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::hir::{is_range_literal, ExprKind, Node};
   7 use rustc::ty::layout::{self, IntegerExt, LayoutOf, SizeSkeleton, VariantIdx};
   8 use rustc::ty::subst::SubstsRef;
   9 use rustc::ty::{self, AdtKind, ParamEnv, Ty, TyCtxt};
  10 use rustc::{lint, util};
  11 use rustc_index::vec::Idx;
  12 use util::nodemap::FxHashSet;
  13
  14 use std::cmp;
  15 use std::{f32, f64, i16, i32, i64, i8, u16, u32, u64, u8};
  16
  17 use rustc_target::spec::abi::Abi;
  18 use syntax::errors::Applicability;
  19 use syntax::symbol::sym;
  20 use syntax::{ast, attr, source_map};
  21 use syntax_pos::Span;
  22
  23 use rustc::hir;
  24
  25 use rustc::mir::interpret::{sign_extend, truncate};
  26
  27 use log::debug;
  28
  29 declare_lint! {
  30     UNUSED_COMPARISONS,
  31     Warn,
  32     "comparisons made useless by limits of the types involved"
  33 }
  34
  35 declare_lint! {
  36     OVERFLOWING_LITERALS,
  37     Deny,
  38     "literal out of range for its type"
  39 }
  40
  41 declare_lint! {
  42     VARIANT_SIZE_DIFFERENCES,
  43     Allow,
  44     "detects enums with widely varying variant sizes"
  45 }
  46
  47 #[derive(Copy, Clone)]
  48 pub struct TypeLimits {
  49     /// Id of the last visited negated expression
  50     negated_expr_id: hir::HirId,
  51 }
  52
  53 impl_lint_pass!(TypeLimits => [UNUSED_COMPARISONS, OVERFLOWING_LITERALS]);
  54
  55 impl TypeLimits {
  56     pub fn new() -> TypeLimits {
  57         TypeLimits { negated_expr_id: hir::DUMMY_HIR_ID }
  58     }
  59 }
  60
  61 /// Attempts to special-case the overflowing literal lint when it occurs as a range endpoint.
  62 /// Returns `true` iff the lint was overridden.
  63 fn lint_overflowing_range_endpoint<'a, 'tcx>(
  64     cx: &LateContext<'a, 'tcx>,
  65     lit: &hir::Lit,
  66     lit_val: u128,
  67     max: u128,
  68     expr: &'tcx hir::Expr<'tcx>,
  69     parent_expr: &'tcx hir::Expr<'tcx>,
  70     ty: &str,
  71 ) -> bool {
  72     // We only want to handle exclusive (`..`) ranges,
  73     // which are represented as `ExprKind::Struct`.
  74     if let ExprKind::Struct(_, eps, _) = &parent_expr.kind {
  75         if eps.len() != 2 {
  76             return false;
  77         }
  78         // We can suggest using an inclusive range
  79         // (`..=`) instead only if it is the `end` that is
  80         // overflowing and only by 1.
  81         if eps[1].expr.hir_id == expr.hir_id && lit_val - 1 == max {
  82             let mut err = cx.struct_span_lint(
  83                 OVERFLOWING_LITERALS,
  84                 parent_expr.span,
  85                 &format!("range endpoint is out of range for `{}`", ty),
  86             );
  87             if let Ok(start) = cx.sess().source_map().span_to_snippet(eps[0].span) {
  88                 use ast::{LitIntType, LitKind};
  89                 // We need to preserve the literal's suffix,
  90                 // as it may determine typing information.
  91                 let suffix = match lit.node {
  92                     LitKind::Int(_, LitIntType::Signed(s)) => format!("{}", s.name_str()),
  93                     LitKind::Int(_, LitIntType::Unsigned(s)) => format!("{}", s.name_str()),
  94                     LitKind::Int(_, LitIntType::Unsuffixed) => "".to_owned(),
  95                     _ => bug!(),
  96                 };
  97                 let suggestion = format!("{}..={}{}", start, lit_val - 1, suffix);
  98                 err.span_suggestion(
  99                     parent_expr.span,
 100                     &"use an inclusive range instead",
 101                     suggestion,
 102                     Applicability::MachineApplicable,
 103                 );
 104                 err.emit();
 105                 return true;
 106             }
 107         }
 108     }
 109
 110     false
 111 }
 112
 113 // For `isize` & `usize`, be conservative with the warnings, so that the
 114 // warnings are consistent between 32- and 64-bit platforms.
