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 // For `isize` & `usize`, be conservative with the warnings, so that the
 112 // warnings are consistent between 32- and 64-bit platforms.
 113 fn int_ty_range(int_ty: ast::IntTy) -> (i128, i128) {
 114     match int_ty {
 115         ast::IntTy::Isize => (i64::min_value() as i128, i64::max_value() as i128),
 116         ast::IntTy::I8 => (i8::min_value() as i64 as i128, i8::max_value() as i128),
 117         ast::IntTy::I16 => (i16::min_value() as i64 as i128, i16::max_value() as i128),
 118         ast::IntTy::I32 => (i32::min_value() as i64 as i128, i32::max_value() as i128),
 119         ast::IntTy::I64 => (i64::min_value() as i128, i64::max_value() as i128),
 120         ast::IntTy::I128 =>(i128::min_value() as i128, i128::max_value()),
 121     }
 122 }
 123
 124 fn uint_ty_range(uint_ty: ast::UintTy) -> (u128, u128) {
 125     match uint_ty {
 126         ast::UintTy::Usize => (u64::min_value() as u128, u64::max_value() as u128),
 127         ast::UintTy::U8 => (u8::min_value() as u128, u8::max_value() as u128),
 128         ast::UintTy::U16 => (u16::min_value() as u128, u16::max_value() as u128),
 129         ast::UintTy::U32 => (u32::min_value() as u128, u32::max_value() as u128),
 130         ast::UintTy::U64 => (u64::min_value() as u128, u64::max_value() as u128),
 131         ast::UintTy::U128 => (u128::min_value(), u128::max_value()),
 132     }
 133 }
 134
 135 fn get_bin_hex_repr(cx: &LateContext<'_, '_>, lit: &ast::Lit) -> Option<String> {
 136     let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?;
 137     let firstch = src.chars().next()?;
 138
 139     if firstch == '0' {
 140         match src.chars().nth(1) {
 141             Some('x') | Some('b') => return Some(src),
 142             _ => return None,
 143         }
 144     }
 145
 146     None
 147 }
 148
 149 fn report_bin_hex_error(
 150     cx: &LateContext<'_, '_>,
 151     expr: &hir::Expr,
 152     ty: attr::IntType,
 153     repr_str: String,
 154     val: u128,
 155     negative: bool,
 156 ) {
 157     let size = layout::Integer::from_attr(&cx.tcx, ty).size();
 158     let (t, actually) = match ty {
 159         attr::IntType::SignedInt(t) => {
 160             let actually = sign_extend(val, size) as i128;
 161             (format!("{:?}", t), actually.to_string())
 162         }
 163         attr::IntType::UnsignedInt(t) => {
 164             let actually = truncate(val, size);
 165             (format!("{:?}", t), actually.to_string())
 166         }
 167     };
 168     let mut err = cx.struct_span_lint(
 169         OVERFLOWING_LITERALS,
 170         expr.span,
 171         &format!("literal out of range for {}", t),
 172     );
 173     err.note(&format!(
 174         "the literal `{}` (decimal `{}`) does not fit into \
 175             an `{}` and will become `{}{}`",
 176         repr_str, val, t, actually, t
 177     ));
 178     if let Some(sugg_ty) =
 179         get_type_suggestion(&cx.tables.node_type(expr.hir_id), val, negative)
 180     {
 181         if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') {
 182             let (sans_suffix, _) = repr_str.split_at(pos);
 183             err.span_suggestion(
 184                 expr.span,
 185                 &format!("consider using `{}` instead", sugg_ty),
 186                 format!("{}{}", sans_suffix, sugg_ty),
 187                 Applicability::MachineApplicable
 188             );
 189         } else {
 190             err.help(&format!("consider using `{}` instead", sugg_ty));
 191         }
 192     }
 193
 194     err.emit();
 195 }
 196
 197 // This function finds the next fitting type and generates a suggestion string.
