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::{Layout, Primitive};
  17 use rustc::traits::Reveal;
  18 use middle::const_val::ConstVal;
  19 use rustc_const_eval::ConstContext;
  20 use util::nodemap::FxHashSet;
  21 use lint::{LateContext, LintContext, LintArray};
  22 use lint::{LintPass, LateLintPass};
  23
  24 use std::cmp;
  25 use std::{i8, i16, i32, i64, u8, u16, u32, u64, f32, f64};
  26
  27 use syntax::ast;
  28 use syntax::abi::Abi;
  29 use syntax::attr;
  30 use syntax_pos::Span;
  31 use syntax::codemap;
  32
  33 use rustc::hir;
  34
  35 declare_lint! {
  36     UNUSED_COMPARISONS,
  37     Warn,
  38     "comparisons made useless by limits of the types involved"
  39 }
  40
  41 declare_lint! {
  42     OVERFLOWING_LITERALS,
  43     Warn,
  44     "literal out of range for its type"
  45 }
  46
  47 declare_lint! {
  48     EXCEEDING_BITSHIFTS,
  49     Deny,
  50     "shift exceeds the type's number of bits"
  51 }
  52
  53 declare_lint! {
  54     VARIANT_SIZE_DIFFERENCES,
  55     Allow,
  56     "detects enums with widely varying variant sizes"
  57 }
  58
  59 #[derive(Copy, Clone)]
  60 pub struct TypeLimits {
  61     /// Id of the last visited negated expression
  62     negated_expr_id: ast::NodeId,
  63 }
  64
  65 impl TypeLimits {
  66     pub fn new() -> TypeLimits {
  67         TypeLimits { negated_expr_id: ast::DUMMY_NODE_ID }
  68     }
  69 }
  70
  71 impl LintPass for TypeLimits {
  72     fn get_lints(&self) -> LintArray {
  73         lint_array!(UNUSED_COMPARISONS,
  74                     OVERFLOWING_LITERALS,
  75                     EXCEEDING_BITSHIFTS)
  76     }
  77 }
  78
  79 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TypeLimits {
  80     fn check_expr(&mut self, cx: &LateContext, e: &hir::Expr) {
  81         match e.node {
  82             hir::ExprUnary(hir::UnNeg, ref expr) => {
  83                 // propagate negation, if the negation itself isn't negated
  84                 if self.negated_expr_id != e.id {
  85                     self.negated_expr_id = expr.id;
  86                 }
  87             }
  88             hir::ExprBinary(binop, ref l, ref r) => {
  89                 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
  90                     cx.span_lint(UNUSED_COMPARISONS,
  91                                  e.span,
  92                                  "comparison is useless due to type limits");
  93                 }
  94
  95                 if binop.node.is_shift() {
  96                     let opt_ty_bits = match cx.tables.node_id_to_type(l.id).sty {
  97                         ty::TyInt(t) => Some(int_ty_bits(t, cx.sess().target.int_type)),
  98                         ty::TyUint(t) => Some(uint_ty_bits(t, cx.sess().target.uint_type)),
  99                         _ => None,
 100                     };
 101
 102                     if let Some(bits) = opt_ty_bits {
 103                         let exceeding = if let hir::ExprLit(ref lit) = r.node {
 104                             if let ast::LitKind::Int(shift, _) = lit.node {
 105                                 shift as u64 >= bits
 106                             } else {
 107                                 false
 108                             }
 109                         } else {
 110                             let const_cx = ConstContext::with_tables(cx.tcx, cx.tables);
 111                             match const_cx.eval(&r) {
 112                                 Ok(ConstVal::Integral(i)) => {
 113                                     i.is_negative() ||
 114                                     i.to_u64()
 115                                         .map(|i| i >= bits)
 116                                         .unwrap_or(true)
 117                                 }
 118                                 _ => false,
 119                             }
 120                         };
 121                         if exceeding {
 122                             cx.span_lint(EXCEEDING_BITSHIFTS,
 123                                          e.span,
 124                                          "bitshift exceeds the type's number of bits");
 125                         }
 126                     };
 127                 }
 128             }
 129             hir::ExprLit(ref lit) => {
 130                 match cx.tables.node_id_to_type(e.id).sty {
 131                     ty::TyInt(t) => {
 132                         match lit.node {
 133                             ast::LitKind::Int(v, ast::LitIntType::Signed(_)) |
 134                             ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => {
 135                                 let int_type = if let ast::IntTy::Is = t {
 136                                     cx.sess().target.int_type
 137                                 } else {
 138                                     t
 139                                 };
