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::Node;
  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 syntax::errors::Applicability;
  26 use rustc_target::spec::abi::Abi;
  27 use syntax::edition::Edition;
  28 use syntax_pos::Span;
  29 use syntax::source_map;
  30
  31 use rustc::hir;
  32
  33 declare_lint! {
  34     UNUSED_COMPARISONS,
  35     Warn,
  36     "comparisons made useless by limits of the types involved"
  37 }
  38
  39 declare_lint! {
  40     OVERFLOWING_LITERALS,
  41     Warn,
  42     "literal out of range for its type",
  43     Edition::Edition2018 => Deny
  44 }
  45
  46 declare_lint! {
  47     VARIANT_SIZE_DIFFERENCES,
  48     Allow,
  49     "detects enums with widely varying variant sizes"
  50 }
  51
  52 #[derive(Copy, Clone)]
  53 pub struct TypeLimits {
  54     /// Id of the last visited negated expression
  55     negated_expr_id: ast::NodeId,
  56 }
  57
  58 impl TypeLimits {
  59     pub fn new() -> TypeLimits {
  60         TypeLimits { negated_expr_id: ast::DUMMY_NODE_ID }
  61     }
  62 }
  63
  64 impl LintPass for TypeLimits {
  65     fn get_lints(&self) -> LintArray {
  66         lint_array!(UNUSED_COMPARISONS,
  67                     OVERFLOWING_LITERALS)
  68     }
  69 }
  70
  71 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TypeLimits {
  72     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx hir::Expr) {
  73         match e.node {
  74             hir::ExprKind::Unary(hir::UnNeg, ref expr) => {
  75                 // propagate negation, if the negation itself isn't negated
  76                 if self.negated_expr_id != e.id {
  77                     self.negated_expr_id = expr.id;
  78                 }
  79             }
  80             hir::ExprKind::Binary(binop, ref l, ref r) => {
  81                 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
  82                     cx.span_lint(UNUSED_COMPARISONS,
  83                                  e.span,
  84                                  "comparison is useless due to type limits");
  85                 }
  86             }
  87             hir::ExprKind::Lit(ref lit) => {
  88                 match cx.tables.node_id_to_type(e.hir_id).sty {
  89                     ty::Int(t) => {
  90                         match lit.node {
  91                             ast::LitKind::Int(v, ast::LitIntType::Signed(_)) |
  92                             ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => {
  93                                 let int_type = if let ast::IntTy::Isize = t {
  94                                     cx.sess().target.isize_ty
  95                                 } else {
  96                                     t
  97                                 };
  98                                 let (_, max) = int_ty_range(int_type);
  99                                 let max = max as u128;
 100                                 let negative = self.negated_expr_id == e.id;
 101
 102                                 // Detect literal value out of range [min, max] inclusive
 103                                 // avoiding use of -min to prevent overflow/panic
 104                                 if (negative && v > max + 1) || (!negative && v > max) {
 105                                     if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 106                                         report_bin_hex_error(
 107                                             cx,
 108                                             e,
 109                                             ty::Int(t),
 110                                             repr_str,
 111                                             v,
 112                                             negative,
 113                                         );
 114                                         return;
 115                                     }
 116                                     cx.span_lint(
 117                                         OVERFLOWING_LITERALS,
 118                                         e.span,
 119                                         &format!("literal out of range for {:?}", t),
 120                                     );
 121                                     return;
 122                                 }
 123                             }
 124                             _ => bug!(),
 125                         };
 126                     }
 127                     ty::Uint(t) => {
 128                         let uint_type = if let ast::UintTy::Usize = t {
 129                             cx.sess().target.usize_ty
 130                         } else {
 131                             t
 132                         };
 133                         let (min, max) = uint_ty_range(uint_type);
 134                         let lit_val: u128 = match lit.node {
 135                             // _v is u8, within range by definition
