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_index::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: &str,
  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.name_str()),
  94                     LitKind::Int(_, LitIntType::Unsigned(s)) => format!("{}", s.name_str()),
  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             (t.name_str(), actually.to_string())
 165         }
 166         attr::IntType::UnsignedInt(t) => {
 167             let actually = truncate(val, size);
 168             (t.name_str(), 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<&'static str> {
 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($utypes.name_str())
 219                         })*
 220                         $(if val <= int_ty_range($itypes).1 as u128 + _neg {
 221                             return Some($itypes.name_str())
 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 = t.normalize(cx.sess().target.ptr_width);
 256     let (_, max) = int_ty_range(int_type);
 257     let max = max as u128;
 258     let negative = type_limits.negated_expr_id == e.hir_id;
 259
 260     // Detect literal value out of range [min, max] inclusive
 261     // avoiding use of -min to prevent overflow/panic
 262     if (negative && v > max + 1) || (!negative && v > max) {
 263         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 264             report_bin_hex_error(
 265                 cx,
 266                 e,
 267                 attr::IntType::SignedInt(t),
 268                 repr_str,
 269                 v,
 270                 negative,
 271             );
 272             return;
 273         }
 274
 275         let par_id = cx.tcx.hir().get_parent_node(e.hir_id);
 276         if let Node::Expr(par_e) = cx.tcx.hir().get(par_id) {
 277             if let hir::ExprKind::Struct(..) = par_e.kind {
 278                 if is_range_literal(cx.sess(), par_e)
 279                     && lint_overflowing_range_endpoint(cx, lit, v, max, e, par_e, t.name_str())
 280                 {
 281                     // The overflowing literal lint was overridden.
 282                     return;
 283                 }
 284             }
 285         }
 286
 287         cx.span_lint(
 288             OVERFLOWING_LITERALS,
 289             e.span,
 290             &format!("literal out of range for `{}`", t.name_str()),
 291         );
 292     }
 293 }
 294
 295 fn lint_uint_literal<'a, 'tcx>(
 296     cx: &LateContext<'a, 'tcx>,
 297     e: &'tcx hir::Expr,
 298     lit: &hir::Lit,
 299     t: ast::UintTy,
 300 ) {
 301     let uint_type = t.normalize(cx.sess().target.ptr_width);
 302     let (min, max) = uint_ty_range(uint_type);
 303     let lit_val: u128 = match lit.node {
 304         // _v is u8, within range by definition
 305         ast::LitKind::Byte(_v) => return,
 306         ast::LitKind::Int(v, _) => v,
 307         _ => bug!(),
 308     };
 309     if lit_val < min || lit_val > max {
 310         let parent_id = cx.tcx.hir().get_parent_node(e.hir_id);
 311         if let Node::Expr(par_e) = cx.tcx.hir().get(parent_id) {
 312             match par_e.kind {
 313                 hir::ExprKind::Cast(..) => {
 314                     if let ty::Char = cx.tables.expr_ty(par_e).kind {
 315                         let mut err = cx.struct_span_lint(
 316                             OVERFLOWING_LITERALS,
 317                             par_e.span,
 318                             "only `u8` can be cast into `char`",
 319                         );
 320                         err.span_suggestion(
 321                             par_e.span,
 322                             &"use a `char` literal instead",
 323                             format!("'\\u{{{:X}}}'", lit_val),
 324                             Applicability::MachineApplicable,
 325                         );
 326                         err.emit();
 327                         return;
 328                     }
 329                 }
 330                 hir::ExprKind::Struct(..)
 331                     if is_range_literal(cx.sess(), par_e) => {
 332                         let t = t.name_str();
 333                         if lint_overflowing_range_endpoint(cx, lit, lit_val, max, e, par_e, t) {
 334                             // The overflowing literal lint was overridden.
