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_attr as attr;
   9 use rustc_data_structures::fx::FxHashSet;
  10 use rustc_errors::Applicability;
  11 use rustc_hir as hir;
  12 use rustc_hir::def_id::DefId;
  13 use rustc_hir::{is_range_literal, ExprKind, Node};
  14 use rustc_index::vec::Idx;
  15 use rustc_span::source_map;
  16 use rustc_span::symbol::sym;
  17 use rustc_span::Span;
  18 use rustc_target::spec::abi::Abi;
  19 use syntax::ast;
  20
  21 use log::debug;
  22 use std::cmp;
  23 use std::{f32, f64, i16, i32, i64, i8, u16, u32, u64, u8};
  24
  25 declare_lint! {
  26     UNUSED_COMPARISONS,
  27     Warn,
  28     "comparisons made useless by limits of the types involved"
  29 }
  30
  31 declare_lint! {
  32     OVERFLOWING_LITERALS,
  33     Deny,
  34     "literal out of range for its type"
  35 }
  36
  37 declare_lint! {
  38     VARIANT_SIZE_DIFFERENCES,
  39     Allow,
  40     "detects enums with widely varying variant sizes"
  41 }
  42
  43 #[derive(Copy, Clone)]
  44 pub struct TypeLimits {
  45     /// Id of the last visited negated expression
  46     negated_expr_id: hir::HirId,
  47 }
  48
  49 impl_lint_pass!(TypeLimits => [UNUSED_COMPARISONS, OVERFLOWING_LITERALS]);
  50
  51 impl TypeLimits {
  52     pub fn new() -> TypeLimits {
  53         TypeLimits { negated_expr_id: hir::DUMMY_HIR_ID }
  54     }
  55 }
  56
  57 /// Attempts to special-case the overflowing literal lint when it occurs as a range endpoint.
  58 /// Returns `true` iff the lint was overridden.
  59 fn lint_overflowing_range_endpoint<'a, 'tcx>(
  60     cx: &LateContext<'a, 'tcx>,
  61     lit: &hir::Lit,
  62     lit_val: u128,
  63     max: u128,
  64     expr: &'tcx hir::Expr<'tcx>,
  65     parent_expr: &'tcx hir::Expr<'tcx>,
  66     ty: &str,
  67 ) -> bool {
  68     // We only want to handle exclusive (`..`) ranges,
  69     // which are represented as `ExprKind::Struct`.
  70     let mut overwritten = false;
  71     if let ExprKind::Struct(_, eps, _) = &parent_expr.kind {
  72         if eps.len() != 2 {
  73             return false;
  74         }
  75         // We can suggest using an inclusive range
  76         // (`..=`) instead only if it is the `end` that is
  77         // overflowing and only by 1.
  78         if eps[1].expr.hir_id == expr.hir_id && lit_val - 1 == max {
  79             cx.struct_span_lint(
  80                 OVERFLOWING_LITERALS,
  81                 parent_expr.span,
  82                 |lint| {
  83                     let mut err = lint.build(&format!("range endpoint is out of range for `{}`", ty));
  84                     if let Ok(start) = cx.sess().source_map().span_to_snippet(eps[0].span) {
  85                         use ast::{LitIntType, LitKind};
  86                         // We need to preserve the literal's suffix,
  87                         // as it may determine typing information.
  88                         let suffix = match lit.node {
  89                             LitKind::Int(_, LitIntType::Signed(s)) => format!("{}", s.name_str()),
  90                             LitKind::Int(_, LitIntType::Unsigned(s)) => format!("{}", s.name_str()),
  91                             LitKind::Int(_, LitIntType::Unsuffixed) => "".to_owned(),
  92                             _ => bug!(),
  93                         };
  94                         let suggestion = format!("{}..={}{}", start, lit_val - 1, suffix);
  95                         err.span_suggestion(
  96                             parent_expr.span,
  97                             &"use an inclusive range instead",
  98                             suggestion,
  99                             Applicability::MachineApplicable,
 100                         );
 101                         err.emit();
 102                         overwritten = true;
 103                     }
 104                 },
 105             );
 106         }
 107     }
 108     overwritten
 109 }
 110
 111 // For `isize` & `usize`, be conservative with the warnings, so that the
 112 // warnings are consistent between 32- and 64-bit platforms.
