src/librustc_lint/types.rs

   1 #![allow(non_snake_case)]
   2
   3 use crate::hir::def_id::DefId;
   4 use lint::{LateContext, LintArray, LintContext};
   5 use lint::{LateLintPass, LintPass};
   6 use rustc::lint;
   7 use rustc::mir::interpret::{sign_extend, truncate};
   8 use rustc::ty::layout::{self, IntegerExt, LayoutOf, SizeSkeleton, VariantIdx};
   9 use rustc::ty::subst::SubstsRef;
  10 use rustc::ty::{self, AdtKind, ParamEnv, Ty, TyCtxt};
  11 use rustc_data_structures::fx::FxHashSet;
  12 use rustc_hir as hir;
  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::errors::Applicability;
  20 use syntax::{ast, attr};
  21
  22 use log::debug;
  23 use std::cmp;
  24 use std::{f32, f64, i16, i32, i64, i8, u16, u32, u64, u8};
  25
  26 declare_lint! {
  27     UNUSED_COMPARISONS,
  28     Warn,
  29     "comparisons made useless by limits of the types involved"
  30 }
  31
  32 declare_lint! {
  33     OVERFLOWING_LITERALS,
  34     Deny,
  35     "literal out of range for its type"
  36 }
  37
  38 declare_lint! {
  39     VARIANT_SIZE_DIFFERENCES,
  40     Allow,
  41     "detects enums with widely varying variant sizes"
  42 }
  43
  44 #[derive(Copy, Clone)]
  45 pub struct TypeLimits {
  46     /// Id of the last visited negated expression
  47     negated_expr_id: hir::HirId,
  48 }
  49
  50 impl_lint_pass!(TypeLimits => [UNUSED_COMPARISONS, OVERFLOWING_LITERALS]);
  51
  52 impl TypeLimits {
  53     pub fn new() -> TypeLimits {
  54         TypeLimits { negated_expr_id: hir::DUMMY_HIR_ID }
  55     }
  56 }
  57
  58 /// Attempts to special-case the overflowing literal lint when it occurs as a range endpoint.
  59 /// Returns `true` iff the lint was overridden.
  60 fn lint_overflowing_range_endpoint<'a, 'tcx>(
  61     cx: &LateContext<'a, 'tcx>,
  62     lit: &hir::Lit,
  63     lit_val: u128,
  64     max: u128,
  65     expr: &'tcx hir::Expr<'tcx>,
  66     parent_expr: &'tcx hir::Expr<'tcx>,
  67     ty: &str,
  68 ) -> bool {
  69     // We only want to handle exclusive (`..`) ranges,
  70     // which are represented as `ExprKind::Struct`.
  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             let mut err = cx.struct_span_lint(
  80                 OVERFLOWING_LITERALS,
  81                 parent_expr.span,
  82                 &format!("range endpoint is out of range for `{}`", ty),
  83             );
  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                 return true;
 103             }
 104         }
 105     }
 106
 107     false
 108 }
 109
 110 // For `isize` & `usize`, be conservative with the warnings, so that the
 111 // warnings are consistent between 32- and 64-bit platforms.
 112 fn int_ty_range(int_ty: ast::IntTy) -> (i128, i128) {
 113     match int_ty {
 114         ast::IntTy::Isize => (i64::min_value() as i128, i64::max_value() as i128),
 115         ast::IntTy::I8 => (i8::min_value() as i64 as i128, i8::max_value() as i128),
 116         ast::IntTy::I16 => (i16::min_value() as i64 as i128, i16::max_value() as i128),
 117         ast::IntTy::I32 => (i32::min_value() as i64 as i128, i32::max_value() as i128),
 118         ast::IntTy::I64 => (i64::min_value() as i128, i64::max_value() as i128),
 119         ast::IntTy::I128 => (i128::min_value() as i128, i128::max_value()),
 120     }
 121 }
 122
 123 fn uint_ty_range(uint_ty: ast::UintTy) -> (u128, u128) {
 124     match uint_ty {
 125         ast::UintTy::Usize => (u64::min_value() as u128, u64::max_value() as u128),
 126         ast::UintTy::U8 => (u8::min_value() as u128, u8::max_value() as u128),
 127         ast::UintTy::U16 => (u16::min_value() as u128, u16::max_value() as u128),
 128         ast::UintTy::U32 => (u32::min_value() as u128, u32::max_value() as u128),
 129         ast::UintTy::U64 => (u64::min_value() as u128, u64::max_value() as u128),
 130         ast::UintTy::U128 => (u128::min_value(), u128::max_value()),
 131     }
 132 }
 133
 134 fn get_bin_hex_repr(cx: &LateContext<'_, '_>, lit: &hir::Lit) -> Option<String> {
 135     let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?;
 136     let firstch = src.chars().next()?;
 137
 138     if firstch == '0' {
 139         match src.chars().nth(1) {
 140             Some('x') | Some('b') => return Some(src),
 141             _ => return None,
 142         }
 143     }
 144
 145     None
 146 }
 147
 148 fn report_bin_hex_error(
 149     cx: &LateContext<'_, '_>,
 150     expr: &hir::Expr<'_>,
 151     ty: attr::IntType,
 152     repr_str: String,
 153     val: u128,
 154     negative: bool,
 155 ) {
 156     let size = layout::Integer::from_attr(&cx.tcx, ty).size();
 157     let (t, actually) = match ty {
 158         attr::IntType::SignedInt(t) => {
