src/librustc_lint/types.rs

   1 #![allow(non_snake_case)]
   2
   3 use rustc::hir::{ExprKind, Node};
   4 use rustc::hir::lowering::is_range_literal;
   5 use rustc::ty::subst::SubstsRef;
   6 use rustc::ty::{self, AdtKind, ParamEnv, Ty, TyCtxt};
   7 use rustc::ty::layout::{self, IntegerExt, LayoutOf, VariantIdx};
   8 use rustc::{lint, util};
   9 use rustc_data_structures::indexed_vec::Idx;
  10 use util::nodemap::FxHashSet;
  11 use lint::{LateContext, LintContext, LintArray};
  12 use lint::{LintPass, LateLintPass};
  13
  14 use std::cmp;
  15 use std::{i8, i16, i32, i64, u8, u16, u32, u64, f32, f64};
  16
  17 use syntax::{ast, attr};
  18 use syntax::errors::Applicability;
  19 use rustc_target::spec::abi::Abi;
  20 use syntax_pos::Span;
  21 use syntax::source_map;
  22
  23 use rustc::hir;
  24
  25 use rustc::mir::interpret::{sign_extend, truncate};
  26
  27 use log::debug;
  28
  29 declare_lint! {
  30     UNUSED_COMPARISONS,
  31     Warn,
  32     "comparisons made useless by limits of the types involved"
  33 }
  34
  35 declare_lint! {
  36     OVERFLOWING_LITERALS,
  37     Deny,
  38     "literal out of range for its type"
  39 }
  40
  41 declare_lint! {
  42     VARIANT_SIZE_DIFFERENCES,
  43     Allow,
  44     "detects enums with widely varying variant sizes"
  45 }
  46
  47 #[derive(Copy, Clone)]
  48 pub struct TypeLimits {
  49     /// Id of the last visited negated expression
  50     negated_expr_id: hir::HirId,
  51 }
  52
  53 impl_lint_pass!(TypeLimits => [UNUSED_COMPARISONS, OVERFLOWING_LITERALS]);
  54
  55 impl TypeLimits {
  56     pub fn new() -> TypeLimits {
  57         TypeLimits { negated_expr_id: hir::DUMMY_HIR_ID }
  58     }
  59 }
  60
  61 /// Attempts to special-case the overflowing literal lint when it occurs as a range endpoint.
  62 /// Returns `true` iff the lint was overridden.
  63 fn lint_overflowing_range_endpoint<'a, 'tcx>(
  64     cx: &LateContext<'a, 'tcx>,
  65     lit: &ast::Lit,
  66     lit_val: u128,
  67     max: u128,
  68     expr: &'tcx hir::Expr,
  69     parent_expr: &'tcx hir::Expr,
  70     ty: impl std::fmt::Debug,
  71 ) -> bool {
  72     // We only want to handle exclusive (`..`) ranges,
  73     // which are represented as `ExprKind::Struct`.
  74     if let ExprKind::Struct(_, eps, _) = &parent_expr.node {
  75         debug_assert_eq!(eps.len(), 2);
  76         // We can suggest using an inclusive range
  77         // (`..=`) instead only if it is the `end` that is
  78         // overflowing and only by 1.
  79         if eps[1].expr.hir_id == expr.hir_id && lit_val - 1 == max {
  80             let mut err = cx.struct_span_lint(
  81                 OVERFLOWING_LITERALS,
  82                 parent_expr.span,
  83                 &format!("range endpoint is out of range for `{:?}`", ty),
  84             );
  85             if let Ok(start) = cx.sess().source_map().span_to_snippet(eps[0].span) {
  86                 use ast::{LitKind, LitIntType};
  87                 // We need to preserve the literal's suffix,
  88                 // as it may determine typing information.