 198 // It searches for fitting types in the following way (`X < Y`):
 199 //  - `iX`: if literal fits in `uX` => `uX`, else => `iY`
 200 //  - `-iX` => `iY`
 201 //  - `uX` => `uY`
 202 //
 203 // No suggestion for: `isize`, `usize`.
 204 fn get_type_suggestion<'a>(
 205     t: Ty<'_>,
 206     val: u128,
 207     negative: bool,
 208 ) -> Option<String> {
 209     use syntax::ast::IntTy::*;
 210     use syntax::ast::UintTy::*;
 211     macro_rules! find_fit {
 212         ($ty:expr, $val:expr, $negative:expr,
 213          $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => {
 214             {
 215                 let _neg = if negative { 1 } else { 0 };
 216                 match $ty {
 217                     $($type => {
 218                         $(if !negative && val <= uint_ty_range($utypes).1 {
 219                             return Some(format!("{:?}", $utypes))
 220                         })*
 221                         $(if val <= int_ty_range($itypes).1 as u128 + _neg {
 222                             return Some(format!("{:?}", $itypes))
 223                         })*
 224                         None
 225                     },)*
 226                     _ => None
 227                 }
 228             }
 229         }
 230     }
 231     match t.sty {
 232         ty::Int(i) => find_fit!(i, val, negative,
 233                       I8 => [U8] => [I16, I32, I64, I128],
 234                       I16 => [U16] => [I32, I64, I128],
 235                       I32 => [U32] => [I64, I128],
 236                       I64 => [U64] => [I128],
 237                       I128 => [U128] => []),
 238         ty::Uint(u) => find_fit!(u, val, negative,
 239                       U8 => [U8, U16, U32, U64, U128] => [],
 240                       U16 => [U16, U32, U64, U128] => [],
 241                       U32 => [U32, U64, U128] => [],
 242                       U64 => [U64, U128] => [],
 243                       U128 => [U128] => []),
 244         _ => None,
 245     }
 246 }
 247
 248 fn lint_int_literal<'a, 'tcx>(
 249     cx: &LateContext<'a, 'tcx>,
 250     type_limits: &TypeLimits,
 251     e: &'tcx hir::Expr,
 252     lit: &ast::Lit,
 253     t: ast::IntTy,
 254     v: u128,
 255 ) {
 256     let int_type = if let ast::IntTy::Isize = t {
 257         cx.sess().target.isize_ty
 258     } else {
 259         t
 260     };
 261
 262     let (_, max) = int_ty_range(int_type);
 263     let max = max as u128;
 264     let negative = type_limits.negated_expr_id == e.hir_id;
 265
 266     // Detect literal value out of range [min, max] inclusive
 267     // avoiding use of -min to prevent overflow/panic
 268     if (negative && v > max + 1) || (!negative && v > max) {
 269         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 270             report_bin_hex_error(
 271                 cx,
 272                 e,
 273                 attr::IntType::SignedInt(t),
 274                 repr_str,
 275                 v,
 276                 negative,
 277             );
 278             return;
 279         }
 280
 281         let par_id = cx.tcx.hir().get_parent_node_by_hir_id(e.hir_id);
 282         if let Node::Expr(par_e) = cx.tcx.hir().get_by_hir_id(par_id) {
 283             if let hir::ExprKind::Struct(..) = par_e.node {
 284                 if is_range_literal(cx.sess(), par_e)
 285                     && lint_overflowing_range_endpoint(cx, lit, v, max, e, par_e, t)
 286                 {
 287                     // The overflowing literal lint was overridden.