 136                             ast::LitKind::Byte(_v) => return,
 137                             ast::LitKind::Int(v, _) => v,
 138                             _ => bug!(),
 139                         };
 140                         if lit_val < min || lit_val > max {
 141                             let parent_id = cx.tcx.hir.get_parent_node(e.id);
 142                             if let Node::Expr(parent_expr) = cx.tcx.hir.get(parent_id) {
 143                                 if let hir::ExprKind::Cast(..) = parent_expr.node {
 144                                     if let ty::Char = cx.tables.expr_ty(parent_expr).sty {
 145                                         let mut err = cx.struct_span_lint(
 146                                                              OVERFLOWING_LITERALS,
 147                                                              parent_expr.span,
 148                                                              "only u8 can be cast into char");
 149                                         err.span_suggestion_with_applicability(
 150                                             parent_expr.span,
 151                                             &"use a char literal instead",
 152                                             format!("'\\u{{{:X}}}'", lit_val),
 153                                             Applicability::MachineApplicable
 154                                         );
 155                                         err.emit();
 156                                         return
 157                                     }
 158                                 }
 159                             }
 160                             if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 161                                 report_bin_hex_error(
 162                                     cx,
 163                                     e,
 164                                     ty::Uint(t),
 165                                     repr_str,
 166                                     lit_val,
 167                                     false,
 168                                 );
 169                                 return;
 170                             }
 171                             cx.span_lint(
 172                                 OVERFLOWING_LITERALS,
 173                                 e.span,
 174                                 &format!("literal out of range for {:?}", t),
 175                             );
 176                         }
 177                     }
 178                     ty::Float(t) => {
 179                         let is_infinite = match lit.node {
 180                             ast::LitKind::Float(v, _) |
 181                             ast::LitKind::FloatUnsuffixed(v) => {
 182                                 match t {
 183                                     ast::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
 184                                     ast::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
 185                                 }
 186                             }
 187                             _ => bug!(),
 188                         };
 189                         if is_infinite == Ok(true) {
 190                             cx.span_lint(OVERFLOWING_LITERALS,
 191                                          e.span,
 192                                          &format!("literal out of range for {:?}", t));
 193                         }
 194                     }
 195                     _ => (),
 196                 };
 197             }
 198             _ => (),
 199         };
 200
 201         fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
 202             match binop.node {
 203                 hir::BinOpKind::Lt => v > min && v <= max,
 204                 hir::BinOpKind::Le => v >= min && v < max,
 205                 hir::BinOpKind::Gt => v >= min && v < max,
 206                 hir::BinOpKind::Ge => v > min && v <= max,
 207                 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
 208                 _ => bug!(),
 209             }
 210         }
 211
 212         fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
 213             source_map::respan(binop.span,
 214                             match binop.node {
 215                                 hir::BinOpKind::Lt => hir::BinOpKind::Gt,
 216                                 hir::BinOpKind::Le => hir::BinOpKind::Ge,
 217                                 hir::BinOpKind::Gt => hir::BinOpKind::Lt,
 218                                 hir::BinOpKind::Ge => hir::BinOpKind::Le,
 219                                 _ => return binop,
 220                             })
 221         }
 222
 223         // for isize & usize, be conservative with the warnings, so that the
 224         // warnings are consistent between 32- and 64-bit platforms
