src/librustc_lint/types.rs

   1 #![allow(non_snake_case)]
   2
   3 use rustc::hir::{ExprKind, Node};
   4 use crate::hir::def_id::DefId;
   5 use rustc::hir::lowering::is_range_literal;
   6 use rustc::ty::subst::SubstsRef;
   7 use rustc::ty::{self, AdtKind, ParamEnv, Ty, TyCtxt};
   8 use rustc::ty::layout::{self, IntegerExt, LayoutOf, VariantIdx, SizeSkeleton};
   9 use rustc::{lint, util};
  10 use rustc_data_structures::indexed_vec::Idx;
  11 use util::nodemap::FxHashSet;
  12 use lint::{LateContext, LintContext, LintArray};
  13 use lint::{LintPass, LateLintPass};
  14
  15 use std::cmp;
  16 use std::{i8, i16, i32, i64, u8, u16, u32, u64, f32, f64};
  17
  18 use syntax::{ast, attr, source_map};
  19 use syntax::errors::Applicability;
  20 use syntax::symbol::sym;
  21 use rustc_target::spec::abi::Abi;
  22 use syntax_pos::Span;
  23
  24 use rustc::hir;
  25
  26 use rustc::mir::interpret::{sign_extend, truncate};
  27
  28 use log::debug;
  29
  30 declare_lint! {
  31     UNUSED_COMPARISONS,
  32     Warn,
  33     "comparisons made useless by limits of the types involved"
  34 }
  35
  36 declare_lint! {
  37     OVERFLOWING_LITERALS,
  38     Deny,
  39     "literal out of range for its type"
  40 }
  41
  42 declare_lint! {
  43     VARIANT_SIZE_DIFFERENCES,
  44     Allow,
  45     "detects enums with widely varying variant sizes"
  46 }
  47
  48 #[derive(Copy, Clone)]
  49 pub struct TypeLimits {
  50     /// Id of the last visited negated expression
  51     negated_expr_id: hir::HirId,
  52 }
  53
  54 impl_lint_pass!(TypeLimits => [UNUSED_COMPARISONS, OVERFLOWING_LITERALS]);
  55
  56 impl TypeLimits {
  57     pub fn new() -> TypeLimits {
  58         TypeLimits { negated_expr_id: hir::DUMMY_HIR_ID }
  59     }
  60 }
  61
  62 /// Attempts to special-case the overflowing literal lint when it occurs as a range endpoint.
  63 /// Returns `true` iff the lint was overridden.
  64 fn lint_overflowing_range_endpoint<'a, 'tcx>(
  65     cx: &LateContext<'a, 'tcx>,
  66     lit: &hir::Lit,
  67     lit_val: u128,
  68     max: u128,
  69     expr: &'tcx hir::Expr,
  70     parent_expr: &'tcx hir::Expr,
  71     ty: impl std::fmt::Debug,
  72 ) -> bool {
  73     // We only want to handle exclusive (`..`) ranges,
  74     // which are represented as `ExprKind::Struct`.
  75     if let ExprKind::Struct(_, eps, _) = &parent_expr.kind {
  76         if eps.len() != 2 {
  77             return false;
  78         }
  79         // We can suggest using an inclusive range
  80         // (`..=`) instead only if it is the `end` that is
  81         // overflowing and only by 1.
  82         if eps[1].expr.hir_id == expr.hir_id && lit_val - 1 == max {
  83             let mut err = cx.struct_span_lint(
  84                 OVERFLOWING_LITERALS,
  85                 parent_expr.span,
  86                 &format!("range endpoint is out of range for `{:?}`", ty),
  87             );
  88             if let Ok(start) = cx.sess().source_map().span_to_snippet(eps[0].span) {
  89                 use ast::{LitKind, LitIntType};
  90                 // We need to preserve the literal's suffix,
  91                 // as it may determine typing information.
  92                 let suffix = match lit.node {
  93                     LitKind::Int(_, LitIntType::Signed(s)) => format!("{}", s),
  94                     LitKind::Int(_, LitIntType::Unsigned(s)) => format!("{}", s),
  95                     LitKind::Int(_, LitIntType::Unsuffixed) => "".to_owned(),
  96                     _ => bug!(),
  97                 };
  98                 let suggestion = format!("{}..={}{}", start, lit_val - 1, suffix);
  99                 err.span_suggestion(
 100                     parent_expr.span,
 101                     &"use an inclusive range instead",
 102                     suggestion,
 103                     Applicability::MachineApplicable,
 104                 );
 105                 err.emit();
 106                 return true;
 107             }
 108         }
 109     }
 110
 111     false
 112 }
 113
 114 // For `isize` & `usize`, be conservative with the warnings, so that the
 115 // warnings are consistent between 32- and 64-bit platforms.
