src/librustc_lint/types.rs

   1 #![allow(non_snake_case)]
   2
   3 use crate::{LateContext, LateLintPass, LintContext};
   4 use rustc::mir::interpret::{sign_extend, truncate};
   5 use rustc::ty::layout::{self, IntegerExt, LayoutOf, SizeSkeleton, VariantIdx};
   6 use rustc::ty::subst::SubstsRef;
   7 use rustc::ty::{self, AdtKind, ParamEnv, Ty, TyCtxt};
   8 use rustc_data_structures::fx::FxHashSet;
   9 use rustc_errors::Applicability;
  10 use rustc_hir as hir;
  11 use rustc_hir::def_id::DefId;
  12 use rustc_hir::{is_range_literal, ExprKind, Node};
  13 use rustc_index::vec::Idx;
  14 use rustc_span::source_map;
  15 use rustc_span::symbol::sym;
  16 use rustc_span::Span;
  17 use rustc_target::spec::abi::Abi;
  18 use syntax::{ast, attr};
  19
  20 use log::debug;
  21 use std::cmp;
  22 use std::{f32, f64, i16, i32, i64, i8, u16, u32, u64, u8};
  23
  24 declare_lint! {
  25     UNUSED_COMPARISONS,
  26     Warn,
  27     "comparisons made useless by limits of the types involved"
  28 }
  29
  30 declare_lint! {
  31     OVERFLOWING_LITERALS,
  32     Deny,
  33     "literal out of range for its type"
  34 }
  35
  36 declare_lint! {
  37     VARIANT_SIZE_DIFFERENCES,
  38     Allow,
  39     "detects enums with widely varying variant sizes"
  40 }
  41
  42 #[derive(Copy, Clone)]
  43 pub struct TypeLimits {
  44     /// Id of the last visited negated expression
  45     negated_expr_id: hir::HirId,
  46 }
  47
  48 impl_lint_pass!(TypeLimits => [UNUSED_COMPARISONS, OVERFLOWING_LITERALS]);
  49
  50 impl TypeLimits {
  51     pub fn new() -> TypeLimits {
  52         TypeLimits { negated_expr_id: hir::DUMMY_HIR_ID }
  53     }
  54 }
  55
  56 /// Attempts to special-case the overflowing literal lint when it occurs as a range endpoint.
  57 /// Returns `true` iff the lint was overridden.
  58 fn lint_overflowing_range_endpoint<'a, 'tcx>(
  59     cx: &LateContext<'a, 'tcx>,
  60     lit: &hir::Lit,
  61     lit_val: u128,
  62     max: u128,
  63     expr: &'tcx hir::Expr<'tcx>,
  64     parent_expr: &'tcx hir::Expr<'tcx>,
  65     ty: &str,
  66 ) -> bool {
  67     // We only want to handle exclusive (`..`) ranges,
  68     // which are represented as `ExprKind::Struct`.
  69     if let ExprKind::Struct(_, eps, _) = &parent_expr.kind {
  70         if eps.len() != 2 {
  71             return false;
  72         }
  73         // We can suggest using an inclusive range
  74         // (`..=`) instead only if it is the `end` that is
  75         // overflowing and only by 1.
  76         if eps[1].expr.hir_id == expr.hir_id && lit_val - 1 == max {
  77             let mut err = cx.struct_span_lint(
  78                 OVERFLOWING_LITERALS,
  79                 parent_expr.span,
  80                 &format!("range endpoint is out of range for `{}`", ty),
  81             );
  82             if let Ok(start) = cx.sess().source_map().span_to_snippet(eps[0].span) {
  83                 use ast::{LitIntType, LitKind};
  84                 // We need to preserve the literal's suffix,
  85                 // as it may determine typing information.
  86                 let suffix = match lit.node {
  87                     LitKind::Int(_, LitIntType::Signed(s)) => format!("{}", s.name_str()),
  88                     LitKind::Int(_, LitIntType::Unsigned(s)) => format!("{}", s.name_str()),
  89                     LitKind::Int(_, LitIntType::Unsuffixed) => "".to_owned(),
  90                     _ => bug!(),
  91                 };
  92                 let suggestion = format!("{}..={}{}", start, lit_val - 1, suffix);
  93                 err.span_suggestion(
  94                     parent_expr.span,
  95                     &"use an inclusive range instead",
  96                     suggestion,
  97                     Applicability::MachineApplicable,
  98                 );
  99                 err.emit();
 100                 return true;
 101             }
 102         }
 103     }
 104
 105     false
 106 }
 107
 108 // For `isize` & `usize`, be conservative with the warnings, so that the
 109 // warnings are consistent between 32- and 64-bit platforms.