 140                                 let (_, max) = int_ty_range(int_type);
 141                                 let max = max as u128;
 142                                 let negative = self.negated_expr_id == e.id;
 143
 144                                 // Detect literal value out of range [min, max] inclusive
 145                                 // avoiding use of -min to prevent overflow/panic
 146                                 if (negative && v > max + 1) ||
 147                                    (!negative && v > max) {
 148                                     cx.span_lint(OVERFLOWING_LITERALS,
 149                                                  e.span,
 150                                                  &format!("literal out of range for {:?}", t));
 151                                     return;
 152                                 }
 153                             }
 154                             _ => bug!(),
 155                         };
 156                     }
 157                     ty::TyUint(t) => {
 158                         let uint_type = if let ast::UintTy::Us = t {
 159                             cx.sess().target.uint_type
 160                         } else {
 161                             t
 162                         };
 163                         let (min, max) = uint_ty_range(uint_type);
 164                         let lit_val: u128 = match lit.node {
 165                             // _v is u8, within range by definition
 166                             ast::LitKind::Byte(_v) => return,
 167                             ast::LitKind::Int(v, _) => v,
 168                             _ => bug!(),
 169                         };
 170                         if lit_val < min || lit_val > max {
 171                             cx.span_lint(OVERFLOWING_LITERALS,
 172                                          e.span,
 173                                          &format!("literal out of range for {:?}", t));
 174                         }
 175                     }
 176                     ty::TyFloat(t) => {
 177                         let (min, max) = float_ty_range(t);
 178                         let lit_val: f64 = match lit.node {
 179                             ast::LitKind::Float(v, _) |
 180                             ast::LitKind::FloatUnsuffixed(v) => {
 181                                 match v.as_str().parse() {
 182                                     Ok(f) => f,
 183                                     Err(_) => return,
 184                                 }
 185                             }
 186                             _ => bug!(),
 187                         };
 188                         if lit_val < min || lit_val > max {
 189                             cx.span_lint(OVERFLOWING_LITERALS,
 190                                          e.span,
 191                                          &format!("literal out of range for {:?}", t));
 192                         }
 193                     }
 194                     _ => (),
 195                 };
 196             }
 197             _ => (),
 198         };
 199
 200         fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
 201             match binop.node {
 202                 hir::BiLt => v > min && v <= max,
 203                 hir::BiLe => v >= min && v < max,
 204                 hir::BiGt => v >= min && v < max,
 205                 hir::BiGe => v > min && v <= max,
 206                 hir::BiEq | hir::BiNe => v >= min && v <= max,
 207                 _ => bug!(),
 208             }
 209         }
 210
 211         fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
 212             codemap::respan(binop.span,
 213                             match binop.node {
 214                                 hir::BiLt => hir::BiGt,
 215                                 hir::BiLe => hir::BiGe,
 216                                 hir::BiGt => hir::BiLt,
 217                                 hir::BiGe => hir::BiLe,
 218                                 _ => return binop,
 219                             })
 220         }
 221
 222         // for isize & usize, be conservative with the warnings, so that the
 223         // warnings are consistent between 32- and 64-bit platforms
 224         fn int_ty_range(int_ty: ast::IntTy) -> (i128, i128) {
 225             match int_ty {
 226                 ast::IntTy::Is => (i64::min_value() as i128, i64::max_value() as i128),
 227                 ast::IntTy::I8 => (i8::min_value() as i64 as i128, i8::max_value() as i128),
 228                 ast::IntTy::I16 => (i16::min_value() as i64 as i128, i16::max_value() as i128),
 229                 ast::IntTy::I32 => (i32::min_value() as i64 as i128, i32::max_value() as i128),
 230                 ast::IntTy::I64 => (i64::min_value() as i128, i64::max_value() as i128),
 231                 ast::IntTy::I128 =>(i128::min_value() as i128, i128::max_value()),