 116 fn int_ty_range(int_ty: ast::IntTy) -> (i128, i128) {
 117     match int_ty {
 118         ast::IntTy::Isize => (i64::min_value() as i128, i64::max_value() as i128),
 119         ast::IntTy::I8 => (i8::min_value() as i64 as i128, i8::max_value() as i128),
 120         ast::IntTy::I16 => (i16::min_value() as i64 as i128, i16::max_value() as i128),
 121         ast::IntTy::I32 => (i32::min_value() as i64 as i128, i32::max_value() as i128),
 122         ast::IntTy::I64 => (i64::min_value() as i128, i64::max_value() as i128),
 123         ast::IntTy::I128 =>(i128::min_value() as i128, i128::max_value()),
 124     }
 125 }
 126
 127 fn uint_ty_range(uint_ty: ast::UintTy) -> (u128, u128) {
 128     match uint_ty {
 129         ast::UintTy::Usize => (u64::min_value() as u128, u64::max_value() as u128),
 130         ast::UintTy::U8 => (u8::min_value() as u128, u8::max_value() as u128),
 131         ast::UintTy::U16 => (u16::min_value() as u128, u16::max_value() as u128),
 132         ast::UintTy::U32 => (u32::min_value() as u128, u32::max_value() as u128),
 133         ast::UintTy::U64 => (u64::min_value() as u128, u64::max_value() as u128),
 134         ast::UintTy::U128 => (u128::min_value(), u128::max_value()),
 135     }
 136 }
 137
 138 fn get_bin_hex_repr(cx: &LateContext<'_, '_>, lit: &hir::Lit) -> Option<String> {
 139     let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?;
 140     let firstch = src.chars().next()?;
 141
 142     if firstch == '0' {
 143         match src.chars().nth(1) {
 144             Some('x') | Some('b') => return Some(src),
 145             _ => return None,
 146         }
 147     }
 148
 149     None
 150 }
 151
 152 fn report_bin_hex_error(
 153     cx: &LateContext<'_, '_>,
 154     expr: &hir::Expr,
 155     ty: attr::IntType,
 156     repr_str: String,
 157     val: u128,
 158     negative: bool,
 159 ) {
 160     let size = layout::Integer::from_attr(&cx.tcx, ty).size();
 161     let (t, actually) = match ty {
 162         attr::IntType::SignedInt(t) => {
 163             let actually = sign_extend(val, size) as i128;
 164             (format!("{:?}", t), actually.to_string())
 165         }
 166         attr::IntType::UnsignedInt(t) => {
 167             let actually = truncate(val, size);
 168             (format!("{:?}", t), actually.to_string())
 169         }
 170     };
 171     let mut err = cx.struct_span_lint(
 172         OVERFLOWING_LITERALS,
 173         expr.span,
 174         &format!("literal out of range for {}", t),
 175     );
 176     err.note(&format!(
 177         "the literal `{}` (decimal `{}`) does not fit into \
 178             an `{}` and will become `{}{}`",
 179         repr_str, val, t, actually, t
 180     ));
 181     if let Some(sugg_ty) =
 182         get_type_suggestion(&cx.tables.node_type(expr.hir_id), val, negative)
 183     {
 184         if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') {
 185             let (sans_suffix, _) = repr_str.split_at(pos);
 186             err.span_suggestion(
 187                 expr.span,
 188                 &format!("consider using `{}` instead", sugg_ty),
 189                 format!("{}{}", sans_suffix, sugg_ty),
 190                 Applicability::MachineApplicable
 191             );
 192         } else {
 193             err.help(&format!("consider using `{}` instead", sugg_ty));
 194         }
 195     }
 196
 197     err.emit();
 198 }
 199
 200 // This function finds the next fitting type and generates a suggestion string.
 201 // It searches for fitting types in the following way (`X < Y`):
 202 //  - `iX`: if literal fits in `uX` => `uX`, else => `iY`
 203 //  - `-iX` => `iY`
 204 //  - `uX` => `uY`
 205 //
 206 // No suggestion for: `isize`, `usize`.