 110 fn int_ty_range(int_ty: ast::IntTy) -> (i128, i128) {
 111     match int_ty {
 112         ast::IntTy::Isize => (i64::min_value() as i128, i64::max_value() as i128),
 113         ast::IntTy::I8 => (i8::min_value() as i64 as i128, i8::max_value() as i128),
 114         ast::IntTy::I16 => (i16::min_value() as i64 as i128, i16::max_value() as i128),
 115         ast::IntTy::I32 => (i32::min_value() as i64 as i128, i32::max_value() as i128),
 116         ast::IntTy::I64 => (i64::min_value() as i128, i64::max_value() as i128),
 117         ast::IntTy::I128 => (i128::min_value() as i128, i128::max_value()),
 118     }
 119 }
 120
 121 fn uint_ty_range(uint_ty: ast::UintTy) -> (u128, u128) {
 122     match uint_ty {
 123         ast::UintTy::Usize => (u64::min_value() as u128, u64::max_value() as u128),
 124         ast::UintTy::U8 => (u8::min_value() as u128, u8::max_value() as u128),
 125         ast::UintTy::U16 => (u16::min_value() as u128, u16::max_value() as u128),
 126         ast::UintTy::U32 => (u32::min_value() as u128, u32::max_value() as u128),
 127         ast::UintTy::U64 => (u64::min_value() as u128, u64::max_value() as u128),
 128         ast::UintTy::U128 => (u128::min_value(), u128::max_value()),
 129     }
 130 }
 131
 132 fn get_bin_hex_repr(cx: &LateContext<'_, '_>, lit: &hir::Lit) -> Option<String> {
 133     let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?;
 134     let firstch = src.chars().next()?;
 135
 136     if firstch == '0' {
 137         match src.chars().nth(1) {
 138             Some('x') | Some('b') => return Some(src),
 139             _ => return None,
 140         }
 141     }
 142
 143     None
 144 }
 145
 146 fn report_bin_hex_error(
 147     cx: &LateContext<'_, '_>,
 148     expr: &hir::Expr<'_>,
 149     ty: attr::IntType,
 150     repr_str: String,
 151     val: u128,
 152     negative: bool,
 153 ) {
 154     let size = layout::Integer::from_attr(&cx.tcx, ty).size();
 155     let (t, actually) = match ty {
 156         attr::IntType::SignedInt(t) => {
 157             let actually = sign_extend(val, size) as i128;
 158             (t.name_str(), actually.to_string())
 159         }
 160         attr::IntType::UnsignedInt(t) => {
 161             let actually = truncate(val, size);
 162             (t.name_str(), actually.to_string())
 163         }
 164     };
 165     let mut err = cx.struct_span_lint(
 166         OVERFLOWING_LITERALS,
 167         expr.span,
 168         &format!("literal out of range for {}", t),
 169     );
 170     err.note(&format!(
 171         "the literal `{}` (decimal `{}`) does not fit into \
 172             an `{}` and will become `{}{}`",
 173         repr_str, val, t, actually, t
 174     ));
 175     if let Some(sugg_ty) = get_type_suggestion(&cx.tables.node_type(expr.hir_id), val, negative) {
 176         if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') {
 177             let (sans_suffix, _) = repr_str.split_at(pos);
 178             err.span_suggestion(
 179                 expr.span,
 180                 &format!("consider using `{}` instead", sugg_ty),
 181                 format!("{}{}", sans_suffix, sugg_ty),
 182                 Applicability::MachineApplicable,
 183             );
 184         } else {
 185             err.help(&format!("consider using `{}` instead", sugg_ty));
 186         }
 187     }
 188
 189     err.emit();
 190 }
 191
 192 // This function finds the next fitting type and generates a suggestion string.
 193 // It searches for fitting types in the following way (`X < Y`):
 194 //  - `iX`: if literal fits in `uX` => `uX`, else => `iY`
 195 //  - `-iX` => `iY`
 196 //  - `uX` => `uY`
 197 //
 198 // No suggestion for: `isize`, `usize`.
 199 fn get_type_suggestion(t: Ty<'_>, val: u128, negative: bool) -> Option<&'static str> {
 200     use syntax::ast::IntTy::*;
 201     use syntax::ast::UintTy::*;
 202     macro_rules! find_fit {
 203         ($ty:expr, $val:expr, $negative:expr,
 204          $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => {
 205             {
 206                 let _neg = if negative { 1 } else { 0 };
 207                 match $ty {
 208                     $($type => {
 209                         $(if !negative && val <= uint_ty_range($utypes).1 {
 210                             return Some($utypes.name_str())
 211                         })*
 212                         $(if val <= int_ty_range($itypes).1 as u128 + _neg {
 213                             return Some($itypes.name_str())
 214                         })*
 215                         None
 216                     },)+
 217                     _ => None
 218                 }
 219             }
 220         }
 221     }
 222     match t.kind {
 223         ty::Int(i) => find_fit!(i, val, negative,
 224                       I8 => [U8] => [I16, I32, I64, I128],
 225                       I16 => [U16] => [I32, I64, I128],
 226                       I32 => [U32] => [I64, I128],
 227                       I64 => [U64] => [I128],
 228                       I128 => [U128] => []),
 229         ty::Uint(u) => find_fit!(u, val, negative,
 230                       U8 => [U8, U16, U32, U64, U128] => [],
 231                       U16 => [U16, U32, U64, U128] => [],
 232                       U32 => [U32, U64, U128] => [],
 233                       U64 => [U64, U128] => [],
 234                       U128 => [U128] => []),
 235         _ => None,
 236     }
 237 }
 238
 239 fn lint_int_literal<'a, 'tcx>(
 240     cx: &LateContext<'a, 'tcx>,
 241     type_limits: &TypeLimits,
 242     e: &'tcx hir::Expr<'tcx>,
 243     lit: &hir::Lit,
 244     t: ast::IntTy,
 245     v: u128,
 246 ) {
 247     let int_type = t.normalize(cx.sess().target.ptr_width);
 248     let (_, max) = int_ty_range(int_type);
 249     let max = max as u128;
 250     let negative = type_limits.negated_expr_id == e.hir_id;
 251
 252     // Detect literal value out of range [min, max] inclusive
 253     // avoiding use of -min to prevent overflow/panic
 254     if (negative && v > max + 1) || (!negative && v > max) {
 255         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 256             report_bin_hex_error(cx, e, attr::IntType::SignedInt(t), repr_str, v, negative);
 257             return;
 258         }
 259
 260         let par_id = cx.tcx.hir().get_parent_node(e.hir_id);
 261         if let Node::Expr(par_e) = cx.tcx.hir().get(par_id) {
 262             if let hir::ExprKind::Struct(..) = par_e.kind {
 263                 if is_range_literal(cx.sess().source_map(), par_e)
 264                     && lint_overflowing_range_endpoint(cx, lit, v, max, e, par_e, t.name_str())
 265                 {
 266                     // The overflowing literal lint was overridden.