 232             }
 233         }
 234
 235         fn uint_ty_range(uint_ty: ast::UintTy) -> (u128, u128) {
 236             match uint_ty {
 237                 ast::UintTy::Us => (u64::min_value() as u128, u64::max_value() as u128),
 238                 ast::UintTy::U8 => (u8::min_value() as u128, u8::max_value() as u128),
 239                 ast::UintTy::U16 => (u16::min_value() as u128, u16::max_value() as u128),
 240                 ast::UintTy::U32 => (u32::min_value() as u128, u32::max_value() as u128),
 241                 ast::UintTy::U64 => (u64::min_value() as u128, u64::max_value() as u128),
 242                 ast::UintTy::U128 => (u128::min_value(), u128::max_value()),
 243             }
 244         }
 245
 246         fn float_ty_range(float_ty: ast::FloatTy) -> (f64, f64) {
 247             match float_ty {
 248                 ast::FloatTy::F32 => (f32::MIN as f64, f32::MAX as f64),
 249                 ast::FloatTy::F64 => (f64::MIN, f64::MAX),
 250             }
 251         }
 252
 253         fn int_ty_bits(int_ty: ast::IntTy, target_int_ty: ast::IntTy) -> u64 {
 254             match int_ty {
 255                 ast::IntTy::Is => int_ty_bits(target_int_ty, target_int_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, target_uint_ty: ast::UintTy) -> u64 {
 265             match uint_ty {
 266                 ast::UintTy::Us => uint_ty_bits(target_uint_ty, target_uint_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.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::Is) | attr::UnsignedInt(ast::UintTy::Us) => 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() {
 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.struct_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) markings; make sure the
 431                         // fields are actually safe.
 432                         let mut all_phantom = true;
 433                         for field in &def.struct_variant().fields {
 434                             let field_ty = cx.normalize_associated_type(&field.ty(cx, substs));
 435                             let r = self.check_type_for_ffi(cache, field_ty);
 436                             match r {
 437                                 FfiSafe => {
 438                                     all_phantom = false;
 439                                 }
 440                                 FfiPhantom => {}
 441                                 FfiBadStruct(..) | FfiBadUnion(..) | FfiBadEnum(..) => {
 442                                     return r;
 443                                 }
 444                                 FfiUnsafe(s) => {
 445                                     return FfiBadStruct(def.did, s);
 446                                 }
 447                             }
 448                         }
 449
 450                         if all_phantom { FfiPhantom } else { FfiSafe }
 451                     }
 452                     AdtKind::Union => {
 453                         if !def.repr.c() {
 454                             return FfiUnsafe("found union without foreign-function-safe \
 455                                               representation annotation in foreign module, \
 456                                               consider adding a #[repr(C)] attribute to the type");
 457                         }
 458
 459                         if def.struct_variant().fields.is_empty() {
 460                             return FfiUnsafe("found zero-size union in foreign module, consider \
 461                                               adding a member to this union");
 462                         }
 463
 464                         let mut all_phantom = true;
 465                         for field in &def.struct_variant().fields {
 466                             let field_ty = cx.normalize_associated_type(&field.ty(cx, substs));
 467                             let r = self.check_type_for_ffi(cache, field_ty);
 468                             match r {
 469                                 FfiSafe => {
 470                                     all_phantom = false;
 471                                 }
 472                                 FfiPhantom => {}
 473                                 FfiBadStruct(..) | FfiBadUnion(..) | FfiBadEnum(..) => {
 474                                     return r;
 475                                 }
 476                                 FfiUnsafe(s) => {
 477                                     return FfiBadUnion(def.did, s);
 478                                 }
 479                             }
 480                         }
 481
 482                         if all_phantom { FfiPhantom } else { FfiSafe }
 483                     }
 484                     AdtKind::Enum => {
 485                         if def.variants.is_empty() {
 486                             // Empty enums are okay... although sort of useless.
