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