 267                     return;
 268                 }
 269             }
 270         }
 271
 272         cx.span_lint(
 273             OVERFLOWING_LITERALS,
 274             e.span,
 275             &format!("literal out of range for `{}`", t.name_str()),
 276         );
 277     }
 278 }
 279
 280 fn lint_uint_literal<'a, 'tcx>(
 281     cx: &LateContext<'a, 'tcx>,
 282     e: &'tcx hir::Expr<'tcx>,
 283     lit: &hir::Lit,
 284     t: ast::UintTy,
 285 ) {
 286     let uint_type = t.normalize(cx.sess().target.ptr_width);
 287     let (min, max) = uint_ty_range(uint_type);
 288     let lit_val: u128 = match lit.node {
 289         // _v is u8, within range by definition
 290         ast::LitKind::Byte(_v) => return,
 291         ast::LitKind::Int(v, _) => v,
 292         _ => bug!(),
 293     };
 294     if lit_val < min || lit_val > max {
 295         let parent_id = cx.tcx.hir().get_parent_node(e.hir_id);
 296         if let Node::Expr(par_e) = cx.tcx.hir().get(parent_id) {
 297             match par_e.kind {
 298                 hir::ExprKind::Cast(..) => {
 299                     if let ty::Char = cx.tables.expr_ty(par_e).kind {
 300                         let mut err = cx.struct_span_lint(
 301                             OVERFLOWING_LITERALS,
 302                             par_e.span,
 303                             "only `u8` can be cast into `char`",
 304                         );
 305                         err.span_suggestion(
 306                             par_e.span,
 307                             &"use a `char` literal instead",
 308                             format!("'\\u{{{:X}}}'", lit_val),
 309                             Applicability::MachineApplicable,
 310                         );
 311                         err.emit();
 312                         return;
 313                     }
 314                 }
 315                 hir::ExprKind::Struct(..) if is_range_literal(cx.sess().source_map(), par_e) => {
 316                     let t = t.name_str();
 317                     if lint_overflowing_range_endpoint(cx, lit, lit_val, max, e, par_e, t) {
 318                         // The overflowing literal lint was overridden.
 319                         return;
 320                     }
 321                 }
 322                 _ => {}
 323             }
 324         }
 325         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 326             report_bin_hex_error(cx, e, attr::IntType::UnsignedInt(t), repr_str, lit_val, false);
 327             return;
 328         }
 329         cx.span_lint(
 330             OVERFLOWING_LITERALS,
 331             e.span,
 332             &format!("literal out of range for `{}`", t.name_str()),
 333         );
 334     }
 335 }
 336
 337 fn lint_literal<'a, 'tcx>(
 338     cx: &LateContext<'a, 'tcx>,
 339     type_limits: &TypeLimits,
 340     e: &'tcx hir::Expr<'tcx>,
 341     lit: &hir::Lit,
 342 ) {
 343     match cx.tables.node_type(e.hir_id).kind {
 344         ty::Int(t) => {
 345             match lit.node {
 346                 ast::LitKind::Int(v, ast::LitIntType::Signed(_))
 347                 | ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => {
 348                     lint_int_literal(cx, type_limits, e, lit, t, v)
 349                 }
 350                 _ => bug!(),
 351             };
 352         }
 353         ty::Uint(t) => lint_uint_literal(cx, e, lit, t),
 354         ty::Float(t) => {
 355             let is_infinite = match lit.node {
 356                 ast::LitKind::Float(v, _) => match t {
 357                     ast::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
 358                     ast::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
 359                 },
 360                 _ => bug!(),
 361             };
 362             if is_infinite == Ok(true) {
 363                 cx.span_lint(
 364                     OVERFLOWING_LITERALS,
 365                     e.span,
 366                     &format!("literal out of range for `{}`", t.name_str()),
 367                 );
 368             }
 369         }
 370         _ => {}
 371     }
 372 }
 373
 374 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TypeLimits {
 375     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx hir::Expr<'tcx>) {
 376         match e.kind {
 377             hir::ExprKind::Unary(hir::UnOp::UnNeg, ref expr) => {
 378                 // propagate negation, if the negation itself isn't negated
 379                 if self.negated_expr_id != e.hir_id {
 380                     self.negated_expr_id = expr.hir_id;
 381                 }
 382             }
 383             hir::ExprKind::Binary(binop, ref l, ref r) => {
 384                 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
 385                     cx.span_lint(
 386                         UNUSED_COMPARISONS,
 387                         e.span,
 388                         "comparison is useless due to type limits",
 389                     );
 390                 }
 391             }
 392             hir::ExprKind::Lit(ref lit) => lint_literal(cx, self, e, lit),
 393             _ => {}
 394         };
 395
 396         fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
 397             match binop.node {
 398                 hir::BinOpKind::Lt => v > min && v <= max,
