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 rustc_const_eval::EvalHint::ExprTypeChecked;
  21 use util::nodemap::FxHashSet;
  22 use lint::{LateContext, LintContext, LintArray};
  23 use lint::{LintPass, LateLintPass};
  24
  25 use std::cmp;
  26 use std::{i8, i16, i32, i64, u8, u16, u32, u64, f32, f64};
  27
  28 use syntax::ast;
  29 use syntax::abi::Abi;
  30 use syntax::attr;
  31 use syntax_pos::Span;
  32 use syntax::codemap;
  33
  34 use rustc::hir;
  35
  36 declare_lint! {
  37     UNUSED_COMPARISONS,
  38     Warn,
  39     "comparisons made useless by limits of the types involved"
  40 }
  41
  42 declare_lint! {
  43     OVERFLOWING_LITERALS,
  44     Warn,
  45     "literal out of range for its type"
  46 }
  47
  48 declare_lint! {
  49     EXCEEDING_BITSHIFTS,
  50     Deny,
  51     "shift exceeds the type's number of bits"
  52 }
  53
  54 declare_lint! {
  55     VARIANT_SIZE_DIFFERENCES,
  56     Allow,
  57     "detects enums with widely varying variant sizes"
  58 }
  59
  60 #[derive(Copy, Clone)]
  61 pub struct TypeLimits {
  62     /// Id of the last visited negated expression
  63     negated_expr_id: ast::NodeId,
  64 }
  65
  66 impl TypeLimits {
  67     pub fn new() -> TypeLimits {
  68         TypeLimits { negated_expr_id: ast::DUMMY_NODE_ID }
  69     }
  70 }
  71
  72 impl LintPass for TypeLimits {
  73     fn get_lints(&self) -> LintArray {
  74         lint_array!(UNUSED_COMPARISONS,
  75                     OVERFLOWING_LITERALS,
  76                     EXCEEDING_BITSHIFTS)
  77     }
  78 }
  79
  80 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TypeLimits {
  81     fn check_expr(&mut self, cx: &LateContext, e: &hir::Expr) {
  82         match e.node {
  83             hir::ExprUnary(hir::UnNeg, ref expr) => {
  84                 // propagate negation, if the negation itself isn't negated
  85                 if self.negated_expr_id != e.id {
  86                     self.negated_expr_id = expr.id;
  87                 }
  88             }
  89             hir::ExprBinary(binop, ref l, ref r) => {
  90                 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
  91                     cx.span_lint(UNUSED_COMPARISONS,
  92                                  e.span,
  93                                  "comparison is useless due to type limits");
  94                 }
  95
  96                 if binop.node.is_shift() {
  97                     let opt_ty_bits = match cx.tables.node_id_to_type(l.id).sty {
  98                         ty::TyInt(t) => Some(int_ty_bits(t, cx.sess().target.int_type)),
  99                         ty::TyUint(t) => Some(uint_ty_bits(t, cx.sess().target.uint_type)),
 100                         _ => None,
 101                     };
 102
 103                     if let Some(bits) = opt_ty_bits {
 104                         let exceeding = if let hir::ExprLit(ref lit) = r.node {
 105                             if let ast::LitKind::Int(shift, _) = lit.node {
 106                                 shift as u64 >= bits
 107                             } else {
 108                                 false
 109                             }
 110                         } else {
 111                             let const_cx = ConstContext::with_tables(cx.tcx, cx.tables);
 112                             match const_cx.eval(&r, ExprTypeChecked) {
 113                                 Ok(ConstVal::Integral(i)) => {
 114                                     i.is_negative() ||
 115                                     i.to_u64()
 116                                         .map(|i| i >= bits)
 117                                         .unwrap_or(true)
 118                                 }
 119                                 _ => false,
 120                             }
 121                         };
 122                         if exceeding {
 123                             cx.span_lint(EXCEEDING_BITSHIFTS,
 124                                          e.span,
 125                                          "bitshift exceeds the type's number of bits");
 126                         }
 127                     };
 128                 }
 129             }
 130             hir::ExprLit(ref lit) => {
 131                 match cx.tables.node_id_to_type(e.id).sty {
 132                     ty::TyInt(t) => {
 133                         match lit.node {
 134                             ast::LitKind::Int(v, ast::LitIntType::Signed(_)) |
 135                             ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => {
 136                                 let int_type = if let ast::IntTy::Is = t {