 113 fn int_ty_range(int_ty: ast::IntTy) -> (i128, i128) {
 114     match int_ty {
 115         ast::IntTy::Isize => (i64::min_value() as i128, i64::max_value() as i128),
 116         ast::IntTy::I8 => (i8::min_value() as i64 as i128, i8::max_value() as i128),
 117         ast::IntTy::I16 => (i16::min_value() as i64 as i128, i16::max_value() as i128),
 118         ast::IntTy::I32 => (i32::min_value() as i64 as i128, i32::max_value() as i128),
 119         ast::IntTy::I64 => (i64::min_value() as i128, i64::max_value() as i128),
 120         ast::IntTy::I128 => (i128::min_value() as i128, i128::max_value()),
 121     }
 122 }
 123
 124 fn uint_ty_range(uint_ty: ast::UintTy) -> (u128, u128) {
 125     match uint_ty {
 126         ast::UintTy::Usize => (u64::min_value() as u128, u64::max_value() as u128),
 127         ast::UintTy::U8 => (u8::min_value() as u128, u8::max_value() as u128),
 128         ast::UintTy::U16 => (u16::min_value() as u128, u16::max_value() as u128),
 129         ast::UintTy::U32 => (u32::min_value() as u128, u32::max_value() as u128),
 130         ast::UintTy::U64 => (u64::min_value() as u128, u64::max_value() as u128),
 131         ast::UintTy::U128 => (u128::min_value(), u128::max_value()),
 132     }
 133 }
 134
 135 fn get_bin_hex_repr(cx: &LateContext<'_, '_>, lit: &hir::Lit) -> Option<String> {
 136     let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?;
 137     let firstch = src.chars().next()?;
 138
 139     if firstch == '0' {
 140         match src.chars().nth(1) {
 141             Some('x') | Some('b') => return Some(src),
 142             _ => return None,
 143         }
 144     }
 145
 146     None
 147 }
 148
 149 fn report_bin_hex_error(
 150     cx: &LateContext<'_, '_>,
 151     expr: &hir::Expr<'_>,
 152     ty: attr::IntType,
 153     repr_str: String,
 154     val: u128,
 155     negative: bool,
 156 ) {
 157     let size = layout::Integer::from_attr(&cx.tcx, ty).size();
 158     let (t, actually) = match ty {
 159         attr::IntType::SignedInt(t) => {
 160             let actually = sign_extend(val, size) as i128;
 161             (t.name_str(), actually.to_string())
 162         }
 163         attr::IntType::UnsignedInt(t) => {
 164             let actually = truncate(val, size);
 165             (t.name_str(), actually.to_string())
 166         }
 167     };
 168     cx.struct_span_lint(
 169         OVERFLOWING_LITERALS,
 170         expr.span,
 171         |lint| {
 172             let mut err = lint.build(&format!("literal out of range for {}", t));
 173             err.note(&format!(
 174                 "the literal `{}` (decimal `{}`) does not fit into \
 175                     an `{}` and will become `{}{}`",
 176                 repr_str, val, t, actually, t
 177             ));
 178             if let Some(sugg_ty) = get_type_suggestion(&cx.tables.node_type(expr.hir_id), val, negative) {
 179                 if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') {
 180                     let (sans_suffix, _) = repr_str.split_at(pos);
 181                     err.span_suggestion(
 182                         expr.span,
 183                         &format!("consider using `{}` instead", sugg_ty),
 184                         format!("{}{}", sans_suffix, sugg_ty),
 185                         Applicability::MachineApplicable,
 186                     );
 187                 } else {
 188                     err.help(&format!("consider using `{}` instead", sugg_ty));
 189                 }
 190             }
 191             err.emit();
 192         },
 193     );
 194 }
 195
 196 // This function finds the next fitting type and generates a suggestion string.
 197 // It searches for fitting types in the following way (`X < Y`):
 198 //  - `iX`: if literal fits in `uX` => `uX`, else => `iY`
 199 //  - `-iX` => `iY`
 200 //  - `uX` => `uY`
 201 //
 202 // No suggestion for: `isize`, `usize`.
 203 fn get_type_suggestion(t: Ty<'_>, val: u128, negative: bool) -> Option<&'static str> {
 204     use syntax::ast::IntTy::*;
 205     use syntax::ast::UintTy::*;
 206     macro_rules! find_fit {
 207         ($ty:expr, $val:expr, $negative:expr,
 208          $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => {
 209             {
 210                 let _neg = if negative { 1 } else { 0 };
 211                 match $ty {
 212                     $($type => {
 213                         $(if !negative && val <= uint_ty_range($utypes).1 {
 214                             return Some($utypes.name_str())
 215                         })*
 216                         $(if val <= int_ty_range($itypes).1 as u128 + _neg {
 217                             return Some($itypes.name_str())
 218                         })*
 219                         None
 220                     },)+
 221                     _ => None
 222                 }
 223             }
 224         }
 225     }
 226     match t.kind {
 227         ty::Int(i) => find_fit!(i, val, negative,
 228                       I8 => [U8] => [I16, I32, I64, I128],
 229                       I16 => [U16] => [I32, I64, I128],
 230                       I32 => [U32] => [I64, I128],
 231                       I64 => [U64] => [I128],
 232                       I128 => [U128] => []),
 233         ty::Uint(u) => find_fit!(u, val, negative,
 234                       U8 => [U8, U16, U32, U64, U128] => [],
 235                       U16 => [U16, U32, U64, U128] => [],
 236                       U32 => [U32, U64, U128] => [],
 237                       U64 => [U64, U128] => [],
 238                       U128 => [U128] => []),
 239         _ => None,
 240     }
 241 }
 242
 243 fn lint_int_literal<'a, 'tcx>(
 244     cx: &LateContext<'a, 'tcx>,
 245     type_limits: &TypeLimits,
 246     e: &'tcx hir::Expr<'tcx>,
 247     lit: &hir::Lit,
 248     t: ast::IntTy,
 249     v: u128,
 250 ) {
 251     let int_type = t.normalize(cx.sess().target.ptr_width);
 252     let (_, max) = int_ty_range(int_type);
 253     let max = max as u128;
 254     let negative = type_limits.negated_expr_id == e.hir_id;
 255
 256     // Detect literal value out of range [min, max] inclusive
 257     // avoiding use of -min to prevent overflow/panic
 258     if (negative && v > max + 1) || (!negative && v > max) {
 259         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 260             report_bin_hex_error(cx, e, attr::IntType::SignedInt(t), repr_str, v, negative);
 261             return;
 262         }
 263
 264         let par_id = cx.tcx.hir().get_parent_node(e.hir_id);
 265         if let Node::Expr(par_e) = cx.tcx.hir().get(par_id) {
 266             if let hir::ExprKind::Struct(..) = par_e.kind {
 267                 if is_range_literal(cx.sess().source_map(), par_e)
 268                     && lint_overflowing_range_endpoint(cx, lit, v, max, e, par_e, t.name_str())
 269                 {
 270                     // The overflowing literal lint was overridden.