 288                     return;
 289                 }
 290             }
 291         }
 292
 293         cx.span_lint(
 294             OVERFLOWING_LITERALS,
 295             e.span,
 296             &format!("literal out of range for `{:?}`", t),
 297         );
 298     }
 299 }
 300
 301 fn lint_uint_literal<'a, 'tcx>(
 302     cx: &LateContext<'a, 'tcx>,
 303     e: &'tcx hir::Expr,
 304     lit: &ast::Lit,
 305     t: ast::UintTy,
 306 ) {
 307     let uint_type = if let ast::UintTy::Usize = t {
 308         cx.sess().target.usize_ty
 309     } else {
 310         t
 311     };
 312     let (min, max) = uint_ty_range(uint_type);
 313     let lit_val: u128 = match lit.node {
 314         // _v is u8, within range by definition
 315         ast::LitKind::Byte(_v) => return,
 316         ast::LitKind::Int(v, _) => v,
 317         _ => bug!(),
 318     };
 319     if lit_val < min || lit_val > max {
 320         let parent_id = cx.tcx.hir().get_parent_node_by_hir_id(e.hir_id);
 321         if let Node::Expr(par_e) = cx.tcx.hir().get_by_hir_id(parent_id) {
 322             match par_e.node {
 323                 hir::ExprKind::Cast(..) => {
 324                     if let ty::Char = cx.tables.expr_ty(par_e).sty {
 325                         let mut err = cx.struct_span_lint(
 326                             OVERFLOWING_LITERALS,
 327                             par_e.span,
 328                             "only `u8` can be cast into `char`",
 329                         );
 330                         err.span_suggestion(
 331                             par_e.span,
 332                             &"use a `char` literal instead",
 333                             format!("'\\u{{{:X}}}'", lit_val),
 334                             Applicability::MachineApplicable,
 335                         );
 336                         err.emit();
 337                         return;
 338                     }
 339                 }
 340                 hir::ExprKind::Struct(..)
 341                     if is_range_literal(cx.sess(), par_e) => {
 342                         if lint_overflowing_range_endpoint(cx, lit, lit_val, max, e, par_e, t) {
 343                             // The overflowing literal lint was overridden.
 344                             return;
 345                         }
 346                     }
 347                 _ => {}
 348             }
 349         }
 350         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 351             report_bin_hex_error(cx, e, attr::IntType::UnsignedInt(t), repr_str, lit_val, false);
 352             return;
 353         }
 354         cx.span_lint(
 355             OVERFLOWING_LITERALS,
 356             e.span,
 357             &format!("literal out of range for `{:?}`", t),
 358         );
 359     }
 360 }
 361
 362 fn lint_literal<'a, 'tcx>(
 363     cx: &LateContext<'a, 'tcx>,
 364     type_limits: &TypeLimits,
 365     e: &'tcx hir::Expr,
 366     lit: &ast::Lit,
 367 ) {
 368     match cx.tables.node_type(e.hir_id).sty {
 369         ty::Int(t) => {
 370             match lit.node {
 371                 ast::LitKind::Int(v, ast::LitIntType::Signed(_)) |
 372                 ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => {
 373                     lint_int_literal(cx, type_limits, e, lit, t, v)
 374                 }
 375                 _ => bug!(),
 376             };
 377         }
 378         ty::Uint(t) => {
 379             lint_uint_literal(cx, e, lit, t)
 380         }
 381         ty::Float(t) => {
 382             let is_infinite = match lit.node {
 383                 ast::LitKind::Float(v, _) |
 384                 ast::LitKind::FloatUnsuffixed(v) => {
 385                     match t {
 386                         ast::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
 387                         ast::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
 388                     }
 389                 }
 390                 _ => bug!(),
 391             };
 392             if is_infinite == Ok(true) {
 393                 cx.span_lint(OVERFLOWING_LITERALS,
 394                              e.span,
 395                              &format!("literal out of range for `{:?}`", t));
 396             }
 397         }
 398         _ => {}
 399     }
 400 }
 401
 402 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TypeLimits {
 403     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx hir::Expr) {
 404         match e.node {
 405             hir::ExprKind::Unary(hir::UnNeg, ref expr) => {
 406                 // propagate negation, if the negation itself isn't negated
 407                 if self.negated_expr_id != e.hir_id {
 408                     self.negated_expr_id = expr.hir_id;
 409                 }
 410             }
 411             hir::ExprKind::Binary(binop, ref l, ref r) => {
 412                 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