 137                                     cx.sess().target.int_type
 138                                 } else {
 139                                     t
 140                                 };
 141                                 let (_, max) = int_ty_range(int_type);
 142                                 let max = max as u128;
 143                                 let negative = self.negated_expr_id == e.id;
 144
 145                                 // Detect literal value out of range [min, max] inclusive
 146                                 // avoiding use of -min to prevent overflow/panic
 147                                 if (negative && v > max + 1) ||
 148                                    (!negative && v > max) {
 149                                     cx.span_lint(OVERFLOWING_LITERALS,
 150                                                  e.span,
 151                                                  &format!("literal out of range for {:?}", t));
 152                                     return;
 153                                 }
 154                             }
 155                             _ => bug!(),
 156                         };
 157                     }
 158                     ty::TyUint(t) => {
 159                         let uint_type = if let ast::UintTy::Us = t {
 160                             cx.sess().target.uint_type
 161                         } else {
 162                             t
 163                         };
 164                         let (min, max) = uint_ty_range(uint_type);
 165                         let lit_val: u128 = match lit.node {
 166                             // _v is u8, within range by definition
 167                             ast::LitKind::Byte(_v) => return,
 168                             ast::LitKind::Int(v, _) => v,
 169                             _ => bug!(),
 170                         };
 171                         if lit_val < min || lit_val > max {
 172                             cx.span_lint(OVERFLOWING_LITERALS,
 173                                          e.span,
 174                                          &format!("literal out of range for {:?}", t));
 175                         }
 176                     }
 177                     ty::TyFloat(t) => {
 178                         let (min, max) = float_ty_range(t);
 179                         let lit_val: f64 = match lit.node {
 180                             ast::LitKind::Float(v, _) |
 181                             ast::LitKind::FloatUnsuffixed(v) => {
 182                                 match v.as_str().parse() {
 183                                     Ok(f) => f,
 184                                     Err(_) => return,
 185                                 }
 186                             }
 187                             _ => bug!(),
 188                         };
 189                         if lit_val < min || lit_val > max {
 190                             cx.span_lint(OVERFLOWING_LITERALS,
 191                                          e.span,
 192                                          &format!("literal out of range for {:?}", t));
 193                         }
 194                     }
 195                     _ => (),
 196                 };
 197             }
 198             _ => (),
 199         };
 200
 201         fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
 202             match binop.node {
 203                 hir::BiLt => v > min && v <= max,
 204                 hir::BiLe => v >= min && v < max,
 205                 hir::BiGt => v >= min && v < max,
 206                 hir::BiGe => v > min && v <= max,
 207                 hir::BiEq | hir::BiNe => v >= min && v <= max,
 208                 _ => bug!(),
 209             }
 210         }
 211
 212         fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
 213             codemap::respan(binop.span,
 214                             match binop.node {
 215                                 hir::BiLt => hir::BiGt,
 216                                 hir::BiLe => hir::BiGe,
 217                                 hir::BiGt => hir::BiLt,
 218                                 hir::BiGe => hir::BiLe,
 219                                 _ => return binop,
 220                             })
 221         }
 222
 223         // for isize & usize, be conservative with the warnings, so that the
 224         // warnings are consistent between 32- and 64-bit platforms
 225         fn int_ty_range(int_ty: ast::IntTy) -> (i128, i128) {
 226             match int_ty {
 227                 ast::IntTy::Is => (i64::min_value() as i128, i64::max_value() as i128),