 335                             return;
 336                         }
 337                     }
 338                 _ => {}
 339             }
 340         }
 341         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 342             report_bin_hex_error(cx, e, attr::IntType::UnsignedInt(t), repr_str, lit_val, false);
 343             return;
 344         }
 345         cx.span_lint(
 346             OVERFLOWING_LITERALS,
 347             e.span,
 348             &format!("literal out of range for `{}`", t.name_str()),
 349         );
 350     }
 351 }
 352
 353 fn lint_literal<'a, 'tcx>(
 354     cx: &LateContext<'a, 'tcx>,
 355     type_limits: &TypeLimits,
 356     e: &'tcx hir::Expr,
 357     lit: &hir::Lit,
 358 ) {
 359     match cx.tables.node_type(e.hir_id).kind {
 360         ty::Int(t) => {
 361             match lit.node {
 362                 ast::LitKind::Int(v, ast::LitIntType::Signed(_)) |
 363                 ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => {
 364                     lint_int_literal(cx, type_limits, e, lit, t, v)
 365                 }
 366                 _ => bug!(),
 367             };
 368         }
 369         ty::Uint(t) => {
 370             lint_uint_literal(cx, e, lit, t)
 371         }
 372         ty::Float(t) => {
 373             let is_infinite = match lit.node {
 374                 ast::LitKind::Float(v, _) => {
 375                     match t {
 376                         ast::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
 377                         ast::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
 378                     }
 379                 }
 380                 _ => bug!(),
 381             };
 382             if is_infinite == Ok(true) {
 383                 cx.span_lint(
 384                     OVERFLOWING_LITERALS,
 385                     e.span,
 386                     &format!("literal out of range for `{}`", t.name_str()),
 387                 );
 388             }
 389         }
 390         _ => {}
 391     }
 392 }
 393
 394 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TypeLimits {
 395     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx hir::Expr) {
 396         match e.kind {
 397             hir::ExprKind::Unary(hir::UnNeg, ref expr) => {
 398                 // propagate negation, if the negation itself isn't negated
 399                 if self.negated_expr_id != e.hir_id {
 400                     self.negated_expr_id = expr.hir_id;
 401                 }
 402             }
 403             hir::ExprKind::Binary(binop, ref l, ref r) => {
 404                 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
 405                     cx.span_lint(UNUSED_COMPARISONS,
 406                                  e.span,
 407                                  "comparison is useless due to type limits");
 408                 }
 409             }
 410             hir::ExprKind::Lit(ref lit) => lint_literal(cx, self, e, lit),
 411             _ => {}
 412         };
 413
 414         fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
 415             match binop.node {
 416                 hir::BinOpKind::Lt => v > min && v <= max,
 417                 hir::BinOpKind::Le => v >= min && v < max,
 418                 hir::BinOpKind::Gt => v >= min && v < max,
 419                 hir::BinOpKind::Ge => v > min && v <= max,
 420                 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
 421                 _ => bug!(),
 422             }
 423         }
 424
 425         fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
 426             source_map::respan(binop.span,
 427                             match binop.node {
 428                                 hir::BinOpKind::Lt => hir::BinOpKind::Gt,
 429                                 hir::BinOpKind::Le => hir::BinOpKind::Ge,
 430                                 hir::BinOpKind::Gt => hir::BinOpKind::Lt,
 431                                 hir::BinOpKind::Ge => hir::BinOpKind::Le,
 432                                 _ => return binop,
 433                             })
 434         }
 435
 436         fn check_limits(cx: &LateContext<'_, '_>,
 437                         binop: hir::BinOp,
 438                         l: &hir::Expr,
 439                         r: &hir::Expr)
 440                         -> bool {
 441             let (lit, expr, swap) = match (&l.kind, &r.kind) {
