src/librustc_lint/types.rs

   1 // Copyright 2012-2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 #![allow(non_snake_case)]
  12
  13 use rustc::hir::def_id::DefId;
  14 use rustc::ty::subst::Substs;
  15 use rustc::ty::{self, AdtKind, Ty, TyCtxt};
  16 use rustc::ty::layout::{self, LayoutOf};
  17 use middle::const_val::ConstVal;
  18 use rustc_const_eval::ConstContext;
  19 use util::nodemap::FxHashSet;
  20 use lint::{LateContext, LintContext, LintArray};
  21 use lint::{LintPass, LateLintPass};
  22
  23 use std::cmp;
  24 use std::{i8, i16, i32, i64, u8, u16, u32, u64, f32, f64};
  25
  26 use syntax::ast;
  27 use syntax::abi::Abi;
  28 use syntax::attr;
  29 use syntax_pos::Span;
  30 use syntax::codemap;
  31
  32 use rustc::hir;
  33
  34 declare_lint! {
  35     UNUSED_COMPARISONS,
  36     Warn,
  37     "comparisons made useless by limits of the types involved"
  38 }
  39
  40 declare_lint! {
  41     OVERFLOWING_LITERALS,
  42     Warn,
  43     "literal out of range for its type"
  44 }
  45
  46 declare_lint! {
  47     EXCEEDING_BITSHIFTS,
  48     Deny,
  49     "shift exceeds the type's number of bits"
  50 }
  51
  52 declare_lint! {
  53     VARIANT_SIZE_DIFFERENCES,
  54     Allow,
  55     "detects enums with widely varying variant sizes"
  56 }
  57
  58 #[derive(Copy, Clone)]
  59 pub struct TypeLimits {
  60     /// Id of the last visited negated expression
  61     negated_expr_id: ast::NodeId,
  62 }
  63
  64 impl TypeLimits {
  65     pub fn new() -> TypeLimits {
  66         TypeLimits { negated_expr_id: ast::DUMMY_NODE_ID }
  67     }
  68 }
  69
  70 impl LintPass for TypeLimits {
  71     fn get_lints(&self) -> LintArray {
  72         lint_array!(UNUSED_COMPARISONS,
  73                     OVERFLOWING_LITERALS,
  74                     EXCEEDING_BITSHIFTS)
  75     }
  76 }
  77
  78 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TypeLimits {
  79     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx hir::Expr) {
  80         match e.node {
  81             hir::ExprUnary(hir::UnNeg, ref expr) => {
  82                 // propagate negation, if the negation itself isn't negated
  83                 if self.negated_expr_id != e.id {
  84                     self.negated_expr_id = expr.id;
  85                 }
  86             }
  87             hir::ExprBinary(binop, ref l, ref r) => {
  88                 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
  89                     cx.span_lint(UNUSED_COMPARISONS,
  90                                  e.span,
  91                                  "comparison is useless due to type limits");
  92                 }
  93
  94                 if binop.node.is_shift() {
  95                     let opt_ty_bits = match cx.tables.node_id_to_type(l.hir_id).sty {
  96                         ty::TyInt(t) => Some(int_ty_bits(t, cx.sess().target.isize_ty)),
  97                         ty::TyUint(t) => Some(uint_ty_bits(t, cx.sess().target.usize_ty)),
  98                         _ => None,
  99                     };
 100
 101                     if let Some(bits) = opt_ty_bits {
 102                         let exceeding = if let hir::ExprLit(ref lit) = r.node {
 103                             if let ast::LitKind::Int(shift, _) = lit.node {
 104                                 shift as u64 >= bits
 105                             } else {
 106                                 false
 107                             }
 108                         } else {
 109                             // HACK(eddyb) This might be quite inefficient.
 110                             // This would be better left to MIR constant propagation,
 111                             // perhaps even at trans time (like is the case already
 112                             // when the value being shifted is *also* constant).