 413                     cx.span_lint(UNUSED_COMPARISONS,
 414                                  e.span,
 415                                  "comparison is useless due to type limits");
 416                 }
 417             }
 418             hir::ExprKind::Lit(ref lit) => lint_literal(cx, self, e, lit),
 419             _ => {}
 420         };
 421
 422         fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
 423             match binop.node {
 424                 hir::BinOpKind::Lt => v > min && v <= max,
 425                 hir::BinOpKind::Le => v >= min && v < max,
 426                 hir::BinOpKind::Gt => v >= min && v < max,
 427                 hir::BinOpKind::Ge => v > min && v <= max,
 428                 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
 429                 _ => bug!(),
 430             }
 431         }
 432
 433         fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
 434             source_map::respan(binop.span,
 435                             match binop.node {
 436                                 hir::BinOpKind::Lt => hir::BinOpKind::Gt,
 437                                 hir::BinOpKind::Le => hir::BinOpKind::Ge,
 438                                 hir::BinOpKind::Gt => hir::BinOpKind::Lt,
 439                                 hir::BinOpKind::Ge => hir::BinOpKind::Le,
 440                                 _ => return binop,
 441                             })
 442         }
 443
 444         fn check_limits(cx: &LateContext<'_, '_>,
 445                         binop: hir::BinOp,
 446                         l: &hir::Expr,
 447                         r: &hir::Expr)
 448                         -> bool {
 449             let (lit, expr, swap) = match (&l.node, &r.node) {
 450                 (&hir::ExprKind::Lit(_), _) => (l, r, true),
 451                 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
 452                 _ => return true,
 453             };
 454             // Normalize the binop so that the literal is always on the RHS in
 455             // the comparison
 456             let norm_binop = if swap { rev_binop(binop) } else { binop };
 457             match cx.tables.node_type(expr.hir_id).sty {
 458                 ty::Int(int_ty) => {
 459                     let (min, max) = int_ty_range(int_ty);
 460                     let lit_val: i128 = match lit.node {
 461                         hir::ExprKind::Lit(ref li) => {
 462                             match li.node {
 463                                 ast::LitKind::Int(v, ast::LitIntType::Signed(_)) |
 464                                 ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => v as i128,
 465                                 _ => return true
 466                             }
 467                         },
 468                         _ => bug!()
 469                     };
 470                     is_valid(norm_binop, lit_val, min, max)
 471                 }
 472                 ty::Uint(uint_ty) => {
 473                     let (min, max) :(u128, u128) = uint_ty_range(uint_ty);
 474                     let lit_val: u128 = match lit.node {
 475                         hir::ExprKind::Lit(ref li) => {
 476                             match li.node {
 477                                 ast::LitKind::Int(v, _) => v,
 478                                 _ => return true
 479                             }
 480                         },
 481                         _ => bug!()
 482                     };
 483                     is_valid(norm_binop, lit_val, min, max)
 484                 }
 485                 _ => true,
 486             }
 487         }
 488
 489         fn is_comparison(binop: hir::BinOp) -> bool {
 490             match binop.node {
 491                 hir::BinOpKind::Eq |
 492                 hir::BinOpKind::Lt |
 493                 hir::BinOpKind::Le |
 494                 hir::BinOpKind::Ne |
 495                 hir::BinOpKind::Ge |
 496                 hir::BinOpKind::Gt => true,
 497                 _ => false,
 498             }
 499         }
 500     }
 501 }
 502
 503 declare_lint! {
 504     IMPROPER_CTYPES,
 505     Warn,
 506     "proper use of libc types in foreign modules"
 507 }
 508
 509 declare_lint_pass!(ImproperCTypes => [IMPROPER_CTYPES]);
 510
 511 struct ImproperCTypesVisitor<'a, 'tcx: 'a> {
 512     cx: &'a LateContext<'a, 'tcx>,
 513 }
 514
 515 enum FfiResult<'tcx> {
 516     FfiSafe,
 517     FfiPhantom(Ty<'tcx>),
 518     FfiUnsafe {
 519         ty: Ty<'tcx>,
 520         reason: &'static str,
 521         help: Option<&'static str>,
 522     },
 523 }
 524
 525 /// Check if this enum can be safely exported based on the
 526 /// "nullable pointer optimization". Currently restricted
 527 /// to function pointers and references, but could be
 528 /// expanded to cover NonZero raw pointers and newtypes.