 225         fn int_ty_range(int_ty: ast::IntTy) -> (i128, i128) {
 226             match int_ty {
 227                 ast::IntTy::Isize => (i64::min_value() as i128, i64::max_value() as i128),
 228                 ast::IntTy::I8 => (i8::min_value() as i64 as i128, i8::max_value() as i128),
 229                 ast::IntTy::I16 => (i16::min_value() as i64 as i128, i16::max_value() as i128),
 230                 ast::IntTy::I32 => (i32::min_value() as i64 as i128, i32::max_value() as i128),
 231                 ast::IntTy::I64 => (i64::min_value() as i128, i64::max_value() as i128),
 232                 ast::IntTy::I128 =>(i128::min_value() as i128, i128::max_value()),
 233             }
 234         }
 235
 236         fn uint_ty_range(uint_ty: ast::UintTy) -> (u128, u128) {
 237             match uint_ty {
 238                 ast::UintTy::Usize => (u64::min_value() as u128, u64::max_value() as u128),
 239                 ast::UintTy::U8 => (u8::min_value() as u128, u8::max_value() as u128),
 240                 ast::UintTy::U16 => (u16::min_value() as u128, u16::max_value() as u128),
 241                 ast::UintTy::U32 => (u32::min_value() as u128, u32::max_value() as u128),
 242                 ast::UintTy::U64 => (u64::min_value() as u128, u64::max_value() as u128),
 243                 ast::UintTy::U128 => (u128::min_value(), u128::max_value()),
 244             }
 245         }
 246
 247         fn check_limits(cx: &LateContext,
 248                         binop: hir::BinOp,
 249                         l: &hir::Expr,
 250                         r: &hir::Expr)
 251                         -> bool {
 252             let (lit, expr, swap) = match (&l.node, &r.node) {
 253                 (&hir::ExprKind::Lit(_), _) => (l, r, true),
 254                 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
 255                 _ => return true,
 256             };
 257             // Normalize the binop so that the literal is always on the RHS in
 258             // the comparison
 259             let norm_binop = if swap { rev_binop(binop) } else { binop };
 260             match cx.tables.node_id_to_type(expr.hir_id).sty {
 261                 ty::Int(int_ty) => {
 262                     let (min, max) = int_ty_range(int_ty);
 263                     let lit_val: i128 = match lit.node {
 264                         hir::ExprKind::Lit(ref li) => {
 265                             match li.node {
 266                                 ast::LitKind::Int(v, ast::LitIntType::Signed(_)) |
 267                                 ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => v as i128,
 268                                 _ => return true
 269                             }
 270                         },
 271                         _ => bug!()
 272                     };
 273                     is_valid(norm_binop, lit_val, min, max)
 274                 }
 275                 ty::Uint(uint_ty) => {
 276                     let (min, max) :(u128, u128) = uint_ty_range(uint_ty);
 277                     let lit_val: u128 = match lit.node {
 278                         hir::ExprKind::Lit(ref li) => {
 279                             match li.node {
 280                                 ast::LitKind::Int(v, _) => v,
 281                                 _ => return true
 282                             }
 283                         },
 284                         _ => bug!()
 285                     };
 286                     is_valid(norm_binop, lit_val, min, max)
 287                 }
 288                 _ => true,
 289             }
 290         }
 291
 292         fn is_comparison(binop: hir::BinOp) -> bool {
 293             match binop.node {
 294                 hir::BinOpKind::Eq |
 295                 hir::BinOpKind::Lt |
 296                 hir::BinOpKind::Le |
 297                 hir::BinOpKind::Ne |
 298                 hir::BinOpKind::Ge |
 299                 hir::BinOpKind::Gt => true,
 300                 _ => false,
 301             }
 302         }
 303
 304         fn get_bin_hex_repr(cx: &LateContext, lit: &ast::Lit) -> Option<String> {
 305             let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?;
 306             let firstch = src.chars().next()?;
 307
 308             if firstch == '0' {
 309                 match src.chars().nth(1) {
 310                     Some('x') | Some('b') => return Some(src),
 311                     _ => return None,
 312                 }
 313             }
 314
 315             None
 316         }
 317
 318         // This function finds the next fitting type and generates a suggestion string.
 319         // It searches for fitting types in the following way (`X < Y`):
 320         //  - `iX`: if literal fits in `uX` => `uX`, else => `iY`
 321         //  - `-iX` => `iY`
 322         //  - `uX` => `uY`
 323         //
 324         // No suggestion for: `isize`, `usize`.