 113                             let parent_item = cx.tcx.hir.get_parent(e.id);
 114                             let parent_def_id = cx.tcx.hir.local_def_id(parent_item);
 115                             let substs = Substs::identity_for_item(cx.tcx, parent_def_id);
 116                             let const_cx = ConstContext::new(cx.tcx,
 117                                                              cx.param_env.and(substs),
 118                                                              cx.tables);
 119                             match const_cx.eval(&r) {
 120                                 Ok(&ty::Const { val: ConstVal::Integral(i), .. }) => {
 121                                     i.is_negative() ||
 122                                     i.to_u64()
 123                                         .map(|i| i >= bits)
 124                                         .unwrap_or(true)
 125                                 }
 126                                 _ => false,
 127                             }
 128                         };
 129                         if exceeding {
 130                             cx.span_lint(EXCEEDING_BITSHIFTS,
 131                                          e.span,
 132                                          "bitshift exceeds the type's number of bits");
 133                         }
 134                     };
 135                 }
 136             }
 137             hir::ExprLit(ref lit) => {
 138                 match cx.tables.node_id_to_type(e.hir_id).sty {
 139                     ty::TyInt(t) => {
 140                         match lit.node {
 141                             ast::LitKind::Int(v, ast::LitIntType::Signed(_)) |
 142                             ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => {
 143                                 let int_type = if let ast::IntTy::Isize = t {
 144                                     cx.sess().target.isize_ty
 145                                 } else {
 146                                     t
 147                                 };
 148                                 let (_, max) = int_ty_range(int_type);
 149                                 let max = max as u128;
 150                                 let negative = self.negated_expr_id == e.id;
 151
 152                                 // Detect literal value out of range [min, max] inclusive
 153                                 // avoiding use of -min to prevent overflow/panic
 154                                 if (negative && v > max + 1) ||
 155                                    (!negative && v > max) {
 156                                     cx.span_lint(OVERFLOWING_LITERALS,
 157                                                  e.span,
 158                                                  &format!("literal out of range for {:?}", t));
 159                                     return;
 160                                 }
 161                             }
 162                             _ => bug!(),
 163                         };
 164                     }
 165                     ty::TyUint(t) => {
 166                         let uint_type = if let ast::UintTy::Usize = t {
 167                             cx.sess().target.usize_ty
 168                         } else {
 169                             t
 170                         };
 171                         let (min, max) = uint_ty_range(uint_type);
 172                         let lit_val: u128 = match lit.node {
 173                             // _v is u8, within range by definition
 174                             ast::LitKind::Byte(_v) => return,
 175                             ast::LitKind::Int(v, _) => v,
 176                             _ => bug!(),
 177                         };
 178                         if lit_val < min || lit_val > max {
 179                             cx.span_lint(OVERFLOWING_LITERALS,
 180                                          e.span,
 181                                          &format!("literal out of range for {:?}", t));
 182                         }
 183                     }
 184                     ty::TyFloat(t) => {
 185                         let is_infinite = match lit.node {
 186                             ast::LitKind::Float(v, _) |
 187                             ast::LitKind::FloatUnsuffixed(v) => {
 188                                 match t {
 189                                     ast::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
 190                                     ast::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
 191                                 }
 192                             }