 207 fn get_type_suggestion(t: Ty<'_>, val: u128, negative: bool) -> Option<String> {
 208     use syntax::ast::IntTy::*;
 209     use syntax::ast::UintTy::*;
 210     macro_rules! find_fit {
 211         ($ty:expr, $val:expr, $negative:expr,
 212          $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => {
 213             {
 214                 let _neg = if negative { 1 } else { 0 };
 215                 match $ty {
 216                     $($type => {
 217                         $(if !negative && val <= uint_ty_range($utypes).1 {
 218                             return Some(format!("{:?}", $utypes))
 219                         })*
 220                         $(if val <= int_ty_range($itypes).1 as u128 + _neg {
 221                             return Some(format!("{:?}", $itypes))
 222                         })*
 223                         None
 224                     },)+
 225                     _ => None
 226                 }
 227             }
 228         }
 229     }
 230     match t.kind {
 231         ty::Int(i) => find_fit!(i, val, negative,
 232                       I8 => [U8] => [I16, I32, I64, I128],
 233                       I16 => [U16] => [I32, I64, I128],
 234                       I32 => [U32] => [I64, I128],
 235                       I64 => [U64] => [I128],
 236                       I128 => [U128] => []),
 237         ty::Uint(u) => find_fit!(u, val, negative,
 238                       U8 => [U8, U16, U32, U64, U128] => [],
 239                       U16 => [U16, U32, U64, U128] => [],
 240                       U32 => [U32, U64, U128] => [],
 241                       U64 => [U64, U128] => [],
 242                       U128 => [U128] => []),
 243         _ => None,
 244     }
 245 }
 246
 247 fn lint_int_literal<'a, 'tcx>(
 248     cx: &LateContext<'a, 'tcx>,
 249     type_limits: &TypeLimits,
 250     e: &'tcx hir::Expr,
 251     lit: &hir::Lit,
 252     t: ast::IntTy,
 253     v: u128,
 254 ) {
 255     let int_type = if let ast::IntTy::Isize = t {
 256         cx.sess().target.isize_ty
 257     } else {
 258         t
 259     };
 260
 261     let (_, max) = int_ty_range(int_type);
 262     let max = max as u128;
 263     let negative = type_limits.negated_expr_id == e.hir_id;
 264
 265     // Detect literal value out of range [min, max] inclusive
 266     // avoiding use of -min to prevent overflow/panic
 267     if (negative && v > max + 1) || (!negative && v > max) {
 268         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 269             report_bin_hex_error(
 270                 cx,
 271                 e,
 272                 attr::IntType::SignedInt(t),
 273                 repr_str,
 274                 v,
 275                 negative,
 276             );
 277             return;
 278         }
 279
 280         let par_id = cx.tcx.hir().get_parent_node(e.hir_id);
 281         if let Node::Expr(par_e) = cx.tcx.hir().get(par_id) {
 282             if let hir::ExprKind::Struct(..) = par_e.kind {
 283                 if is_range_literal(cx.sess(), par_e)
 284                     && lint_overflowing_range_endpoint(cx, lit, v, max, e, par_e, t)
 285                 {
 286                     // The overflowing literal lint was overridden.
 287                     return;
 288                 }
 289             }
 290         }
 291
 292         cx.span_lint(
 293             OVERFLOWING_LITERALS,
 294             e.span,
 295             &format!("literal out of range for `{:?}`", t),
 296         );
 297     }
 298 }
 299
 300 fn lint_uint_literal<'a, 'tcx>(
 301     cx: &LateContext<'a, 'tcx>,
 302     e: &'tcx hir::Expr,
 303     lit: &hir::Lit,
 304     t: ast::UintTy,
 305 ) {
 306     let uint_type = if let ast::UintTy::Usize = t {
 307         cx.sess().target.usize_ty
 308     } else {
 309         t
 310     };
 311     let (min, max) = uint_ty_range(uint_type);
 312     let lit_val: u128 = match lit.node {
 313         // _v is u8, within range by definition
 314         ast::LitKind::Byte(_v) => return,
 315         ast::LitKind::Int(v, _) => v,
 316         _ => bug!(),
 317     };
 318     if lit_val < min || lit_val > max {
 319         let parent_id = cx.tcx.hir().get_parent_node(e.hir_id);
 320         if let Node::Expr(par_e) = cx.tcx.hir().get(parent_id) {
 321             match par_e.kind {
 322                 hir::ExprKind::Cast(..) => {
 323                     if let ty::Char = cx.tables.expr_ty(par_e).kind {
 324                         let mut err = cx.struct_span_lint(
 325                             OVERFLOWING_LITERALS,
 326                             par_e.span,
 327                             "only `u8` can be cast into `char`",
 328                         );
 329                         err.span_suggestion(
 330                             par_e.span,
 331                             &"use a `char` literal instead",
 332                             format!("'\\u{{{:X}}}'", lit_val),
 333                             Applicability::MachineApplicable,
 334                         );
 335                         err.emit();
 336                         return;
 337                     }
 338                 }
 339                 hir::ExprKind::Struct(..)
 340                     if is_range_literal(cx.sess(), par_e) => {
 341                         if lint_overflowing_range_endpoint(cx, lit, lit_val, max, e, par_e, t) {
 342                             // The overflowing literal lint was overridden.