  89                 let suffix = match lit.node {
  90                     LitKind::Int(_, LitIntType::Signed(s)) => format!("{}", s),
  91                     LitKind::Int(_, LitIntType::Unsigned(s)) => format!("{}", s),
  92                     LitKind::Int(_, LitIntType::Unsuffixed) => "".to_owned(),
  93                     _ => bug!(),
  94                 };
  95                 let suggestion = format!("{}..={}{}", start, lit_val - 1, suffix);
  96                 err.span_suggestion(
  97                     parent_expr.span,
  98                     &"use an inclusive range instead",
  99                     suggestion,
 100                     Applicability::MachineApplicable,
 101                 );
 102                 err.emit();
 103                 return true;
 104             }
 105         }
 106     }
 107
 108     false
 109 }
 110
 111 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TypeLimits {
 112     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx hir::Expr) {
 113         match e.node {
 114             hir::ExprKind::Unary(hir::UnNeg, ref expr) => {
 115                 // propagate negation, if the negation itself isn't negated
 116                 if self.negated_expr_id != e.hir_id {
 117                     self.negated_expr_id = expr.hir_id;
 118                 }
 119             }
 120             hir::ExprKind::Binary(binop, ref l, ref r) => {
 121                 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
 122                     cx.span_lint(UNUSED_COMPARISONS,
 123                                  e.span,
 124                                  "comparison is useless due to type limits");
 125                 }
 126             }
 127             hir::ExprKind::Lit(ref lit) => {
 128                 match cx.tables.node_type(e.hir_id).sty {
 129                     ty::Int(t) => {
 130                         match lit.node {
 131                             ast::LitKind::Int(v, ast::LitIntType::Signed(_)) |
 132                             ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => {
 133                                 let int_type = if let ast::IntTy::Isize = t {
 134                                     cx.sess().target.isize_ty
 135                                 } else {
 136                                     t
 137                                 };
 138                                 let (_, max) = int_ty_range(int_type);
 139                                 let max = max as u128;
 140                                 let negative = self.negated_expr_id == e.hir_id;
 141
 142                                 // Detect literal value out of range [min, max] inclusive
 143                                 // avoiding use of -min to prevent overflow/panic
 144                                 if (negative && v > max + 1) || (!negative && v > max) {
 145                                     if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 146                                         report_bin_hex_error(
 147                                             cx,
 148                                             e,
 149                                             attr::IntType::SignedInt(t),
 150                                             repr_str,
 151                                             v,
 152                                             negative,
 153                                         );
 154                                         return;
 155                                     }
 156
 157                                     let par_id = cx.tcx.hir().get_parent_node_by_hir_id(e.hir_id);
 158                                     if let Node::Expr(par_e) = cx.tcx.hir().get_by_hir_id(par_id) {
 159                                         if let hir::ExprKind::Struct(..) = par_e.node {
 160                                             if is_range_literal(cx.sess(), par_e)
 161                                                 && lint_overflowing_range_endpoint(
 162                                                     cx,
 163                                                     lit,
 164                                                     v,
 165                                                     max,
 166                                                     e,
 167                                                     par_e,
 168                                                     t,
 169                                                 )
 170                                             {
 171                                                     // The overflowing literal lint was overridden.
 172                                                     return;
 173                                             }
 174                                         }
 175                                     }
 176
 177                                     cx.span_lint(
 178                                         OVERFLOWING_LITERALS,
 179                                         e.span,
 180                                         &format!("literal out of range for `{:?}`", t),
 181                                     );
 182                                     return;
 183                                 }
 184                             }
 185                             _ => bug!(),
 186                         };
 187                     }
 188                     ty::Uint(t) => {
 189                         let uint_type = if let ast::UintTy::Usize = t {
 190                             cx.sess().target.usize_ty
 191                         } else {
 192                             t
 193                         };
 194                         let (min, max) = uint_ty_range(uint_type);
 195                         let lit_val: u128 = match lit.node {
 196                             // _v is u8, within range by definition
 197                             ast::LitKind::Byte(_v) => return,
 198                             ast::LitKind::Int(v, _) => v,
 199                             _ => bug!(),
 200                         };
 201                         if lit_val < min || lit_val > max {
 202                             let parent_id = cx.tcx.hir().get_parent_node_by_hir_id(e.hir_id);
 203                             if let Node::Expr(parent_expr) = cx.tcx.hir().get_by_hir_id(parent_id) {
 204                                 match parent_expr.node {
 205                                     hir::ExprKind::Cast(..) => {
 206                                         if let ty::Char = cx.tables.expr_ty(parent_expr).sty {
 207                                             let mut err = cx.struct_span_lint(
 208                                                 OVERFLOWING_LITERALS,
 209                                                 parent_expr.span,
 210                                                 "only `u8` can be cast into `char`",
 211                                             );
 212                                             err.span_suggestion(
 213                                                 parent_expr.span,
 214                                                 &"use a `char` literal instead",
 215                                                 format!("'\\u{{{:X}}}'", lit_val),
 216                                                 Applicability::MachineApplicable,
 217                                             );
 218                                             err.emit();
 219                                             return;
 220                                         }
 221                                     }
 222                                     hir::ExprKind::Struct(..)
 223                                         if is_range_literal(cx.sess(), parent_expr) => {
 224                                             if lint_overflowing_range_endpoint(
 225                                                 cx,
 226                                                 lit,
 227                                                 lit_val,
 228                                                 max,
 229                                                 e,
 230                                                 parent_expr,
 231                                                 t,
 232                                             ) {
 233                                                 // The overflowing literal lint was overridden.