 228                 ast::IntTy::I8 => (i8::min_value() as i64 as i128, i8::max_value() as i128),
 229                 ast::IntTy::I16 => (i16::min_value() as i64 as i128, i16::max_value() as i128),
 230                 ast::IntTy::I32 => (i32::min_value() as i64 as i128, i32::max_value() as i128),
 231                 ast::IntTy::I64 => (i64::min_value() as i128, i64::max_value() as i128),
 232                 ast::IntTy::I128 =>(i128::min_value() as i128, i128::max_value()),
 233             }
 234         }
 235
 236         fn uint_ty_range(uint_ty: ast::UintTy) -> (u128, u128) {
 237             match uint_ty {
 238                 ast::UintTy::Us => (u64::min_value() as u128, u64::max_value() as u128),
 239                 ast::UintTy::U8 => (u8::min_value() as u128, u8::max_value() as u128),
 240                 ast::UintTy::U16 => (u16::min_value() as u128, u16::max_value() as u128),
 241                 ast::UintTy::U32 => (u32::min_value() as u128, u32::max_value() as u128),
 242                 ast::UintTy::U64 => (u64::min_value() as u128, u64::max_value() as u128),
 243                 ast::UintTy::U128 => (u128::min_value(), u128::max_value()),
 244             }
 245         }
 246
 247         fn float_ty_range(float_ty: ast::FloatTy) -> (f64, f64) {
 248             match float_ty {
 249                 ast::FloatTy::F32 => (f32::MIN as f64, f32::MAX as f64),
 250                 ast::FloatTy::F64 => (f64::MIN, f64::MAX),
 251             }
 252         }
 253
 254         fn int_ty_bits(int_ty: ast::IntTy, target_int_ty: ast::IntTy) -> u64 {
 255             match int_ty {
 256                 ast::IntTy::Is => int_ty_bits(target_int_ty, target_int_ty),
 257                 ast::IntTy::I8 => 8,
 258                 ast::IntTy::I16 => 16 as u64,
 259                 ast::IntTy::I32 => 32,
 260                 ast::IntTy::I64 => 64,
 261                 ast::IntTy::I128 => 128,
 262             }
 263         }
 264
 265         fn uint_ty_bits(uint_ty: ast::UintTy, target_uint_ty: ast::UintTy) -> u64 {
 266             match uint_ty {
 267                 ast::UintTy::Us => uint_ty_bits(target_uint_ty, target_uint_ty),
 268                 ast::UintTy::U8 => 8,
 269                 ast::UintTy::U16 => 16,
 270                 ast::UintTy::U32 => 32,
 271                 ast::UintTy::U64 => 64,
 272                 ast::UintTy::U128 => 128,
 273             }
 274         }
 275
 276         fn check_limits(cx: &LateContext,
 277                         binop: hir::BinOp,
 278                         l: &hir::Expr,
 279                         r: &hir::Expr)
 280                         -> bool {
 281             let (lit, expr, swap) = match (&l.node, &r.node) {
 282                 (&hir::ExprLit(_), _) => (l, r, true),
 283                 (_, &hir::ExprLit(_)) => (r, l, false),
 284                 _ => return true,
 285             };
 286             // Normalize the binop so that the literal is always on the RHS in
 287             // the comparison
 288             let norm_binop = if swap { rev_binop(binop) } else { binop };
 289             match cx.tables.node_id_to_type(expr.id).sty {
 290                 ty::TyInt(int_ty) => {
 291                     let (min, max) = int_ty_range(int_ty);
 292                     let lit_val: i128 = match lit.node {
 293                         hir::ExprLit(ref li) => {
 294                             match li.node {
 295                                 ast::LitKind::Int(v, ast::LitIntType::Signed(_)) |
 296                                 ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => v as i128,
 297                                 _ => return true
 298                             }
 299                         },
 300                         _ => bug!()
 301                     };
 302                     is_valid(norm_binop, lit_val, min, max)
 303                 }
 304                 ty::TyUint(uint_ty) => {
 305                     let (min, max) :(u128, u128) = uint_ty_range(uint_ty);
 306                     let lit_val: u128 = match lit.node {
 307                         hir::ExprLit(ref li) => {
 308                             match li.node {
 309                                 ast::LitKind::Int(v, _) => v,
 310                                 _ => return true
 311                             }
 312                         },
 313                         _ => bug!()
 314                     };
 315                     is_valid(norm_binop, lit_val, min, max)
 316                 }
 317                 _ => true,
 318             }
 319         }