 399                 hir::BinOpKind::Le => v >= min && v < max,
 400                 hir::BinOpKind::Gt => v >= min && v < max,
 401                 hir::BinOpKind::Ge => v > min && v <= max,
 402                 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
 403                 _ => bug!(),
 404             }
 405         }
 406
 407         fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
 408             source_map::respan(
 409                 binop.span,
 410                 match binop.node {
 411                     hir::BinOpKind::Lt => hir::BinOpKind::Gt,
 412                     hir::BinOpKind::Le => hir::BinOpKind::Ge,
 413                     hir::BinOpKind::Gt => hir::BinOpKind::Lt,
 414                     hir::BinOpKind::Ge => hir::BinOpKind::Le,
 415                     _ => return binop,
 416                 },
 417             )
 418         }
 419
 420         fn check_limits(
 421             cx: &LateContext<'_, '_>,
 422             binop: hir::BinOp,
 423             l: &hir::Expr<'_>,
 424             r: &hir::Expr<'_>,
 425         ) -> bool {
 426             let (lit, expr, swap) = match (&l.kind, &r.kind) {
 427                 (&hir::ExprKind::Lit(_), _) => (l, r, true),
 428                 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
 429                 _ => return true,
 430             };
 431             // Normalize the binop so that the literal is always on the RHS in
 432             // the comparison
 433             let norm_binop = if swap { rev_binop(binop) } else { binop };
 434             match cx.tables.node_type(expr.hir_id).kind {
 435                 ty::Int(int_ty) => {
 436                     let (min, max) = int_ty_range(int_ty);
 437                     let lit_val: i128 = match lit.kind {
 438                         hir::ExprKind::Lit(ref li) => match li.node {
 439                             ast::LitKind::Int(v, ast::LitIntType::Signed(_))
 440                             | ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => v as i128,
 441                             _ => return true,
 442                         },
 443                         _ => bug!(),
 444                     };
 445                     is_valid(norm_binop, lit_val, min, max)
 446                 }
 447                 ty::Uint(uint_ty) => {
 448                     let (min, max): (u128, u128) = uint_ty_range(uint_ty);
 449                     let lit_val: u128 = match lit.kind {
 450                         hir::ExprKind::Lit(ref li) => match li.node {
 451                             ast::LitKind::Int(v, _) => v,
 452                             _ => return true,
 453                         },
 454                         _ => bug!(),
 455                     };
 456                     is_valid(norm_binop, lit_val, min, max)
 457                 }
 458                 _ => true,
 459             }
 460         }
 461
 462         fn is_comparison(binop: hir::BinOp) -> bool {
 463             match binop.node {
 464                 hir::BinOpKind::Eq
 465                 | hir::BinOpKind::Lt
 466                 | hir::BinOpKind::Le
 467                 | hir::BinOpKind::Ne
 468                 | hir::BinOpKind::Ge
 469                 | hir::BinOpKind::Gt => true,
 470                 _ => false,
 471             }
 472         }
 473     }
 474 }
 475
 476 declare_lint! {
 477     IMPROPER_CTYPES,
 478     Warn,
 479     "proper use of libc types in foreign modules"
 480 }
 481
 482 declare_lint_pass!(ImproperCTypes => [IMPROPER_CTYPES]);
 483
 484 struct ImproperCTypesVisitor<'a, 'tcx> {
 485     cx: &'a LateContext<'a, 'tcx>,
 486 }
 487
 488 enum FfiResult<'tcx> {
 489     FfiSafe,
 490     FfiPhantom(Ty<'tcx>),
 491     FfiUnsafe { ty: Ty<'tcx>, reason: &'static str, help: Option<&'static str> },
 492 }
 493
 494 fn is_zst<'tcx>(tcx: TyCtxt<'tcx>, did: DefId, ty: Ty<'tcx>) -> bool {
 495     tcx.layout_of(tcx.param_env(did).and(ty)).map(|layout| layout.is_zst()).unwrap_or(false)
 496 }
 497
 498 fn ty_is_known_nonnull<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool {
 499     match ty.kind {
 500         ty::FnPtr(_) => true,
 501         ty::Ref(..) => true,
 502         ty::Adt(field_def, substs) if field_def.repr.transparent() && !field_def.is_union() => {
 503             for field in field_def.all_fields() {
 504                 let field_ty =
 505                     tcx.normalize_erasing_regions(ParamEnv::reveal_all(), field.ty(tcx, substs));
 506                 if is_zst(tcx, field.did, field_ty) {
 507                     continue;
 508                 }
 509
 510                 let attrs = tcx.get_attrs(field_def.did);
 511                 if attrs.iter().any(|a| a.check_name(sym::rustc_nonnull_optimization_guaranteed))
 512                     || ty_is_known_nonnull(tcx, field_ty)
 513                 {
 514                     return true;
 515                 }
 516             }
 517
 518             false
 519         }
 520         _ => false,
 521     }
 522 }
 523
 524 /// Check if this enum can be safely exported based on the
 525 /// "nullable pointer optimization". Currently restricted
 526 /// to function pointers, references, core::num::NonZero*,
 527 /// core::ptr::NonNull, and #[repr(transparent)] newtypes.