 234                                                 return;
 235                                             }
 236                                         }
 237                                     _ => {}
 238                                 }
 239                             }
 240                             if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 241                                 report_bin_hex_error(
 242                                     cx,
 243                                     e,
 244                                     attr::IntType::UnsignedInt(t),
 245                                     repr_str,
 246                                     lit_val,
 247                                     false,
 248                                 );
 249                                 return;
 250                             }
 251                             cx.span_lint(
 252                                 OVERFLOWING_LITERALS,
 253                                 e.span,
 254                                 &format!("literal out of range for `{:?}`", t),
 255                             );
 256                         }
 257                     }
 258                     ty::Float(t) => {
 259                         let is_infinite = match lit.node {
 260                             ast::LitKind::Float(v, _) |
 261                             ast::LitKind::FloatUnsuffixed(v) => {
 262                                 match t {
 263                                     ast::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
 264                                     ast::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
 265                                 }
 266                             }
 267                             _ => bug!(),
 268                         };
 269                         if is_infinite == Ok(true) {
 270                             cx.span_lint(OVERFLOWING_LITERALS,
 271                                          e.span,
 272                                          &format!("literal out of range for `{:?}`", t));
 273                         }
 274                     }
 275                     _ => (),
 276                 };
 277             }
 278             _ => (),
 279         };
 280
 281         fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
 282             match binop.node {
 283                 hir::BinOpKind::Lt => v > min && v <= max,
 284                 hir::BinOpKind::Le => v >= min && v < max,
 285                 hir::BinOpKind::Gt => v >= min && v < max,
 286                 hir::BinOpKind::Ge => v > min && v <= max,
 287                 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
 288                 _ => bug!(),
 289             }
 290         }
 291
 292         fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
 293             source_map::respan(binop.span,
 294                             match binop.node {
 295                                 hir::BinOpKind::Lt => hir::BinOpKind::Gt,
 296                                 hir::BinOpKind::Le => hir::BinOpKind::Ge,
 297                                 hir::BinOpKind::Gt => hir::BinOpKind::Lt,
 298                                 hir::BinOpKind::Ge => hir::BinOpKind::Le,
 299                                 _ => return binop,
 300                             })
 301         }
 302
 303         // for isize & usize, be conservative with the warnings, so that the
 304         // warnings are consistent between 32- and 64-bit platforms
 305         fn int_ty_range(int_ty: ast::IntTy) -> (i128, i128) {
 306             match int_ty {
 307                 ast::IntTy::Isize => (i64::min_value() as i128, i64::max_value() as i128),
 308                 ast::IntTy::I8 => (i8::min_value() as i64 as i128, i8::max_value() as i128),
 309                 ast::IntTy::I16 => (i16::min_value() as i64 as i128, i16::max_value() as i128),
 310                 ast::IntTy::I32 => (i32::min_value() as i64 as i128, i32::max_value() as i128),
 311                 ast::IntTy::I64 => (i64::min_value() as i128, i64::max_value() as i128),
 312                 ast::IntTy::I128 =>(i128::min_value() as i128, i128::max_value()),
 313             }
 314         }
 315
 316         fn uint_ty_range(uint_ty: ast::UintTy) -> (u128, u128) {
 317             match uint_ty {
 318                 ast::UintTy::Usize => (u64::min_value() as u128, u64::max_value() as u128),
 319                 ast::UintTy::U8 => (u8::min_value() as u128, u8::max_value() as u128),
 320                 ast::UintTy::U16 => (u16::min_value() as u128, u16::max_value() as u128),
 321                 ast::UintTy::U32 => (u32::min_value() as u128, u32::max_value() as u128),
 322                 ast::UintTy::U64 => (u64::min_value() as u128, u64::max_value() as u128),
 323                 ast::UintTy::U128 => (u128::min_value(), u128::max_value()),
 324             }
 325         }
 326
 327         fn check_limits(cx: &LateContext<'_, '_>,
 328                         binop: hir::BinOp,
 329                         l: &hir::Expr,