 442                 (&hir::ExprKind::Lit(_), _) => (l, r, true),
 443                 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
 444                 _ => return true,
 445             };
 446             // Normalize the binop so that the literal is always on the RHS in
 447             // the comparison
 448             let norm_binop = if swap { rev_binop(binop) } else { binop };
 449             match cx.tables.node_type(expr.hir_id).kind {
 450                 ty::Int(int_ty) => {
 451                     let (min, max) = int_ty_range(int_ty);
 452                     let lit_val: i128 = match lit.kind {
 453                         hir::ExprKind::Lit(ref li) => {
 454                             match li.node {
 455                                 ast::LitKind::Int(v, ast::LitIntType::Signed(_)) |
 456                                 ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => v as i128,
 457                                 _ => return true
 458                             }
 459                         },
 460                         _ => bug!()
 461                     };
 462                     is_valid(norm_binop, lit_val, min, max)
 463                 }
 464                 ty::Uint(uint_ty) => {
 465                     let (min, max) :(u128, u128) = uint_ty_range(uint_ty);
 466                     let lit_val: u128 = match lit.kind {
 467                         hir::ExprKind::Lit(ref li) => {
 468                             match li.node {
 469                                 ast::LitKind::Int(v, _) => v,
 470                                 _ => return true
 471                             }
 472                         },
 473                         _ => bug!()
 474                     };
 475                     is_valid(norm_binop, lit_val, min, max)
 476                 }
 477                 _ => true,
 478             }
 479         }
 480
 481         fn is_comparison(binop: hir::BinOp) -> bool {
 482             match binop.node {
 483                 hir::BinOpKind::Eq |
 484                 hir::BinOpKind::Lt |
 485                 hir::BinOpKind::Le |
 486                 hir::BinOpKind::Ne |
 487                 hir::BinOpKind::Ge |
 488                 hir::BinOpKind::Gt => true,
 489                 _ => false,
 490             }
 491         }
 492     }
 493 }
 494
 495 declare_lint! {
 496     IMPROPER_CTYPES,
 497     Warn,
 498     "proper use of libc types in foreign modules"
 499 }
 500
 501 declare_lint_pass!(ImproperCTypes => [IMPROPER_CTYPES]);
 502
 503 struct ImproperCTypesVisitor<'a, 'tcx> {
 504     cx: &'a LateContext<'a, 'tcx>,
 505 }
 506
 507 enum FfiResult<'tcx> {
 508     FfiSafe,
 509     FfiPhantom(Ty<'tcx>),
 510     FfiUnsafe {
 511         ty: Ty<'tcx>,
 512         reason: &'static str,
 513         help: Option<&'static str>,
 514     },
 515 }
 516
 517 fn is_zst<'tcx>(tcx: TyCtxt<'tcx>, did: DefId, ty: Ty<'tcx>) -> bool {
 518     tcx.layout_of(tcx.param_env(did).and(ty)).map(|layout| layout.is_zst()).unwrap_or(false)
 519 }
 520
 521 fn ty_is_known_nonnull<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool {
 522     match ty.kind {
 523         ty::FnPtr(_) => true,
 524         ty::Ref(..) => true,
 525         ty::Adt(field_def, substs) if field_def.repr.transparent() && !field_def.is_union() => {
 526             for field in field_def.all_fields() {
 527                 let field_ty = tcx.normalize_erasing_regions(
 528                     ParamEnv::reveal_all(),
 529                     field.ty(tcx, substs),
 530                 );
 531                 if is_zst(tcx, field.did, field_ty) {
 532                     continue;
 533                 }
 534
 535                 let attrs = tcx.get_attrs(field_def.did);
 536                 if attrs.iter().any(|a| a.check_name(sym::rustc_nonnull_optimization_guaranteed)) ||
 537                     ty_is_known_nonnull(tcx, field_ty) {
 538                     return true;
 539                 }
 540             }
 541
 542             false
 543         }
 544         _ => false,
 545     }
 546 }
 547
 548 /// Check if this enum can be safely exported based on the
 549 /// "nullable pointer optimization". Currently restricted
 550 /// to function pointers, references, core::num::NonZero*,
 551 /// core::ptr::NonNull, and #[repr(transparent)] newtypes.
 552 /// FIXME: This duplicates code in codegen.