 115 fn int_ty_range(int_ty: ast::IntTy) -> (i128, i128) {
 116     match int_ty {
 117         ast::IntTy::Isize => (i64::min_value() as i128, i64::max_value() as i128),
 118         ast::IntTy::I8 => (i8::min_value() as i64 as i128, i8::max_value() as i128),
 119         ast::IntTy::I16 => (i16::min_value() as i64 as i128, i16::max_value() as i128),
 120         ast::IntTy::I32 => (i32::min_value() as i64 as i128, i32::max_value() as i128),
 121         ast::IntTy::I64 => (i64::min_value() as i128, i64::max_value() as i128),
 122         ast::IntTy::I128 => (i128::min_value() as i128, i128::max_value()),
 123     }
 124 }
 125
 126 fn uint_ty_range(uint_ty: ast::UintTy) -> (u128, u128) {
 127     match uint_ty {
 128         ast::UintTy::Usize => (u64::min_value() as u128, u64::max_value() as u128),
 129         ast::UintTy::U8 => (u8::min_value() as u128, u8::max_value() as u128),
 130         ast::UintTy::U16 => (u16::min_value() as u128, u16::max_value() as u128),
 131         ast::UintTy::U32 => (u32::min_value() as u128, u32::max_value() as u128),
 132         ast::UintTy::U64 => (u64::min_value() as u128, u64::max_value() as u128),
 133         ast::UintTy::U128 => (u128::min_value(), u128::max_value()),
 134     }
 135 }
 136
 137 fn get_bin_hex_repr(cx: &LateContext<'_, '_>, lit: &hir::Lit) -> Option<String> {
 138     let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?;
 139     let firstch = src.chars().next()?;
 140
 141     if firstch == '0' {
 142         match src.chars().nth(1) {
 143             Some('x') | Some('b') => return Some(src),
 144             _ => return None,
 145         }
 146     }
 147
 148     None
 149 }
 150
 151 fn report_bin_hex_error(
 152     cx: &LateContext<'_, '_>,
 153     expr: &hir::Expr<'_>,
 154     ty: attr::IntType,
 155     repr_str: String,
 156     val: u128,
 157     negative: bool,
 158 ) {
 159     let size = layout::Integer::from_attr(&cx.tcx, ty).size();
 160     let (t, actually) = match ty {
 161         attr::IntType::SignedInt(t) => {
 162             let actually = sign_extend(val, size) as i128;
 163             (t.name_str(), actually.to_string())
 164         }
 165         attr::IntType::UnsignedInt(t) => {
 166             let actually = truncate(val, size);
 167             (t.name_str(), actually.to_string())
 168         }
 169     };
 170     let mut err = cx.struct_span_lint(
 171         OVERFLOWING_LITERALS,
 172         expr.span,
 173         &format!("literal out of range for {}", t),
 174     );
 175     err.note(&format!(
 176         "the literal `{}` (decimal `{}`) does not fit into \
 177             an `{}` and will become `{}{}`",
 178         repr_str, val, t, actually, t
 179     ));
 180     if let Some(sugg_ty) = get_type_suggestion(&cx.tables.node_type(expr.hir_id), val, negative) {
 181         if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') {
 182             let (sans_suffix, _) = repr_str.split_at(pos);
 183             err.span_suggestion(
 184                 expr.span,
 185                 &format!("consider using `{}` instead", sugg_ty),
 186                 format!("{}{}", sans_suffix, sugg_ty),
 187                 Applicability::MachineApplicable,
 188             );
 189         } else {
 190             err.help(&format!("consider using `{}` instead", sugg_ty));
 191         }
 192     }
 193
 194     err.emit();
 195 }
 196
 197 // This function finds the next fitting type and generates a suggestion string.
 198 // It searches for fitting types in the following way (`X < Y`):
 199 //  - `iX`: if literal fits in `uX` => `uX`, else => `iY`
 200 //  - `-iX` => `iY`
 201 //  - `uX` => `uY`
 202 //
 203 // No suggestion for: `isize`, `usize`.