 330                         r: &hir::Expr)
 331                         -> bool {
 332             let (lit, expr, swap) = match (&l.node, &r.node) {
 333                 (&hir::ExprKind::Lit(_), _) => (l, r, true),
 334                 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
 335                 _ => return true,
 336             };
 337             // Normalize the binop so that the literal is always on the RHS in
 338             // the comparison
 339             let norm_binop = if swap { rev_binop(binop) } else { binop };
 340             match cx.tables.node_type(expr.hir_id).sty {
 341                 ty::Int(int_ty) => {
 342                     let (min, max) = int_ty_range(int_ty);
 343                     let lit_val: i128 = match lit.node {
 344                         hir::ExprKind::Lit(ref li) => {
 345                             match li.node {
 346                                 ast::LitKind::Int(v, ast::LitIntType::Signed(_)) |
 347                                 ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => v as i128,
 348                                 _ => return true
 349                             }
 350                         },
 351                         _ => bug!()
 352                     };
 353                     is_valid(norm_binop, lit_val, min, max)
 354                 }
 355                 ty::Uint(uint_ty) => {
 356                     let (min, max) :(u128, u128) = uint_ty_range(uint_ty);
 357                     let lit_val: u128 = match lit.node {
 358                         hir::ExprKind::Lit(ref li) => {
 359                             match li.node {
 360                                 ast::LitKind::Int(v, _) => v,
 361                                 _ => return true
 362                             }
 363                         },
 364                         _ => bug!()
 365                     };
 366                     is_valid(norm_binop, lit_val, min, max)
 367                 }
 368                 _ => true,
 369             }
 370         }
 371
 372         fn is_comparison(binop: hir::BinOp) -> bool {
 373             match binop.node {
 374                 hir::BinOpKind::Eq |
 375                 hir::BinOpKind::Lt |
 376                 hir::BinOpKind::Le |
 377                 hir::BinOpKind::Ne |
 378                 hir::BinOpKind::Ge |
 379                 hir::BinOpKind::Gt => true,
 380                 _ => false,
 381             }
 382         }
 383
 384         fn get_bin_hex_repr(cx: &LateContext<'_, '_>, lit: &ast::Lit) -> Option<String> {
 385             let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?;
 386             let firstch = src.chars().next()?;
 387
 388             if firstch == '0' {
 389                 match src.chars().nth(1) {
 390                     Some('x') | Some('b') => return Some(src),
 391                     _ => return None,
 392                 }
 393             }
 394
 395             None
 396         }
 397
 398         // This function finds the next fitting type and generates a suggestion string.
 399         // It searches for fitting types in the following way (`X < Y`):
 400         //  - `iX`: if literal fits in `uX` => `uX`, else => `iY`
 401         //  - `-iX` => `iY`
 402         //  - `uX` => `uY`
 403         //
 404         // No suggestion for: `isize`, `usize`.
 405         fn get_type_suggestion<'a>(
 406             t: Ty<'_>,
 407             val: u128,
 408             negative: bool,
 409         ) -> Option<String> {
 410             use syntax::ast::IntTy::*;
 411             use syntax::ast::UintTy::*;
 412             macro_rules! find_fit {
 413                 ($ty:expr, $val:expr, $negative:expr,
 414                  $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => {
 415                     {
 416                         let _neg = if negative { 1 } else { 0 };
 417                         match $ty {
 418                             $($type => {
 419                                 $(if !negative && val <= uint_ty_range($utypes).1 {
 420                                     return Some(format!("{:?}", $utypes))
 421                                 })*
 422                                 $(if val <= int_ty_range($itypes).1 as u128 + _neg {
 423                                     return Some(format!("{:?}", $itypes))
 424                                 })*
 425                                 None
 426                             },)*
 427                             _ => None
 428                         }
 429                     }
 430                 }
 431             }
 432             match t.sty {
 433                 ty::Int(i) => find_fit!(i, val, negative,
 434                               I8 => [U8] => [I16, I32, I64, I128],
 435                               I16 => [U16] => [I32, I64, I128],
 436                               I32 => [U32] => [I64, I128],
 437                               I64 => [U64] => [I128],
 438                               I128 => [U128] => []),
 439                 ty::Uint(u) => find_fit!(u, val, negative,