 553 fn is_repr_nullable_ptr<'tcx>(
 554     tcx: TyCtxt<'tcx>,
 555     ty: Ty<'tcx>,
 556     ty_def: &'tcx ty::AdtDef,
 557     substs: SubstsRef<'tcx>,
 558 ) -> bool {
 559     if ty_def.variants.len() != 2 {
 560         return false;
 561     }
 562
 563     let get_variant_fields = |index| &ty_def.variants[VariantIdx::new(index)].fields;
 564     let variant_fields = [get_variant_fields(0), get_variant_fields(1)];
 565     let fields = if variant_fields[0].is_empty() {
 566         &variant_fields[1]
 567     } else if variant_fields[1].is_empty() {
 568         &variant_fields[0]
 569     } else {
 570         return false;
 571     };
 572
 573     if fields.len() != 1 {
 574         return false;
 575     }
 576
 577     let field_ty = fields[0].ty(tcx, substs);
 578     if !ty_is_known_nonnull(tcx, field_ty) {
 579         return false;
 580     }
 581
 582     // At this point, the field's type is known to be nonnull and the parent enum is Option-like.
 583     // If the computed size for the field and the enum are different, the nonnull optimization isn't
 584     // being applied (and we've got a problem somewhere).
 585     let compute_size_skeleton = |t| SizeSkeleton::compute(t, tcx, ParamEnv::reveal_all()).unwrap();
 586     if !compute_size_skeleton(ty).same_size(compute_size_skeleton(field_ty)) {
 587         bug!("improper_ctypes: Option nonnull optimization not applied?");
 588     }
 589
 590     true
 591 }
 592
 593 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
 594
 595     /// Check if the type is array and emit an unsafe type lint.
 596     fn check_for_array_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
 597         if let ty::Array(..) = ty.kind {
 598             self.emit_ffi_unsafe_type_lint(
 599                 ty,
 600                 sp,
 601                 "passing raw arrays by value is not FFI-safe",
 602                 Some("consider passing a pointer to the array"),
 603             );
 604             true
 605         } else {
 606             false
 607         }
 608     }
 609
 610
 611     /// Checks if the given type is "ffi-safe" (has a stable, well-defined
 612     /// representation which can be exported to C code).
 613     fn check_type_for_ffi(&self,
 614                           cache: &mut FxHashSet<Ty<'tcx>>,
 615                           ty: Ty<'tcx>) -> FfiResult<'tcx> {
 616         use FfiResult::*;
 617
 618         let cx = self.cx.tcx;
 619
 620         // Protect against infinite recursion, for example
 621         // `struct S(*mut S);`.
 622         // FIXME: A recursion limit is necessary as well, for irregular
 623         // recursive types.
 624         if !cache.insert(ty) {
 625             return FfiSafe;
 626         }
 627
 628         match ty.kind {
 629             ty::Adt(def, substs) => {
 630                 if def.is_phantom_data() {
 631                     return FfiPhantom(ty);
 632                 }
 633                 match def.adt_kind() {
 634                     AdtKind::Struct => {
 635                         if !def.repr.c() && !def.repr.transparent() {
 636                             return FfiUnsafe {
 637                                 ty,
 638                                 reason: "this struct has unspecified layout",
 639                                 help: Some("consider adding a `#[repr(C)]` or \
 640                                             `#[repr(transparent)]` attribute to this struct"),
 641                             };
 642                         }
 643
 644                         let is_non_exhaustive =
 645                             def.non_enum_variant().is_field_list_non_exhaustive();
 646                         if is_non_exhaustive && !def.did.is_local() {
 647                             return FfiUnsafe {
 648                                 ty,
 649                                 reason: "this struct is non-exhaustive",
 650                                 help: None,
 651                             };
 652                         }
 653
 654                         if def.non_enum_variant().fields.is_empty() {
 655                             return FfiUnsafe {
 656                                 ty,
 657                                 reason: "this struct has no fields",
 658                                 help: Some("consider adding a member to this struct"),
 659                             };
 660                         }
 661
 662                         // We can't completely trust repr(C) and repr(transparent) markings;
 663                         // make sure the fields are actually safe.