 204 fn get_type_suggestion(t: Ty<'_>, val: u128, negative: bool) -> Option<&'static str> {
 205     use syntax::ast::IntTy::*;
 206     use syntax::ast::UintTy::*;
 207     macro_rules! find_fit {
 208         ($ty:expr, $val:expr, $negative:expr,
 209          $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => {
 210             {
 211                 let _neg = if negative { 1 } else { 0 };
 212                 match $ty {
 213                     $($type => {
 214                         $(if !negative && val <= uint_ty_range($utypes).1 {
 215                             return Some($utypes.name_str())
 216                         })*
 217                         $(if val <= int_ty_range($itypes).1 as u128 + _neg {
 218                             return Some($itypes.name_str())
 219                         })*
 220                         None
 221                     },)+
 222                     _ => None
 223                 }
 224             }
 225         }
 226     }
 227     match t.kind {
 228         ty::Int(i) => find_fit!(i, val, negative,
 229                       I8 => [U8] => [I16, I32, I64, I128],
 230                       I16 => [U16] => [I32, I64, I128],
 231                       I32 => [U32] => [I64, I128],
 232                       I64 => [U64] => [I128],
 233                       I128 => [U128] => []),
 234         ty::Uint(u) => find_fit!(u, val, negative,
 235                       U8 => [U8, U16, U32, U64, U128] => [],
 236                       U16 => [U16, U32, U64, U128] => [],
 237                       U32 => [U32, U64, U128] => [],
 238                       U64 => [U64, U128] => [],
 239                       U128 => [U128] => []),
 240         _ => None,
 241     }
 242 }
 243
 244 fn lint_int_literal<'a, 'tcx>(
 245     cx: &LateContext<'a, 'tcx>,
 246     type_limits: &TypeLimits,
 247     e: &'tcx hir::Expr<'tcx>,
 248     lit: &hir::Lit,
 249     t: ast::IntTy,
 250     v: u128,
 251 ) {
 252     let int_type = t.normalize(cx.sess().target.ptr_width);
 253     let (_, max) = int_ty_range(int_type);
 254     let max = max as u128;
 255     let negative = type_limits.negated_expr_id == e.hir_id;
 256
 257     // Detect literal value out of range [min, max] inclusive
 258     // avoiding use of -min to prevent overflow/panic
 259     if (negative && v > max + 1) || (!negative && v > max) {
 260         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 261             report_bin_hex_error(cx, e, attr::IntType::SignedInt(t), repr_str, v, negative);
 262             return;
 263         }
 264
 265         let par_id = cx.tcx.hir().get_parent_node(e.hir_id);
 266         if let Node::Expr(par_e) = cx.tcx.hir().get(par_id) {
 267             if let hir::ExprKind::Struct(..) = par_e.kind {
 268                 if is_range_literal(cx.sess().source_map(), par_e)
 269                     && lint_overflowing_range_endpoint(cx, lit, v, max, e, par_e, t.name_str())
 270                 {
 271                     // The overflowing literal lint was overridden.
 272                     return;
 273                 }
 274             }
 275         }
 276
 277         cx.span_lint(
 278             OVERFLOWING_LITERALS,
 279             e.span,
 280             &format!("literal out of range for `{}`", t.name_str()),
 281         );
 282     }
 283 }
 284
 285 fn lint_uint_literal<'a, 'tcx>(
 286     cx: &LateContext<'a, 'tcx>,
 287     e: &'tcx hir::Expr<'tcx>,
 288     lit: &hir::Lit,
 289     t: ast::UintTy,
 290 ) {
 291     let uint_type = t.normalize(cx.sess().target.ptr_width);
 292     let (min, max) = uint_ty_range(uint_type);
 293     let lit_val: u128 = match lit.node {
 294         // _v is u8, within range by definition
 295         ast::LitKind::Byte(_v) => return,
 296         ast::LitKind::Int(v, _) => v,
 297         _ => bug!(),
 298     };
 299     if lit_val < min || lit_val > max {
 300         let parent_id = cx.tcx.hir().get_parent_node(e.hir_id);
 301         if let Node::Expr(par_e) = cx.tcx.hir().get(parent_id) {
 302             match par_e.kind {
 303                 hir::ExprKind::Cast(..) => {
 304                     if let ty::Char = cx.tables.expr_ty(par_e).kind {
 305                         let mut err = cx.struct_span_lint(
 306                             OVERFLOWING_LITERALS,
 307                             par_e.span,
 308                             "only `u8` can be cast into `char`",
 309                         );
 310                         err.span_suggestion(
 311                             par_e.span,
 312                             &"use a `char` literal instead",
 313                             format!("'\\u{{{:X}}}'", lit_val),
 314                             Applicability::MachineApplicable,
 315                         );
 316                         err.emit();
 317                         return;
 318                     }
 319                 }
 320                 hir::ExprKind::Struct(..) if is_range_literal(cx.sess().source_map(), par_e) => {
 321                     let t = t.name_str();
 322                     if lint_overflowing_range_endpoint(cx, lit, lit_val, max, e, par_e, t) {
 323                         // The overflowing literal lint was overridden.