 320
 321         fn is_comparison(binop: hir::BinOp) -> bool {
 322             match binop.node {
 323                 hir::BiEq | hir::BiLt | hir::BiLe | hir::BiNe | hir::BiGe | hir::BiGt => true,
 324                 _ => false,
 325             }
 326         }
 327     }
 328 }
 329
 330 declare_lint! {
 331     IMPROPER_CTYPES,
 332     Warn,
 333     "proper use of libc types in foreign modules"
 334 }
 335
 336 struct ImproperCTypesVisitor<'a, 'tcx: 'a> {
 337     cx: &'a LateContext<'a, 'tcx>,
 338 }
 339
 340 enum FfiResult {
 341     FfiSafe,
 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 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
 384     /// Check if the given type is "ffi-safe" (has a stable, well-defined
 385     /// representation which can be exported to C code).
 386     fn check_type_for_ffi(&self, cache: &mut FxHashSet<Ty<'tcx>>, ty: Ty<'tcx>) -> FfiResult {
 387         use self::FfiResult::*;
 388         let cx = self.cx.tcx;
 389
 390         // Protect against infinite recursion, for example
 391         // `struct S(*mut S);`.
 392         // FIXME: A recursion limit is necessary as well, for irregular
 393         // recusive types.
 394         if !cache.insert(ty) {
 395             return FfiSafe;
 396         }
 397
 398         match ty.sty {
 399             ty::TyAdt(def, substs) => {
 400                 match def.adt_kind() {
 401                     AdtKind::Struct => {
 402                         if !cx.lookup_repr_hints(def.did).contains(&attr::ReprExtern) {
 403                             return FfiUnsafe("found struct without foreign-function-safe \
 404                                               representation annotation in foreign module, \
 405                                               consider adding a #[repr(C)] attribute to the type");
 406                         }
 407
 408                         // We can't completely trust repr(C) markings; make sure the
 409                         // fields are actually safe.
 410                         if def.struct_variant().fields.is_empty() {
 411                             return FfiUnsafe("found zero-size struct in foreign module, consider \
 412                                               adding a member to this struct");
 413                         }
 414
 415                         for field in &def.struct_variant().fields {
 416                             let field_ty = cx.normalize_associated_type(&field.ty(cx, substs));
 417                             let r = self.check_type_for_ffi(cache, field_ty);
 418                             match r {
 419                                 FfiSafe => {}
 420                                 FfiBadStruct(..) | FfiBadUnion(..) | FfiBadEnum(..) => {
 421                                     return r;
 422                                 }
 423                                 FfiUnsafe(s) => {
 424                                     return FfiBadStruct(def.did, s);
 425                                 }
 426                             }
 427                         }
 428                         FfiSafe
 429                     }
 430                     AdtKind::Union => {
 431                         if !cx.lookup_repr_hints(def.did).contains(&attr::ReprExtern) {
 432                             return FfiUnsafe("found union without foreign-function-safe \
 433                                               representation annotation in foreign module, \
 434                                               consider adding a #[repr(C)] attribute to the type");
 435                         }
 436
 437                         for field in &def.struct_variant().fields {
 438                             let field_ty = cx.normalize_associated_type(&field.ty(cx, substs));
 439                             let r = self.check_type_for_ffi(cache, field_ty);
 440                             match r {
 441                                 FfiSafe => {}
 442                                 FfiBadStruct(..) | FfiBadUnion(..) | FfiBadEnum(..) => {
 443                                     return r;
 444                                 }
 445                                 FfiUnsafe(s) => {
 446                                     return FfiBadUnion(def.did, s);
 447                                 }
 448                             }
 449                         }
 450                         FfiSafe
 451                     }
 452                     AdtKind::Enum => {
 453                         if def.variants.is_empty() {
 454                             // Empty enums are okay... although sort of useless.