 664                         let mut all_phantom = true;
 665                         for field in &def.non_enum_variant().fields {
 666                             let field_ty = cx.normalize_erasing_regions(
 667                                 ParamEnv::reveal_all(),
 668                                 field.ty(cx, substs),
 669                             );
 670                             // repr(transparent) types are allowed to have arbitrary ZSTs, not just
 671                             // PhantomData -- skip checking all ZST fields
 672                             if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 673                                 continue;
 674                             }
 675                             let r = self.check_type_for_ffi(cache, field_ty);
 676                             match r {
 677                                 FfiSafe => {
 678                                     all_phantom = false;
 679                                 }
 680                                 FfiPhantom(..) => {}
 681                                 FfiUnsafe { .. } => {
 682                                     return r;
 683                                 }
 684                             }
 685                         }
 686
 687                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 688                     }
 689                     AdtKind::Union => {
 690                         if !def.repr.c() && !def.repr.transparent() {
 691                             return FfiUnsafe {
 692                                 ty,
 693                                 reason: "this union has unspecified layout",
 694                                 help: Some("consider adding a `#[repr(C)]` or \
 695                                             `#[repr(transparent)]` attribute to this union"),
 696                             };
 697                         }
 698
 699                         if def.non_enum_variant().fields.is_empty() {
 700                             return FfiUnsafe {
 701                                 ty,
 702                                 reason: "this union has no fields",
 703                                 help: Some("consider adding a field to this union"),
 704                             };
 705                         }
 706
 707                         let mut all_phantom = true;
 708                         for field in &def.non_enum_variant().fields {
 709                             let field_ty = cx.normalize_erasing_regions(
 710                                 ParamEnv::reveal_all(),
 711                                 field.ty(cx, substs),
 712                             );
 713                             // repr(transparent) types are allowed to have arbitrary ZSTs, not just
 714                             // PhantomData -- skip checking all ZST fields.
 715                             if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 716                                 continue;
 717                             }
 718                             let r = self.check_type_for_ffi(cache, field_ty);
 719                             match r {
 720                                 FfiSafe => {
 721                                     all_phantom = false;
 722                                 }
 723                                 FfiPhantom(..) => {}
 724                                 FfiUnsafe { .. } => {
 725                                     return r;
 726                                 }
 727                             }
 728                         }
 729
 730                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 731                     }
 732                     AdtKind::Enum => {
 733                         if def.variants.is_empty() {
 734                             // Empty enums are okay... although sort of useless.
 735                             return FfiSafe;
 736                         }
 737
 738                         // Check for a repr() attribute to specify the size of the
 739                         // discriminant.
 740                         if !def.repr.c() && !def.repr.transparent() && def.repr.int.is_none() {
 741                             // Special-case types like `Option<extern fn()>`.
 742                             if !is_repr_nullable_ptr(cx, ty, def, substs) {
 743                                 return FfiUnsafe {
 744                                     ty,
 745                                     reason: "enum has no representation hint",
 746                                     help: Some("consider adding a `#[repr(C)]`, \
 747                                                 `#[repr(transparent)]`, or integer `#[repr(...)]` \
 748                                                 attribute to this enum"),
 749                                 };
 750                             }
 751                         }
 752
 753                         if def.is_variant_list_non_exhaustive() && !def.did.is_local() {
 754                             return FfiUnsafe {
 755                                 ty,
 756                                 reason: "this enum is non-exhaustive",
 757                                 help: None,
 758                             };
 759                         }
 760
 761                         // Check the contained variants.