 528 /// FIXME: This duplicates code in codegen.
 529 fn is_repr_nullable_ptr<'tcx>(
 530     tcx: TyCtxt<'tcx>,
 531     ty: Ty<'tcx>,
 532     ty_def: &'tcx ty::AdtDef,
 533     substs: SubstsRef<'tcx>,
 534 ) -> bool {
 535     if ty_def.variants.len() != 2 {
 536         return false;
 537     }
 538
 539     let get_variant_fields = |index| &ty_def.variants[VariantIdx::new(index)].fields;
 540     let variant_fields = [get_variant_fields(0), get_variant_fields(1)];
 541     let fields = if variant_fields[0].is_empty() {
 542         &variant_fields[1]
 543     } else if variant_fields[1].is_empty() {
 544         &variant_fields[0]
 545     } else {
 546         return false;
 547     };
 548
 549     if fields.len() != 1 {
 550         return false;
 551     }
 552
 553     let field_ty = fields[0].ty(tcx, substs);
 554     if !ty_is_known_nonnull(tcx, field_ty) {
 555         return false;
 556     }
 557
 558     // At this point, the field's type is known to be nonnull and the parent enum is Option-like.
 559     // If the computed size for the field and the enum are different, the nonnull optimization isn't
 560     // being applied (and we've got a problem somewhere).
 561     let compute_size_skeleton = |t| SizeSkeleton::compute(t, tcx, ParamEnv::reveal_all()).unwrap();
 562     if !compute_size_skeleton(ty).same_size(compute_size_skeleton(field_ty)) {
 563         bug!("improper_ctypes: Option nonnull optimization not applied?");
 564     }
 565
 566     true
 567 }
 568
 569 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
 570     /// Check if the type is array and emit an unsafe type lint.
 571     fn check_for_array_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
 572         if let ty::Array(..) = ty.kind {
 573             self.emit_ffi_unsafe_type_lint(
 574                 ty,
 575                 sp,
 576                 "passing raw arrays by value is not FFI-safe",
 577                 Some("consider passing a pointer to the array"),
 578             );
 579             true
 580         } else {
 581             false
 582         }
 583     }
 584
 585     /// Checks if the given type is "ffi-safe" (has a stable, well-defined
 586     /// representation which can be exported to C code).
 587     fn check_type_for_ffi(&self, cache: &mut FxHashSet<Ty<'tcx>>, ty: Ty<'tcx>) -> FfiResult<'tcx> {
 588         use FfiResult::*;
 589
 590         let cx = self.cx.tcx;
 591
 592         // Protect against infinite recursion, for example
 593         // `struct S(*mut S);`.
 594         // FIXME: A recursion limit is necessary as well, for irregular
 595         // recursive types.
 596         if !cache.insert(ty) {
 597             return FfiSafe;
 598         }
 599
 600         match ty.kind {
 601             ty::Adt(def, substs) => {
 602                 if def.is_phantom_data() {
 603                     return FfiPhantom(ty);
 604                 }
 605                 match def.adt_kind() {
 606                     AdtKind::Struct => {
 607                         if !def.repr.c() && !def.repr.transparent() {
 608                             return FfiUnsafe {
 609                                 ty,
 610                                 reason: "this struct has unspecified layout",
 611                                 help: Some(
 612                                     "consider adding a `#[repr(C)]` or \
 613                                             `#[repr(transparent)]` attribute to this struct",
 614                                 ),
 615                             };
 616                         }
 617
 618                         let is_non_exhaustive =
 619                             def.non_enum_variant().is_field_list_non_exhaustive();
 620                         if is_non_exhaustive && !def.did.is_local() {
 621                             return FfiUnsafe {
 622                                 ty,
 623                                 reason: "this struct is non-exhaustive",
 624                                 help: None,
 625                             };
 626                         }
 627
 628                         if def.non_enum_variant().fields.is_empty() {
 629                             return FfiUnsafe {
 630                                 ty,
 631                                 reason: "this struct has no fields",
 632                                 help: Some("consider adding a member to this struct"),
 633                             };
 634                         }
 635
 636                         // We can't completely trust repr(C) and repr(transparent) markings;
 637                         // make sure the fields are actually safe.