 455                             return FfiSafe;
 456                         }
 457
 458                         // Check for a repr() attribute to specify the size of the
 459                         // discriminant.
 460                         let repr_hints = cx.lookup_repr_hints(def.did);
 461                         match &repr_hints[..] {
 462                             &[] => {
 463                                 // Special-case types like `Option<extern fn()>`.
 464                                 if !is_repr_nullable_ptr(cx, def, substs) {
 465                                     return FfiUnsafe("found enum without foreign-function-safe \
 466                                                       representation annotation in foreign \
 467                                                       module, consider adding a #[repr(...)] \
 468                                                       attribute to the type");
 469                                 }
 470                             }
 471                             &[ref hint] => {
 472                                 if !hint.is_ffi_safe() {
 473                                     // FIXME: This shouldn't be reachable: we should check
 474                                     // this earlier.
 475                                     return FfiUnsafe("enum has unexpected #[repr(...)] attribute");
 476                                 }
 477
 478                                 // Enum with an explicitly sized discriminant; either
 479                                 // a C-style enum or a discriminated union.
 480
 481                                 // The layout of enum variants is implicitly repr(C).
 482                                 // FIXME: Is that correct?
 483                             }
 484                             _ => {
 485                                 // FIXME: This shouldn't be reachable: we should check
 486                                 // this earlier.
 487                                 return FfiUnsafe("enum has too many #[repr(...)] attributes");
 488                             }
 489                         }
 490
 491                         // Check the contained variants.
 492                         for variant in &def.variants {
 493                             for field in &variant.fields {
 494                                 let arg = cx.normalize_associated_type(&field.ty(cx, substs));
 495                                 let r = self.check_type_for_ffi(cache, arg);
 496                                 match r {
 497                                     FfiSafe => {}
 498                                     FfiBadStruct(..) | FfiBadUnion(..) | FfiBadEnum(..) => {
 499                                         return r;
 500                                     }
 501                                     FfiUnsafe(s) => {
 502                                         return FfiBadEnum(def.did, s);
 503                                     }
 504                                 }
 505                             }
 506                         }
 507                         FfiSafe
 508                     }
 509                 }
 510             }
 511
 512             ty::TyChar => {
 513                 FfiUnsafe("found Rust type `char` in foreign module, while \
 514                            `u32` or `libc::wchar_t` should be used")
 515             }
 516
 517             // Primitive types with a stable representation.
 518             ty::TyBool | ty::TyInt(..) | ty::TyUint(..) | ty::TyFloat(..) | ty::TyNever => FfiSafe,
 519
 520             ty::TySlice(_) => {
 521                 FfiUnsafe("found Rust slice type in foreign module, \
 522                            consider using a raw pointer instead")
 523             }
 524
 525             ty::TyDynamic(..) => {
 526                 FfiUnsafe("found Rust trait type in foreign module, \
 527                            consider using a raw pointer instead")
 528             }
 529
 530             ty::TyStr => {