 325         fn get_type_suggestion<'a>(
 326             t: &ty::TyKind,
 327             val: u128,
 328             negative: bool,
 329         ) -> Option<String> {
 330             use syntax::ast::IntTy::*;
 331             use syntax::ast::UintTy::*;
 332             macro_rules! find_fit {
 333                 ($ty:expr, $val:expr, $negative:expr,
 334                  $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => {
 335                     {
 336                         let _neg = if negative { 1 } else { 0 };
 337                         match $ty {
 338                             $($type => {
 339                                 $(if !negative && val <= uint_ty_range($utypes).1 {
 340                                     return Some(format!("{:?}", $utypes))
 341                                 })*
 342                                 $(if val <= int_ty_range($itypes).1 as u128 + _neg {
 343                                     return Some(format!("{:?}", $itypes))
 344                                 })*
 345                                 None
 346                             },)*
 347                             _ => None
 348                         }
 349                     }
 350                 }
 351             }
 352             match t {
 353                 &ty::Int(i) => find_fit!(i, val, negative,
 354                               I8 => [U8] => [I16, I32, I64, I128],
 355                               I16 => [U16] => [I32, I64, I128],
 356                               I32 => [U32] => [I64, I128],
 357                               I64 => [U64] => [I128],
 358                               I128 => [U128] => []),
 359                 &ty::Uint(u) => find_fit!(u, val, negative,
 360                               U8 => [U8, U16, U32, U64, U128] => [],
 361                               U16 => [U16, U32, U64, U128] => [],
 362                               U32 => [U32, U64, U128] => [],
 363                               U64 => [U64, U128] => [],
 364                               U128 => [U128] => []),
 365                 _ => None,
 366             }
 367         }
 368
 369         fn report_bin_hex_error(
 370             cx: &LateContext,
 371             expr: &hir::Expr,
 372             ty: ty::TyKind,
 373             repr_str: String,
 374             val: u128,
 375             negative: bool,
 376         ) {
 377             let (t, actually) = match ty {
 378                 ty::Int(t) => {
 379                     let ity = attr::IntType::SignedInt(t);
 380                     let bits = layout::Integer::from_attr(cx.tcx, ity).size().bits();
 381                     let actually = (val << (128 - bits)) as i128 >> (128 - bits);
 382                     (format!("{:?}", t), actually.to_string())
 383                 }
 384                 ty::Uint(t) => {
 385                     let ity = attr::IntType::UnsignedInt(t);
 386                     let bits = layout::Integer::from_attr(cx.tcx, ity).size().bits();
 387                     let actually = (val << (128 - bits)) >> (128 - bits);
 388                     (format!("{:?}", t), actually.to_string())
 389                 }
 390                 _ => bug!(),
 391             };
 392             let mut err = cx.struct_span_lint(
 393                 OVERFLOWING_LITERALS,
 394                 expr.span,
 395                 &format!("literal out of range for {}", t),
 396             );
 397             err.note(&format!(
 398                 "the literal `{}` (decimal `{}`) does not fit into \
 399                  an `{}` and will become `{}{}`",
 400                 repr_str, val, t, actually, t
 401             ));
 402             if let Some(sugg_ty) =
 403                 get_type_suggestion(&cx.tables.node_id_to_type(expr.hir_id).sty, val, negative)
 404             {
 405                 if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') {
 406                     let (sans_suffix, _) = repr_str.split_at(pos);
 407                     err.span_suggestion_with_applicability(
 408                         expr.span,
 409                         &format!("consider using `{}` instead", sugg_ty),
 410                         format!("{}{}", sans_suffix, sugg_ty),
 411                         Applicability::MachineApplicable
 412                     );
 413                 } else {
 414                     err.help(&format!("consider using `{}` instead", sugg_ty));
 415                 }
 416             }
 417
 418             err.emit();
 419         }
 420     }
 421 }
 422
 423 declare_lint! {
 424     IMPROPER_CTYPES,
 425     Warn,
 426     "proper use of libc types in foreign modules"
 427 }
 428
 429 struct ImproperCTypesVisitor<'a, 'tcx: 'a> {
 430     cx: &'a LateContext<'a, 'tcx>,
 431 }
 432
 433 enum FfiResult<'tcx> {
 434     FfiSafe,
 435     FfiPhantom(Ty<'tcx>),
 436     FfiUnsafe {
 437         ty: Ty<'tcx>,
 438         reason: &'static str,
 439         help: Option<&'static str>,
 440     },
 441 }
 442
 443 /// Check if this enum can be safely exported based on the
 444 /// "nullable pointer optimization". Currently restricted
 445 /// to function pointers and references, but could be
 446 /// expanded to cover NonZero raw pointers and newtypes.