 638                         let mut all_phantom = true;
 639                         for field in &def.non_enum_variant().fields {
 640                             let field_ty = cx.normalize_erasing_regions(
 641                                 ParamEnv::reveal_all(),
 642                                 field.ty(cx, substs),
 643                             );
 644                             // repr(transparent) types are allowed to have arbitrary ZSTs, not just
 645                             // PhantomData -- skip checking all ZST fields
 646                             if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 647                                 continue;
 648                             }
 649                             let r = self.check_type_for_ffi(cache, field_ty);
 650                             match r {
 651                                 FfiSafe => {
 652                                     all_phantom = false;
 653                                 }
 654                                 FfiPhantom(..) => {}
 655                                 FfiUnsafe { .. } => {
 656                                     return r;
 657                                 }
 658                             }
 659                         }
 660
 661                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 662                     }
 663                     AdtKind::Union => {
 664                         if !def.repr.c() && !def.repr.transparent() {
 665                             return FfiUnsafe {
 666                                 ty,
 667                                 reason: "this union has unspecified layout",
 668                                 help: Some(
 669                                     "consider adding a `#[repr(C)]` or \
 670                                             `#[repr(transparent)]` attribute to this union",
 671                                 ),
 672                             };
 673                         }
 674
 675                         if def.non_enum_variant().fields.is_empty() {
 676                             return FfiUnsafe {
 677                                 ty,
 678                                 reason: "this union has no fields",
 679                                 help: Some("consider adding a field to this union"),
 680                             };
 681                         }
 682
 683                         let mut all_phantom = true;
 684                         for field in &def.non_enum_variant().fields {
 685                             let field_ty = cx.normalize_erasing_regions(
 686                                 ParamEnv::reveal_all(),
 687                                 field.ty(cx, substs),
 688                             );
 689                             // repr(transparent) types are allowed to have arbitrary ZSTs, not just
 690                             // PhantomData -- skip checking all ZST fields.
 691                             if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 692                                 continue;
 693                             }
 694                             let r = self.check_type_for_ffi(cache, field_ty);
 695                             match r {
 696                                 FfiSafe => {
 697                                     all_phantom = false;
 698                                 }
 699                                 FfiPhantom(..) => {}
 700                                 FfiUnsafe { .. } => {
 701                                     return r;
 702                                 }
 703                             }
 704                         }
 705
 706                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 707                     }
 708                     AdtKind::Enum => {
 709                         if def.variants.is_empty() {
 710                             // Empty enums are okay... although sort of useless.
 711                             return FfiSafe;
 712                         }
 713
 714                         // Check for a repr() attribute to specify the size of the
 715                         // discriminant.
 716                         if !def.repr.c() && !def.repr.transparent() && def.repr.int.is_none() {
 717                             // Special-case types like `Option<extern fn()>`.
 718                             if !is_repr_nullable_ptr(cx, ty, def, substs) {
 719                                 return FfiUnsafe {
 720                                     ty,
 721                                     reason: "enum has no representation hint",
 722                                     help: Some(
 723                                         "consider adding a `#[repr(C)]`, \
 724                                                 `#[repr(transparent)]`, or integer `#[repr(...)]` \
 725                                                 attribute to this enum",
 726                                     ),
 727                                 };
 728                             }
 729                         }
 730
 731                         if def.is_variant_list_non_exhaustive() && !def.did.is_local() {
 732                             return FfiUnsafe {
 733                                 ty,
 734                                 reason: "this enum is non-exhaustive",
 735                                 help: None,
 736                             };
 737                         }
 738
 739                         // Check the contained variants.
 740                         for variant in &def.variants {
 741                             let is_non_exhaustive = variant.is_field_list_non_exhaustive();
 742                             if is_non_exhaustive && !variant.def_id.is_local() {
 743                                 return FfiUnsafe {
 744                                     ty,
 745                                     reason: "this enum has non-exhaustive variants",
 746                                     help: None,
 747                                 };
 748                             }
 749
 750                             for field in &variant.fields {
 751                                 let field_ty = cx.normalize_erasing_regions(
 752                                     ParamEnv::reveal_all(),
 753                                     field.ty(cx, substs),
 754                                 );
 755                                 // repr(transparent) types are allowed to have arbitrary ZSTs, not
 756                                 // just PhantomData -- skip checking all ZST fields.
 757                                 if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 758                                     continue;
 759                                 }
 760                                 let r = self.check_type_for_ffi(cache, field_ty);
 761                                 match r {
 762                                     FfiSafe => {}
 763                                     FfiUnsafe { .. } => {
 764                                         return r;
 765                                     }
 766                                     FfiPhantom(..) => {
 767                                         return FfiUnsafe {
 768                                             ty,
 769                                             reason: "this enum contains a PhantomData field",
 770                                             help: None,
 771                                         };
 772                                     }
 773                                 }
 774                             }
 775                         }
 776                         FfiSafe
 777                     }
 778                 }
 779             }
 780
 781             ty::Char => FfiUnsafe {
 782                 ty,
 783                 reason: "the `char` type has no C equivalent",
 784                 help: Some("consider using `u32` or `libc::wchar_t` instead"),
 785             },
 786
 787             ty::Int(ast::IntTy::I128) | ty::Uint(ast::UintTy::U128) => FfiUnsafe {
 788                 ty,
 789                 reason: "128-bit integers don't currently have a known stable ABI",
 790                 help: None,
 791             },
 792
 793             // Primitive types with a stable representation.