 531                 FfiUnsafe("found Rust type `str` in foreign module; \
 532                            consider using a `*const libc::c_char`")
 533             }
 534
 535             ty::TyTuple(..) => {
 536                 FfiUnsafe("found Rust tuple type in foreign module; \
 537                            consider using a struct instead")
 538             }
 539
 540             ty::TyRawPtr(ref m) |
 541             ty::TyRef(_, ref m) => self.check_type_for_ffi(cache, m.ty),
 542
 543             ty::TyArray(ty, _) => self.check_type_for_ffi(cache, ty),
 544
 545             ty::TyFnPtr(bare_fn) => {
 546                 match bare_fn.abi {
 547                     Abi::Rust | Abi::RustIntrinsic | Abi::PlatformIntrinsic | Abi::RustCall => {
 548                         return FfiUnsafe("found function pointer with Rust calling convention in \
 549                                           foreign module; consider using an `extern` function \
 550                                           pointer")
 551                     }
 552                     _ => {}
 553                 }
 554
 555                 let sig = cx.erase_late_bound_regions(&bare_fn.sig);
 556                 if !sig.output().is_nil() {
 557                     let r = self.check_type_for_ffi(cache, sig.output());
 558                     match r {
 559                         FfiSafe => {}
 560                         _ => {
 561                             return r;
 562                         }
 563                     }
 564                 }
 565                 for arg in sig.inputs() {
 566                     let r = self.check_type_for_ffi(cache, arg);
 567                     match r {
 568                         FfiSafe => {}
 569                         _ => {
 570                             return r;
 571                         }
 572                     }
 573                 }
 574                 FfiSafe
 575             }
 576
 577             ty::TyParam(..) |
 578             ty::TyInfer(..) |
 579             ty::TyError |
 580             ty::TyClosure(..) |
 581             ty::TyProjection(..) |
 582             ty::TyAnon(..) |
 583             ty::TyFnDef(..) => bug!("Unexpected type in foreign function"),
 584         }
 585     }
 586
 587     fn check_type_for_ffi_and_report_errors(&mut self, sp: Span, ty: Ty<'tcx>) {
 588         // it is only OK to use this function because extern fns cannot have
 589         // any generic types right now:
 590         let ty = self.cx.tcx.normalize_associated_type(&ty);
 591
 592         match self.check_type_for_ffi(&mut FxHashSet(), ty) {
 593             FfiResult::FfiSafe => {}
 594             FfiResult::FfiUnsafe(s) => {
 595                 self.cx.span_lint(IMPROPER_CTYPES, sp, s);
 596             }
 597             FfiResult::FfiBadStruct(_, s) => {
 598                 // FIXME: This diagnostic is difficult to read, and doesn't
 599                 // point at the relevant field.
 600                 self.cx.span_lint(IMPROPER_CTYPES,
 601                                   sp,
 602                                   &format!("found non-foreign-function-safe member in struct \
 603                                             marked #[repr(C)]: {}",
 604                                            s));
 605             }
 606             FfiResult::FfiBadUnion(_, s) => {
 607                 // FIXME: This diagnostic is difficult to read, and doesn't
 608                 // point at the relevant field.
 609                 self.cx.span_lint(IMPROPER_CTYPES,
 610                                   sp,
 611                                   &format!("found non-foreign-function-safe member in union \
 612                                             marked #[repr(C)]: {}",
 613                                            s));
 614             }
 615             FfiResult::FfiBadEnum(_, s) => {
 616                 // FIXME: This diagnostic is difficult to read, and doesn't
 617                 // point at the relevant variant.