 343                             return;
 344                         }
 345                     }
 346                 _ => {}
 347             }
 348         }
 349         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 350             report_bin_hex_error(cx, e, attr::IntType::UnsignedInt(t), repr_str, lit_val, false);
 351             return;
 352         }
 353         cx.span_lint(
 354             OVERFLOWING_LITERALS,
 355             e.span,
 356             &format!("literal out of range for `{:?}`", t),
 357         );
 358     }
 359 }
 360
 361 fn lint_literal<'a, 'tcx>(
 362     cx: &LateContext<'a, 'tcx>,
 363     type_limits: &TypeLimits,
 364     e: &'tcx hir::Expr,
 365     lit: &hir::Lit,
 366 ) {
 367     match cx.tables.node_type(e.hir_id).kind {
 368         ty::Int(t) => {
 369             match lit.node {
 370                 ast::LitKind::Int(v, ast::LitIntType::Signed(_)) |
 371                 ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => {
 372                     lint_int_literal(cx, type_limits, e, lit, t, v)
 373                 }
 374                 _ => bug!(),
 375             };
 376         }
 377         ty::Uint(t) => {
 378             lint_uint_literal(cx, e, lit, t)
 379         }
 380         ty::Float(t) => {
 381             let is_infinite = match lit.node {
 382                 ast::LitKind::Float(v, _) |
 383                 ast::LitKind::FloatUnsuffixed(v) => {
 384                     match t {
 385                         ast::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
 386                         ast::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
 387                     }
 388                 }
 389                 _ => bug!(),
 390             };
 391             if is_infinite == Ok(true) {
 392                 cx.span_lint(OVERFLOWING_LITERALS,
 393                              e.span,
 394                              &format!("literal out of range for `{:?}`", t));
 395             }
 396         }
 397         _ => {}
 398     }
 399 }
 400
 401 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TypeLimits {
 402     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx hir::Expr) {
 403         match e.kind {
 404             hir::ExprKind::Unary(hir::UnNeg, ref expr) => {
 405                 // propagate negation, if the negation itself isn't negated
 406                 if self.negated_expr_id != e.hir_id {
 407                     self.negated_expr_id = expr.hir_id;
 408                 }
 409             }
 410             hir::ExprKind::Binary(binop, ref l, ref r) => {
 411                 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
 412                     cx.span_lint(UNUSED_COMPARISONS,
 413                                  e.span,
 414                                  "comparison is useless due to type limits");
 415                 }
 416             }
 417             hir::ExprKind::Lit(ref lit) => lint_literal(cx, self, e, lit),
 418             _ => {}
 419         };
 420
 421         fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
 422             match binop.node {
 423                 hir::BinOpKind::Lt => v > min && v <= max,
 424                 hir::BinOpKind::Le => v >= min && v < max,
 425                 hir::BinOpKind::Gt => v >= min && v < max,
 426                 hir::BinOpKind::Ge => v > min && v <= max,
 427                 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
 428                 _ => bug!(),
 429             }
 430         }
 431
 432         fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
 433             source_map::respan(binop.span,
 434                             match binop.node {
 435                                 hir::BinOpKind::Lt => hir::BinOpKind::Gt,
 436                                 hir::BinOpKind::Le => hir::BinOpKind::Ge,
 437                                 hir::BinOpKind::Gt => hir::BinOpKind::Lt,
 438                                 hir::BinOpKind::Ge => hir::BinOpKind::Le,
 439                                 _ => return binop,
 440                             })
 441         }
 442
 443         fn check_limits(cx: &LateContext<'_, '_>,
 444                         binop: hir::BinOp,
 445                         l: &hir::Expr,
 446                         r: &hir::Expr)
 447                         -> bool {
 448             let (lit, expr, swap) = match (&l.kind, &r.kind) {
 449                 (&hir::ExprKind::Lit(_), _) => (l, r, true),
 450                 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
 451                 _ => return true,
 452             };
 453             // Normalize the binop so that the literal is always on the RHS in
 454             // the comparison
 455             let norm_binop = if swap { rev_binop(binop) } else { binop };
 456             match cx.tables.node_type(expr.hir_id).kind {
 457                 ty::Int(int_ty) => {
 458                     let (min, max) = int_ty_range(int_ty);
 459                     let lit_val: i128 = match lit.kind {
 460                         hir::ExprKind::Lit(ref li) => {
 461                             match li.node {
 462                                 ast::LitKind::Int(v, ast::LitIntType::Signed(_)) |
 463                                 ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => v as i128,
 464                                 _ => return true
 465                             }
 466                         },
 467                         _ => bug!()
 468                     };
 469                     is_valid(norm_binop, lit_val, min, max)
 470                 }
 471                 ty::Uint(uint_ty) => {
 472                     let (min, max) :(u128, u128) = uint_ty_range(uint_ty);
 473                     let lit_val: u128 = match lit.kind {
 474                         hir::ExprKind::Lit(ref li) => {
 475                             match li.node {
 476                                 ast::LitKind::Int(v, _) => v,
 477                                 _ => return true
 478                             }
 479                         },
 480                         _ => bug!()
 481                     };