 794             ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
 795
 796             ty::Slice(_) => FfiUnsafe {
 797                 ty,
 798                 reason: "slices have no C equivalent",
 799                 help: Some("consider using a raw pointer instead"),
 800             },
 801
 802             ty::Dynamic(..) => {
 803                 FfiUnsafe { ty, reason: "trait objects have no C equivalent", help: None }
 804             }
 805
 806             ty::Str => FfiUnsafe {
 807                 ty,
 808                 reason: "string slices have no C equivalent",
 809                 help: Some("consider using `*const u8` and a length instead"),
 810             },
 811
 812             ty::Tuple(..) => FfiUnsafe {
 813                 ty,
 814                 reason: "tuples have unspecified layout",
 815                 help: Some("consider using a struct instead"),
 816             },
 817
 818             ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _) => {
 819                 self.check_type_for_ffi(cache, ty)
 820             }
 821
 822             ty::Array(inner_ty, _) => self.check_type_for_ffi(cache, inner_ty),
 823
 824             ty::FnPtr(sig) => {
 825                 match sig.abi() {
 826                     Abi::Rust | Abi::RustIntrinsic | Abi::PlatformIntrinsic | Abi::RustCall => {
 827                         return FfiUnsafe {
 828                             ty,
 829                             reason: "this function pointer has Rust-specific calling convention",
 830                             help: Some(
 831                                 "consider using an `extern fn(...) -> ...` \
 832                                         function pointer instead",
 833                             ),
 834                         };
 835                     }
 836                     _ => {}
 837                 }
 838
 839                 let sig = cx.erase_late_bound_regions(&sig);
 840                 if !sig.output().is_unit() {
 841                     let r = self.check_type_for_ffi(cache, sig.output());
 842                     match r {
 843                         FfiSafe => {}
 844                         _ => {
 845                             return r;
 846                         }
 847                     }
 848                 }
 849                 for arg in sig.inputs() {
 850                     let r = self.check_type_for_ffi(cache, arg);
 851                     match r {
 852                         FfiSafe => {}
 853                         _ => {
 854                             return r;
 855                         }
 856                     }
 857                 }
 858                 FfiSafe
 859             }
 860
 861             ty::Foreign(..) => FfiSafe,
 862
 863             ty::Param(..)
 864             | ty::Infer(..)
 865             | ty::Bound(..)
 866             | ty::Error
 867             | ty::Closure(..)
 868             | ty::Generator(..)
 869             | ty::GeneratorWitness(..)
 870             | ty::Placeholder(..)
 871             | ty::UnnormalizedProjection(..)
 872             | ty::Projection(..)
 873             | ty::Opaque(..)
 874             | ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty),
 875         }
 876     }
 877
 878     fn emit_ffi_unsafe_type_lint(
 879         &mut self,
 880         ty: Ty<'tcx>,
 881         sp: Span,
 882         note: &str,
 883         help: Option<&str>,
 884     ) {
 885         let mut diag = self.cx.struct_span_lint(
 886             IMPROPER_CTYPES,
 887             sp,
 888             &format!("`extern` block uses type `{}`, which is not FFI-safe", ty),
 889         );
 890         diag.span_label(sp, "not FFI-safe");
 891         if let Some(help) = help {
 892             diag.help(help);
 893         }
 894         diag.note(note);
 895         if let ty::Adt(def, _) = ty.kind {
 896             if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did) {
 897                 diag.span_note(sp, "type defined here");
 898             }
 899         }
 900         diag.emit();
 901     }
 902
 903     fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
 904         use crate::rustc::ty::TypeFoldable;
 905
 906         struct ProhibitOpaqueTypes<'tcx> {
 907             ty: Option<Ty<'tcx>>,
 908         };
 909
 910         impl<'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'tcx> {
 911             fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
 912                 if let ty::Opaque(..) = ty.kind {
 913                     self.ty = Some(ty);
 914                     true
 915                 } else {
 916                     ty.super_visit_with(self)
 917                 }
 918             }
 919         }
 920
 921         let mut visitor = ProhibitOpaqueTypes { ty: None };
 922         ty.visit_with(&mut visitor);
 923         if let Some(ty) = visitor.ty {
 924             self.emit_ffi_unsafe_type_lint(ty, sp, "opaque types have no C equivalent", None);
 925             true
 926         } else {
 927             false
 928         }
 929     }
 930
 931     fn check_type_for_ffi_and_report_errors(&mut self, sp: Span, ty: Ty<'tcx>, is_static: bool) {
 932         // We have to check for opaque types before `normalize_erasing_regions`,
 933         // which will replace opaque types with their underlying concrete type.
 934         if self.check_for_opaque_ty(sp, ty) {
 935             // We've already emitted an error due to an opaque type.
 936             return;
 937         }
 938
 939         // it is only OK to use this function because extern fns cannot have
 940         // any generic types right now:
 941         let ty = self.cx.tcx.normalize_erasing_regions(ParamEnv::reveal_all(), ty);
 942         // C doesn't really support passing arrays by value.