 447 /// FIXME: This duplicates code in codegen.
 448 fn is_repr_nullable_ptr<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 449                                   def: &'tcx ty::AdtDef,
 450                                   substs: &Substs<'tcx>)
 451                                   -> bool {
 452     if def.variants.len() == 2 {
 453         let data_idx;
 454
 455         if def.variants[0].fields.is_empty() {
 456             data_idx = 1;
 457         } else if def.variants[1].fields.is_empty() {
 458             data_idx = 0;
 459         } else {
 460             return false;
 461         }
 462
 463         if def.variants[data_idx].fields.len() == 1 {
 464             match def.variants[data_idx].fields[0].ty(tcx, substs).sty {
 465                 ty::FnPtr(_) => {
 466                     return true;
 467                 }
 468                 ty::Ref(..) => {
 469                     return true;
 470                 }
 471                 _ => {}
 472             }
 473         }
 474     }
 475     false
 476 }
 477
 478 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
 479     /// Check if the given type is "ffi-safe" (has a stable, well-defined
 480     /// representation which can be exported to C code).
 481     fn check_type_for_ffi(&self,
 482                           cache: &mut FxHashSet<Ty<'tcx>>,
 483                           ty: Ty<'tcx>) -> FfiResult<'tcx> {
 484         use self::FfiResult::*;
 485
 486         let cx = self.cx.tcx;
 487
 488         // Protect against infinite recursion, for example
 489         // `struct S(*mut S);`.
 490         // FIXME: A recursion limit is necessary as well, for irregular
 491         // recursive types.
 492         if !cache.insert(ty) {
 493             return FfiSafe;
 494         }
 495
 496         match ty.sty {
 497             ty::Adt(def, substs) => {
 498                 if def.is_phantom_data() {
 499                     return FfiPhantom(ty);
 500                 }
 501                 match def.adt_kind() {
 502                     AdtKind::Struct => {
 503                         if !def.repr.c() && !def.repr.transparent() {
 504                             return FfiUnsafe {
 505                                 ty: ty,
 506                                 reason: "this struct has unspecified layout",
 507                                 help: Some("consider adding a #[repr(C)] or #[repr(transparent)] \
 508                                             attribute to this struct"),
 509                             };
 510                         }
 511
 512                         if def.non_enum_variant().fields.is_empty() {
 513                             return FfiUnsafe {
 514                                 ty: ty,
 515                                 reason: "this struct has no fields",
 516                                 help: Some("consider adding a member to this struct"),
 517                             };
 518                         }
 519
 520                         // We can't completely trust repr(C) and repr(transparent) markings;
 521                         // make sure the fields are actually safe.
 522                         let mut all_phantom = true;
 523                         for field in &def.non_enum_variant().fields {
 524                             let field_ty = cx.normalize_erasing_regions(
 525                                 ParamEnv::reveal_all(),
 526                                 field.ty(cx, substs),
 527                             );
 528                             // repr(transparent) types are allowed to have arbitrary ZSTs, not just
 529                             // PhantomData -- skip checking all ZST fields
 530                             if def.repr.transparent() {
 531                                 let is_zst = cx
 532                                     .layout_of(cx.param_env(field.did).and(field_ty))
 533                                     .map(|layout| layout.is_zst())
 534                                     .unwrap_or(false);
 535                                 if is_zst {
 536                                     continue;
 537                                 }
 538                             }
 539                             let r = self.check_type_for_ffi(cache, field_ty);
 540                             match r {
 541                                 FfiSafe => {
 542                                     all_phantom = false;
 543                                 }
 544                                 FfiPhantom(..) => {}
 545                                 FfiUnsafe { .. } => {
 546                                     return r;
 547                                 }
 548                             }
 549                         }
 550
 551                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 552                     }
 553                     AdtKind::Union => {
 554                         if !def.repr.c() {
 555                             return FfiUnsafe {
 556                                 ty: ty,
 557                                 reason: "this union has unspecified layout",
 558                                 help: Some("consider adding a #[repr(C)] attribute to this union"),
 559                             };
 560                         }
 561
 562                         if def.non_enum_variant().fields.is_empty() {
 563                             return FfiUnsafe {
 564                                 ty: ty,
 565                                 reason: "this union has no fields",
 566                                 help: Some("consider adding a field to this union"),
 567                             };
 568                         }
 569
 570                         let mut all_phantom = true;
 571                         for field in &def.non_enum_variant().fields {
 572                             let field_ty = cx.normalize_erasing_regions(
 573                                 ParamEnv::reveal_all(),
 574                                 field.ty(cx, substs),
 575                             );
 576                             let r = self.check_type_for_ffi(cache, field_ty);
 577                             match r {
 578                                 FfiSafe => {
 579                                     all_phantom = false;
 580                                 }
 581                                 FfiPhantom(..) => {}
 582                                 FfiUnsafe { .. } => {
 583                                     return r;
 584                                 }
 585                             }
 586                         }
 587
 588                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 589                     }
 590                     AdtKind::Enum => {
 591                         if def.variants.is_empty() {
 592                             // Empty enums are okay... although sort of useless.