 529 /// FIXME: This duplicates code in codegen.
 530 fn is_repr_nullable_ptr<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 531                                   def: &'tcx ty::AdtDef,
 532                                   substs: SubstsRef<'tcx>)
 533                                   -> bool {
 534     if def.variants.len() == 2 {
 535         let data_idx;
 536
 537         let zero = VariantIdx::new(0);
 538         let one = VariantIdx::new(1);
 539
 540         if def.variants[zero].fields.is_empty() {
 541             data_idx = one;
 542         } else if def.variants[one].fields.is_empty() {
 543             data_idx = zero;
 544         } else {
 545             return false;
 546         }
 547
 548         if def.variants[data_idx].fields.len() == 1 {
 549             match def.variants[data_idx].fields[0].ty(tcx, substs).sty {
 550                 ty::FnPtr(_) => {
 551                     return true;
 552                 }
 553                 ty::Ref(..) => {
 554                     return true;
 555                 }
 556                 _ => {}
 557             }
 558         }
 559     }
 560     false
 561 }
 562
 563 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
 564     /// Checks if the given type is "ffi-safe" (has a stable, well-defined
 565     /// representation which can be exported to C code).
 566     fn check_type_for_ffi(&self,
 567                           cache: &mut FxHashSet<Ty<'tcx>>,
 568                           ty: Ty<'tcx>) -> FfiResult<'tcx> {
 569         use FfiResult::*;
 570
 571         let cx = self.cx.tcx;
 572
 573         // Protect against infinite recursion, for example
 574         // `struct S(*mut S);`.
 575         // FIXME: A recursion limit is necessary as well, for irregular
 576         // recursive types.
 577         if !cache.insert(ty) {
 578             return FfiSafe;
 579         }
 580
 581         match ty.sty {
 582             ty::Adt(def, substs) => {
 583                 if def.is_phantom_data() {
 584                     return FfiPhantom(ty);
 585                 }
 586                 match def.adt_kind() {
 587                     AdtKind::Struct => {
 588                         if !def.repr.c() && !def.repr.transparent() {
 589                             return FfiUnsafe {
 590                                 ty: ty,
 591                                 reason: "this struct has unspecified layout",
 592                                 help: Some("consider adding a #[repr(C)] or #[repr(transparent)] \
 593                                             attribute to this struct"),
 594                             };
 595                         }
 596
 597                         if def.non_enum_variant().fields.is_empty() {
 598                             return FfiUnsafe {
 599                                 ty: ty,
 600                                 reason: "this struct has no fields",
 601                                 help: Some("consider adding a member to this struct"),
 602                             };
 603                         }
 604
 605                         // We can't completely trust repr(C) and repr(transparent) markings;
 606                         // make sure the fields are actually safe.