 440                               U8 => [U8, U16, U32, U64, U128] => [],
 441                               U16 => [U16, U32, U64, U128] => [],
 442                               U32 => [U32, U64, U128] => [],
 443                               U64 => [U64, U128] => [],
 444                               U128 => [U128] => []),
 445                 _ => None,
 446             }
 447         }
 448
 449         fn report_bin_hex_error(
 450             cx: &LateContext<'_, '_>,
 451             expr: &hir::Expr,
 452             ty: attr::IntType,
 453             repr_str: String,
 454             val: u128,
 455             negative: bool,
 456         ) {
 457             let size = layout::Integer::from_attr(&cx.tcx, ty).size();
 458             let (t, actually) = match ty {
 459                 attr::IntType::SignedInt(t) => {
 460                     let actually = sign_extend(val, size) as i128;
 461                     (format!("{:?}", t), actually.to_string())
 462                 }
 463                 attr::IntType::UnsignedInt(t) => {
 464                     let actually = truncate(val, size);
 465                     (format!("{:?}", t), actually.to_string())
 466                 }
 467             };
 468             let mut err = cx.struct_span_lint(
 469                 OVERFLOWING_LITERALS,
 470                 expr.span,
 471                 &format!("literal out of range for {}", t),
 472             );
 473             err.note(&format!(
 474                 "the literal `{}` (decimal `{}`) does not fit into \
 475                  an `{}` and will become `{}{}`",
 476                 repr_str, val, t, actually, t
 477             ));
 478             if let Some(sugg_ty) =
 479                 get_type_suggestion(&cx.tables.node_type(expr.hir_id), val, negative)
 480             {
 481                 if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') {
 482                     let (sans_suffix, _) = repr_str.split_at(pos);
 483                     err.span_suggestion(
 484                         expr.span,
 485                         &format!("consider using `{}` instead", sugg_ty),
 486                         format!("{}{}", sans_suffix, sugg_ty),
 487                         Applicability::MachineApplicable
 488                     );
 489                 } else {
 490                     err.help(&format!("consider using `{}` instead", sugg_ty));
 491                 }
 492             }
 493
 494             err.emit();
 495         }
 496     }
 497 }
 498
 499 declare_lint! {
 500     IMPROPER_CTYPES,
 501     Warn,
 502     "proper use of libc types in foreign modules"
 503 }
 504
 505 declare_lint_pass!(ImproperCTypes => [IMPROPER_CTYPES]);
 506
 507 struct ImproperCTypesVisitor<'a, 'tcx: 'a> {
 508     cx: &'a LateContext<'a, 'tcx>,
 509 }
 510
 511 enum FfiResult<'tcx> {
 512     FfiSafe,
 513     FfiPhantom(Ty<'tcx>),
 514     FfiUnsafe {
 515         ty: Ty<'tcx>,
 516         reason: &'static str,
 517         help: Option<&'static str>,
 518     },
 519 }
 520
 521 /// Check if this enum can be safely exported based on the
 522 /// "nullable pointer optimization". Currently restricted
 523 /// to function pointers and references, but could be
 524 /// expanded to cover NonZero raw pointers and newtypes.
 525 /// FIXME: This duplicates code in codegen.
 526 fn is_repr_nullable_ptr<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 527                                   def: &'tcx ty::AdtDef,
 528                                   substs: SubstsRef<'tcx>)
 529                                   -> bool {
 530     if def.variants.len() == 2 {
 531         let data_idx;
 532
 533         let zero = VariantIdx::new(0);
 534         let one = VariantIdx::new(1);
 535
 536         if def.variants[zero].fields.is_empty() {
 537             data_idx = one;
 538         } else if def.variants[one].fields.is_empty() {
 539             data_idx = zero;
 540         } else {
 541             return false;
 542         }
 543
 544         if def.variants[data_idx].fields.len() == 1 {
 545             match def.variants[data_idx].fields[0].ty(tcx, substs).sty {
 546                 ty::FnPtr(_) => {
 547                     return true;
 548                 }
 549                 ty::Ref(..) => {
 550                     return true;
 551                 }
 552                 _ => {}
 553             }
 554         }
 555     }
 556     false
 557 }
 558
 559 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
 560     /// Checks if the given type is "ffi-safe" (has a stable, well-defined
 561     /// representation which can be exported to C code).
 562     fn check_type_for_ffi(&self,
 563                           cache: &mut FxHashSet<Ty<'tcx>>,
 564                           ty: Ty<'tcx>) -> FfiResult<'tcx> {
 565         use FfiResult::*;
 566
 567         let cx = self.cx.tcx;
 568
 569         // Protect against infinite recursion, for example
 570         // `struct S(*mut S);`.
 571         // FIXME: A recursion limit is necessary as well, for irregular
 572         // recursive types.