 593                             return FfiSafe;
 594                         }
 595
 596                         // Check for a repr() attribute to specify the size of the
 597                         // discriminant.
 598                         if !def.repr.c() && def.repr.int.is_none() {
 599                             // Special-case types like `Option<extern fn()>`.
 600                             if !is_repr_nullable_ptr(cx, def, substs) {
 601                                 return FfiUnsafe {
 602                                     ty: ty,
 603                                     reason: "enum has no representation hint",
 604                                     help: Some("consider adding a #[repr(...)] attribute \
 605                                                 to this enum"),
 606                                 };
 607                             }
 608                         }
 609
 610                         // Check the contained variants.
 611                         for variant in &def.variants {
 612                             for field in &variant.fields {
 613                                 let arg = cx.normalize_erasing_regions(
 614                                     ParamEnv::reveal_all(),
 615                                     field.ty(cx, substs),
 616                                 );
 617                                 let r = self.check_type_for_ffi(cache, arg);
 618                                 match r {
 619                                     FfiSafe => {}
 620                                     FfiUnsafe { .. } => {
 621                                         return r;
 622                                     }
 623                                     FfiPhantom(..) => {
 624                                         return FfiUnsafe {
 625                                             ty: ty,
 626                                             reason: "this enum contains a PhantomData field",
 627                                             help: None,
 628                                         };
 629                                     }
 630                                 }
 631                             }
 632                         }
 633                         FfiSafe
 634                     }
 635                 }
 636             }
 637
 638             ty::Char => FfiUnsafe {
 639                 ty: ty,
 640                 reason: "the `char` type has no C equivalent",
 641                 help: Some("consider using `u32` or `libc::wchar_t` instead"),
 642             },
 643
 644             ty::Int(ast::IntTy::I128) | ty::Uint(ast::UintTy::U128) => FfiUnsafe {
 645                 ty: ty,
 646                 reason: "128-bit integers don't currently have a known stable ABI",
 647                 help: None,
 648             },
 649
 650             // Primitive types with a stable representation.
