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