 618                 self.cx.span_lint(IMPROPER_CTYPES,
 619                                   sp,
 620                                   &format!("found non-foreign-function-safe member in enum: {}",
 621                                            s));
 622             }
 623         }
 624     }
 625
 626     fn check_foreign_fn(&mut self, id: ast::NodeId, decl: &hir::FnDecl) {
 627         let def_id = self.cx.tcx.hir.local_def_id(id);
 628         let sig = self.cx.tcx.item_type(def_id).fn_sig();
 629         let sig = self.cx.tcx.erase_late_bound_regions(&sig);
 630
 631         for (input_ty, input_hir) in sig.inputs().iter().zip(&decl.inputs) {
 632             self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty);
 633         }
 634
 635         if let hir::Return(ref ret_hir) = decl.output {
 636             let ret_ty = sig.output();
 637             if !ret_ty.is_nil() {
 638                 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty);
 639             }
 640         }
 641     }
 642
 643     fn check_foreign_static(&mut self, id: ast::NodeId, span: Span) {
 644         let def_id = self.cx.tcx.hir.local_def_id(id);
 645         let ty = self.cx.tcx.item_type(def_id);
 646         self.check_type_for_ffi_and_report_errors(span, ty);
 647     }
 648 }
 649
 650 #[derive(Copy, Clone)]
 651 pub struct ImproperCTypes;
 652
 653 impl LintPass for ImproperCTypes {
 654     fn get_lints(&self) -> LintArray {
 655         lint_array!(IMPROPER_CTYPES)
 656     }
 657 }
 658
 659 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImproperCTypes {
 660     fn check_item(&mut self, cx: &LateContext, it: &hir::Item) {
 661         let mut vis = ImproperCTypesVisitor { cx: cx };
 662         if let hir::ItemForeignMod(ref nmod) = it.node {
 663             if nmod.abi != Abi::RustIntrinsic && nmod.abi != Abi::PlatformIntrinsic {
 664                 for ni in &nmod.items {
 665                     match ni.node {
 666                         hir::ForeignItemFn(ref decl, _, _) => {
 667                             vis.check_foreign_fn(ni.id, decl);
 668                         }
 669                         hir::ForeignItemStatic(ref ty, _) => {
 670                             vis.check_foreign_static(ni.id, ty.span);
 671                         }
 672                     }
 673                 }
 674             }
 675         }
 676     }
 677 }
 678
 679 pub struct VariantSizeDifferences;
 680
 681 impl LintPass for VariantSizeDifferences {
 682     fn get_lints(&self) -> LintArray {
 683         lint_array!(VARIANT_SIZE_DIFFERENCES)
 684     }
 685 }
 686
 687 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for VariantSizeDifferences {
 688     fn check_item(&mut self, cx: &LateContext, it: &hir::Item) {
 689         if let hir::ItemEnum(ref enum_definition, ref gens) = it.node {
 690             if gens.ty_params.is_empty() {
 691                 // sizes only make sense for non-generic types
 692                 let t = cx.tcx.item_type(cx.tcx.hir.local_def_id(it.id));
 693                 let layout = cx.tcx.infer_ctxt((), Reveal::All).enter(|infcx| {
 694                     let ty = cx.tcx.erase_regions(&t);
 695                     ty.layout(&infcx).unwrap_or_else(|e| {
 696                         bug!("failed to get layout for `{}`: {}", t, e)
 697                     })
 698                 });
 699
 700                 if let Layout::General { ref variants, ref size, discr, .. } = *layout {
 701                     let discr_size = Primitive::Int(discr).size(&cx.tcx.data_layout).bytes();
 702
 703                     debug!("enum `{}` is {} bytes large with layout:\n{:#?}",
 704                       t, size.bytes(), layout);
 705
 706                     let (largest, slargest, largest_index) = enum_definition.variants
 707                         .iter()
 708                         .zip(variants)
 709                         .map(|(variant, variant_layout)| {
 710                             // Subtract the size of the enum discriminant
 711                             let bytes = variant_layout.min_size
 712                                 .bytes()
 713                                 .saturating_sub(discr_size);
 714
 715                             debug!("- variant `{}` is {} bytes large", variant.node.name, bytes);
 716                             bytes
 717                         })
 718                         .enumerate()
 719                         .fold((0, 0, 0), |(l, s, li), (idx, size)| if size > l {
 720                             (size, l, idx)
 721                         } else if size > s {
 722                             (l, size, li)
 723                         } else {
 724                             (l, s, li)
 725                         });
 726
 727                     // we only warn if the largest variant is at least thrice as large as
 728                     // the second-largest.
 729                     if largest > slargest * 3 && slargest > 0 {
 730                         cx.span_lint(VARIANT_SIZE_DIFFERENCES,
 731                                      enum_definition.variants[largest_index].span,
 732                                      &format!("enum variant is more than three times larger \
 733                                                ({} bytes) than the next largest",
 734                                               largest));
 735                     }
 736                 }
 737             }
 738         }
 739     }
 740 }