 271                     return;
 272                 }
 273             }
 274         }
 275
 276         cx.span_lint(
 277             OVERFLOWING_LITERALS,
 278             e.span,
 279             &format!("literal out of range for `{}`", t.name_str()),
 280         );
 281     }
 282 }
 283
 284 fn lint_uint_literal<'a, 'tcx>(
 285     cx: &LateContext<'a, 'tcx>,
 286     e: &'tcx hir::Expr<'tcx>,
 287     lit: &hir::Lit,
 288     t: ast::UintTy,
 289 ) {
 290     let uint_type = t.normalize(cx.sess().target.ptr_width);
 291     let (min, max) = uint_ty_range(uint_type);
 292     let lit_val: u128 = match lit.node {
 293         // _v is u8, within range by definition
 294         ast::LitKind::Byte(_v) => return,
 295         ast::LitKind::Int(v, _) => v,
 296         _ => bug!(),
 297     };
 298     if lit_val < min || lit_val > max {
 299         let parent_id = cx.tcx.hir().get_parent_node(e.hir_id);
 300         if let Node::Expr(par_e) = cx.tcx.hir().get(parent_id) {
 301             match par_e.kind {
 302                 hir::ExprKind::Cast(..) => {
 303                     if let ty::Char = cx.tables.expr_ty(par_e).kind {
 304                         cx.struct_span_lint(OVERFLOWING_LITERALS, par_e.span, |lint| {
 305                             lint.build("only `u8` can be cast into `char`")
 306                                 .span_suggestion(
 307                                     par_e.span,
 308                                     &"use a `char` literal instead",
 309                                     format!("'\\u{{{:X}}}'", lit_val),
 310                                     Applicability::MachineApplicable,
 311                                 )
 312                                 .emit();
 313                         });
 314                         return;
 315                     }
 316                 }
 317                 hir::ExprKind::Struct(..) if is_range_literal(cx.sess().source_map(), par_e) => {
 318                     let t = t.name_str();
 319                     if lint_overflowing_range_endpoint(cx, lit, lit_val, max, e, par_e, t) {
 320                         // The overflowing literal lint was overridden.
 321                         return;
 322                     }
 323                 }
 324                 _ => {}
 325             }
 326         }
 327         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 328             report_bin_hex_error(cx, e, attr::IntType::UnsignedInt(t), repr_str, lit_val, false);
 329             return;
 330         }
 331         cx.span_lint(
 332             OVERFLOWING_LITERALS,
 333             e.span,
 334             &format!("literal out of range for `{}`", t.name_str()),
 335         );
 336     }
 337 }
 338
 339 fn lint_literal<'a, 'tcx>(
 340     cx: &LateContext<'a, 'tcx>,
 341     type_limits: &TypeLimits,
 342     e: &'tcx hir::Expr<'tcx>,
 343     lit: &hir::Lit,
 344 ) {
 345     match cx.tables.node_type(e.hir_id).kind {
 346         ty::Int(t) => {
 347             match lit.node {
 348                 ast::LitKind::Int(v, ast::LitIntType::Signed(_))
 349                 | ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => {
 350                     lint_int_literal(cx, type_limits, e, lit, t, v)
 351                 }
 352                 _ => bug!(),
 353             };
 354         }
 355         ty::Uint(t) => lint_uint_literal(cx, e, lit, t),
 356         ty::Float(t) => {
 357             let is_infinite = match lit.node {
 358                 ast::LitKind::Float(v, _) => match t {
 359                     ast::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
 360                     ast::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
 361                 },
 362                 _ => bug!(),
 363             };
 364             if is_infinite == Ok(true) {
 365                 cx.span_lint(
 366                     OVERFLOWING_LITERALS,
 367                     e.span,
 368                     &format!("literal out of range for `{}`", t.name_str()),
 369                 );
 370             }
 371         }
 372         _ => {}
 373     }
 374 }
 375
 376 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TypeLimits {
 377     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx hir::Expr<'tcx>) {
 378         match e.kind {
 379             hir::ExprKind::Unary(hir::UnOp::UnNeg, ref expr) => {
 380                 // propagate negation, if the negation itself isn't negated
 381                 if self.negated_expr_id != e.hir_id {
 382                     self.negated_expr_id = expr.hir_id;
 383                 }
 384             }
 385             hir::ExprKind::Binary(binop, ref l, ref r) => {
 386                 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
 387                     cx.span_lint(
 388                         UNUSED_COMPARISONS,
 389                         e.span,
 390                         "comparison is useless due to type limits",
 391                     );
 392                 }
 393             }
 394             hir::ExprKind::Lit(ref lit) => lint_literal(cx, self, e, lit),
 395             _ => {}
 396         };
 397
 398         fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
 399             match binop.node {
 400                 hir::BinOpKind::Lt => v > min && v <= max,