 482                     is_valid(norm_binop, lit_val, min, max)
 483                 }
 484                 _ => true,
 485             }
 486         }
 487
 488         fn is_comparison(binop: hir::BinOp) -> bool {
 489             match binop.node {
 490                 hir::BinOpKind::Eq |
 491                 hir::BinOpKind::Lt |
 492                 hir::BinOpKind::Le |
 493                 hir::BinOpKind::Ne |
 494                 hir::BinOpKind::Ge |
 495                 hir::BinOpKind::Gt => true,
 496                 _ => false,
 497             }
 498         }
 499     }
 500 }
 501
 502 declare_lint! {
 503     IMPROPER_CTYPES,
 504     Warn,
 505     "proper use of libc types in foreign modules"
 506 }
 507
 508 declare_lint_pass!(ImproperCTypes => [IMPROPER_CTYPES]);
 509
 510 struct ImproperCTypesVisitor<'a, 'tcx> {
 511     cx: &'a LateContext<'a, 'tcx>,
 512 }
 513
 514 enum FfiResult<'tcx> {
 515     FfiSafe,
 516     FfiPhantom(Ty<'tcx>),
 517     FfiUnsafe {
 518         ty: Ty<'tcx>,
 519         reason: &'static str,
 520         help: Option<&'static str>,
 521     },
 522 }
 523
 524 fn is_zst<'tcx>(tcx: TyCtxt<'tcx>, did: DefId, ty: Ty<'tcx>) -> bool {
 525     tcx.layout_of(tcx.param_env(did).and(ty)).map(|layout| layout.is_zst()).unwrap_or(false)
 526 }
 527
 528 fn ty_is_known_nonnull<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool {
 529     match ty.kind {
 530         ty::FnPtr(_) => true,
 531         ty::Ref(..) => true,
 532         ty::Adt(field_def, substs) if field_def.repr.transparent() && !field_def.is_union() => {
 533             for field in field_def.all_fields() {
 534                 let field_ty = tcx.normalize_erasing_regions(
 535                     ParamEnv::reveal_all(),
 536                     field.ty(tcx, substs),
 537                 );
 538                 if is_zst(tcx, field.did, field_ty) {
 539                     continue;
 540                 }
 541
 542                 let attrs = tcx.get_attrs(field_def.did);
 543                 if attrs.iter().any(|a| a.check_name(sym::rustc_nonnull_optimization_guaranteed)) ||
 544                     ty_is_known_nonnull(tcx, field_ty) {
 545                     return true;
 546                 }
 547             }
 548
 549             false
 550         }
 551         _ => false,
 552     }
 553 }
 554
 555 /// Check if this enum can be safely exported based on the
 556 /// "nullable pointer optimization". Currently restricted
 557 /// to function pointers, references, core::num::NonZero*,
 558 /// core::ptr::NonNull, and #[repr(transparent)] newtypes.
 559 /// FIXME: This duplicates code in codegen.
 560 fn is_repr_nullable_ptr<'tcx>(
 561     tcx: TyCtxt<'tcx>,
 562     ty: Ty<'tcx>,
 563     ty_def: &'tcx ty::AdtDef,
 564     substs: SubstsRef<'tcx>,
 565 ) -> bool {
 566     if ty_def.variants.len() != 2 {
 567         return false;
 568     }
 569
 570     let get_variant_fields = |index| &ty_def.variants[VariantIdx::new(index)].fields;
 571     let variant_fields = [get_variant_fields(0), get_variant_fields(1)];
 572     let fields = if variant_fields[0].is_empty() {
 573         &variant_fields[1]
 574     } else if variant_fields[1].is_empty() {
 575         &variant_fields[0]
 576     } else {
 577         return false;
 578     };
 579
 580     if fields.len() != 1 {
 581         return false;
 582     }
 583
 584     let field_ty = fields[0].ty(tcx, substs);
 585     if !ty_is_known_nonnull(tcx, field_ty) {
 586         return false;
 587     }
 588
 589     // At this point, the field's type is known to be nonnull and the parent enum is Option-like.
 590     // If the computed size for the field and the enum are different, the nonnull optimization isn't
 591     // being applied (and we've got a problem somewhere).
 592     let compute_size_skeleton = |t| SizeSkeleton::compute(t, tcx, ParamEnv::reveal_all()).unwrap();
 593     if !compute_size_skeleton(ty).same_size(compute_size_skeleton(field_ty)) {
 594         bug!("improper_ctypes: Option nonnull optimization not applied?");
 595     }
 596
 597     true
 598 }
 599
 600 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
 601     /// Checks if the given type is "ffi-safe" (has a stable, well-defined
 602     /// representation which can be exported to C code).
 603     fn check_type_for_ffi(&self,
 604                           cache: &mut FxHashSet<Ty<'tcx>>,
 605                           ty: Ty<'tcx>) -> FfiResult<'tcx> {
 606         use FfiResult::*;
 607
 608         let cx = self.cx.tcx;
 609
 610         // Protect against infinite recursion, for example
 611         // `struct S(*mut S);`.
 612         // FIXME: A recursion limit is necessary as well, for irregular
 613         // recursive types.
 614         if !cache.insert(ty) {
 615             return FfiSafe;
 616         }
 617
 618         match ty.kind {
 619             ty::Adt(def, substs) => {
 620                 if def.is_phantom_data() {
 621                     return FfiPhantom(ty);
 622                 }
 623                 match def.adt_kind() {
 624                     AdtKind::Struct => {
 625                         if !def.repr.c() && !def.repr.transparent() {
 626                             return FfiUnsafe {
 627                                 ty,
 628                                 reason: "this struct has unspecified layout",
 629                                 help: Some("consider adding a `#[repr(C)]` or \
 630                                             `#[repr(transparent)]` attribute to this struct"),
 631                             };
 632                         }
 633
 634                         if def.non_enum_variant().fields.is_empty() {
 635                             return FfiUnsafe {
 636                                 ty,
 637                                 reason: "this struct has no fields",
 638                                 help: Some("consider adding a member to this struct"),
 639                             };
 640                         }
 641
 642                         // We can't completely trust repr(C) and repr(transparent) markings;
 643                         // make sure the fields are actually safe.