 324                         return;
 325                     }
 326                 }
 327                 _ => {}
 328             }
 329         }
 330         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 331             report_bin_hex_error(cx, e, attr::IntType::UnsignedInt(t), repr_str, lit_val, false);
 332             return;
 333         }
 334         cx.span_lint(
 335             OVERFLOWING_LITERALS,
 336             e.span,
 337             &format!("literal out of range for `{}`", t.name_str()),
 338         );
 339     }
 340 }
 341
 342 fn lint_literal<'a, 'tcx>(
 343     cx: &LateContext<'a, 'tcx>,
 344     type_limits: &TypeLimits,
 345     e: &'tcx hir::Expr<'tcx>,
 346     lit: &hir::Lit,
 347 ) {
 348     match cx.tables.node_type(e.hir_id).kind {
 349         ty::Int(t) => {
 350             match lit.node {
 351                 ast::LitKind::Int(v, ast::LitIntType::Signed(_))
 352                 | ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => {
 353                     lint_int_literal(cx, type_limits, e, lit, t, v)
 354                 }
 355                 _ => bug!(),
 356             };
 357         }
 358         ty::Uint(t) => lint_uint_literal(cx, e, lit, t),
 359         ty::Float(t) => {
 360             let is_infinite = match lit.node {
 361                 ast::LitKind::Float(v, _) => match t {
 362                     ast::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
 363                     ast::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
 364                 },
 365                 _ => bug!(),
 366             };
 367             if is_infinite == Ok(true) {
 368                 cx.span_lint(
 369                     OVERFLOWING_LITERALS,
 370                     e.span,
 371                     &format!("literal out of range for `{}`", t.name_str()),
 372                 );
 373             }
 374         }
 375         _ => {}
 376     }
 377 }
 378
 379 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TypeLimits {
 380     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx hir::Expr<'tcx>) {
 381         match e.kind {
 382             hir::ExprKind::Unary(hir::UnNeg, ref expr) => {
 383                 // propagate negation, if the negation itself isn't negated
 384                 if self.negated_expr_id != e.hir_id {
 385                     self.negated_expr_id = expr.hir_id;
 386                 }
 387             }
 388             hir::ExprKind::Binary(binop, ref l, ref r) => {
 389                 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
 390                     cx.span_lint(
 391                         UNUSED_COMPARISONS,
 392                         e.span,
 393                         "comparison is useless due to type limits",
 394                     );
 395                 }
 396             }
 397             hir::ExprKind::Lit(ref lit) => lint_literal(cx, self, e, lit),
 398             _ => {}
 399         };
 400
 401         fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
 402             match binop.node {
 403                 hir::BinOpKind::Lt => v > min && v <= max,
 404                 hir::BinOpKind::Le => v >= min && v < max,
 405                 hir::BinOpKind::Gt => v >= min && v < max,
 406                 hir::BinOpKind::Ge => v > min && v <= max,
 407                 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
 408                 _ => bug!(),
 409             }
 410         }
 411
 412         fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
 413             source_map::respan(
 414                 binop.span,
 415                 match binop.node {
 416                     hir::BinOpKind::Lt => hir::BinOpKind::Gt,
 417                     hir::BinOpKind::Le => hir::BinOpKind::Ge,
 418                     hir::BinOpKind::Gt => hir::BinOpKind::Lt,
 419                     hir::BinOpKind::Ge => hir::BinOpKind::Le,
 420                     _ => return binop,
 421                 },
 422             )
 423         }
 424
 425         fn check_limits(
 426             cx: &LateContext<'_, '_>,
 427             binop: hir::BinOp,
 428             l: &hir::Expr<'_>,