 487                             return FfiSafe;
 488                         }
 489
 490                         // Check for a repr() attribute to specify the size of the
 491                         // discriminant.
 492                         if !def.repr.c() && def.repr.int.is_none() {
 493                             // Special-case types like `Option<extern fn()>`.
 494                             if !is_repr_nullable_ptr(cx, def, substs) {
 495                                 return FfiUnsafe("found enum without foreign-function-safe \
 496                                                   representation annotation in foreign \
 497                                                   module, consider adding a #[repr(...)] \
 498                                                   attribute to the type");
 499                             }
 500                         }
 501
 502                         if let Some(int_ty) = def.repr.int {
 503                             if !is_ffi_safe(int_ty) {
 504                                 // FIXME: This shouldn't be reachable: we should check
 505                                 // this earlier.
 506                                 return FfiUnsafe("enum has unexpected #[repr(...)] attribute");
 507                             }
 508
 509                             // Enum with an explicitly sized discriminant; either
 510                             // a C-style enum or a discriminated union.
 511
 512                             // The layout of enum variants is implicitly repr(C).
 513                             // FIXME: Is that correct?
 514                         }
 515
 516                         // Check the contained variants.
 517                         for variant in &def.variants {
 518                             for field in &variant.fields {
 519                                 let arg = cx.normalize_associated_type(&field.ty(cx, substs));
 520                                 let r = self.check_type_for_ffi(cache, arg);
 521                                 match r {
 522                                     FfiSafe => {}
 523                                     FfiBadStruct(..) | FfiBadUnion(..) | FfiBadEnum(..) => {
 524                                         return r;
 525                                     }
 526                                     FfiPhantom => {
 527                                         return FfiBadEnum(def.did,
 528                                                           "Found phantom data in enum variant");
 529                                     }
 530                                     FfiUnsafe(s) => {
 531                                         return FfiBadEnum(def.did, s);
 532                                     }
 533                                 }
 534                             }
 535                         }
 536                         FfiSafe
 537                     }
 538                 }
 539             }
 540
 541             ty::TyChar => {
 542                 FfiUnsafe("found Rust type `char` in foreign module, while \
 543                            `u32` or `libc::wchar_t` should be used")
 544             }
 545
 546             // Primitive types with a stable representation.
 547             ty::TyBool | ty::TyInt(..) | ty::TyUint(..) | ty::TyFloat(..) | ty::TyNever => FfiSafe,
 548
 549             ty::TySlice(_) => {
 550                 FfiUnsafe("found Rust slice type in foreign module, \
 551                            consider using a raw pointer instead")
 552             }
 553
 554             ty::TyDynamic(..) => {
 555                 FfiUnsafe("found Rust trait type in foreign module, \
 556                            consider using a raw pointer instead")
 557             }
 558
 559             ty::TyStr => {
 560                 FfiUnsafe("found Rust type `str` in foreign module; \
 561                            consider using a `*const libc::c_char`")
 562             }
 563
 564             ty::TyTuple(..) => {
 565                 FfiUnsafe("found Rust tuple type in foreign module; \