 644                         let mut all_phantom = true;
 645                         for field in &def.non_enum_variant().fields {
 646                             let field_ty = cx.normalize_erasing_regions(
 647                                 ParamEnv::reveal_all(),
 648                                 field.ty(cx, substs),
 649                             );
 650                             // repr(transparent) types are allowed to have arbitrary ZSTs, not just
 651                             // PhantomData -- skip checking all ZST fields
 652                             if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 653                                 continue;
 654                             }
 655                             let r = self.check_type_for_ffi(cache, field_ty);
 656                             match r {
 657                                 FfiSafe => {
 658                                     all_phantom = false;
 659                                 }
 660                                 FfiPhantom(..) => {}
 661                                 FfiUnsafe { .. } => {
 662                                     return r;
 663                                 }
 664                             }
 665                         }
 666
 667                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 668                     }
 669                     AdtKind::Union => {
 670                         if !def.repr.c() && !def.repr.transparent() {
 671                             return FfiUnsafe {
 672                                 ty,
 673                                 reason: "this union has unspecified layout",
 674                                 help: Some("consider adding a `#[repr(C)]` or \
 675                                             `#[repr(transparent)]` attribute to this union"),
 676                             };
 677                         }
 678
 679                         if def.non_enum_variant().fields.is_empty() {
 680                             return FfiUnsafe {
 681                                 ty,
 682                                 reason: "this union has no fields",
 683                                 help: Some("consider adding a field to this union"),
 684                             };
 685                         }
 686
 687                         let mut all_phantom = true;
 688                         for field in &def.non_enum_variant().fields {
 689                             let field_ty = cx.normalize_erasing_regions(
 690                                 ParamEnv::reveal_all(),
 691                                 field.ty(cx, substs),
 692                             );
 693                             // repr(transparent) types are allowed to have arbitrary ZSTs, not just
 694                             // PhantomData -- skip checking all ZST fields.
 695                             if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 696                                 continue;
 697                             }
 698                             let r = self.check_type_for_ffi(cache, field_ty);
 699                             match r {
 700                                 FfiSafe => {
 701                                     all_phantom = false;
 702                                 }
 703                                 FfiPhantom(..) => {}
 704                                 FfiUnsafe { .. } => {
 705                                     return r;
 706                                 }
 707                             }
 708                         }
 709
 710                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 711                     }
 712                     AdtKind::Enum => {
 713                         if def.variants.is_empty() {
 714                             // Empty enums are okay... although sort of useless.
 715                             return FfiSafe;
 716                         }
 717
 718                         // Check for a repr() attribute to specify the size of the
 719                         // discriminant.
 720                         if !def.repr.c() && !def.repr.transparent() && def.repr.int.is_none() {
 721                             // Special-case types like `Option<extern fn()>`.
 722                             if !is_repr_nullable_ptr(cx, ty, def, substs) {
 723                                 return FfiUnsafe {
 724                                     ty,
 725                                     reason: "enum has no representation hint",
 726                                     help: Some("consider adding a `#[repr(C)]`, \
 727                                                 `#[repr(transparent)]`, or integer `#[repr(...)]` \
 728                                                 attribute to this enum"),
 729                                 };
 730                             }
 731                         }
 732
 733                         // Check the contained variants.
 734                         for variant in &def.variants {
 735                             for field in &variant.fields {
 736                                 let field_ty = cx.normalize_erasing_regions(
 737                                     ParamEnv::reveal_all(),
 738                                     field.ty(cx, substs),
 739                                 );
 740                                 // repr(transparent) types are allowed to have arbitrary ZSTs, not
 741                                 // just PhantomData -- skip checking all ZST fields.
 742                                 if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 743                                     continue;
 744                                 }
 745                                 let r = self.check_type_for_ffi(cache, field_ty);
 746                                 match r {
 747                                     FfiSafe => {}
 748                                     FfiUnsafe { .. } => {
 749                                         return r;
 750                                     }
 751                                     FfiPhantom(..) => {
 752                                         return FfiUnsafe {
 753                                             ty,
 754                                             reason: "this enum contains a PhantomData field",
 755                                             help: None,
 756                                         };
 757                                     }
 758                                 }
 759                             }
 760                         }
 761                         FfiSafe
 762                     }
 763                 }
 764             }
 765
 766             ty::Char => FfiUnsafe {
 767                 ty,
 768                 reason: "the `char` type has no C equivalent",
 769                 help: Some("consider using `u32` or `libc::wchar_t` instead"),
 770             },
 771
 772             ty::Int(ast::IntTy::I128) | ty::Uint(ast::UintTy::U128) => FfiUnsafe {
 773                 ty,
 774                 reason: "128-bit integers don't currently have a known stable ABI",
 775                 help: None,
 776             },
 777
 778             // Primitive types with a stable representation.