 762                         for variant in &def.variants {
 763                             let is_non_exhaustive = variant.is_field_list_non_exhaustive();
 764                             if is_non_exhaustive && !variant.def_id.is_local() {
 765                                 return FfiUnsafe {
 766                                     ty,
 767                                     reason: "this enum has non-exhaustive variants",
 768                                     help: None,
 769                                 };
 770                             }
 771
 772                             for field in &variant.fields {
 773                                 let field_ty = cx.normalize_erasing_regions(
 774                                     ParamEnv::reveal_all(),
 775                                     field.ty(cx, substs),
 776                                 );
 777                                 // repr(transparent) types are allowed to have arbitrary ZSTs, not
 778                                 // just PhantomData -- skip checking all ZST fields.
 779                                 if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 780                                     continue;
 781                                 }
 782                                 let r = self.check_type_for_ffi(cache, field_ty);
 783                                 match r {
 784                                     FfiSafe => {}
 785                                     FfiUnsafe { .. } => {
 786                                         return r;
 787                                     }
 788                                     FfiPhantom(..) => {
 789                                         return FfiUnsafe {
 790                                             ty,
 791                                             reason: "this enum contains a PhantomData field",
 792                                             help: None,
 793                                         };
 794                                     }
 795                                 }
 796                             }
 797                         }
 798                         FfiSafe
 799                     }
 800                 }
 801             }
 802
 803             ty::Char => FfiUnsafe {
 804                 ty,
 805                 reason: "the `char` type has no C equivalent",
 806                 help: Some("consider using `u32` or `libc::wchar_t` instead"),
 807             },
 808
 809             ty::Int(ast::IntTy::I128) | ty::Uint(ast::UintTy::U128) => FfiUnsafe {
 810                 ty,
 811                 reason: "128-bit integers don't currently have a known stable ABI",
 812                 help: None,
 813             },
 814
 815             // Primitive types with a stable representation.
 816             ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
 817
 818             ty::Slice(_) => FfiUnsafe {
 819                 ty,
 820                 reason: "slices have no C equivalent",
 821                 help: Some("consider using a raw pointer instead"),
 822             },
 823
 824             ty::Dynamic(..) => FfiUnsafe {
 825                 ty,
 826                 reason: "trait objects have no C equivalent",
 827                 help: None,
 828             },
 829
 830             ty::Str => FfiUnsafe {
 831                 ty,
 832                 reason: "string slices have no C equivalent",
 833                 help: Some("consider using `*const u8` and a length instead"),
 834             },
 835
 836             ty::Tuple(..) => FfiUnsafe {
 837                 ty,
 838                 reason: "tuples have unspecified layout",
 839                 help: Some("consider using a struct instead"),
 840             },
 841
 842             ty::RawPtr(ty::TypeAndMut { ty, .. }) |
 843             ty::Ref(_, ty, _) => self.check_type_for_ffi(cache, ty),
 844
 845             ty::Array(inner_ty, _) => self.check_type_for_ffi(cache, inner_ty),
 846
 847             ty::FnPtr(sig) => {
 848                 match sig.abi() {
 849                     Abi::Rust | Abi::RustIntrinsic | Abi::PlatformIntrinsic | Abi::RustCall => {
 850                         return FfiUnsafe {
 851                             ty,
 852                             reason: "this function pointer has Rust-specific calling convention",
 853                             help: Some("consider using an `extern fn(...) -> ...` \
