627                 }
 628             }
 629
 630             ty::Char => FfiUnsafe {
 631                 ty: ty,
 632                 reason: "the `char` type has no C equivalent",
 633                 help: Some("consider using `u32` or `libc::wchar_t` instead"),
 634             },
 635
 636             ty::Int(ast::IntTy::I128) | ty::Uint(ast::UintTy::U128) => FfiUnsafe {
 637                 ty: ty,
 638                 reason: "128-bit integers don't currently have a known stable ABI",
 639                 help: None,
 640             },
 641
 642             // Primitive types with a stable representation.
 643             ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
 644
 645             ty::Slice(_) => FfiUnsafe {
 646                 ty: ty,
 647                 reason: "slices have no C equivalent",
 648                 help: Some("consider using a raw pointer instead"),
 649             },
 650
 651             ty::Dynamic(..) => FfiUnsafe {
 652                 ty: ty,
 653                 reason: "trait objects have no C equivalent",
 654                 help: None,
 655             },
 656
 657             ty::Str => FfiUnsafe {
 658                 ty: ty,
 659                 reason: "string slices have no C equivalent",
 660                 help: Some("consider using `*const u8` and a length instead"),
 661             },
 662
 663             ty::Tuple(..) => FfiUnsafe {
 664                 ty: ty,
 665                 reason: "tuples have unspecified layout",
 666                 help: Some("consider using a struct instead"),
 667             },
 668
 669             ty::RawPtr(ty::TypeAndMut { ty, .. }) |
 670             ty::Ref(_, ty, _) => self.check_type_for_ffi(cache, ty),
 671
 672             ty::Array(ty, _) => self.check_type_for_ffi(cache, ty),
 673
 674             ty::FnPtr(sig) => {
 675                 match sig.abi() {
 676                     Abi::Rust | Abi::RustIntrinsic | Abi::PlatformIntrinsic | Abi::RustCall => {
 677                         return FfiUnsafe {
 678                             ty: ty,
 679                             reason: "this function pointer has Rust-specific calling convention",
 680                             help: Some("consider using an `extern fn(...) -> ...` \
 681                                         function pointer instead"),
 682                         }
 683                     }
 684                     _ => {}
 685                 }
 686
 687                 let sig = cx.erase_late_bound_regions(&sig);
 688                 if !sig.output().is_unit() {
 689                     let r = self.check_type_for_ffi(cache, sig.output());
 690                     match r {
 691                         FfiSafe => {}
 692                         _ => {
 693                             return r;
 694                         }
 695                     }
 696                 }
 697                 for arg in sig.inputs() {
 698                     let r = self.check_type_for_ffi(cache, arg);
 699                     match r {
 700                         FfiSafe => {}
 701                         _ => {
 702                             return r;
 703                         }
 704                     }
 705                 }
 706                 FfiSafe
 707             }
 708
 709             ty::Foreign(..) => FfiSafe,
 710
 711             ty::Param(..) |
 712             ty::Infer(..) |
 713             ty::Bound(..) |
 714             ty::Error |
 715             ty::Closure(..) |
 716             ty::Generator(..) |
 717             ty::GeneratorWitness(..) |
 718             ty::Placeholder(..) |
 719             ty::UnnormalizedProjection(..) |
 720             ty::Projection(..) |
 721             ty::Opaque(..) |
 722             ty::FnDef(..) => bug!("Unexpected type in foreign function"),
 723         }
 724     }
 725
 726     fn check_type_for_ffi_and_report_errors(&mut self, sp: Span, ty: Ty<'tcx>) {
 727         // it is only OK to use this function because extern fns cannot have
 728         // any generic types right now:
 729         let ty = self.cx.tcx.normalize_erasing_regions(ParamEnv::reveal_all(), ty);
 730
 731         match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
 732             FfiResult::FfiSafe => {}
 733             FfiResult::FfiPhantom(ty) => {
 734                 self.cx.span_lint(IMPROPER_CTYPES,
 735                                   sp,
 736                                   &format!("`extern` block uses type `{}` which is not FFI-safe: \
 737                                             composed only of PhantomData", ty));
 738             }
 739             FfiResult::FfiUnsafe { ty: unsafe_ty, reason, help } => {
 740                 let msg = format!("`extern` block uses type `{}` which is not FFI-safe: {}",
 741                                   unsafe_ty, reason);
 742                 let mut diag = self.cx.struct_span_lint(IMPROPER_CTYPES, sp, &msg);
 743                 if let Some(s) = help {
 744                     diag.help(s);
 745                 }
 746                 if let ty::Adt(def, _) = unsafe_ty.sty {
 747                     if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did) {
 748                         diag.span_note(sp, "type defined here");
 749                     }
 750                 }