 651             ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
 652
 653             ty::Slice(_) => FfiUnsafe {
 654                 ty: ty,
 655                 reason: "slices have no C equivalent",
 656                 help: Some("consider using a raw pointer instead"),
 657             },
 658
 659             ty::Dynamic(..) => FfiUnsafe {
 660                 ty: ty,
 661                 reason: "trait objects have no C equivalent",
 662                 help: None,
 663             },
 664
 665             ty::Str => FfiUnsafe {
 666                 ty: ty,
 667                 reason: "string slices have no C equivalent",
 668                 help: Some("consider using `*const u8` and a length instead"),
 669             },
 670
 671             ty::Tuple(..) => FfiUnsafe {
 672                 ty: ty,
 673                 reason: "tuples have unspecified layout",
 674                 help: Some("consider using a struct instead"),
 675             },
 676
 677             ty::RawPtr(ty::TypeAndMut { ty, .. }) |
 678             ty::Ref(_, ty, _) => self.check_type_for_ffi(cache, ty),
 679
 680             ty::Array(ty, _) => self.check_type_for_ffi(cache, ty),
 681
 682             ty::FnPtr(sig) => {
 683                 match sig.abi() {
 684                     Abi::Rust | Abi::RustIntrinsic | Abi::PlatformIntrinsic | Abi::RustCall => {
 685                         return FfiUnsafe {
 686                             ty: ty,
 687                             reason: "this function pointer has Rust-specific calling convention",
 688                             help: Some("consider using an `extern fn(...) -> ...` \
 689                                         function pointer instead"),
 690                         }
 691                     }
 692                     _ => {}
 693                 }
 694
 695                 let sig = cx.erase_late_bound_regions(&sig);
 696                 if !sig.output().is_unit() {
 697                     let r = self.check_type_for_ffi(cache, sig.output());
 698                     match r {
 699                         FfiSafe => {}
 700                         _ => {
 701                             return r;
 702                         }
 703                     }
 704                 }
 705                 for arg in sig.inputs() {
 706                     let r = self.check_type_for_ffi(cache, arg);
 707                     match r {
 708                         FfiSafe => {}
 709                         _ => {
 710                             return r;
 711                         }
 712                     }
 713                 }
 714                 FfiSafe
 715             }
 716
 717             ty::Foreign(..) => FfiSafe,
 718
 719             ty::Param(..) |
 720             ty::Infer(..) |
 721             ty::Bound(..) |
 722             ty::Error |
 723             ty::Closure(..) |
 724             ty::Generator(..) |
 725             ty::GeneratorWitness(..) |
 726             ty::UnnormalizedProjection(..) |
 727             ty::Projection(..) |
 728             ty::Opaque(..) |
 729             ty::FnDef(..) => bug!("Unexpected type in foreign function"),
 730         }
 731     }
 732
 733     fn check_type_for_ffi_and_report_errors(&mut self, sp: Span, ty: Ty<'tcx>) {
 734         // it is only OK to use this function because extern fns cannot have
 735         // any generic types right now:
 736         let ty = self.cx.tcx.normalize_erasing_regions(ParamEnv::reveal_all(), ty);
 737
 738         match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
 739             FfiResult::FfiSafe => {}
 740             FfiResult::FfiPhantom(ty) => {
 741                 self.cx.span_lint(IMPROPER_CTYPES,
 742                                   sp,
 743                                   &format!("`extern` block uses type `{}` which is not FFI-safe: \
 744                                             composed only of PhantomData", ty));
 745             }
 746             FfiResult::FfiUnsafe { ty: unsafe_ty, reason, help } => {
 747                 let msg = format!("`extern` block uses type `{}` which is not FFI-safe: {}",
 748                                   unsafe_ty, reason);
 749                 let mut diag = self.cx.struct_span_lint(IMPROPER_CTYPES, sp, &msg);
 750                 if let Some(s) = help {
 751                     diag.help(s);
 752                 }
 753                 if let ty::Adt(def, _) = unsafe_ty.sty {
 754                     if let Some(sp) = self.cx.tcx.hir.span_if_local(def.did) {
 755                         diag.span_note(sp, "type defined here");
 756                     }
 757                 }
 758                 diag.emit();
 759             }
 760         }
 761     }
 762
 763     fn check_foreign_fn(&mut self, id: ast::NodeId, decl: &hir::FnDecl) {
 764         let def_id = self.cx.tcx.hir.local_def_id(id);
 765         let sig = self.cx.tcx.fn_sig(def_id);
 766         let sig = self.cx.tcx.erase_late_bound_regions(&sig);
 767