 854                                         function pointer instead"),
 855                         }
 856                     }
 857                     _ => {}
 858                 }
 859
 860                 let sig = cx.erase_late_bound_regions(&sig);
 861                 if !sig.output().is_unit() {
 862                     let r = self.check_type_for_ffi(cache, sig.output());
 863                     match r {
 864                         FfiSafe => {}
 865                         _ => {
 866                             return r;
 867                         }
 868                     }
 869                 }
 870                 for arg in sig.inputs() {
 871                     let r = self.check_type_for_ffi(cache, arg);
 872                     match r {
 873                         FfiSafe => {}
 874                         _ => {
 875                             return r;
 876                         }
 877                     }
 878                 }
 879                 FfiSafe
 880             }
 881
 882             ty::Foreign(..) => FfiSafe,
 883
 884             ty::Param(..) |
 885             ty::Infer(..) |
 886             ty::Bound(..) |
 887             ty::Error |
 888             ty::Closure(..) |
 889             ty::Generator(..) |
 890             ty::GeneratorWitness(..) |
 891             ty::Placeholder(..) |
 892             ty::UnnormalizedProjection(..) |
 893             ty::Projection(..) |
 894             ty::Opaque(..) |
 895             ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty),
 896         }
 897     }
 898
 899     fn emit_ffi_unsafe_type_lint(
 900         &mut self,
 901         ty: Ty<'tcx>,
 902         sp: Span,
 903         note: &str,
 904         help: Option<&str>,
 905     ) {
 906         let mut diag = self.cx.struct_span_lint(
 907             IMPROPER_CTYPES,
 908             sp,
 909             &format!("`extern` block uses type `{}`, which is not FFI-safe", ty),
 910         );
 911         diag.span_label(sp, "not FFI-safe");
 912         if let Some(help) = help {
 913             diag.help(help);
 914         }
 915         diag.note(note);
 916         if let ty::Adt(def, _) = ty.kind {
 917             if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did) {
 918                 diag.span_note(sp, "type defined here");
 919             }
 920         }
 921         diag.emit();
 922     }
 923
 924     fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
 925         use crate::rustc::ty::TypeFoldable;
 926
 927         struct ProhibitOpaqueTypes<'tcx> {
 928             ty: Option<Ty<'tcx>>,
 929         };
 930
 931         impl<'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'tcx> {
 932             fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
 933                 if let ty::Opaque(..) = ty.kind {
 934                     self.ty = Some(ty);
 935                     true
 936                 } else {
 937                     ty.super_visit_with(self)
 938                 }
 939             }
 940         }
 941
 942         let mut visitor = ProhibitOpaqueTypes { ty: None };
 943         ty.visit_with(&mut visitor);
 944         if let Some(ty) = visitor.ty {
 945             self.emit_ffi_unsafe_type_lint(
 946                 ty,
 947                 sp,
 948                 "opaque types have no C equivalent",
 949                 None,
 950             );
 951             true
 952         } else {
 953             false
 954         }
 955     }
 956
 957     fn check_type_for_ffi_and_report_errors(&mut self, sp: Span, ty: Ty<'tcx>, is_static: bool) {
 958         // We have to check for opaque types before `normalize_erasing_regions`,
 959         // which will replace opaque types with their underlying concrete type.
 960         if self.check_for_opaque_ty(sp, ty) {
 961             // We've already emitted an error due to an opaque type.
 962             return;
 963         }
 964
 965         // it is only OK to use this function because extern fns cannot have
 966         // any generic types right now:
 967         let ty = self.cx.tcx.normalize_erasing_regions(ParamEnv::reveal_all(), ty);
 968         // C doesn't really support passing arrays by value.
 969         // The only way to pass an array by value is through a struct.
 970         // So we first test that the top level isn't an array,
 971         // and then recursively check the types inside.