 751                 diag.emit();
 752             }
 753         }
 754     }
 755
 756     fn check_foreign_fn(&mut self, id: ast::NodeId, decl: &hir::FnDecl) {
 757         let def_id = self.cx.tcx.hir().local_def_id(id);
 758         let sig = self.cx.tcx.fn_sig(def_id);
 759         let sig = self.cx.tcx.erase_late_bound_regions(&sig);
 760
 761         for (input_ty, input_hir) in sig.inputs().iter().zip(&decl.inputs) {
 762             self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty);
 763         }
 764
 765         if let hir::Return(ref ret_hir) = decl.output {
 766             let ret_ty = sig.output();
 767             if !ret_ty.is_unit() {
 768                 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty);
 769             }
 770         }
 771     }
 772
 773     fn check_foreign_static(&mut self, id: ast::NodeId, span: Span) {
 774         let def_id = self.cx.tcx.hir().local_def_id(id);
 775         let ty = self.cx.tcx.type_of(def_id);
 776         self.check_type_for_ffi_and_report_errors(span, ty);
 777     }
 778 }
 779
 780 #[derive(Copy, Clone)]
 781 pub struct ImproperCTypes;
 782
 783 impl LintPass for ImproperCTypes {
 784     fn get_lints(&self) -> LintArray {
 785         lint_array!(IMPROPER_CTYPES)
 786     }
 787 }
 788
 789 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImproperCTypes {
 790     fn check_foreign_item(&mut self, cx: &LateContext, it: &hir::ForeignItem) {
 791         let mut vis = ImproperCTypesVisitor { cx };
 792         let abi = cx.tcx.hir().get_foreign_abi(it.id);
 793         if abi != Abi::RustIntrinsic && abi != Abi::PlatformIntrinsic {
 794             match it.node {
 795                 hir::ForeignItemKind::Fn(ref decl, _, _) => {
 796                     vis.check_foreign_fn(it.id, decl);
 797                 }
 798                 hir::ForeignItemKind::Static(ref ty, _) => {
 799                     vis.check_foreign_static(it.id, ty.span);
 800                 }
 801                 hir::ForeignItemKind::Type => ()
 802             }
 803         }
 804     }
 805 }
 806
 807 pub struct VariantSizeDifferences;
 808
 809 impl LintPass for VariantSizeDifferences {
 810     fn get_lints(&self) -> LintArray {
 811         lint_array!(VARIANT_SIZE_DIFFERENCES)
 812     }
 813 }
 814
 815 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for VariantSizeDifferences {
 816     fn check_item(&mut self, cx: &LateContext, it: &hir::Item) {
 817         if let hir::ItemKind::Enum(ref enum_definition, _) = it.node {
 818             let item_def_id = cx.tcx.hir().local_def_id(it.id);
 819             let t = cx.tcx.type_of(item_def_id);
 820             let ty = cx.tcx.erase_regions(&t);
 821             match cx.layout_of(ty) {
 822                 Ok(layout) => {
 823                     let variants = &layout.variants;
 824                     if let layout::Variants::Tagged { ref variants, ref tag, .. } = variants {
 825                         let discr_size = tag.value.size(&cx.tcx).bytes();
 826
 827                         debug!("enum `{}` is {} bytes large with layout:\n{:#?}",
 828                                t, layout.size.bytes(), layout);
 829
 830                         let (largest, slargest, largest_index) = enum_definition.variants
 831                             .iter()
 832                             .zip(variants)
 833                             .map(|(variant, variant_layout)| {
 834                                 // Subtract the size of the enum discriminant.
 835                                 let bytes = variant_layout.size.bytes().saturating_sub(discr_size);
 836
 837                                 debug!("- variant `{}` is {} bytes large",
 838                                        variant.node.ident,
 839                                        bytes);
 840                                 bytes
 841                             })
 842                             .enumerate()
 843                             .fold((0, 0, 0), |(l, s, li), (idx, size)| if size > l {
 844                                 (size, l, idx)
 845                             } else if size > s {
 846                                 (l, size, li)
 847                             } else {
 848                                 (l, s, li)
 849                             });
 850
 851                         // We only warn if the largest variant is at least thrice as large as
 852                         // the second-largest.
 853                         if largest > slargest * 3 && slargest > 0 {
 854                             cx.span_lint(VARIANT_SIZE_DIFFERENCES,
 855                                             enum_definition.variants[largest_index].span,
 856                                             &format!("enum variant is more than three times \
 857                                                       larger ({} bytes) than the next largest",
 858                                                      largest));
 859                         }
 860                     }
 861                 }
 862                 Err(ty::layout::LayoutError::Unknown(_)) => return,
 863                 Err(err @ ty::layout::LayoutError::SizeOverflow(_)) => {
 864                     bug!("failed to get layout for `{}`: {}", t, err);
 865                 }
 866             }
 867         }
 868     }
 869 }