 607                         let mut all_phantom = true;
 608                         for field in &def.non_enum_variant().fields {
 609                             let field_ty = cx.normalize_erasing_regions(
 610                                 ParamEnv::reveal_all(),
 611                                 field.ty(cx, substs),
 612                             );
 613                             // repr(transparent) types are allowed to have arbitrary ZSTs, not just
 614                             // PhantomData -- skip checking all ZST fields
 615                             if def.repr.transparent() {
 616                                 let is_zst = cx
 617                                     .layout_of(cx.param_env(field.did).and(field_ty))
 618                                     .map(|layout| layout.is_zst())
 619                                     .unwrap_or(false);
 620                                 if is_zst {
 621                                     continue;
 622                                 }
 623                             }
 624                             let r = self.check_type_for_ffi(cache, field_ty);
 625                             match r {
 626                                 FfiSafe => {
 627                                     all_phantom = false;
 628                                 }
 629                                 FfiPhantom(..) => {}
 630                                 FfiUnsafe { .. } => {
 631                                     return r;
 632                                 }
 633                             }
 634                         }
 635
 636                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 637                     }
 638                     AdtKind::Union => {
 639                         if !def.repr.c() {
 640                             return FfiUnsafe {
 641                                 ty: ty,
 642                                 reason: "this union has unspecified layout",
 643                                 help: Some("consider adding a #[repr(C)] attribute to this union"),
 644                             };
 645                         }
 646
 647                         if def.non_enum_variant().fields.is_empty() {
 648                             return FfiUnsafe {
 649                                 ty: ty,
 650                                 reason: "this union has no fields",
 651                                 help: Some("consider adding a field to this union"),
 652                             };
 653                         }
 654
 655                         let mut all_phantom = true;
 656                         for field in &def.non_enum_variant().fields {
 657                             let field_ty = cx.normalize_erasing_regions(
 658                                 ParamEnv::reveal_all(),
 659                                 field.ty(cx, substs),
 660                             );
 661                             let r = self.check_type_for_ffi(cache, field_ty);
 662                             match r {
 663                                 FfiSafe => {
 664                                     all_phantom = false;
 665                                 }
 666                                 FfiPhantom(..) => {}
 667                                 FfiUnsafe { .. } => {
 668                                     return r;
 669                                 }
 670                             }
 671                         }
 672
 673                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 674                     }
 675                     AdtKind::Enum => {
 676                         if def.variants.is_empty() {
 677                             // Empty enums are okay... although sort of useless.
 678                             return FfiSafe;
 679                         }
 680
 681                         // Check for a repr() attribute to specify the size of the
 682                         // discriminant.
 683                         if !def.repr.c() && def.repr.int.is_none() {
 684                             // Special-case types like `Option<extern fn()>`.
 685                             if !is_repr_nullable_ptr(cx, def, substs) {
 686                                 return FfiUnsafe {
 687                                     ty: ty,
 688                                     reason: "enum has no representation hint",
 689                                     help: Some("consider adding a #[repr(...)] attribute \
 690                                                 to this enum"),
 691                                 };
 692                             }
 693                         }
 694
 695                         // Check the contained variants.
 696                         for variant in &def.variants {
 697                             for field in &variant.fields {
 698                                 let arg = cx.normalize_erasing_regions(
 699                                     ParamEnv::reveal_all(),
 700                                     field.ty(cx, substs),
 701                                 );
 702                                 let r = self.check_type_for_ffi(cache, arg);
 703                                 match r {
 704                                     FfiSafe => {}
 705                                     FfiUnsafe { .. } => {
 706                                         return r;
 707                                     }
 708                                     FfiPhantom(..) => {
 709                                         return FfiUnsafe {
 710                                             ty: ty,
 711                                             reason: "this enum contains a PhantomData field",
 712                                             help: None,
 713                                         };
 714                                     }
 715                                 }
 716                             }
 717                         }
 718                         FfiSafe
 719                     }
 720                 }
 721             }
 722
 723             ty::Char => FfiUnsafe {
 724                 ty: ty,
 725                 reason: "the `char` type has no C equivalent",
 726                 help: Some("consider using `u32` or `libc::wchar_t` instead"),
 727             },
 728
 729             ty::Int(ast::IntTy::I128) | ty::Uint(ast::UintTy::U128) => FfiUnsafe {
 730                 ty: ty,
 731                 reason: "128-bit integers don't currently have a known stable ABI",
 732                 help: None,
 733             },
 734
 735             // Primitive types with a stable representation.
