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     /// Checks if the given type is "ffi-safe" (has a stable, well-defined
 595     /// representation which can be exported to C code).
 596     fn check_type_for_ffi(&self,
 597                           cache: &mut FxHashSet<Ty<'tcx>>,
 598                           ty: Ty<'tcx>) -> FfiResult<'tcx> {
 599         use FfiResult::*;
 600
 601         let cx = self.cx.tcx;
 602
 603         // Protect against infinite recursion, for example
 604         // `struct S(*mut S);`.
 605         // FIXME: A recursion limit is necessary as well, for irregular
 606         // recursive types.
 607         if !cache.insert(ty) {
 608             return FfiSafe;
 609         }
 610
 611         match ty.kind {
 612             ty::Adt(def, substs) => {
 613                 if def.is_phantom_data() {
 614                     return FfiPhantom(ty);
 615                 }
 616                 match def.adt_kind() {
 617                     AdtKind::Struct => {
 618                         if !def.repr.c() && !def.repr.transparent() {
 619                             return FfiUnsafe {
 620                                 ty,
 621                                 reason: "this struct has unspecified layout",
 622                                 help: Some("consider adding a `#[repr(C)]` or \
 623                                             `#[repr(transparent)]` attribute to this struct"),
 624                             };
 625                         }
 626
 627                         let is_non_exhaustive =
 628                             def.non_enum_variant().is_field_list_non_exhaustive();
 629                         if is_non_exhaustive && !def.did.is_local() {
 630                             return FfiUnsafe {
 631                                 ty,
 632                                 reason: "this struct is non-exhaustive",
 633                                 help: None,
 634                             };
 635                         }
 636
 637                         if def.non_enum_variant().fields.is_empty() {
 638                             return FfiUnsafe {
 639                                 ty,
 640                                 reason: "this struct has no fields",
 641                                 help: Some("consider adding a member to this struct"),
 642                             };
 643                         }
 644
 645                         // We can't completely trust repr(C) and repr(transparent) markings;
 646                         // make sure the fields are actually safe.
 647                         let mut all_phantom = true;
 648                         for field in &def.non_enum_variant().fields {
 649                             let field_ty = cx.normalize_erasing_regions(
 650                                 ParamEnv::reveal_all(),
 651                                 field.ty(cx, substs),
 652                             );
 653                             // repr(transparent) types are allowed to have arbitrary ZSTs, not just
 654                             // PhantomData -- skip checking all ZST fields
 655                             if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 656                                 continue;
 657                             }
 658                             let r = self.check_type_for_ffi(cache, field_ty);
 659                             match r {
 660                                 FfiSafe => {
 661                                     all_phantom = false;
 662                                 }
 663                                 FfiPhantom(..) => {}
 664                                 FfiUnsafe { .. } => {
 665                                     return r;
 666                                 }
 667                             }
 668                         }
 669
 670                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 671                     }
 672                     AdtKind::Union => {
 673                         if !def.repr.c() && !def.repr.transparent() {
 674                             return FfiUnsafe {
 675                                 ty,
 676                                 reason: "this union has unspecified layout",
 677                                 help: Some("consider adding a `#[repr(C)]` or \
 678                                             `#[repr(transparent)]` attribute to this union"),
 679                             };
 680                         }
 681
 682                         if def.non_enum_variant().fields.is_empty() {
 683                             return FfiUnsafe {
 684                                 ty,
 685                                 reason: "this union has no fields",
 686                                 help: Some("consider adding a field to this union"),
 687                             };
 688                         }
 689
 690                         let mut all_phantom = true;
 691                         for field in &def.non_enum_variant().fields {
 692                             let field_ty = cx.normalize_erasing_regions(
 693                                 ParamEnv::reveal_all(),
 694                                 field.ty(cx, substs),
 695                             );
 696                             // repr(transparent) types are allowed to have arbitrary ZSTs, not just
 697                             // PhantomData -- skip checking all ZST fields.
 698                             if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 699                                 continue;
 700                             }
 701                             let r = self.check_type_for_ffi(cache, field_ty);
 702                             match r {
 703                                 FfiSafe => {
 704                                     all_phantom = false;
 705                                 }
 706                                 FfiPhantom(..) => {}
 707                                 FfiUnsafe { .. } => {
 708                                     return r;
 709                                 }
 710                             }
 711                         }
 712
 713                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 714                     }
 715                     AdtKind::Enum => {
 716                         if def.variants.is_empty() {
 717                             // Empty enums are okay... although sort of useless.