 573         if !cache.insert(ty) {
 574             return FfiSafe;
 575         }
 576
 577         match ty.sty {
 578             ty::Adt(def, substs) => {
 579                 if def.is_phantom_data() {
 580                     return FfiPhantom(ty);
 581                 }
 582                 match def.adt_kind() {
 583                     AdtKind::Struct => {
 584                         if !def.repr.c() && !def.repr.transparent() {
 585                             return FfiUnsafe {
 586                                 ty: ty,
 587                                 reason: "this struct has unspecified layout",
 588                                 help: Some("consider adding a #[repr(C)] or #[repr(transparent)] \
 589                                             attribute to this struct"),
 590                             };
 591                         }
 592
 593                         if def.non_enum_variant().fields.is_empty() {
 594                             return FfiUnsafe {
 595                                 ty: ty,
 596                                 reason: "this struct has no fields",
 597                                 help: Some("consider adding a member to this struct"),
 598                             };
 599                         }
 600
 601                         // We can't completely trust repr(C) and repr(transparent) markings;
 602                         // make sure the fields are actually safe.
 603                         let mut all_phantom = true;
 604                         for field in &def.non_enum_variant().fields {
 605                             let field_ty = cx.normalize_erasing_regions(
 606                                 ParamEnv::reveal_all(),
 607                                 field.ty(cx, substs),
 608                             );
 609                             // repr(transparent) types are allowed to have arbitrary ZSTs, not just
 610                             // PhantomData -- skip checking all ZST fields
 611                             if def.repr.transparent() {
 612                                 let is_zst = cx
 613                                     .layout_of(cx.param_env(field.did).and(field_ty))
 614                                     .map(|layout| layout.is_zst())
 615                                     .unwrap_or(false);
 616                                 if is_zst {
 617                                     continue;
 618                                 }
 619                             }
 620                             let r = self.check_type_for_ffi(cache, field_ty);
 621                             match r {
 622                                 FfiSafe => {
 623                                     all_phantom = false;
 624                                 }
 625                                 FfiPhantom(..) => {}
 626                                 FfiUnsafe { .. } => {
 627                                     return r;
 628                                 }
 629                             }
 630                         }
 631
 632                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 633                     }
 634                     AdtKind::Union => {
 635                         if !def.repr.c() {
 636                             return FfiUnsafe {
 637                                 ty: ty,
 638                                 reason: "this union has unspecified layout",
 639                                 help: Some("consider adding a #[repr(C)] attribute to this union"),
 640                             };
 641                         }
 642
 643                         if def.non_enum_variant().fields.is_empty() {
 644                             return FfiUnsafe {
 645                                 ty: ty,
 646                                 reason: "this union has no fields",
 647                                 help: Some("consider adding a field to this union"),
 648                             };
 649                         }
 650
 651                         let mut all_phantom = true;
 652                         for field in &def.non_enum_variant().fields {
 653                             let field_ty = cx.normalize_erasing_regions(
 654                                 ParamEnv::reveal_all(),
 655                                 field.ty(cx, substs),
 656                             );
 657                             let r = self.check_type_for_ffi(cache, field_ty);
 658                             match r {
 659                                 FfiSafe => {
 660                                     all_phantom = false;
 661                                 }
 662                                 FfiPhantom(..) => {}
 663                                 FfiUnsafe { .. } => {
 664                                     return r;
 665                                 }
 666                             }
 667                         }
 668
 669                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 670                     }
 671                     AdtKind::Enum => {
 672                         if def.variants.is_empty() {
 673                             // Empty enums are okay... although sort of useless.
 674                             return FfiSafe;
 675                         }
 676
 677                         // Check for a repr() attribute to specify the size of the
 678                         // discriminant.
 679                         if !def.repr.c() && def.repr.int.is_none() {
 680                             // Special-case types like `Option<extern fn()>`.
 681                             if !is_repr_nullable_ptr(cx, def, substs) {
 682                                 return FfiUnsafe {
 683                                     ty: ty,
 684                                     reason: "enum has no representation hint",
 685                                     help: Some("consider adding a #[repr(...)] attribute \
 686                                                 to this enum"),
 687                                 };
 688                             }
 689                         }
 690
 691                         // Check the contained variants.
 692                         for variant in &def.variants {
 693                             for field in &variant.fields {
 694                                 let arg = cx.normalize_erasing_regions(
 695                                     ParamEnv::reveal_all(),
 696                                     field.ty(cx, substs),
 697                                 );
 698                                 let r = self.check_type_for_ffi(cache, arg);
 699                                 match r {
 700                                     FfiSafe => {}
 701                                     FfiUnsafe { .. } => {
 702                                         return r;
 703                                     }
 704                                     FfiPhantom(..) => {
 705                                         return FfiUnsafe {
 706                                             ty: ty,
 707                                             reason: "this enum contains a PhantomData field",
 708                                             help: None,
 709                                         };
 710                                     }
 711                                 }
 712                             }
 713                         }
 714                         FfiSafe
 715                     }
 716                 }
 717             }
 718
 719             ty::Char => FfiUnsafe {
 720                 ty: ty,
 721                 reason: "the `char` type has no C equivalent",
 722                 help: Some("consider using `u32` or `libc::wchar_t` instead"),
 723             },
 724
 725             ty::Int(ast::IntTy::I128) | ty::Uint(ast::UintTy::U128) => FfiUnsafe {
 726                 ty: ty,
 727                 reason: "128-bit integers don't currently have a known stable ABI",
 728                 help: None,
 729             },
 730
 731             // Primitive types with a stable representation.