 159             let actually = sign_extend(val, size) as i128;
 160             (t.name_str(), actually.to_string())
 161         }
 162         attr::IntType::UnsignedInt(t) => {
 163             let actually = truncate(val, size);
 164             (t.name_str(), actually.to_string())
 165         }
 166     };
 167     let mut err = cx.struct_span_lint(
 168         OVERFLOWING_LITERALS,
 169         expr.span,
 170         &format!("literal out of range for {}", t),
 171     );
 172     err.note(&format!(
 173         "the literal `{}` (decimal `{}`) does not fit into \
 174             an `{}` and will become `{}{}`",
 175         repr_str, val, t, actually, t
 176     ));
 177     if let Some(sugg_ty) = get_type_suggestion(&cx.tables.node_type(expr.hir_id), val, negative) {
 178         if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') {
 179             let (sans_suffix, _) = repr_str.split_at(pos);
 180             err.span_suggestion(
 181                 expr.span,
 182                 &format!("consider using `{}` instead", sugg_ty),
 183                 format!("{}{}", sans_suffix, sugg_ty),
 184                 Applicability::MachineApplicable,
 185             );
 186         } else {
 187             err.help(&format!("consider using `{}` instead", sugg_ty));
 188         }
 189     }
 190
 191     err.emit();
 192 }
 193
 194 // This function finds the next fitting type and generates a suggestion string.
 195 // It searches for fitting types in the following way (`X < Y`):
 196 //  - `iX`: if literal fits in `uX` => `uX`, else => `iY`
 197 //  - `-iX` => `iY`
 198 //  - `uX` => `uY`
 199 //
 200 // No suggestion for: `isize`, `usize`.
 201 fn get_type_suggestion(t: Ty<'_>, val: u128, negative: bool) -> Option<&'static str> {
 202     use syntax::ast::IntTy::*;
 203     use syntax::ast::UintTy::*;
 204     macro_rules! find_fit {
 205         ($ty:expr, $val:expr, $negative:expr,
 206          $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => {
 207             {
 208                 let _neg = if negative { 1 } else { 0 };
 209                 match $ty {
 210                     $($type => {
 211                         $(if !negative && val <= uint_ty_range($utypes).1 {
 212                             return Some($utypes.name_str())
 213                         })*
 214                         $(if val <= int_ty_range($itypes).1 as u128 + _neg {
 215                             return Some($itypes.name_str())
 216                         })*
 217                         None
 218                     },)+
 219                     _ => None
 220                 }
 221             }
 222         }
 223     }
 224     match t.kind {
 225         ty::Int(i) => find_fit!(i, val, negative,
 226                       I8 => [U8] => [I16, I32, I64, I128],
 227                       I16 => [U16] => [I32, I64, I128],
 228                       I32 => [U32] => [I64, I128],
 229                       I64 => [U64] => [I128],
 230                       I128 => [U128] => []),
 231         ty::Uint(u) => find_fit!(u, val, negative,
 232                       U8 => [U8, U16, U32, U64, U128] => [],
 233                       U16 => [U16, U32, U64, U128] => [],
 234                       U32 => [U32, U64, U128] => [],
 235                       U64 => [U64, U128] => [],
 236                       U128 => [U128] => []),
 237         _ => None,
 238     }
 239 }
 240
 241 fn lint_int_literal<'a, 'tcx>(
 242     cx: &LateContext<'a, 'tcx>,
 243     type_limits: &TypeLimits,
 244     e: &'tcx hir::Expr<'tcx>,
 245     lit: &hir::Lit,
 246     t: ast::IntTy,
 247     v: u128,
 248 ) {
 249     let int_type = t.normalize(cx.sess().target.ptr_width);
 250     let (_, max) = int_ty_range(int_type);
 251     let max = max as u128;
 252     let negative = type_limits.negated_expr_id == e.hir_id;
 253
 254     // Detect literal value out of range [min, max] inclusive
 255     // avoiding use of -min to prevent overflow/panic
 256     if (negative && v > max + 1) || (!negative && v > max) {
 257         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 258             report_bin_hex_error(cx, e, attr::IntType::SignedInt(t), repr_str, v, negative);
 259             return;
 260         }
 261
 262         let par_id = cx.tcx.hir().get_parent_node(e.hir_id);
 263         if let Node::Expr(par_e) = cx.tcx.hir().get(par_id) {
 264             if let hir::ExprKind::Struct(..) = par_e.kind {
 265                 if is_range_literal(cx.sess().source_map(), par_e)
 266                     && lint_overflowing_range_endpoint(cx, lit, v, max, e, par_e, t.name_str())
 267                 {
 268                     // The overflowing literal lint was overridden.