 779             ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
 780
 781             ty::Slice(_) => FfiUnsafe {
 782                 ty,
 783                 reason: "slices have no C equivalent",
 784                 help: Some("consider using a raw pointer instead"),
 785             },
 786
 787             ty::Dynamic(..) => FfiUnsafe {
 788                 ty,
 789                 reason: "trait objects have no C equivalent",
 790                 help: None,
 791             },
 792
 793             ty::Str => FfiUnsafe {
 794                 ty,
 795                 reason: "string slices have no C equivalent",
 796                 help: Some("consider using `*const u8` and a length instead"),
 797             },
 798
 799             ty::Tuple(..) => FfiUnsafe {
 800                 ty,
 801                 reason: "tuples have unspecified layout",
 802                 help: Some("consider using a struct instead"),
 803             },
 804
 805             ty::RawPtr(ty::TypeAndMut { ty, .. }) |
 806             ty::Ref(_, ty, _) => self.check_type_for_ffi(cache, ty),
 807
 808             ty::Array(ty, _) => self.check_type_for_ffi(cache, ty),
 809
 810             ty::FnPtr(sig) => {
 811                 match sig.abi() {
 812                     Abi::Rust | Abi::RustIntrinsic | Abi::PlatformIntrinsic | Abi::RustCall => {
 813                         return FfiUnsafe {
 814                             ty,
 815                             reason: "this function pointer has Rust-specific calling convention",
 816                             help: Some("consider using an `extern fn(...) -> ...` \
 817                                         function pointer instead"),
 818                         }
 819                     }
 820                     _ => {}
 821                 }
 822
 823                 let sig = cx.erase_late_bound_regions(&sig);
 824                 if !sig.output().is_unit() {
 825                     let r = self.check_type_for_ffi(cache, sig.output());
 826                     match r {
 827                         FfiSafe => {}
 828                         _ => {
 829                             return r;
 830                         }
 831                     }
 832                 }
 833                 for arg in sig.inputs() {
 834                     let r = self.check_type_for_ffi(cache, arg);
 835                     match r {
 836                         FfiSafe => {}
 837                         _ => {
 838                             return r;
 839                         }
 840                     }
 841                 }
 842                 FfiSafe
 843             }
 844
 845             ty::Foreign(..) => FfiSafe,
 846
 847             ty::Param(..) |
 848             ty::Infer(..) |
 849             ty::Bound(..) |
 850             ty::Error |
 851             ty::Closure(..) |
 852             ty::Generator(..) |
 853             ty::GeneratorWitness(..) |
 854             ty::Placeholder(..) |
 855             ty::UnnormalizedProjection(..) |
 856             ty::Projection(..) |
 857             ty::Opaque(..) |
 858             ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty),
 859         }
 860     }
 861
 862     fn emit_ffi_unsafe_type_lint(
 863         &mut self,
 864         ty: Ty<'tcx>,
 865         sp: Span,
 866         note: &str,
 867         help: Option<&str>,
 868     ) {
 869         let mut diag = self.cx.struct_span_lint(
 870             IMPROPER_CTYPES,
 871             sp,
 872             &format!("`extern` block uses type `{}`, which is not FFI-safe", ty),
 873         );
 874         diag.span_label(sp, "not FFI-safe");
 875         if let Some(help) = help {
 876             diag.help(help);
 877         }
 878         diag.note(note);
 879         if let ty::Adt(def, _) = ty.kind {
 880             if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did) {
 881                 diag.span_note(sp, "type defined here");
 882             }
 883         }
 884         diag.emit();
 885     }
 886
 887     fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
 888         use crate::rustc::ty::TypeFoldable;
 889
 890         struct ProhibitOpaqueTypes<'tcx> {
 891             ty: Option<Ty<'tcx>>,
 892         };
 893
 894         impl<'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'tcx> {
 895             fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
 896                 if let ty::Opaque(..) = ty.kind {
 897                     self.ty = Some(ty);
 898                     true
 899                 } else {
 900                     ty.super_visit_with(self)
 901                 }
 902             }
 903         }
 904
 905         let mut visitor = ProhibitOpaqueTypes { ty: None };
 906         ty.visit_with(&mut visitor);
 907         if let Some(ty) = visitor.ty {
 908             self.emit_ffi_unsafe_type_lint(
 909                 ty,
 910                 sp,
 911                 "opaque types have no C equivalent",
 912                 None,
 913             );
 914             true
 915         } else {
 916             false
 917         }
 918     }
 919
 920     fn check_type_for_ffi_and_report_errors(&mut self, sp: Span, ty: Ty<'tcx>) {
 921         // We have to check for opaque types before `normalize_erasing_regions`,
 922         // which will replace opaque types with their underlying concrete type.
 923         if self.check_for_opaque_ty(sp, ty) {
 924             // We've already emitted an error due to an opaque type.