 193                             _ => bug!(),
 194                         };
 195                         if is_infinite == Ok(true) {
 196                             cx.span_lint(OVERFLOWING_LITERALS,
 197                                          e.span,
 198                                          &format!("literal out of range for {:?}", t));
 199                         }
 200                     }
 201                     _ => (),
 202                 };
 203             }
 204             _ => (),
 205         };
 206
 207         fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
 208             match binop.node {
 209                 hir::BiLt => v > min && v <= max,
 210                 hir::BiLe => v >= min && v < max,
 211                 hir::BiGt => v >= min && v < max,
 212                 hir::BiGe => v > min && v <= max,
 213                 hir::BiEq | hir::BiNe => v >= min && v <= max,
 214                 _ => bug!(),
 215             }
 216         }
 217
 218         fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
 219             codemap::respan(binop.span,
 220                             match binop.node {
 221                                 hir::BiLt => hir::BiGt,
 222                                 hir::BiLe => hir::BiGe,
 223                                 hir::BiGt => hir::BiLt,
 224                                 hir::BiGe => hir::BiLe,
 225                                 _ => return binop,
 226                             })
 227         }
 228
 229         // for isize & usize, be conservative with the warnings, so that the
 230         // warnings are consistent between 32- and 64-bit platforms
 231         fn int_ty_range(int_ty: ast::IntTy) -> (i128, i128) {
 232             match int_ty {
 233                 ast::IntTy::Isize => (i64::min_value() as i128, i64::max_value() as i128),
 234                 ast::IntTy::I8 => (i8::min_value() as i64 as i128, i8::max_value() as i128),
 235                 ast::IntTy::I16 => (i16::min_value() as i64 as i128, i16::max_value() as i128),
 236                 ast::IntTy::I32 => (i32::min_value() as i64 as i128, i32::max_value() as i128),
 237                 ast::IntTy::I64 => (i64::min_value() as i128, i64::max_value() as i128),
 238                 ast::IntTy::I128 =>(i128::min_value() as i128, i128::max_value()),
 239             }
 240         }
 241
 242         fn uint_ty_range(uint_ty: ast::UintTy) -> (u128, u128) {
 243             match uint_ty {
 244                 ast::UintTy::Usize => (u64::min_value() as u128, u64::max_value() as u128),
 245                 ast::UintTy::U8 => (u8::min_value() as u128, u8::max_value() as u128),
 246                 ast::UintTy::U16 => (u16::min_value() as u128, u16::max_value() as u128),
 247                 ast::UintTy::U32 => (u32::min_value() as u128, u32::max_value() as u128),
 248                 ast::UintTy::U64 => (u64::min_value() as u128, u64::max_value() as u128),
 249                 ast::UintTy::U128 => (u128::min_value(), u128::max_value()),
 250             }
 251         }
 252
 253         fn int_ty_bits(int_ty: ast::IntTy, isize_ty: ast::IntTy) -> u64 {
 254             match int_ty {
 255                 ast::IntTy::Isize => int_ty_bits(isize_ty, isize_ty),
 256                 ast::IntTy::I8 => 8,
 257                 ast::IntTy::I16 => 16 as u64,
 258                 ast::IntTy::I32 => 32,
 259                 ast::IntTy::I64 => 64,
 260                 ast::IntTy::I128 => 128,
 261             }
 262         }
 263
 264         fn uint_ty_bits(uint_ty: ast::UintTy, usize_ty: ast::UintTy) -> u64 {
 265             match uint_ty {
 266                 ast::UintTy::Usize => uint_ty_bits(usize_ty, usize_ty),
 267                 ast::UintTy::U8 => 8,
 268                 ast::UintTy::U16 => 16,
 269                 ast::UintTy::U32 => 32,
 270                 ast::UintTy::U64 => 64,
 271                 ast::UintTy::U128 => 128,
 272             }
 273         }
 274
 275         fn check_limits(cx: &LateContext,
 276                         binop: hir::BinOp,
 277                         l: &hir::Expr,
 278                         r: &hir::Expr)
 279                         -> bool {
 280             let (lit, expr, swap) = match (&l.node, &r.node) {
 281                 (&hir::ExprLit(_), _) => (l, r, true),
 282                 (_, &hir::ExprLit(_)) => (r, l, false),
 283                 _ => return true,
 284             };
 285             // Normalize the binop so that the literal is always on the RHS in
 286             // the comparison
 287             let norm_binop = if swap { rev_binop(binop) } else { binop };
 288             match cx.tables.node_id_to_type(expr.hir_id).sty {