 736             ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
 737
 738             ty::Slice(_) => FfiUnsafe {
 739                 ty: ty,
 740                 reason: "slices have no C equivalent",
 741                 help: Some("consider using a raw pointer instead"),
 742             },
 743
 744             ty::Dynamic(..) => FfiUnsafe {
 745                 ty: ty,
 746                 reason: "trait objects have no C equivalent",
 747                 help: None,
 748             },
 749
 750             ty::Str => FfiUnsafe {
 751                 ty: ty,
 752                 reason: "string slices have no C equivalent",
 753                 help: Some("consider using `*const u8` and a length instead"),
 754             },
 755
 756             ty::Tuple(..) => FfiUnsafe {
 757                 ty: ty,
 758                 reason: "tuples have unspecified layout",
 759                 help: Some("consider using a struct instead"),
 760             },
 761
 762             ty::RawPtr(ty::TypeAndMut { ty, .. }) |
 763             ty::Ref(_, ty, _) => self.check_type_for_ffi(cache, ty),
 764
 765             ty::Array(ty, _) => self.check_type_for_ffi(cache, ty),
 766
 767             ty::FnPtr(sig) => {
 768                 match sig.abi() {
 769                     Abi::Rust | Abi::RustIntrinsic | Abi::PlatformIntrinsic | Abi::RustCall => {
 770                         return FfiUnsafe {
 771                             ty: ty,
 772                             reason: "this function pointer has Rust-specific calling convention",
 773                             help: Some("consider using an `extern fn(...) -> ...` \
 774                                         function pointer instead"),
 775                         }
 776                     }
 777                     _ => {}
 778                 }
 779
 780                 let sig = cx.erase_late_bound_regions(&sig);
 781                 if !sig.output().is_unit() {
 782                     let r = self.check_type_for_ffi(cache, sig.output());
 783                     match r {
 784                         FfiSafe => {}
 785                         _ => {
 786                             return r;
 787                         }
 788                     }
 789                 }
 790                 for arg in sig.inputs() {
 791                     let r = self.check_type_for_ffi(cache, arg);
 792                     match r {
 793                         FfiSafe => {}
 794                         _ => {
 795                             return r;
 796                         }
 797                     }
 798                 }
 799                 FfiSafe
 800             }
 801
 802             ty::Foreign(..) => FfiSafe,
 803
 804             ty::Param(..) |
 805             ty::Infer(..) |
 806             ty::Bound(..) |
 807             ty::Error |
 808             ty::Closure(..) |
 809             ty::Generator(..) |
 810             ty::GeneratorWitness(..) |
 811             ty::Placeholder(..) |
 812             ty::UnnormalizedProjection(..) |
 813             ty::Projection(..) |
 814             ty::Opaque(..) |
 815             ty::FnDef(..) => bug!("Unexpected type in foreign function"),
 816         }
 817     }
 818
 819     fn check_type_for_ffi_and_report_errors(&mut self, sp: Span, ty: Ty<'tcx>) {
 820         // it is only OK to use this function because extern fns cannot have
 821         // any generic types right now:
 822         let ty = self.cx.tcx.normalize_erasing_regions(ParamEnv::reveal_all(), ty);
 823
 824         match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
 825             FfiResult::FfiSafe => {}
 826             FfiResult::FfiPhantom(ty) => {
 827                 self.cx.span_lint(IMPROPER_CTYPES,
 828                                   sp,
 829                                   &format!("`extern` block uses type `{}` which is not FFI-safe: \
 830                                             composed only of PhantomData", ty));
 831             }
 832             FfiResult::FfiUnsafe { ty: unsafe_ty, reason, help } => {
 833                 let msg = format!("`extern` block uses type `{}` which is not FFI-safe: {}",
 834                                   unsafe_ty, reason);
 835                 let mut diag = self.cx.struct_span_lint(IMPROPER_CTYPES, sp, &msg);
 836                 if let Some(s) = help {
 837                     diag.help(s);
 838                 }
 839                 if let ty::Adt(def, _) = unsafe_ty.sty {
 840                     if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did) {
 841                         diag.span_note(sp, "type defined here");
 842                     }
 843                 }
 844                 diag.emit();
 845             }
 846         }
 847     }
 848
 849     fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl) {
 850         let def_id = self.cx.tcx.hir().local_def_id_from_hir_id(id);
 851         let sig = self.cx.tcx.fn_sig(def_id);
 852         let sig = self.cx.tcx.erase_late_bound_regions(&sig);
 853         let inputs = if sig.c_variadic {
 854             // Don't include the spoofed `VaList` in the functions list
 855             // of inputs.