 269                     return;
 270                 }
 271             }
 272         }
 273
 274         cx.span_lint(
 275             OVERFLOWING_LITERALS,
 276             e.span,
 277             &format!("literal out of range for `{}`", t.name_str()),
 278         );
 279     }
 280 }
 281
 282 fn lint_uint_literal<'a, 'tcx>(
 283     cx: &LateContext<'a, 'tcx>,
 284     e: &'tcx hir::Expr<'tcx>,
 285     lit: &hir::Lit,
 286     t: ast::UintTy,
 287 ) {
 288     let uint_type = t.normalize(cx.sess().target.ptr_width);
 289     let (min, max) = uint_ty_range(uint_type);
 290     let lit_val: u128 = match lit.node {
 291         // _v is u8, within range by definition
 292         ast::LitKind::Byte(_v) => return,
 293         ast::LitKind::Int(v, _) => v,
 294         _ => bug!(),
 295     };
 296     if lit_val < min || lit_val > max {
 297         let parent_id = cx.tcx.hir().get_parent_node(e.hir_id);
 298         if let Node::Expr(par_e) = cx.tcx.hir().get(parent_id) {
 299             match par_e.kind {
 300                 hir::ExprKind::Cast(..) => {
 301                     if let ty::Char = cx.tables.expr_ty(par_e).kind {
 302                         let mut err = cx.struct_span_lint(
 303                             OVERFLOWING_LITERALS,
 304                             par_e.span,
 305                             "only `u8` can be cast into `char`",
 306                         );
 307                         err.span_suggestion(
 308                             par_e.span,
 309                             &"use a `char` literal instead",
 310                             format!("'\\u{{{:X}}}'", lit_val),
 311                             Applicability::MachineApplicable,
 312                         );
 313                         err.emit();
 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         let mut diag = self.cx.struct_span_lint(
 888             IMPROPER_CTYPES,
 889             sp,
 890             &format!("`extern` block uses type `{}`, which is not FFI-safe", ty),
 891         );
 892         diag.span_label(sp, "not FFI-safe");
 893         if let Some(help) = help {
 894             diag.help(help);
 895         }
 896         diag.note(note);
 897         if let ty::Adt(def, _) = ty.kind {
 898             if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did) {
 899                 diag.span_note(sp, "type defined here");
 900             }
 901         }
 902         diag.emit();
 903     }
 904
 905     fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
 906         use crate::rustc::ty::TypeFoldable;
 907
 908         struct ProhibitOpaqueTypes<'tcx> {
 909             ty: Option<Ty<'tcx>>,
 910         };
 911
 912         impl<'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'tcx> {
 913             fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
 914                 if let ty::Opaque(..) = ty.kind {
 915                     self.ty = Some(ty);
 916                     true
 917                 } else {
 918                     ty.super_visit_with(self)
 919                 }
 920             }
 921         }
 922
 923         let mut visitor = ProhibitOpaqueTypes { ty: None };
 924         ty.visit_with(&mut visitor);
 925         if let Some(ty) = visitor.ty {
 926             self.emit_ffi_unsafe_type_lint(ty, sp, "opaque types have no C equivalent", None);
 927             true
 928         } else {
 929             false
 930         }
 931     }
 932
 933     fn check_type_for_ffi_and_report_errors(&mut self, sp: Span, ty: Ty<'tcx>, is_static: bool) {
 934         // We have to check for opaque types before `normalize_erasing_regions`,
 935         // which will replace opaque types with their underlying concrete type.
 936         if self.check_for_opaque_ty(sp, ty) {
 937             // We've already emitted an error due to an opaque type.
 938             return;
 939         }
 940
 941         // it is only OK to use this function because extern fns cannot have
 942         // any generic types right now:
 943         let ty = self.cx.tcx.normalize_erasing_regions(ParamEnv::reveal_all(), ty);
 944         // C doesn't really support passing arrays by value.
 945         // The only way to pass an array by value is through a struct.
 946         // So we first test that the top level isn't an array,
 947         // and then recursively check the types inside.