 289                 ty::TyInt(int_ty) => {
 290                     let (min, max) = int_ty_range(int_ty);
 291                     let lit_val: i128 = match lit.node {
 292                         hir::ExprLit(ref li) => {
 293                             match li.node {
 294                                 ast::LitKind::Int(v, ast::LitIntType::Signed(_)) |
 295                                 ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => v as i128,
 296                                 _ => return true
 297                             }
 298                         },
 299                         _ => bug!()
 300                     };
 301                     is_valid(norm_binop, lit_val, min, max)
 302                 }
 303                 ty::TyUint(uint_ty) => {
 304                     let (min, max) :(u128, u128) = uint_ty_range(uint_ty);
 305                     let lit_val: u128 = match lit.node {
 306                         hir::ExprLit(ref li) => {
 307                             match li.node {
 308                                 ast::LitKind::Int(v, _) => v,
 309                                 _ => return true
 310                             }
 311                         },
 312                         _ => bug!()
 313                     };
 314                     is_valid(norm_binop, lit_val, min, max)
 315                 }
 316                 _ => true,
 317             }
 318         }
 319
 320         fn is_comparison(binop: hir::BinOp) -> bool {
 321             match binop.node {
 322                 hir::BiEq | hir::BiLt | hir::BiLe | hir::BiNe | hir::BiGe | hir::BiGt => true,
 323                 _ => false,
 324             }
 325         }
 326     }
 327 }
 328
 329 declare_lint! {
 330     IMPROPER_CTYPES,
 331     Warn,
 332     "proper use of libc types in foreign modules"
 333 }
 334
 335 struct ImproperCTypesVisitor<'a, 'tcx: 'a> {
 336     cx: &'a LateContext<'a, 'tcx>,
 337 }
 338
 339 enum FfiResult {
 340     FfiSafe,
 341     FfiPhantom,
 342     FfiUnsafe(&'static str),
 343     FfiBadStruct(DefId, &'static str),
 344     FfiBadUnion(DefId, &'static str),
 345     FfiBadEnum(DefId, &'static str),
 346 }
 347
 348 /// Check if this enum can be safely exported based on the
 349 /// "nullable pointer optimization". Currently restricted
 350 /// to function pointers and references, but could be
 351 /// expanded to cover NonZero raw pointers and newtypes.
 352 /// FIXME: This duplicates code in trans.
 353 fn is_repr_nullable_ptr<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 354                                   def: &'tcx ty::AdtDef,
 355                                   substs: &Substs<'tcx>)
 356                                   -> bool {
 357     if def.variants.len() == 2 {
 358         let data_idx;
 359
 360         if def.variants[0].fields.is_empty() {
 361             data_idx = 1;
 362         } else if def.variants[1].fields.is_empty() {
 363             data_idx = 0;
 364         } else {
 365             return false;
 366         }
 367
 368         if def.variants[data_idx].fields.len() == 1 {
 369             match def.variants[data_idx].fields[0].ty(tcx, substs).sty {
 370                 ty::TyFnPtr(_) => {
 371                     return true;
 372                 }
 373                 ty::TyRef(..) => {
 374                     return true;
 375                 }
 376                 _ => {}
 377             }
 378         }
 379     }
 380     false
 381 }
 382
 383 fn is_ffi_safe(ty: attr::IntType) -> bool {
 384     match ty {
 385         attr::SignedInt(ast::IntTy::I8) | attr::UnsignedInt(ast::UintTy::U8) |
 386         attr::SignedInt(ast::IntTy::I16) | attr::UnsignedInt(ast::UintTy::U16) |
 387         attr::SignedInt(ast::IntTy::I32) | attr::UnsignedInt(ast::UintTy::U32) |
 388         attr::SignedInt(ast::IntTy::I64) | attr::UnsignedInt(ast::UintTy::U64) |
 389         attr::SignedInt(ast::IntTy::I128) | attr::UnsignedInt(ast::UintTy::U128) => true,
 390         attr::SignedInt(ast::IntTy::Isize) | attr::UnsignedInt(ast::UintTy::Usize) => false
 391     }
 392 }
 393
 394 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
 395     /// Check if the given type is "ffi-safe" (has a stable, well-defined
 396     /// representation which can be exported to C code).
 397     fn check_type_for_ffi(&self,
 398                           cache: &mut FxHashSet<Ty<'tcx>>,
 399                           ty: Ty<'tcx>) -> FfiResult {
 400         use self::FfiResult::*;
 401
 402         let cx = self.cx.tcx;
 403
 404         // Protect against infinite recursion, for example
 405         // `struct S(*mut S);`.