 401                 hir::BinOpKind::Le => v >= min && v < max,
 402                 hir::BinOpKind::Gt => v >= min && v < max,
 403                 hir::BinOpKind::Ge => v > min && v <= max,
 404                 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
 405                 _ => bug!(),
 406             }
 407         }
 408
 409         fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
 410             source_map::respan(
 411                 binop.span,
 412                 match binop.node {
 413                     hir::BinOpKind::Lt => hir::BinOpKind::Gt,
 414                     hir::BinOpKind::Le => hir::BinOpKind::Ge,
 415                     hir::BinOpKind::Gt => hir::BinOpKind::Lt,
 416                     hir::BinOpKind::Ge => hir::BinOpKind::Le,
 417                     _ => return binop,
 418                 },
 419             )
 420         }
 421
 422         fn check_limits(
 423             cx: &LateContext<'_, '_>,
 424             binop: hir::BinOp,
 425             l: &hir::Expr<'_>,
 426             r: &hir::Expr<'_>,
 427         ) -> bool {
 428             let (lit, expr, swap) = match (&l.kind, &r.kind) {
 429                 (&hir::ExprKind::Lit(_), _) => (l, r, true),
 430                 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
 431                 _ => return true,
 432             };
 433             // Normalize the binop so that the literal is always on the RHS in
 434             // the comparison
 435             let norm_binop = if swap { rev_binop(binop) } else { binop };
 436             match cx.tables.node_type(expr.hir_id).kind {
 437                 ty::Int(int_ty) => {
 438                     let (min, max) = int_ty_range(int_ty);
 439                     let lit_val: i128 = match lit.kind {
 440                         hir::ExprKind::Lit(ref li) => match li.node {
 441                             ast::LitKind::Int(v, ast::LitIntType::Signed(_))
 442                             | ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => v as i128,
 443                             _ => return true,
 444                         },
 445                         _ => bug!(),
 446                     };
 447                     is_valid(norm_binop, lit_val, min, max)
 448                 }
 449                 ty::Uint(uint_ty) => {
 450                     let (min, max): (u128, u128) = uint_ty_range(uint_ty);
 451                     let lit_val: u128 = match lit.kind {
 452                         hir::ExprKind::Lit(ref li) => match li.node {
 453                             ast::LitKind::Int(v, _) => v,
 454                             _ => return true,
 455                         },
 456                         _ => bug!(),
 457                     };
 458                     is_valid(norm_binop, lit_val, min, max)
 459                 }
 460                 _ => true,
 461             }
 462         }
 463
 464         fn is_comparison(binop: hir::BinOp) -> bool {
 465             match binop.node {
 466                 hir::BinOpKind::Eq
 467                 | hir::BinOpKind::Lt
 468                 | hir::BinOpKind::Le
 469                 | hir::BinOpKind::Ne
 470                 | hir::BinOpKind::Ge
 471                 | hir::BinOpKind::Gt => true,
 472                 _ => false,
 473             }
 474         }
 475     }
 476 }
 477
 478 declare_lint! {
 479     IMPROPER_CTYPES,
 480     Warn,
 481     "proper use of libc types in foreign modules"
 482 }
 483
 484 declare_lint_pass!(ImproperCTypes => [IMPROPER_CTYPES]);
 485
 486 struct ImproperCTypesVisitor<'a, 'tcx> {
 487     cx: &'a LateContext<'a, 'tcx>,
 488 }
 489
 490 enum FfiResult<'tcx> {
 491     FfiSafe,
 492     FfiPhantom(Ty<'tcx>),
 493     FfiUnsafe { ty: Ty<'tcx>, reason: &'static str, help: Option<&'static str> },
 494 }
 495
 496 fn is_zst<'tcx>(tcx: TyCtxt<'tcx>, did: DefId, ty: Ty<'tcx>) -> bool {
 497     tcx.layout_of(tcx.param_env(did).and(ty)).map(|layout| layout.is_zst()).unwrap_or(false)
 498 }
 499
 500 fn ty_is_known_nonnull<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool {
 501     match ty.kind {
 502         ty::FnPtr(_) => true,
 503         ty::Ref(..) => true,
 504         ty::Adt(field_def, substs) if field_def.repr.transparent() && !field_def.is_union() => {
 505             for field in field_def.all_fields() {
 506                 let field_ty =
 507                     tcx.normalize_erasing_regions(ParamEnv::reveal_all(), field.ty(tcx, substs));
 508                 if is_zst(tcx, field.did, field_ty) {
 509                     continue;
 510                 }
 511
 512                 let attrs = tcx.get_attrs(field_def.did);
 513                 if attrs.iter().any(|a| a.check_name(sym::rustc_nonnull_optimization_guaranteed))
 514                     || ty_is_known_nonnull(tcx, field_ty)
 515                 {
 516                     return true;
 517                 }
 518             }
 519
 520             false
 521         }
 522         _ => false,
 523     }
 524 }
 525
 526 /// Check if this enum can be safely exported based on the
 527 /// "nullable pointer optimization". Currently restricted
 528 /// to function pointers, references, core::num::NonZero*,
 529 /// core::ptr::NonNull, and #[repr(transparent)] newtypes.