 566                            consider using a struct instead")
 567             }
 568
 569             ty::TyRawPtr(ref m) |
 570             ty::TyRef(_, ref m) => self.check_type_for_ffi(cache, m.ty),
 571
 572             ty::TyArray(ty, _) => self.check_type_for_ffi(cache, ty),
 573
 574             ty::TyFnPtr(sig) => {
 575                 match sig.abi() {
 576                     Abi::Rust | Abi::RustIntrinsic | Abi::PlatformIntrinsic | Abi::RustCall => {
 577                         return FfiUnsafe("found function pointer with Rust calling convention in \
 578                                           foreign module; consider using an `extern` function \
 579                                           pointer")
 580                     }
 581                     _ => {}
 582                 }
 583
 584                 let sig = cx.erase_late_bound_regions(&sig);
 585                 if !sig.output().is_nil() {
 586                     let r = self.check_type_for_ffi(cache, sig.output());
 587                     match r {
 588                         FfiSafe => {}
 589                         _ => {
 590                             return r;
 591                         }
 592                     }
 593                 }
 594                 for arg in sig.inputs() {
 595                     let r = self.check_type_for_ffi(cache, arg);
 596                     match r {
 597                         FfiSafe => {}
 598                         _ => {
 599                             return r;
 600                         }
 601                     }
 602                 }
 603                 FfiSafe
 604             }
 605
 606             ty::TyParam(..) |
 607             ty::TyInfer(..) |
 608             ty::TyError |
 609             ty::TyClosure(..) |
 610             ty::TyProjection(..) |
 611             ty::TyAnon(..) |
 612             ty::TyFnDef(..) => bug!("Unexpected type in foreign function"),
 613         }
 614     }
 615
 616     fn check_type_for_ffi_and_report_errors(&mut self, sp: Span, ty: Ty<'tcx>) {
 617         // it is only OK to use this function because extern fns cannot have
 618         // any generic types right now:
 619         let ty = self.cx.tcx.normalize_associated_type(&ty);
 620
 621         match self.check_type_for_ffi(&mut FxHashSet(), ty) {
 622             FfiResult::FfiSafe => {}
 623             FfiResult::FfiPhantom => {
 624                 self.cx.span_lint(IMPROPER_CTYPES,
 625                                   sp,
 626                                   &format!("found zero-sized type composed only \
 627                                             of phantom-data in a foreign-function."));
 628             }
 629             FfiResult::FfiUnsafe(s) => {
 630                 self.cx.span_lint(IMPROPER_CTYPES, sp, s);
 631             }
 632             FfiResult::FfiBadStruct(_, s) => {
 633                 // FIXME: This diagnostic is difficult to read, and doesn't
 634                 // point at the relevant field.
 635                 self.cx.span_lint(IMPROPER_CTYPES,
 636                                   sp,
 637                                   &format!("found non-foreign-function-safe member in struct \
 638                                             marked #[repr(C)]: {}",
 639                                            s));
 640             }
 641             FfiResult::FfiBadUnion(_, s) => {
 642                 // FIXME: This diagnostic is difficult to read, and doesn't
 643                 // point at the relevant field.
 644                 self.cx.span_lint(IMPROPER_CTYPES,
 645                                   sp,
 646                                   &format!("found non-foreign-function-safe member in union \
 647                                             marked #[repr(C)]: {}",
 648                                            s));
 649             }
 650             FfiResult::FfiBadEnum(_, s) => {
 651                 // FIXME: This diagnostic is difficult to read, and doesn't
 652                 // point at the relevant variant.