 718                             return FfiSafe;
 719                         }
 720
 721                         // Check for a repr() attribute to specify the size of the
 722                         // discriminant.
 723                         if !def.repr.c() && !def.repr.transparent() && def.repr.int.is_none() {
 724                             // Special-case types like `Option<extern fn()>`.
 725                             if !is_repr_nullable_ptr(cx, ty, def, substs) {
 726                                 return FfiUnsafe {
 727                                     ty,
 728                                     reason: "enum has no representation hint",
 729                                     help: Some("consider adding a `#[repr(C)]`, \
 730                                                 `#[repr(transparent)]`, or integer `#[repr(...)]` \
 731                                                 attribute to this enum"),
 732                                 };
 733                             }
 734                         }
 735
 736                         if def.is_variant_list_non_exhaustive() && !def.did.is_local() {
 737                             return FfiUnsafe {
 738                                 ty,
 739                                 reason: "this enum is non-exhaustive",
 740                                 help: None,
 741                             };
 742                         }
 743
 744                         // Check the contained variants.
 745                         for variant in &def.variants {
 746                             let is_non_exhaustive = variant.is_field_list_non_exhaustive();
 747                             if is_non_exhaustive && !variant.def_id.is_local() {
 748                                 return FfiUnsafe {
 749                                     ty,
 750                                     reason: "this enum has non-exhaustive variants",
 751                                     help: None,
 752                                 };
 753                             }
 754
 755                             for field in &variant.fields {
 756                                 let field_ty = cx.normalize_erasing_regions(
 757                                     ParamEnv::reveal_all(),
 758                                     field.ty(cx, substs),
 759                                 );
 760                                 // repr(transparent) types are allowed to have arbitrary ZSTs, not
 761                                 // just PhantomData -- skip checking all ZST fields.
 762                                 if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 763                                     continue;
 764                                 }
 765                                 let r = self.check_type_for_ffi(cache, field_ty);
 766                                 match r {
 767                                     FfiSafe => {}
 768                                     FfiUnsafe { .. } => {
 769                                         return r;
 770                                     }
 771                                     FfiPhantom(..) => {
 772                                         return FfiUnsafe {
 773                                             ty,
 774                                             reason: "this enum contains a PhantomData field",
 775                                             help: None,
 776                                         };
 777                                     }
 778                                 }
 779                             }
 780                         }
 781                         FfiSafe
 782                     }
 783                 }
 784             }
 785
 786             ty::Char => FfiUnsafe {
 787                 ty,
 788                 reason: "the `char` type has no C equivalent",
 789                 help: Some("consider using `u32` or `libc::wchar_t` instead"),
 790             },
 791
 792             ty::Int(ast::IntTy::I128) | ty::Uint(ast::UintTy::U128) => FfiUnsafe {
 793                 ty,
 794                 reason: "128-bit integers don't currently have a known stable ABI",
 795                 help: None,
 796             },
 797
 798             // Primitive types with a stable representation.