 530 /// FIXME: This duplicates code in codegen.
 531 fn is_repr_nullable_ptr<'tcx>(
 532     tcx: TyCtxt<'tcx>,
 533     ty: Ty<'tcx>,
 534     ty_def: &'tcx ty::AdtDef,
 535     substs: SubstsRef<'tcx>,
 536 ) -> bool {
 537     if ty_def.variants.len() != 2 {
 538         return false;
 539     }
 540
 541     let get_variant_fields = |index| &ty_def.variants[VariantIdx::new(index)].fields;
 542     let variant_fields = [get_variant_fields(0), get_variant_fields(1)];
 543     let fields = if variant_fields[0].is_empty() {
 544         &variant_fields[1]
 545     } else if variant_fields[1].is_empty() {
 546         &variant_fields[0]
 547     } else {
 548         return false;
 549     };
 550
 551     if fields.len() != 1 {
 552         return false;
 553     }
 554
 555     let field_ty = fields[0].ty(tcx, substs);
 556     if !ty_is_known_nonnull(tcx, field_ty) {
 557         return false;
 558     }
 559
 560     // At this point, the field's type is known to be nonnull and the parent enum is Option-like.
 561     // If the computed size for the field and the enum are different, the nonnull optimization isn't
 562     // being applied (and we've got a problem somewhere).
 563     let compute_size_skeleton = |t| SizeSkeleton::compute(t, tcx, ParamEnv::reveal_all()).unwrap();
 564     if !compute_size_skeleton(ty).same_size(compute_size_skeleton(field_ty)) {
 565         bug!("improper_ctypes: Option nonnull optimization not applied?");
 566     }
 567
 568     true
 569 }
 570
 571 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
 572     /// Check if the type is array and emit an unsafe type lint.
 573     fn check_for_array_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
 574         if let ty::Array(..) = ty.kind {
 575             self.emit_ffi_unsafe_type_lint(
 576                 ty,
 577                 sp,
 578                 "passing raw arrays by value is not FFI-safe",
 579                 Some("consider passing a pointer to the array"),
 580             );
 581             true
 582         } else {
 583             false
 584         }
 585     }
 586
 587     /// Checks if the given type is "ffi-safe" (has a stable, well-defined
 588     /// representation which can be exported to C code).
 589     fn check_type_for_ffi(&self, cache: &mut FxHashSet<Ty<'tcx>>, ty: Ty<'tcx>) -> FfiResult<'tcx> {
 590         use FfiResult::*;
 591
 592         let cx = self.cx.tcx;
 593
 594         // Protect against infinite recursion, for example
 595         // `struct S(*mut S);`.
 596         // FIXME: A recursion limit is necessary as well, for irregular
 597         // recursive types.
 598         if !cache.insert(ty) {
 599             return FfiSafe;
 600         }
 601
 602         match ty.kind {
 603             ty::Adt(def, substs) => {
 604                 if def.is_phantom_data() {
 605                     return FfiPhantom(ty);
 606                 }
 607                 match def.adt_kind() {
 608                     AdtKind::Struct => {
 609                         if !def.repr.c() && !def.repr.transparent() {
 610                             return FfiUnsafe {
 611                                 ty,
 612                                 reason: "this struct has unspecified layout",
 613                                 help: Some(
 614                                     "consider adding a `#[repr(C)]` or \
 615                                             `#[repr(transparent)]` attribute to this struct",
 616                                 ),
 617                             };
 618                         }
 619
 620                         let is_non_exhaustive =
 621                             def.non_enum_variant().is_field_list_non_exhaustive();
 622                         if is_non_exhaustive && !def.did.is_local() {
 623                             return FfiUnsafe {
 624                                 ty,
 625                                 reason: "this struct is non-exhaustive",
 626                                 help: None,
 627                             };
 628                         }
 629
 630                         if def.non_enum_variant().fields.is_empty() {
 631                             return FfiUnsafe {
 632                                 ty,
 633                                 reason: "this struct has no fields",
 634                                 help: Some("consider adding a member to this struct"),
 635                             };
 636                         }
 637
 638                         // We can't completely trust repr(C) and repr(transparent) markings;
 639                         // make sure the fields are actually safe.