 406         // FIXME: A recursion limit is necessary as well, for irregular
 407         // recusive types.
 408         if !cache.insert(ty) {
 409             return FfiSafe;
 410         }
 411
 412         match ty.sty {
 413             ty::TyAdt(def, substs) => {
 414                 if def.is_phantom_data() {
 415                     return FfiPhantom;
 416                 }
 417                 match def.adt_kind() {
 418                     AdtKind::Struct => {
 419                         if !def.repr.c() && !def.repr.transparent() {
 420                             return FfiUnsafe("found struct without foreign-function-safe \
 421                                               representation annotation in foreign module, \
 422                                               consider adding a #[repr(C)] attribute to the type");
 423                         }
 424
 425                         if def.non_enum_variant().fields.is_empty() {
 426                             return FfiUnsafe("found zero-size struct in foreign module, consider \
 427                                               adding a member to this struct");
 428                         }
 429
 430                         // We can't completely trust repr(C) and repr(transparent) markings;
 431                         // make sure the fields are actually safe.
 432                         let mut all_phantom = true;
 433                         for field in &def.non_enum_variant().fields {
 434                             let field_ty = cx.fully_normalize_associated_types_in(
 435                                 &field.ty(cx, substs)
 436                             );
 437                             // repr(transparent) types are allowed to have arbitrary ZSTs, not just
 438                             // PhantomData -- skip checking all ZST fields
 439                             if def.repr.transparent() {
 440                                 let is_zst = (cx, cx.param_env(field.did))
 441                                     .layout_of(field_ty)
 442                                     .map(|layout| layout.is_zst())
 443                                     .unwrap_or(false);
 444                                 if is_zst {
 445                                     continue;
 446                                 }
 447                             }
 448                             let r = self.check_type_for_ffi(cache, field_ty);
 449                             match r {
 450                                 FfiSafe => {
 451                                     all_phantom = false;
 452                                 }
 453                                 FfiPhantom => {}
 454                                 FfiBadStruct(..) | FfiBadUnion(..) | FfiBadEnum(..) => {
 455                                     return r;
 456                                 }
 457                                 FfiUnsafe(s) => {
 458                                     return FfiBadStruct(def.did, s);
 459                                 }
 460                             }
 461                         }
 462
 463                         if all_phantom { FfiPhantom } else { FfiSafe }
 464                     }
 465                     AdtKind::Union => {
 466                         if !def.repr.c() {
 467                             return FfiUnsafe("found union without foreign-function-safe \
 468                                               representation annotation in foreign module, \
 469                                               consider adding a #[repr(C)] attribute to the type");
 470                         }
 471
 472                         if def.non_enum_variant().fields.is_empty() {
 473                             return FfiUnsafe("found zero-size union in foreign module, consider \
 474                                               adding a member to this union");
 475                         }
 476
 477                         let mut all_phantom = true;
 478                         for field in &def.non_enum_variant().fields {
 479                             let field_ty = cx.fully_normalize_associated_types_in(
 480                                 &field.ty(cx, substs)
 481                             );
 482                             let r = self.check_type_for_ffi(cache, field_ty);
 483                             match r {
 484                                 FfiSafe => {
 485                                     all_phantom = false;
 486                                 }
 487                                 FfiPhantom => {}
 488                                 FfiBadStruct(..) | FfiBadUnion(..) | FfiBadEnum(..) => {
 489                                     return r;
 490                                 }
 491                                 FfiUnsafe(s) => {
 492                                     return FfiBadUnion(def.did, s);
 493                                 }
 494                             }
 495                         }
 496
 497                         if all_phantom { FfiPhantom } else { FfiSafe }
 498                     }
 499                     AdtKind::Enum => {
 500                         if def.variants.is_empty() {
 501                             // Empty enums are okay... although sort of useless.
 502                             return FfiSafe;
 503                         }
 504
 505                         // Check for a repr() attribute to specify the size of the
 506                         // discriminant.