 799             ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
 800
 801             ty::Slice(_) => FfiUnsafe {
 802                 ty,
 803                 reason: "slices have no C equivalent",
 804                 help: Some("consider using a raw pointer instead"),
 805             },
 806
 807             ty::Dynamic(..) => FfiUnsafe {
 808                 ty,
 809                 reason: "trait objects have no C equivalent",
 810                 help: None,
 811             },
 812
 813             ty::Str => FfiUnsafe {
 814                 ty,
 815                 reason: "string slices have no C equivalent",
 816                 help: Some("consider using `*const u8` and a length instead"),
 817             },
 818
 819             ty::Tuple(..) => FfiUnsafe {
 820                 ty,
 821                 reason: "tuples have unspecified layout",
 822                 help: Some("consider using a struct instead"),
 823             },
 824
 825             ty::RawPtr(ty::TypeAndMut { ty, .. }) |
 826             ty::Ref(_, ty, _) => self.check_type_for_ffi(cache, ty),
 827
 828             ty::Array(ty, _) => self.check_type_for_ffi(cache, ty),
 829
 830             ty::FnPtr(sig) => {
 831                 match sig.abi() {
 832                     Abi::Rust | Abi::RustIntrinsic | Abi::PlatformIntrinsic | Abi::RustCall => {
 833                         return FfiUnsafe {
 834                             ty,
 835                             reason: "this function pointer has Rust-specific calling convention",
 836                             help: Some("consider using an `extern fn(...) -> ...` \
 837                                         function pointer instead"),
 838                         }
 839                     }
 840                     _ => {}
 841                 }
 842
 843                 let sig = cx.erase_late_bound_regions(&sig);
 844                 if !sig.output().is_unit() {
 845                     let r = self.check_type_for_ffi(cache, sig.output());
 846                     match r {
 847                         FfiSafe => {}
 848                         _ => {
 849                             return r;
 850                         }
 851                     }
 852                 }
 853                 for arg in sig.inputs() {
 854                     let r = self.check_type_for_ffi(cache, arg);
 855                     match r {
 856                         FfiSafe => {}
 857                         _ => {
 858                             return r;
 859                         }
 860                     }
 861                 }
 862                 FfiSafe
 863             }
 864
 865             ty::Foreign(..) => FfiSafe,
 866
 867             ty::Param(..) |
 868             ty::Infer(..) |
 869             ty::Bound(..) |
 870             ty::Error |
 871             ty::Closure(..) |
 872             ty::Generator(..) |
 873             ty::GeneratorWitness(..) |
 874             ty::Placeholder(..) |
 875             ty::UnnormalizedProjection(..) |
 876             ty::Projection(..) |
 877             ty::Opaque(..) |
 878             ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty),
 879         }
 880     }
 881
 882     fn emit_ffi_unsafe_type_lint(
 883         &mut self,
 884         ty: Ty<'tcx>,
 885         sp: Span,
 886         note: &str,
 887         help: Option<&str>,
 888     ) {
 889         let mut diag = self.cx.struct_span_lint(
 890             IMPROPER_CTYPES,
 891             sp,
 892             &format!("`extern` block uses type `{}`, which is not FFI-safe", ty),
 893         );
 894         diag.span_label(sp, "not FFI-safe");
 895         if let Some(help) = help {
 896             diag.help(help);
 897         }
 898         diag.note(note);
 899         if let ty::Adt(def, _) = ty.kind {
 900             if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did) {
 901                 diag.span_note(sp, "type defined here");
 902             }
 903         }
 904         diag.emit();
 905     }
 906
 907     fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
 908         use crate::rustc::ty::TypeFoldable;
 909
 910         struct ProhibitOpaqueTypes<'tcx> {
 911             ty: Option<Ty<'tcx>>,
 912         };
 913
 914         impl<'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'tcx> {
 915             fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
 916                 if let ty::Opaque(..) = ty.kind {
 917                     self.ty = Some(ty);
 918                     true
 919                 } else {
 920                     ty.super_visit_with(self)
 921                 }
 922             }
 923         }
 924
 925         let mut visitor = ProhibitOpaqueTypes { ty: None };
 926         ty.visit_with(&mut visitor);
 927         if let Some(ty) = visitor.ty {
 928             self.emit_ffi_unsafe_type_lint(
 929                 ty,
 930                 sp,
 931                 "opaque types have no C equivalent",
 932                 None,
 933             );
 934             true
 935         } else {
 936             false
 937         }
 938     }
 939
 940     fn check_type_for_ffi_and_report_errors(&mut self, sp: Span, ty: Ty<'tcx>) {
 941         // We have to check for opaque types before `normalize_erasing_regions`,
 942         // which will replace opaque types with their underlying concrete type.
 943         if self.check_for_opaque_ty(sp, ty) {
 944             // We've already emitted an error due to an opaque type.