 732             ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
 733
 734             ty::Slice(_) => FfiUnsafe {
 735                 ty: ty,
 736                 reason: "slices have no C equivalent",
 737                 help: Some("consider using a raw pointer instead"),
 738             },
 739
 740             ty::Dynamic(..) => FfiUnsafe {
 741                 ty: ty,
 742                 reason: "trait objects have no C equivalent",
 743                 help: None,
 744             },
 745
 746             ty::Str => FfiUnsafe {
 747                 ty: ty,
 748                 reason: "string slices have no C equivalent",
 749                 help: Some("consider using `*const u8` and a length instead"),
 750             },
 751
 752             ty::Tuple(..) => FfiUnsafe {
 753                 ty: ty,
 754                 reason: "tuples have unspecified layout",
 755                 help: Some("consider using a struct instead"),
 756             },
 757
 758             ty::RawPtr(ty::TypeAndMut { ty, .. }) |
 759             ty::Ref(_, ty, _) => self.check_type_for_ffi(cache, ty),
 760
 761             ty::Array(ty, _) => self.check_type_for_ffi(cache, ty),
 762
 763             ty::FnPtr(sig) => {
 764                 match sig.abi() {
 765                     Abi::Rust | Abi::RustIntrinsic | Abi::PlatformIntrinsic | Abi::RustCall => {
 766                         return FfiUnsafe {
 767                             ty: ty,
 768                             reason: "this function pointer has Rust-specific calling convention",
 769                             help: Some("consider using an `extern fn(...) -> ...` \
 770                                         function pointer instead"),
 771                         }
 772                     }
 773                     _ => {}
 774                 }
 775
 776                 let sig = cx.erase_late_bound_regions(&sig);
 777                 if !sig.output().is_unit() {
 778                     let r = self.check_type_for_ffi(cache, sig.output());
 779                     match r {
 780                         FfiSafe => {}
 781                         _ => {
 782                             return r;
 783                         }
 784                     }
 785                 }
 786                 for arg in sig.inputs() {
 787                     let r = self.check_type_for_ffi(cache, arg);
 788                     match r {
 789                         FfiSafe => {}
 790                         _ => {
 791                             return r;
 792                         }
 793                     }
 794                 }
 795                 FfiSafe
 796             }
 797
 798             ty::Foreign(..) => FfiSafe,
 799
 800             ty::Param(..) |
 801             ty::Infer(..) |
 802             ty::Bound(..) |
 803             ty::Error |
 804             ty::Closure(..) |
 805             ty::Generator(..) |
 806             ty::GeneratorWitness(..) |
 807             ty::Placeholder(..) |
 808             ty::UnnormalizedProjection(..) |
 809             ty::Projection(..) |
 810             ty::Opaque(..) |
 811             ty::FnDef(..) => bug!("Unexpected type in foreign function"),
 812         }
 813     }
 814
 815     fn check_type_for_ffi_and_report_errors(&mut self, sp: Span, ty: Ty<'tcx>) {
 816         // it is only OK to use this function because extern fns cannot have
 817         // any generic types right now:
 818         let ty = self.cx.tcx.normalize_erasing_regions(ParamEnv::reveal_all(), ty);
 819
 820         match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
 821             FfiResult::FfiSafe => {}
 822             FfiResult::FfiPhantom(ty) => {
 823                 self.cx.span_lint(IMPROPER_CTYPES,
 824                                   sp,
 825                                   &format!("`extern` block uses type `{}` which is not FFI-safe: \
 826                                             composed only of PhantomData", ty));
 827             }
 828             FfiResult::FfiUnsafe { ty: unsafe_ty, reason, help } => {
 829                 let msg = format!("`extern` block uses type `{}` which is not FFI-safe: {}",
 830                                   unsafe_ty, reason);
 831                 let mut diag = self.cx.struct_span_lint(IMPROPER_CTYPES, sp, &msg);
 832                 if let Some(s) = help {
 833                     diag.help(s);
 834                 }
 835                 if let ty::Adt(def, _) = unsafe_ty.sty {
 836                     if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did) {
 837                         diag.span_note(sp, "type defined here");
 838                     }
 839                 }
 840                 diag.emit();
 841             }
 842         }
 843     }
 844
 845     fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl) {
 846         let def_id = self.cx.tcx.hir().local_def_id_from_hir_id(id);
 847         let sig = self.cx.tcx.fn_sig(def_id);
 848         let sig = self.cx.tcx.erase_late_bound_regions(&sig);
 849         let inputs = if sig.c_variadic {
 850             // Don't include the spoofed `VaList` in the functions list
 851             // of inputs.