 507                         if !def.repr.c() && def.repr.int.is_none() {
 508                             // Special-case types like `Option<extern fn()>`.
 509                             if !is_repr_nullable_ptr(cx, def, substs) {
 510                                 return FfiUnsafe("found enum without foreign-function-safe \
 511                                                   representation annotation in foreign \
 512                                                   module, consider adding a #[repr(...)] \
 513                                                   attribute to the type");
 514                             }
 515                         }
 516
 517                         if let Some(int_ty) = def.repr.int {
 518                             if !is_ffi_safe(int_ty) {
 519                                 // FIXME: This shouldn't be reachable: we should check
 520                                 // this earlier.
 521                                 return FfiUnsafe("enum has unexpected #[repr(...)] attribute");
 522                             }
 523
 524                             // Enum with an explicitly sized discriminant; either
 525                             // a C-style enum or a discriminated union.
 526
 527                             // The layout of enum variants is implicitly repr(C).
 528                             // FIXME: Is that correct?
 529                         }
 530
 531                         // Check the contained variants.
 532                         for variant in &def.variants {
 533                             for field in &variant.fields {
 534                                 let arg = cx.fully_normalize_associated_types_in(
 535                                     &field.ty(cx, substs)
 536                                 );
 537                                 let r = self.check_type_for_ffi(cache, arg);
 538                                 match r {
 539                                     FfiSafe => {}
 540                                     FfiBadStruct(..) | FfiBadUnion(..) | FfiBadEnum(..) => {
 541                                         return r;
 542                                     }
 543                                     FfiPhantom => {
 544                                         return FfiBadEnum(def.did,
 545                                                           "Found phantom data in enum variant");
 546                                     }
 547                                     FfiUnsafe(s) => {
 548                                         return FfiBadEnum(def.did, s);
 549                                     }
 550                                 }
 551                             }
 552                         }
 553                         FfiSafe
 554                     }
 555                 }
 556             }
 557
 558             ty::TyChar => {
 559                 FfiUnsafe("found Rust type `char` in foreign module, while \
 560                            `u32` or `libc::wchar_t` should be used")
 561             }
 562
 563             ty::TyInt(ast::IntTy::I128) => {
 564                 FfiUnsafe("found Rust type `i128` in foreign module, but \
 565                            128-bit integers don't currently have a known \
 566                            stable ABI")
 567             }
 568
 569             ty::TyUint(ast::UintTy::U128) => {
 570                 FfiUnsafe("found Rust type `u128` in foreign module, but \
 571                            128-bit integers don't currently have a known \
 572                            stable ABI")
 573             }
 574
 575             // Primitive types with a stable representation.
 576             ty::TyBool | ty::TyInt(..) | ty::TyUint(..) | ty::TyFloat(..) | ty::TyNever => FfiSafe,
 577
 578             ty::TySlice(_) => {
 579                 FfiUnsafe("found Rust slice type in foreign module, \
 580                            consider using a raw pointer instead")
 581             }
 582
 583             ty::TyDynamic(..) => {
 584                 FfiUnsafe("found Rust trait type in foreign module, \
 585                            consider using a raw pointer instead")
 586             }
 587
 588             ty::TyStr => {
 589                 FfiUnsafe("found Rust type `str` in foreign module; \
 590                            consider using a `*const libc::c_char`")