 925             return;
 926         }
 927
 928         // it is only OK to use this function because extern fns cannot have
 929         // any generic types right now:
 930         let ty = self.cx.tcx.normalize_erasing_regions(ParamEnv::reveal_all(), ty);
 931
 932         match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
 933             FfiResult::FfiSafe => {}
 934             FfiResult::FfiPhantom(ty) => {
 935                 self.emit_ffi_unsafe_type_lint(ty, sp, "composed only of `PhantomData`", None);
 936             }
 937             FfiResult::FfiUnsafe { ty, reason, help } => {
 938                 self.emit_ffi_unsafe_type_lint(ty, sp, reason, help);
 939             }
 940         }
 941     }
 942
 943     fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl) {
 944         let def_id = self.cx.tcx.hir().local_def_id(id);
 945         let sig = self.cx.tcx.fn_sig(def_id);
 946         let sig = self.cx.tcx.erase_late_bound_regions(&sig);
 947         let inputs = if sig.c_variadic {
 948             // Don't include the spoofed `VaListImpl` in the functions list
 949             // of inputs.
 950             &sig.inputs()[..sig.inputs().len() - 1]
 951         } else {
 952             &sig.inputs()[..]
 953         };
 954
 955         for (input_ty, input_hir) in inputs.iter().zip(&decl.inputs) {
 956             self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty);
 957         }
 958
 959         if let hir::Return(ref ret_hir) = decl.output {
 960             let ret_ty = sig.output();
 961             if !ret_ty.is_unit() {
 962                 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty);
 963             }
 964         }
 965     }
 966
 967     fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
 968         let def_id = self.cx.tcx.hir().local_def_id(id);
 969         let ty = self.cx.tcx.type_of(def_id);
 970         self.check_type_for_ffi_and_report_errors(span, ty);
 971     }
 972 }
 973
 974 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImproperCTypes {
 975     fn check_foreign_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::ForeignItem) {
 976         let mut vis = ImproperCTypesVisitor { cx };
 977         let abi = cx.tcx.hir().get_foreign_abi(it.hir_id);
 978         if let Abi::Rust | Abi::RustCall | Abi::RustIntrinsic | Abi::PlatformIntrinsic = abi {
 979             // Don't worry about types in internal ABIs.
 980         } else {
 981             match it.node {
 982                 hir::ForeignItemKind::Fn(ref decl, _, _) => {
 983                     vis.check_foreign_fn(it.hir_id, decl);
 984                 }
 985                 hir::ForeignItemKind::Static(ref ty, _) => {
 986                     vis.check_foreign_static(it.hir_id, ty.span);
 987                 }
 988                 hir::ForeignItemKind::Type => ()
 989             }
 990         }
 991     }
 992 }
 993
 994 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
 995
 996 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for VariantSizeDifferences {
 997     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item) {
 998         if let hir::ItemKind::Enum(ref enum_definition, _) = it.node {
 999             let item_def_id = cx.tcx.hir().local_def_id(it.hir_id);
1000             let t = cx.tcx.type_of(item_def_id);
1001             let ty = cx.tcx.erase_regions(&t);
1002             let layout = match cx.layout_of(ty) {
1003                 Ok(layout) => layout,
1004                 Err(ty::layout::LayoutError::Unknown(_)) => return,
1005                 Err(err @ ty::layout::LayoutError::SizeOverflow(_)) => {
1006                     bug!("failed to get layout for `{}`: {}", t, err);
1007                 }
1008             };
1009             let (variants, tag) = match layout.variants {
1010                 layout::Variants::Multiple {
1011                     discr_kind: layout::DiscriminantKind::Tag,
1012                     ref discr,
1013                     ref variants,
1014                     ..
1015                 } => (variants, discr),
1016                 _ => return,
1017             };
1018
1019             let discr_size = tag.value.size(&cx.tcx).bytes();
1020
1021             debug!("enum `{}` is {} bytes large with layout:\n{:#?}",
1022                    t, layout.size.bytes(), layout);
1023
1024             let (largest, slargest, largest_index) = enum_definition.variants
1025                 .iter()
1026                 .zip(variants)
1027                 .map(|(variant, variant_layout)| {
1028                     // Subtract the size of the enum discriminant.
1029                     let bytes = variant_layout.size.bytes().saturating_sub(discr_size);
1030
1031                     debug!("- variant `{}` is {} bytes large",
1032                            variant.ident,
1033                            bytes);
1034                     bytes
1035                 })
1036                 .enumerate()
1037                 .fold((0, 0, 0), |(l, s, li), (idx, size)| if size > l {
1038                     (size, l, idx)
1039                 } else if size > s {
1040                     (l, size, li)
1041                 } else {
1042                     (l, s, li)
1043                 });
1044
1045             // We only warn if the largest variant is at least thrice as large as
1046             // the second-largest.
1047             if largest > slargest * 3 && slargest > 0 {
1048                 cx.span_lint(VARIANT_SIZE_DIFFERENCES,
1049                                 enum_definition.variants[largest_index].span,
1050                                 &format!("enum variant is more than three times \
1051                                           larger ({} bytes) than the next largest",
1052                                          largest));
1053             }
1054         }
1055     }
1056 }