 948         if !is_static && self.check_for_array_ty(sp, ty) {
 949             return;
 950         }
 951
 952         match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
 953             FfiResult::FfiSafe => {}
 954             FfiResult::FfiPhantom(ty) => {
 955                 self.emit_ffi_unsafe_type_lint(ty, sp, "composed only of `PhantomData`", None);
 956             }
 957             FfiResult::FfiUnsafe { ty, reason, help } => {
 958                 self.emit_ffi_unsafe_type_lint(ty, sp, reason, help);
 959             }
 960         }
 961     }
 962
 963     fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl<'_>) {
 964         let def_id = self.cx.tcx.hir().local_def_id(id);
 965         let sig = self.cx.tcx.fn_sig(def_id);
 966         let sig = self.cx.tcx.erase_late_bound_regions(&sig);
 967
 968         for (input_ty, input_hir) in sig.inputs().iter().zip(decl.inputs) {
 969             self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty, false);
 970         }
 971
 972         if let hir::FunctionRetTy::Return(ref ret_hir) = decl.output {
 973             let ret_ty = sig.output();
 974             if !ret_ty.is_unit() {
 975                 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty, false);
 976             }
 977         }
 978     }
 979
 980     fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
 981         let def_id = self.cx.tcx.hir().local_def_id(id);
 982         let ty = self.cx.tcx.type_of(def_id);
 983         self.check_type_for_ffi_and_report_errors(span, ty, true);
 984     }
 985 }
 986
 987 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImproperCTypes {
 988     fn check_foreign_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::ForeignItem<'_>) {
 989         let mut vis = ImproperCTypesVisitor { cx };
 990         let abi = cx.tcx.hir().get_foreign_abi(it.hir_id);
 991         if let Abi::Rust | Abi::RustCall | Abi::RustIntrinsic | Abi::PlatformIntrinsic = abi {
 992             // Don't worry about types in internal ABIs.
 993         } else {
 994             match it.kind {
 995                 hir::ForeignItemKind::Fn(ref decl, _, _) => {
 996                     vis.check_foreign_fn(it.hir_id, decl);
 997                 }
 998                 hir::ForeignItemKind::Static(ref ty, _) => {
 999                     vis.check_foreign_static(it.hir_id, ty.span);
1000                 }
1001                 hir::ForeignItemKind::Type => (),
1002             }
1003         }
1004     }
1005 }
1006
1007 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
1008
1009 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for VariantSizeDifferences {
1010     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item<'_>) {
1011         if let hir::ItemKind::Enum(ref enum_definition, _) = it.kind {
1012             let item_def_id = cx.tcx.hir().local_def_id(it.hir_id);
1013             let t = cx.tcx.type_of(item_def_id);
1014             let ty = cx.tcx.erase_regions(&t);
1015             let layout = match cx.layout_of(ty) {
1016                 Ok(layout) => layout,
1017                 Err(ty::layout::LayoutError::Unknown(_)) => return,
1018                 Err(err @ ty::layout::LayoutError::SizeOverflow(_)) => {
1019                     bug!("failed to get layout for `{}`: {}", t, err);
1020                 }
1021             };
1022             let (variants, tag) = match layout.variants {
1023                 layout::Variants::Multiple {
1024                     discr_kind: layout::DiscriminantKind::Tag,
1025                     ref discr,
1026                     ref variants,
1027                     ..
1028                 } => (variants, discr),
1029                 _ => return,
1030             };
1031
1032             let discr_size = tag.value.size(&cx.tcx).bytes();
1033
1034             debug!(
1035                 "enum `{}` is {} bytes large with layout:\n{:#?}",
1036                 t,
1037                 layout.size.bytes(),
1038                 layout
1039             );
1040
1041             let (largest, slargest, largest_index) = enum_definition
1042                 .variants
1043                 .iter()
1044                 .zip(variants)
1045                 .map(|(variant, variant_layout)| {
1046                     // Subtract the size of the enum discriminant.
1047                     let bytes = variant_layout.size.bytes().saturating_sub(discr_size);
1048
1049                     debug!("- variant `{}` is {} bytes large", variant.ident, bytes);
1050                     bytes
1051                 })
1052                 .enumerate()
1053                 .fold((0, 0, 0), |(l, s, li), (idx, size)| {
1054                     if size > l {
1055                         (size, l, idx)
1056                     } else if size > s {
1057                         (l, size, li)
1058                     } else {
1059                         (l, s, li)
1060                     }
1061                 });
1062
1063             // We only warn if the largest variant is at least thrice as large as
1064             // the second-largest.
1065             if largest > slargest * 3 && slargest > 0 {
1066                 cx.span_lint(
1067                     VARIANT_SIZE_DIFFERENCES,
1068                     enum_definition.variants[largest_index].span,
1069                     &format!(
1070                         "enum variant is more than three times \
1071                                           larger ({} bytes) than the next largest",
1072                         largest
1073                     ),
1074                 );
1075             }
1076         }
1077     }
1078 }