 591             }
 592
 593             ty::TyTuple(..) => {
 594                 FfiUnsafe("found Rust tuple type in foreign module; \
 595                            consider using a struct instead")
 596             }
 597
 598             ty::TyRawPtr(ref m) |
 599             ty::TyRef(_, ref m) => self.check_type_for_ffi(cache, m.ty),
 600
 601             ty::TyArray(ty, _) => self.check_type_for_ffi(cache, ty),
 602
 603             ty::TyFnPtr(sig) => {
 604                 match sig.abi() {
 605                     Abi::Rust | Abi::RustIntrinsic | Abi::PlatformIntrinsic | Abi::RustCall => {
 606                         return FfiUnsafe("found function pointer with Rust calling convention in \
 607                                           foreign module; consider using an `extern` function \
 608                                           pointer")
 609                     }
 610                     _ => {}
 611                 }
 612
 613                 let sig = cx.erase_late_bound_regions(&sig);
 614                 if !sig.output().is_nil() {
 615                     let r = self.check_type_for_ffi(cache, sig.output());
 616                     match r {
 617                         FfiSafe => {}
 618                         _ => {
 619                             return r;
 620                         }
 621                     }
 622                 }
 623                 for arg in sig.inputs() {
 624                     let r = self.check_type_for_ffi(cache, arg);
 625                     match r {
 626                         FfiSafe => {}
 627                         _ => {
 628                             return r;
 629                         }
 630                     }
 631                 }
 632                 FfiSafe
 633             }
 634
 635             ty::TyForeign(..) => FfiSafe,
 636
 637             ty::TyParam(..) |
 638             ty::TyInfer(..) |
 639             ty::TyError |
 640             ty::TyClosure(..) |
 641             ty::TyGenerator(..) |
 642             ty::TyGeneratorWitness(..) |
 643             ty::TyProjection(..) |
 644             ty::TyAnon(..) |
 645             ty::TyFnDef(..) => bug!("Unexpected type in foreign function"),
 646         }
 647     }
 648
 649     fn check_type_for_ffi_and_report_errors(&mut self, sp: Span, ty: Ty<'tcx>) {
 650         // it is only OK to use this function because extern fns cannot have
 651         // any generic types right now:
 652         let ty = self.cx.tcx.fully_normalize_associated_types_in(&ty);
 653
 654         match self.check_type_for_ffi(&mut FxHashSet(), ty) {
 655             FfiResult::FfiSafe => {}
 656             FfiResult::FfiPhantom => {
 657                 self.cx.span_lint(IMPROPER_CTYPES,
 658                                   sp,
 659                                   &format!("found zero-sized type composed only \
 660                                             of phantom-data in a foreign-function."));
 661             }
 662             FfiResult::FfiUnsafe(s) => {
 663                 self.cx.span_lint(IMPROPER_CTYPES, sp, s);
 664             }
 665             FfiResult::FfiBadStruct(_, s) => {
 666                 // FIXME: This diagnostic is difficult to read, and doesn't
 667                 // point at the relevant field.
 668                 self.cx.span_lint(IMPROPER_CTYPES,
 669                                   sp,
 670                                   &format!("found non-foreign-function-safe member in struct \
 671                                             marked #[repr(C)]: {}",
 672                                            s));
 673             }
 674             FfiResult::FfiBadUnion(_, s) => {
 675                 // FIXME: This diagnostic is difficult to read, and doesn't
 676                 // point at the relevant field.
 677                 self.cx.span_lint(IMPROPER_CTYPES,
 678                                   sp,
 679                                   &format!("found non-foreign-function-safe member in union \
 680                                             marked #[repr(C)]: {}",
 681                                            s));
 682             }
 683             FfiResult::FfiBadEnum(_, s) => {
 684                 // FIXME: This diagnostic is difficult to read, and doesn't
 685                 // point at the relevant variant.