 653                 self.cx.span_lint(IMPROPER_CTYPES,
 654                                   sp,
 655                                   &format!("found non-foreign-function-safe member in enum: {}",
 656                                            s));
 657             }
 658         }
 659     }
 660
 661     fn check_foreign_fn(&mut self, id: ast::NodeId, decl: &hir::FnDecl) {
 662         let def_id = self.cx.tcx.hir.local_def_id(id);
 663         let sig = self.cx.tcx.type_of(def_id).fn_sig();
 664         let sig = self.cx.tcx.erase_late_bound_regions(&sig);
 665
 666         for (input_ty, input_hir) in sig.inputs().iter().zip(&decl.inputs) {
 667             self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty);
 668         }
 669
 670         if let hir::Return(ref ret_hir) = decl.output {
 671             let ret_ty = sig.output();
 672             if !ret_ty.is_nil() {
 673                 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty);
 674             }
 675         }
 676     }
 677
 678     fn check_foreign_static(&mut self, id: ast::NodeId, span: Span) {
 679         let def_id = self.cx.tcx.hir.local_def_id(id);
 680         let ty = self.cx.tcx.type_of(def_id);
 681         self.check_type_for_ffi_and_report_errors(span, ty);
 682     }
 683 }
 684
 685 #[derive(Copy, Clone)]
 686 pub struct ImproperCTypes;
 687
 688 impl LintPass for ImproperCTypes {
 689     fn get_lints(&self) -> LintArray {
 690         lint_array!(IMPROPER_CTYPES)
 691     }
 692 }
 693
 694 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImproperCTypes {
 695     fn check_item(&mut self, cx: &LateContext, it: &hir::Item) {
 696         let mut vis = ImproperCTypesVisitor { cx: cx };
 697         if let hir::ItemForeignMod(ref nmod) = it.node {
 698             if nmod.abi != Abi::RustIntrinsic && nmod.abi != Abi::PlatformIntrinsic {
 699                 for ni in &nmod.items {
 700                     match ni.node {
 701                         hir::ForeignItemFn(ref decl, _, _) => {
 702                             vis.check_foreign_fn(ni.id, decl);
 703                         }
 704                         hir::ForeignItemStatic(ref ty, _) => {
 705                             vis.check_foreign_static(ni.id, ty.span);
 706                         }
 707                     }
 708                 }
 709             }
 710         }
 711     }
 712 }
 713
 714 pub struct VariantSizeDifferences;
 715
 716 impl LintPass for VariantSizeDifferences {
 717     fn get_lints(&self) -> LintArray {
 718         lint_array!(VARIANT_SIZE_DIFFERENCES)
 719     }
 720 }
 721
 722 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for VariantSizeDifferences {
 723     fn check_item(&mut self, cx: &LateContext, it: &hir::Item) {
 724         if let hir::ItemEnum(ref enum_definition, ref gens) = it.node {
 725             if gens.ty_params.is_empty() {
 726                 // sizes only make sense for non-generic types
 727                 let t = cx.tcx.type_of(cx.tcx.hir.local_def_id(it.id));
 728                 let layout = cx.tcx.infer_ctxt((), Reveal::All).enter(|infcx| {
 729                     let ty = cx.tcx.erase_regions(&t);
 730                     ty.layout(&infcx).unwrap_or_else(|e| {
 731                         bug!("failed to get layout for `{}`: {}", t, e)
 732                     })
 733                 });
 734
 735                 if let Layout::General { ref variants, ref size, discr, .. } = *layout {
 736                     let discr_size = Primitive::Int(discr).size(cx.tcx).bytes();
 737
 738                     debug!("enum `{}` is {} bytes large with layout:\n{:#?}",
 739                       t, size.bytes(), layout);
 740
 741                     let (largest, slargest, largest_index) = enum_definition.variants
 742                         .iter()
 743                         .zip(variants)
 744                         .map(|(variant, variant_layout)| {
 745                             // Subtract the size of the enum discriminant
 746                             let bytes = variant_layout.min_size
 747                                 .bytes()
 748                                 .saturating_sub(discr_size);
 749
 750                             debug!("- variant `{}` is {} bytes large", variant.node.name, bytes);
 751                             bytes
 752                         })
 753                         .enumerate()
 754                         .fold((0, 0, 0), |(l, s, li), (idx, size)| if size > l {
 755                             (size, l, idx)
 756                         } else if size > s {
 757                             (l, size, li)
 758                         } else {
 759                             (l, s, li)
 760                         });
 761
 762                     // we only warn if the largest variant is at least thrice as large as
 763                     // the second-largest.
 764                     if largest > slargest * 3 && slargest > 0 {
 765                         cx.span_lint(VARIANT_SIZE_DIFFERENCES,
 766                                      enum_definition.variants[largest_index].span,
 767                                      &format!("enum variant is more than three times larger \
 768                                                ({} bytes) than the next largest",
 769                                               largest));
 770                     }
 771                 }
 772             }
 773         }
 774     }
 775 }