 945             return;
 946         }
 947
 948         // it is only OK to use this function because extern fns cannot have
 949         // any generic types right now:
 950         let ty = self.cx.tcx.normalize_erasing_regions(ParamEnv::reveal_all(), ty);
 951
 952         match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
 953             FfiResult::FfiSafe => {}
 954             FfiResult::FfiPhantom(ty) => {
 955                 self.emit_ffi_unsafe_type_lint(ty, sp, "composed only of `PhantomData`", None);
 956             }
 957             FfiResult::FfiUnsafe { ty, reason, help } => {
 958                 self.emit_ffi_unsafe_type_lint(ty, sp, reason, help);
 959             }
 960         }
 961     }
 962
 963     fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl) {
 964         let def_id = self.cx.tcx.hir().local_def_id(id);
 965         let sig = self.cx.tcx.fn_sig(def_id);
 966         let sig = self.cx.tcx.erase_late_bound_regions(&sig);
 967
 968         for (input_ty, input_hir) in sig.inputs().iter().zip(&decl.inputs) {
 969             self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty);
 970         }
 971
 972         if let hir::Return(ref ret_hir) = decl.output {
 973             let ret_ty = sig.output();
 974             if !ret_ty.is_unit() {
 975                 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty);
 976             }
 977         }
 978     }
 979
 980     fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
 981         let def_id = self.cx.tcx.hir().local_def_id(id);
 982         let ty = self.cx.tcx.type_of(def_id);
 983         self.check_type_for_ffi_and_report_errors(span, ty);
 984     }
 985 }
 986
 987 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImproperCTypes {
 988     fn check_foreign_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::ForeignItem) {
 989         let mut vis = ImproperCTypesVisitor { cx };
 990         let abi = cx.tcx.hir().get_foreign_abi(it.hir_id);
 991         if let Abi::Rust | Abi::RustCall | Abi::RustIntrinsic | Abi::PlatformIntrinsic = abi {
 992             // Don't worry about types in internal ABIs.
 993         } else {
 994             match it.kind {
 995                 hir::ForeignItemKind::Fn(ref decl, _, _) => {
 996                     vis.check_foreign_fn(it.hir_id, decl);
 997                 }
 998                 hir::ForeignItemKind::Static(ref ty, _) => {
 999                     vis.check_foreign_static(it.hir_id, ty.span);
1000                 }
1001                 hir::ForeignItemKind::Type => ()
1002             }
1003         }
1004     }
1005 }
1006
1007 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
1008
1009 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for VariantSizeDifferences {
1010     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item) {
1011         if let hir::ItemKind::Enum(ref enum_definition, _) = it.kind {
1012             let item_def_id = cx.tcx.hir().local_def_id(it.hir_id);
1013             let t = cx.tcx.type_of(item_def_id);
1014             let ty = cx.tcx.erase_regions(&t);
1015             let layout = match cx.layout_of(ty) {
1016                 Ok(layout) => layout,
1017                 Err(ty::layout::LayoutError::Unknown(_)) => return,
1018                 Err(err @ ty::layout::LayoutError::SizeOverflow(_)) => {
1019                     bug!("failed to get layout for `{}`: {}", t, err);
1020                 }
1021             };
1022             let (variants, tag) = match layout.variants {
1023                 layout::Variants::Multiple {
1024                     discr_kind: layout::DiscriminantKind::Tag,
1025                     ref discr,
1026                     ref variants,
1027                     ..
1028                 } => (variants, discr),
1029                 _ => return,
1030             };
1031
1032             let discr_size = tag.value.size(&cx.tcx).bytes();
1033
1034             debug!("enum `{}` is {} bytes large with layout:\n{:#?}",
1035                    t, layout.size.bytes(), layout);
1036
1037             let (largest, slargest, largest_index) = enum_definition.variants
1038                 .iter()
1039                 .zip(variants)
1040                 .map(|(variant, variant_layout)| {
1041                     // Subtract the size of the enum discriminant.
1042                     let bytes = variant_layout.size.bytes().saturating_sub(discr_size);
1043
1044                     debug!("- variant `{}` is {} bytes large",
1045                            variant.ident,
1046                            bytes);
1047                     bytes
1048                 })
1049                 .enumerate()
1050                 .fold((0, 0, 0), |(l, s, li), (idx, size)| if size > l {
1051                     (size, l, idx)
1052                 } else if size > s {
1053                     (l, size, li)
1054                 } else {
1055                     (l, s, li)
1056                 });
1057
1058             // We only warn if the largest variant is at least thrice as large as
1059             // the second-largest.
1060             if largest > slargest * 3 && slargest > 0 {
1061                 cx.span_lint(VARIANT_SIZE_DIFFERENCES,
1062                                 enum_definition.variants[largest_index].span,
1063                                 &format!("enum variant is more than three times \
1064                                           larger ({} bytes) than the next largest",
1065                                          largest));
1066             }
1067         }
1068     }
1069 }