 686                 self.cx.span_lint(IMPROPER_CTYPES,
 687                                   sp,
 688                                   &format!("found non-foreign-function-safe member in enum: {}",
 689                                            s));
 690             }
 691         }
 692     }
 693
 694     fn check_foreign_fn(&mut self, id: ast::NodeId, decl: &hir::FnDecl) {
 695         let def_id = self.cx.tcx.hir.local_def_id(id);
 696         let sig = self.cx.tcx.fn_sig(def_id);
 697         let sig = self.cx.tcx.erase_late_bound_regions(&sig);
 698
 699         for (input_ty, input_hir) in sig.inputs().iter().zip(&decl.inputs) {
 700             self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty);
 701         }
 702
 703         if let hir::Return(ref ret_hir) = decl.output {
 704             let ret_ty = sig.output();
 705             if !ret_ty.is_nil() {
 706                 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty);
 707             }
 708         }
 709     }
 710
 711     fn check_foreign_static(&mut self, id: ast::NodeId, span: Span) {
 712         let def_id = self.cx.tcx.hir.local_def_id(id);
 713         let ty = self.cx.tcx.type_of(def_id);
 714         self.check_type_for_ffi_and_report_errors(span, ty);
 715     }
 716 }
 717
 718 #[derive(Copy, Clone)]
 719 pub struct ImproperCTypes;
 720
 721 impl LintPass for ImproperCTypes {
 722     fn get_lints(&self) -> LintArray {
 723         lint_array!(IMPROPER_CTYPES)
 724     }
 725 }
 726
 727 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImproperCTypes {
 728     fn check_item(&mut self, cx: &LateContext, it: &hir::Item) {
 729         let mut vis = ImproperCTypesVisitor { cx: cx };
 730         if let hir::ItemForeignMod(ref nmod) = it.node {
 731             if nmod.abi != Abi::RustIntrinsic && nmod.abi != Abi::PlatformIntrinsic {
 732                 for ni in &nmod.items {
 733                     match ni.node {
 734                         hir::ForeignItemFn(ref decl, _, _) => {
 735                             vis.check_foreign_fn(ni.id, decl);
 736                         }
 737                         hir::ForeignItemStatic(ref ty, _) => {
 738                             vis.check_foreign_static(ni.id, ty.span);
 739                         }
 740                         hir::ForeignItemType => ()
 741                     }
 742                 }
 743             }
 744         }
 745     }
 746 }
 747
 748 pub struct VariantSizeDifferences;
 749
 750 impl LintPass for VariantSizeDifferences {
 751     fn get_lints(&self) -> LintArray {
 752         lint_array!(VARIANT_SIZE_DIFFERENCES)
 753     }
 754 }
 755
 756 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for VariantSizeDifferences {
 757     fn check_item(&mut self, cx: &LateContext, it: &hir::Item) {
 758         if let hir::ItemEnum(ref enum_definition, ref gens) = it.node {
 759             if gens.params.iter().all(|param| param.is_lifetime_param()) {
 760                 // sizes only make sense for non-generic types
 761                 let item_def_id = cx.tcx.hir.local_def_id(it.id);
 762                 let t = cx.tcx.type_of(item_def_id);
 763                 let ty = cx.tcx.erase_regions(&t);
 764                 let layout = cx.layout_of(ty).unwrap_or_else(|e| {
 765                     bug!("failed to get layout for `{}`: {}", t, e)
 766                 });
 767
 768                 if let layout::Variants::Tagged { ref variants, ref discr, .. } = layout.variants {
 769                     let discr_size = discr.value.size(cx.tcx).bytes();
 770
 771                     debug!("enum `{}` is {} bytes large with layout:\n{:#?}",
 772                       t, layout.size.bytes(), layout);
 773
 774                     let (largest, slargest, largest_index) = enum_definition.variants
 775                         .iter()
 776                         .zip(variants)
 777                         .map(|(variant, variant_layout)| {
 778                             // Subtract the size of the enum discriminant
 779                             let bytes = variant_layout.size.bytes()
 780                                 .saturating_sub(discr_size);
 781
 782                             debug!("- variant `{}` is {} bytes large", variant.node.name, bytes);
 783                             bytes
 784                         })
 785                         .enumerate()
 786                         .fold((0, 0, 0), |(l, s, li), (idx, size)| if size > l {
 787                             (size, l, idx)
 788                         } else if size > s {
 789                             (l, size, li)
 790                         } else {
 791                             (l, s, li)
 792                         });
 793
 794                     // we only warn if the largest variant is at least thrice as large as
 795                     // the second-largest.
 796                     if largest > slargest * 3 && slargest > 0 {
 797                         cx.span_lint(VARIANT_SIZE_DIFFERENCES,
 798                                      enum_definition.variants[largest_index].span,
 799                                      &format!("enum variant is more than three times larger \
 800                                                ({} bytes) than the next largest",
 801                                               largest));
 802                     }
 803                 }
 804             }
 805         }
 806     }
 807 }