src/librustc_lint/types.rs

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