 856             &sig.inputs()[..sig.inputs().len() - 1]
 857         } else {
 858             &sig.inputs()[..]
 859         };
 860
 861         for (input_ty, input_hir) in inputs.iter().zip(&decl.inputs) {
 862             self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty);
 863         }
 864
 865         if let hir::Return(ref ret_hir) = decl.output {
 866             let ret_ty = sig.output();
 867             if !ret_ty.is_unit() {
 868                 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty);
 869             }
 870         }
 871     }
 872
 873     fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
 874         let def_id = self.cx.tcx.hir().local_def_id_from_hir_id(id);
 875         let ty = self.cx.tcx.type_of(def_id);
 876         self.check_type_for_ffi_and_report_errors(span, ty);
 877     }
 878 }
 879
 880 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImproperCTypes {
 881     fn check_foreign_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::ForeignItem) {
 882         let mut vis = ImproperCTypesVisitor { cx };
 883         let abi = cx.tcx.hir().get_foreign_abi_by_hir_id(it.hir_id);
 884         if abi != Abi::RustIntrinsic && abi != Abi::PlatformIntrinsic {
 885             match it.node {
 886                 hir::ForeignItemKind::Fn(ref decl, _, _) => {
 887                     vis.check_foreign_fn(it.hir_id, decl);
 888                 }
 889                 hir::ForeignItemKind::Static(ref ty, _) => {
 890                     vis.check_foreign_static(it.hir_id, ty.span);
 891                 }
 892                 hir::ForeignItemKind::Type => ()
 893             }
 894         }
 895     }
 896 }
 897
 898 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
 899
 900 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for VariantSizeDifferences {
 901     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item) {
 902         if let hir::ItemKind::Enum(ref enum_definition, _) = it.node {
 903             let item_def_id = cx.tcx.hir().local_def_id_from_hir_id(it.hir_id);
 904             let t = cx.tcx.type_of(item_def_id);
 905             let ty = cx.tcx.erase_regions(&t);
 906             let layout = match cx.layout_of(ty) {
 907                 Ok(layout) => layout,
 908                 Err(ty::layout::LayoutError::Unknown(_)) => return,
 909                 Err(err @ ty::layout::LayoutError::SizeOverflow(_)) => {
 910                     bug!("failed to get layout for `{}`: {}", t, err);
 911                 }
 912             };
 913             let (variants, tag) = match layout.variants {
 914                 layout::Variants::Multiple {
 915                     discr_kind: layout::DiscriminantKind::Tag,
 916                     ref discr,
 917                     ref variants,
 918                     ..
 919                 } => (variants, discr),
 920                 _ => return,
 921             };
 922
 923             let discr_size = tag.value.size(&cx.tcx).bytes();
 924
 925             debug!("enum `{}` is {} bytes large with layout:\n{:#?}",
 926                    t, layout.size.bytes(), layout);
 927
 928             let (largest, slargest, largest_index) = enum_definition.variants
 929                 .iter()
 930                 .zip(variants)
 931                 .map(|(variant, variant_layout)| {
 932                     // Subtract the size of the enum discriminant.
 933                     let bytes = variant_layout.size.bytes().saturating_sub(discr_size);
 934
 935                     debug!("- variant `{}` is {} bytes large",
 936                            variant.node.ident,
 937                            bytes);
 938                     bytes
 939                 })
 940                 .enumerate()
 941                 .fold((0, 0, 0), |(l, s, li), (idx, size)| if size > l {
 942                     (size, l, idx)
 943                 } else if size > s {
 944                     (l, size, li)
 945                 } else {
 946                     (l, s, li)
 947                 });
 948
 949             // We only warn if the largest variant is at least thrice as large as
 950             // the second-largest.
 951             if largest > slargest * 3 && slargest > 0 {
 952                 cx.span_lint(VARIANT_SIZE_DIFFERENCES,
 953                                 enum_definition.variants[largest_index].span,
 954                                 &format!("enum variant is more than three times \
 955                                           larger ({} bytes) than the next largest",
 956                                          largest));
 957             }
 958         }
 959     }
 960 }