 972         if !is_static && self.check_for_array_ty(sp, ty) {
 973             return;
 974         }
 975
 976         match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
 977             FfiResult::FfiSafe => {}
 978             FfiResult::FfiPhantom(ty) => {
 979                 self.emit_ffi_unsafe_type_lint(ty, sp, "composed only of `PhantomData`", None);
 980             }
 981             FfiResult::FfiUnsafe { ty, reason, help } => {
 982                 self.emit_ffi_unsafe_type_lint(ty, sp, reason, help);
 983             }
 984         }
 985     }
 986
 987     fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl) {
 988         let def_id = self.cx.tcx.hir().local_def_id(id);
 989         let sig = self.cx.tcx.fn_sig(def_id);
 990         let sig = self.cx.tcx.erase_late_bound_regions(&sig);
 991
 992         for (input_ty, input_hir) in sig.inputs().iter().zip(&decl.inputs) {
 993             self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty, false);
 994         }
 995
 996         if let hir::Return(ref ret_hir) = decl.output {
 997             let ret_ty = sig.output();
 998             if !ret_ty.is_unit() {
 999                 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty, false);
1000             }
1001         }
1002     }
1003
1004     fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
1005         let def_id = self.cx.tcx.hir().local_def_id(id);
1006         let ty = self.cx.tcx.type_of(def_id);
1007         self.check_type_for_ffi_and_report_errors(span, ty, true);
1008     }
1009 }
1010
1011 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImproperCTypes {
1012     fn check_foreign_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::ForeignItem) {
1013         let mut vis = ImproperCTypesVisitor { cx };
1014         let abi = cx.tcx.hir().get_foreign_abi(it.hir_id);
1015         if let Abi::Rust | Abi::RustCall | Abi::RustIntrinsic | Abi::PlatformIntrinsic = abi {
1016             // Don't worry about types in internal ABIs.
1017         } else {
1018             match it.kind {
1019                 hir::ForeignItemKind::Fn(ref decl, _, _) => {
1020                     vis.check_foreign_fn(it.hir_id, decl);
1021                 }
1022                 hir::ForeignItemKind::Static(ref ty, _) => {
1023                     vis.check_foreign_static(it.hir_id, ty.span);
1024                 }
1025                 hir::ForeignItemKind::Type => ()
1026             }
1027         }
1028     }
1029 }
1030
1031 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
1032
1033 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for VariantSizeDifferences {
1034     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item) {
1035         if let hir::ItemKind::Enum(ref enum_definition, _) = it.kind {
1036             let item_def_id = cx.tcx.hir().local_def_id(it.hir_id);
1037             let t = cx.tcx.type_of(item_def_id);
1038             let ty = cx.tcx.erase_regions(&t);
1039             let layout = match cx.layout_of(ty) {
1040                 Ok(layout) => layout,
1041                 Err(ty::layout::LayoutError::Unknown(_)) => return,
1042                 Err(err @ ty::layout::LayoutError::SizeOverflow(_)) => {
1043                     bug!("failed to get layout for `{}`: {}", t, err);
1044                 }
1045             };
1046             let (variants, tag) = match layout.variants {
1047                 layout::Variants::Multiple {
1048                     discr_kind: layout::DiscriminantKind::Tag,
1049                     ref discr,
1050                     ref variants,
1051                     ..
1052                 } => (variants, discr),
1053                 _ => return,
1054             };
1055
1056             let discr_size = tag.value.size(&cx.tcx).bytes();
1057
1058             debug!("enum `{}` is {} bytes large with layout:\n{:#?}",
1059                    t, layout.size.bytes(), layout);
1060
1061             let (largest, slargest, largest_index) = enum_definition.variants
1062                 .iter()
1063                 .zip(variants)
1064                 .map(|(variant, variant_layout)| {
1065                     // Subtract the size of the enum discriminant.
1066                     let bytes = variant_layout.size.bytes().saturating_sub(discr_size);
1067
1068                     debug!("- variant `{}` is {} bytes large",
1069                            variant.ident,
1070                            bytes);
1071                     bytes
1072                 })
1073                 .enumerate()
1074                 .fold((0, 0, 0), |(l, s, li), (idx, size)| if size > l {
1075                     (size, l, idx)
1076                 } else if size > s {
1077                     (l, size, li)
1078                 } else {
1079                     (l, s, li)
1080                 });
1081
1082             // We only warn if the largest variant is at least thrice as large as
1083             // the second-largest.
1084             if largest > slargest * 3 && slargest > 0 {
1085                 cx.span_lint(VARIANT_SIZE_DIFFERENCES,
1086                                 enum_definition.variants[largest_index].span,
1087                                 &format!("enum variant is more than three times \
1088                                           larger ({} bytes) than the next largest",
1089                                          largest));
1090             }
1091         }
1092     }
1093 }