 640                         let mut all_phantom = true;
 641                         for field in &def.non_enum_variant().fields {
 642                             let field_ty = cx.normalize_erasing_regions(
 643                                 ParamEnv::reveal_all(),
 644                                 field.ty(cx, substs),
 645                             );
 646                             // repr(transparent) types are allowed to have arbitrary ZSTs, not just
 647                             // PhantomData -- skip checking all ZST fields
 648                             if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 649                                 continue;
 650                             }
 651                             let r = self.check_type_for_ffi(cache, field_ty);
 652                             match r {
 653                                 FfiSafe => {
 654                                     all_phantom = false;
 655                                 }
 656                                 FfiPhantom(..) => {}
 657                                 FfiUnsafe { .. } => {
 658                                     return r;
 659                                 }
 660                             }
 661                         }
 662
 663                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 664                     }
 665                     AdtKind::Union => {
 666                         if !def.repr.c() && !def.repr.transparent() {
 667                             return FfiUnsafe {
 668                                 ty,
 669                                 reason: "this union has unspecified layout",
 670                                 help: Some(
 671                                     "consider adding a `#[repr(C)]` or \
 672                                             `#[repr(transparent)]` attribute to this union",
 673                                 ),
 674                             };
 675                         }
 676
 677                         if def.non_enum_variant().fields.is_empty() {
 678                             return FfiUnsafe {
 679                                 ty,
 680                                 reason: "this union has no fields",
 681                                 help: Some("consider adding a field to this union"),
 682                             };
 683                         }
 684
 685                         let mut all_phantom = true;
 686                         for field in &def.non_enum_variant().fields {
 687                             let field_ty = cx.normalize_erasing_regions(
 688                                 ParamEnv::reveal_all(),
 689                                 field.ty(cx, substs),
 690                             );
 691                             // repr(transparent) types are allowed to have arbitrary ZSTs, not just
 692                             // PhantomData -- skip checking all ZST fields.
 693                             if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 694                                 continue;
 695                             }
 696                             let r = self.check_type_for_ffi(cache, field_ty);
 697                             match r {
 698                                 FfiSafe => {
 699                                     all_phantom = false;
 700                                 }
 701                                 FfiPhantom(..) => {}
 702                                 FfiUnsafe { .. } => {
 703                                     return r;
 704                                 }
 705                             }
 706                         }
 707
 708                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 709                     }
 710                     AdtKind::Enum => {
 711                         if def.variants.is_empty() {
 712                             // Empty enums are okay... although sort of useless.
 713                             return FfiSafe;
 714                         }
 715
 716                         // Check for a repr() attribute to specify the size of the
 717                         // discriminant.
 718                         if !def.repr.c() && !def.repr.transparent() && def.repr.int.is_none() {
 719                             // Special-case types like `Option<extern fn()>`.
 720                             if !is_repr_nullable_ptr(cx, ty, def, substs) {
 721                                 return FfiUnsafe {
 722                                     ty,
 723                                     reason: "enum has no representation hint",
 724                                     help: Some(
 725                                         "consider adding a `#[repr(C)]`, \
 726                                                 `#[repr(transparent)]`, or integer `#[repr(...)]` \
 727                                                 attribute to this enum",
 728                                     ),
 729                                 };
 730                             }
 731                         }
 732
 733                         if def.is_variant_list_non_exhaustive() && !def.did.is_local() {
 734                             return FfiUnsafe {
 735                                 ty,
 736                                 reason: "this enum is non-exhaustive",
 737                                 help: None,
 738                             };
 739                         }
 740
 741                         // Check the contained variants.
 742                         for variant in &def.variants {
 743                             let is_non_exhaustive = variant.is_field_list_non_exhaustive();
 744                             if is_non_exhaustive && !variant.def_id.is_local() {
 745                                 return FfiUnsafe {
 746                                     ty,
 747                                     reason: "this enum has non-exhaustive variants",
 748                                     help: None,
 749                                 };
 750                             }
 751
 752                             for field in &variant.fields {
 753                                 let field_ty = cx.normalize_erasing_regions(
 754                                     ParamEnv::reveal_all(),
 755                                     field.ty(cx, substs),
 756                                 );
 757                                 // repr(transparent) types are allowed to have arbitrary ZSTs, not
 758                                 // just PhantomData -- skip checking all ZST fields.
 759                                 if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 760                                     continue;
 761                                 }
 762                                 let r = self.check_type_for_ffi(cache, field_ty);
 763                                 match r {
 764                                     FfiSafe => {}
 765                                     FfiUnsafe { .. } => {
 766                                         return r;
 767                                     }
 768                                     FfiPhantom(..) => {
 769                                         return FfiUnsafe {
 770                                             ty,
 771                                             reason: "this enum contains a PhantomData field",
 772                                             help: None,
 773                                         };
 774                                     }
 775                                 }
 776                             }
 777                         }
 778                         FfiSafe
 779                     }
 780                 }
 781             }
 782
 783             ty::Char => FfiUnsafe {
 784                 ty,
 785                 reason: "the `char` type has no C equivalent",
 786                 help: Some("consider using `u32` or `libc::wchar_t` instead"),
 787             },
 788
 789             ty::Int(ast::IntTy::I128) | ty::Uint(ast::UintTy::U128) => FfiUnsafe {
 790                 ty,
 791                 reason: "128-bit integers don't currently have a known stable ABI",
 792                 help: None,
 793             },
 794
 795             // Primitive types with a stable representation.