 943         // The only way to pass an array by value is through a struct.
 944         // So we first test that the top level isn't an array,
 945         // and then recursively check the types inside.
 946         if !is_static && self.check_for_array_ty(sp, ty) {
 947             return;
 948         }
 949
 950         match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
 951             FfiResult::FfiSafe => {}
 952             FfiResult::FfiPhantom(ty) => {
 953                 self.emit_ffi_unsafe_type_lint(ty, sp, "composed only of `PhantomData`", None);
 954             }
 955             FfiResult::FfiUnsafe { ty, reason, help } => {
 956                 self.emit_ffi_unsafe_type_lint(ty, sp, reason, help);
 957             }
 958         }
 959     }
 960
 961     fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl<'_>) {
 962         let def_id = self.cx.tcx.hir().local_def_id(id);
 963         let sig = self.cx.tcx.fn_sig(def_id);
 964         let sig = self.cx.tcx.erase_late_bound_regions(&sig);
 965
 966         for (input_ty, input_hir) in sig.inputs().iter().zip(decl.inputs) {
 967             self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty, false);
 968         }
 969
 970         if let hir::FunctionRetTy::Return(ref ret_hir) = decl.output {
 971             let ret_ty = sig.output();
 972             if !ret_ty.is_unit() {
 973                 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty, false);
 974             }
 975         }
 976     }
 977
 978     fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
 979         let def_id = self.cx.tcx.hir().local_def_id(id);
 980         let ty = self.cx.tcx.type_of(def_id);
 981         self.check_type_for_ffi_and_report_errors(span, ty, true);
 982     }
 983 }
 984
 985 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImproperCTypes {
 986     fn check_foreign_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::ForeignItem<'_>) {
 987         let mut vis = ImproperCTypesVisitor { cx };
 988         let abi = cx.tcx.hir().get_foreign_abi(it.hir_id);
 989         if let Abi::Rust | Abi::RustCall | Abi::RustIntrinsic | Abi::PlatformIntrinsic = abi {
 990             // Don't worry about types in internal ABIs.
 991         } else {
 992             match it.kind {
 993                 hir::ForeignItemKind::Fn(ref decl, _, _) => {
 994                     vis.check_foreign_fn(it.hir_id, decl);
 995                 }
 996                 hir::ForeignItemKind::Static(ref ty, _) => {
 997                     vis.check_foreign_static(it.hir_id, ty.span);
 998                 }
 999                 hir::ForeignItemKind::Type => (),
1000             }
1001         }
1002     }
1003 }
1004
1005 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
1006
1007 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for VariantSizeDifferences {
1008     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item<'_>) {
1009         if let hir::ItemKind::Enum(ref enum_definition, _) = it.kind {
1010             let item_def_id = cx.tcx.hir().local_def_id(it.hir_id);
1011             let t = cx.tcx.type_of(item_def_id);
1012             let ty = cx.tcx.erase_regions(&t);
1013             let layout = match cx.layout_of(ty) {
1014                 Ok(layout) => layout,
1015                 Err(ty::layout::LayoutError::Unknown(_)) => return,
1016                 Err(err @ ty::layout::LayoutError::SizeOverflow(_)) => {
1017                     bug!("failed to get layout for `{}`: {}", t, err);
1018                 }
1019             };
1020             let (variants, tag) = match layout.variants {
1021                 layout::Variants::Multiple {
1022                     discr_kind: layout::DiscriminantKind::Tag,
1023                     ref discr,
1024                     ref variants,
1025                     ..
1026                 } => (variants, discr),
1027                 _ => return,
1028             };
1029
1030             let discr_size = tag.value.size(&cx.tcx).bytes();
1031
1032             debug!(
1033                 "enum `{}` is {} bytes large with layout:\n{:#?}",
1034                 t,
1035                 layout.size.bytes(),
1036                 layout
1037             );
1038
1039             let (largest, slargest, largest_index) = enum_definition
1040                 .variants
1041                 .iter()
1042                 .zip(variants)
1043                 .map(|(variant, variant_layout)| {
1044                     // Subtract the size of the enum discriminant.
1045                     let bytes = variant_layout.size.bytes().saturating_sub(discr_size);
1046
1047                     debug!("- variant `{}` is {} bytes large", variant.ident, bytes);
1048                     bytes
1049                 })
1050                 .enumerate()
1051                 .fold((0, 0, 0), |(l, s, li), (idx, size)| {
1052                     if size > l {
1053                         (size, l, idx)
1054                     } else if size > s {
1055                         (l, size, li)
1056                     } else {
1057                         (l, s, li)
1058                     }
1059                 });
1060
1061             // We only warn if the largest variant is at least thrice as large as
1062             // the second-largest.
1063             if largest > slargest * 3 && slargest > 0 {
1064                 cx.span_lint(
1065                     VARIANT_SIZE_DIFFERENCES,
1066                     enum_definition.variants[largest_index].span,
1067                     &format!(
1068                         "enum variant is more than three times \
1069                                           larger ({} bytes) than the next largest",
1070                         largest
1071                     ),
1072                 );
1073             }
1074         }
1075     }
1076 }