 768         for (input_ty, input_hir) in sig.inputs().iter().zip(&decl.inputs) {
 769             self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty);
 770         }
 771
 772         if let hir::Return(ref ret_hir) = decl.output {
 773             let ret_ty = sig.output();
 774             if !ret_ty.is_unit() {
 775                 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty);
 776             }
 777         }
 778     }
 779
 780     fn check_foreign_static(&mut self, id: ast::NodeId, span: Span) {
 781         let def_id = self.cx.tcx.hir.local_def_id(id);
 782         let ty = self.cx.tcx.type_of(def_id);
 783         self.check_type_for_ffi_and_report_errors(span, ty);
 784     }
 785 }
 786
 787 #[derive(Copy, Clone)]
 788 pub struct ImproperCTypes;
 789
 790 impl LintPass for ImproperCTypes {
 791     fn get_lints(&self) -> LintArray {
 792         lint_array!(IMPROPER_CTYPES)
 793     }
 794 }
 795
 796 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImproperCTypes {
 797     fn check_foreign_item(&mut self, cx: &LateContext, it: &hir::ForeignItem) {
 798         let mut vis = ImproperCTypesVisitor { cx: cx };
 799         let abi = cx.tcx.hir.get_foreign_abi(it.id);
 800         if abi != Abi::RustIntrinsic && abi != Abi::PlatformIntrinsic {
 801             match it.node {
 802                 hir::ForeignItemKind::Fn(ref decl, _, _) => {
 803                     vis.check_foreign_fn(it.id, decl);
 804                 }
 805                 hir::ForeignItemKind::Static(ref ty, _) => {
 806                     vis.check_foreign_static(it.id, ty.span);
 807                 }
 808                 hir::ForeignItemKind::Type => ()
 809             }
 810         }
 811     }
 812 }
 813
 814 pub struct VariantSizeDifferences;
 815
 816 impl LintPass for VariantSizeDifferences {
 817     fn get_lints(&self) -> LintArray {
 818         lint_array!(VARIANT_SIZE_DIFFERENCES)
 819     }
 820 }
 821
 822 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for VariantSizeDifferences {
 823     fn check_item(&mut self, cx: &LateContext, it: &hir::Item) {
 824         if let hir::ItemKind::Enum(ref enum_definition, _) = it.node {
 825             let item_def_id = cx.tcx.hir.local_def_id(it.id);
 826             let t = cx.tcx.type_of(item_def_id);
 827             let ty = cx.tcx.erase_regions(&t);
 828             match cx.layout_of(ty) {
 829                 Ok(layout) => {
 830                     let variants = &layout.variants;
 831                     if let layout::Variants::Tagged { ref variants, ref tag, .. } = variants {
 832                         let discr_size = tag.value.size(cx.tcx).bytes();
 833
 834                         debug!("enum `{}` is {} bytes large with layout:\n{:#?}",
 835                                t, layout.size.bytes(), layout);
 836
 837                         let (largest, slargest, largest_index) = enum_definition.variants
 838                             .iter()
 839                             .zip(variants)
 840                             .map(|(variant, variant_layout)| {
 841                                 // Subtract the size of the enum discriminant.
 842                                 let bytes = variant_layout.size.bytes().saturating_sub(discr_size);
 843
 844                                 debug!("- variant `{}` is {} bytes large",
 845                                        variant.node.name,
 846                                        bytes);
 847                                 bytes
 848                             })
 849                             .enumerate()
 850                             .fold((0, 0, 0), |(l, s, li), (idx, size)| if size > l {
 851                                 (size, l, idx)
 852                             } else if size > s {
 853                                 (l, size, li)
 854                             } else {
 855                                 (l, s, li)
 856                             });
 857
 858                         // We only warn if the largest variant is at least thrice as large as
 859                         // the second-largest.
 860                         if largest > slargest * 3 && slargest > 0 {
 861                             cx.span_lint(VARIANT_SIZE_DIFFERENCES,
 862                                             enum_definition.variants[largest_index].span,
 863                                             &format!("enum variant is more than three times \
 864                                                       larger ({} bytes) than the next largest",
 865                                                      largest));
 866                         }
 867                     }
 868                 }
 869                 Err(ty::layout::LayoutError::Unknown(_)) => return,
 870                 Err(err @ ty::layout::LayoutError::SizeOverflow(_)) => {
 871                     bug!("failed to get layout for `{}`: {}", t, err);
 872                 }
 873             }
 874         }
 875     }
 876 }