 796             ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
 797
 798             ty::Slice(_) => FfiUnsafe {
 799                 ty,
 800                 reason: "slices have no C equivalent",
 801                 help: Some("consider using a raw pointer instead"),
 802             },
 803
 804             ty::Dynamic(..) => {
 805                 FfiUnsafe { ty, reason: "trait objects have no C equivalent", help: None }
 806             }
 807
 808             ty::Str => FfiUnsafe {
 809                 ty,
 810                 reason: "string slices have no C equivalent",
 811                 help: Some("consider using `*const u8` and a length instead"),
 812             },
 813
 814             ty::Tuple(..) => FfiUnsafe {
 815                 ty,
 816                 reason: "tuples have unspecified layout",
 817                 help: Some("consider using a struct instead"),
 818             },
 819
 820             ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _) => {
 821                 self.check_type_for_ffi(cache, ty)
 822             }
 823
 824             ty::Array(inner_ty, _) => self.check_type_for_ffi(cache, inner_ty),
 825
 826             ty::FnPtr(sig) => {
 827                 match sig.abi() {
 828                     Abi::Rust | Abi::RustIntrinsic | Abi::PlatformIntrinsic | Abi::RustCall => {
 829                         return FfiUnsafe {
 830                             ty,
 831                             reason: "this function pointer has Rust-specific calling convention",
 832                             help: Some(
 833                                 "consider using an `extern fn(...) -> ...` \
 834                                         function pointer instead",
 835                             ),
 836                         };
 837                     }
 838                     _ => {}
 839                 }
 840
 841                 let sig = cx.erase_late_bound_regions(&sig);
 842                 if !sig.output().is_unit() {
 843                     let r = self.check_type_for_ffi(cache, sig.output());
 844                     match r {
 845                         FfiSafe => {}
 846                         _ => {
 847                             return r;
 848                         }
 849                     }
 850                 }
 851                 for arg in sig.inputs() {
 852                     let r = self.check_type_for_ffi(cache, arg);
 853                     match r {
 854                         FfiSafe => {}
 855                         _ => {
 856                             return r;
 857                         }
 858                     }
 859                 }
 860                 FfiSafe
 861             }
 862
 863             ty::Foreign(..) => FfiSafe,
 864
 865             ty::Param(..)
 866             | ty::Infer(..)
 867             | ty::Bound(..)
 868             | ty::Error
 869             | ty::Closure(..)
 870             | ty::Generator(..)
 871             | ty::GeneratorWitness(..)
 872             | ty::Placeholder(..)
 873             | ty::UnnormalizedProjection(..)
 874             | ty::Projection(..)
 875             | ty::Opaque(..)
 876             | ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty),
 877         }
 878     }
 879
 880     fn emit_ffi_unsafe_type_lint(
 881         &mut self,
 882         ty: Ty<'tcx>,
 883         sp: Span,
 884         note: &str,
 885         help: Option<&str>,
 886     ) {
 887         self.cx.struct_span_lint(IMPROPER_CTYPES, sp, |lint| {
 888             let mut diag =
 889                 lint.build(&format!("`extern` block uses type `{}`, which is not FFI-safe", ty));
 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, "the type is defined here");
 898                 }
 899             }
 900             diag.emit();
 901         });
 902     }
 903
 904     fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
 905         use crate::rustc::ty::TypeFoldable;
 906
 907         struct ProhibitOpaqueTypes<'tcx> {
 908             ty: Option<Ty<'tcx>>,
 909         };
 910
 911         impl<'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'tcx> {
 912             fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
 913                 if let ty::Opaque(..) = ty.kind {
 914                     self.ty = Some(ty);
 915                     true
 916                 } else {
 917                     ty.super_visit_with(self)
 918                 }
 919             }
 920         }
 921
 922         let mut visitor = ProhibitOpaqueTypes { ty: None };
 923         ty.visit_with(&mut visitor);
 924         if let Some(ty) = visitor.ty {
 925             self.emit_ffi_unsafe_type_lint(ty, sp, "opaque types have no C equivalent", None);
 926             true
 927         } else {
 928             false
 929         }
 930     }
 931
 932     fn check_type_for_ffi_and_report_errors(&mut self, sp: Span, ty: Ty<'tcx>, is_static: bool) {
 933         // We have to check for opaque types before `normalize_erasing_regions`,
 934         // which will replace opaque types with their underlying concrete type.
 935         if self.check_for_opaque_ty(sp, ty) {
 936             // We've already emitted an error due to an opaque type.
 937             return;
 938         }
 939
 940         // it is only OK to use this function because extern fns cannot have
 941         // any generic types right now:
 942         let ty = self.cx.tcx.normalize_erasing_regions(ParamEnv::reveal_all(), ty);
 943         // C doesn't really support passing arrays by value.