 852             &sig.inputs()[..sig.inputs().len() - 1]
 853         } else {
 854             &sig.inputs()[..]
 855         };
 856
 857         for (input_ty, input_hir) in inputs.iter().zip(&decl.inputs) {
 858             self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty);
 859         }
 860
 861         if let hir::Return(ref ret_hir) = decl.output {
 862             let ret_ty = sig.output();
 863             if !ret_ty.is_unit() {
 864                 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty);
 865             }
 866         }
 867     }
 868
 869     fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
 870         let def_id = self.cx.tcx.hir().local_def_id_from_hir_id(id);
 871         let ty = self.cx.tcx.type_of(def_id);
 872         self.check_type_for_ffi_and_report_errors(span, ty);
 873     }
 874 }
 875
 876 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImproperCTypes {
 877     fn check_foreign_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::ForeignItem) {
 878         let mut vis = ImproperCTypesVisitor { cx };
 879         let abi = cx.tcx.hir().get_foreign_abi_by_hir_id(it.hir_id);
 880         if abi != Abi::RustIntrinsic && abi != Abi::PlatformIntrinsic {
 881             match it.node {
 882                 hir::ForeignItemKind::Fn(ref decl, _, _) => {
 883                     vis.check_foreign_fn(it.hir_id, decl);
 884                 }
 885                 hir::ForeignItemKind::Static(ref ty, _) => {
 886                     vis.check_foreign_static(it.hir_id, ty.span);
 887                 }
 888                 hir::ForeignItemKind::Type => ()
 889             }
 890         }
 891     }
 892 }
 893
 894 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
 895
 896 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for VariantSizeDifferences {
 897     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item) {
 898         if let hir::ItemKind::Enum(ref enum_definition, _) = it.node {
 899             let item_def_id = cx.tcx.hir().local_def_id_from_hir_id(it.hir_id);
 900             let t = cx.tcx.type_of(item_def_id);
 901             let ty = cx.tcx.erase_regions(&t);
 902             let layout = match cx.layout_of(ty) {
 903                 Ok(layout) => layout,
 904                 Err(ty::layout::LayoutError::Unknown(_)) => return,
 905                 Err(err @ ty::layout::LayoutError::SizeOverflow(_)) => {
 906                     bug!("failed to get layout for `{}`: {}", t, err);
 907                 }
 908             };
 909             let (variants, tag) = match layout.variants {
 910                 layout::Variants::Multiple {
 911                     discr_kind: layout::DiscriminantKind::Tag,
 912                     ref discr,
 913                     ref variants,
 914                     ..
 915                 } => (variants, discr),
 916                 _ => return,
 917             };
 918
 919             let discr_size = tag.value.size(&cx.tcx).bytes();
 920
 921             debug!("enum `{}` is {} bytes large with layout:\n{:#?}",
 922                    t, layout.size.bytes(), layout);
 923
 924             let (largest, slargest, largest_index) = enum_definition.variants
 925                 .iter()
 926                 .zip(variants)
 927                 .map(|(variant, variant_layout)| {
 928                     // Subtract the size of the enum discriminant.
 929                     let bytes = variant_layout.size.bytes().saturating_sub(discr_size);
 930
 931                     debug!("- variant `{}` is {} bytes large",
 932                            variant.node.ident,
 933                            bytes);
 934                     bytes
 935                 })
 936                 .enumerate()
 937                 .fold((0, 0, 0), |(l, s, li), (idx, size)| if size > l {
 938                     (size, l, idx)
 939                 } else if size > s {
 940                     (l, size, li)
 941                 } else {
 942                     (l, s, li)
 943                 });
 944
 945             // We only warn if the largest variant is at least thrice as large as
 946             // the second-largest.
 947             if largest > slargest * 3 && slargest > 0 {
 948                 cx.span_lint(VARIANT_SIZE_DIFFERENCES,
 949                                 enum_definition.variants[largest_index].span,
 950                                 &format!("enum variant is more than three times \
 951                                           larger ({} bytes) than the next largest",
 952                                          largest));
 953             }
 954         }
 955     }
 956 }