 944         // The only way to pass an array by value is through a struct.
 945         // So we first test that the top level isn't an array,
 946         // and then recursively check the types inside.
 947         if !is_static && self.check_for_array_ty(sp, ty) {
 948             return;
 949         }
 950
 951         match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
 952             FfiResult::FfiSafe => {}
 953             FfiResult::FfiPhantom(ty) => {
 954                 self.emit_ffi_unsafe_type_lint(ty, sp, "composed only of `PhantomData`", None);
 955             }
 956             FfiResult::FfiUnsafe { ty, reason, help } => {
 957                 self.emit_ffi_unsafe_type_lint(ty, sp, reason, help);
 958             }
 959         }
 960     }
 961
 962     fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl<'_>) {
 963         let def_id = self.cx.tcx.hir().local_def_id(id);
 964         let sig = self.cx.tcx.fn_sig(def_id);
 965         let sig = self.cx.tcx.erase_late_bound_regions(&sig);
 966
 967         for (input_ty, input_hir) in sig.inputs().iter().zip(decl.inputs) {
 968             self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty, false);
 969         }
 970
 971         if let hir::FunctionRetTy::Return(ref ret_hir) = decl.output {
 972             let ret_ty = sig.output();
 973             if !ret_ty.is_unit() {
 974                 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty, false);
 975             }
 976         }
 977     }
 978
 979     fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
 980         let def_id = self.cx.tcx.hir().local_def_id(id);
 981         let ty = self.cx.tcx.type_of(def_id);
 982         self.check_type_for_ffi_and_report_errors(span, ty, true);
 983     }
 984 }
 985
 986 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImproperCTypes {
 987     fn check_foreign_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::ForeignItem<'_>) {
 988         let mut vis = ImproperCTypesVisitor { cx };
 989         let abi = cx.tcx.hir().get_foreign_abi(it.hir_id);
 990         if let Abi::Rust | Abi::RustCall | Abi::RustIntrinsic | Abi::PlatformIntrinsic = abi {
 991             // Don't worry about types in internal ABIs.
 992         } else {
 993             match it.kind {
 994                 hir::ForeignItemKind::Fn(ref decl, _, _) => {
 995                     vis.check_foreign_fn(it.hir_id, decl);
 996                 }
 997                 hir::ForeignItemKind::Static(ref ty, _) => {
 998                     vis.check_foreign_static(it.hir_id, ty.span);
 999                 }
1000                 hir::ForeignItemKind::Type => (),
1001             }
1002         }
1003     }
1004 }
1005
1006 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
1007
1008 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for VariantSizeDifferences {
1009     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item<'_>) {
1010         if let hir::ItemKind::Enum(ref enum_definition, _) = it.kind {
1011             let item_def_id = cx.tcx.hir().local_def_id(it.hir_id);
1012             let t = cx.tcx.type_of(item_def_id);
1013             let ty = cx.tcx.erase_regions(&t);
1014             let layout = match cx.layout_of(ty) {
1015                 Ok(layout) => layout,
1016                 Err(ty::layout::LayoutError::Unknown(_)) => return,
1017                 Err(err @ ty::layout::LayoutError::SizeOverflow(_)) => {
1018                     bug!("failed to get layout for `{}`: {}", t, err);
1019                 }
1020             };
1021             let (variants, tag) = match layout.variants {
1022                 layout::Variants::Multiple {
1023                     discr_kind: layout::DiscriminantKind::Tag,
1024                     ref discr,
1025                     ref variants,
1026                     ..
1027                 } => (variants, discr),
1028                 _ => return,
1029             };
1030
1031             let discr_size = tag.value.size(&cx.tcx).bytes();
1032
1033             debug!(
1034                 "enum `{}` is {} bytes large with layout:\n{:#?}",
1035                 t,
1036                 layout.size.bytes(),
1037                 layout
1038             );
1039
1040             let (largest, slargest, largest_index) = enum_definition
1041                 .variants
1042                 .iter()
1043                 .zip(variants)
1044                 .map(|(variant, variant_layout)| {
1045                     // Subtract the size of the enum discriminant.
1046                     let bytes = variant_layout.size.bytes().saturating_sub(discr_size);
1047
1048                     debug!("- variant `{}` is {} bytes large", variant.ident, bytes);
1049                     bytes
1050                 })
1051                 .enumerate()
1052                 .fold((0, 0, 0), |(l, s, li), (idx, size)| {
1053                     if size > l {
1054                         (size, l, idx)
1055                     } else if size > s {
1056                         (l, size, li)
1057                     } else {
1058                         (l, s, li)
1059                     }
1060                 });
1061
1062             // We only warn if the largest variant is at least thrice as large as
1063             // the second-largest.
1064             if largest > slargest * 3 && slargest > 0 {
1065                 cx.span_lint(
1066                     VARIANT_SIZE_DIFFERENCES,
1067                     enum_definition.variants[largest_index].span,
1068                     &format!(
1069                         "enum variant is more than three times \
1070                                           larger ({} bytes) than the next largest",
1071                         largest
1072                     ),
1073                 );
1074             }
1075         }
1076     }
1077 }