 429             r: &hir::Expr<'_>,
 430         ) -> bool {
 431             let (lit, expr, swap) = match (&l.kind, &r.kind) {
 432                 (&hir::ExprKind::Lit(_), _) => (l, r, true),
 433                 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
 434                 _ => return true,
 435             };
 436             // Normalize the binop so that the literal is always on the RHS in
 437             // the comparison
 438             let norm_binop = if swap { rev_binop(binop) } else { binop };
 439             match cx.tables.node_type(expr.hir_id).kind {
 440                 ty::Int(int_ty) => {
 441                     let (min, max) = int_ty_range(int_ty);
 442                     let lit_val: i128 = match lit.kind {
 443                         hir::ExprKind::Lit(ref li) => match li.node {
 444                             ast::LitKind::Int(v, ast::LitIntType::Signed(_))
 445                             | ast::LitKind::Int(v, ast::LitIntType::Unsuffixed) => v as i128,
 446                             _ => return true,
 447                         },
 448                         _ => bug!(),
 449                     };
 450                     is_valid(norm_binop, lit_val, min, max)
 451                 }
 452                 ty::Uint(uint_ty) => {
 453                     let (min, max): (u128, u128) = uint_ty_range(uint_ty);
 454                     let lit_val: u128 = match lit.kind {
 455                         hir::ExprKind::Lit(ref li) => match li.node {
 456                             ast::LitKind::Int(v, _) => v,
 457                             _ => return true,
 458                         },
 459                         _ => bug!(),
 460                     };
 461                     is_valid(norm_binop, lit_val, min, max)
 462                 }
 463                 _ => true,
 464             }
 465         }
 466
 467         fn is_comparison(binop: hir::BinOp) -> bool {
 468             match binop.node {
 469                 hir::BinOpKind::Eq
 470                 | hir::BinOpKind::Lt
 471                 | hir::BinOpKind::Le
 472                 | hir::BinOpKind::Ne
 473                 | hir::BinOpKind::Ge
 474                 | hir::BinOpKind::Gt => true,
 475                 _ => false,
 476             }
 477         }
 478     }
 479 }
 480
 481 declare_lint! {
 482     IMPROPER_CTYPES,
 483     Warn,
 484     "proper use of libc types in foreign modules"
 485 }
 486
 487 declare_lint_pass!(ImproperCTypes => [IMPROPER_CTYPES]);
 488
 489 struct ImproperCTypesVisitor<'a, 'tcx> {
 490     cx: &'a LateContext<'a, 'tcx>,
 491 }
 492
 493 enum FfiResult<'tcx> {
 494     FfiSafe,
 495     FfiPhantom(Ty<'tcx>),
 496     FfiUnsafe { ty: Ty<'tcx>, reason: &'static str, help: Option<&'static str> },
 497 }
 498
 499 fn is_zst<'tcx>(tcx: TyCtxt<'tcx>, did: DefId, ty: Ty<'tcx>) -> bool {
 500     tcx.layout_of(tcx.param_env(did).and(ty)).map(|layout| layout.is_zst()).unwrap_or(false)
 501 }
 502
 503 fn ty_is_known_nonnull<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool {
 504     match ty.kind {
 505         ty::FnPtr(_) => true,
 506         ty::Ref(..) => true,
 507         ty::Adt(field_def, substs) if field_def.repr.transparent() && !field_def.is_union() => {
 508             for field in field_def.all_fields() {
 509                 let field_ty =
 510                     tcx.normalize_erasing_regions(ParamEnv::reveal_all(), field.ty(tcx, substs));
 511                 if is_zst(tcx, field.did, field_ty) {
 512                     continue;
 513                 }
 514
 515                 let attrs = tcx.get_attrs(field_def.did);
 516                 if attrs.iter().any(|a| a.check_name(sym::rustc_nonnull_optimization_guaranteed))
 517                     || ty_is_known_nonnull(tcx, field_ty)
 518                 {
 519                     return true;
 520                 }
 521             }
 522
 523             false
 524         }
 525         _ => false,
 526     }
 527 }
 528
 529 /// Check if this enum can be safely exported based on the
 530 /// "nullable pointer optimization". Currently restricted
 531 /// to function pointers, references, core::num::NonZero*,
 532 /// core::ptr::NonNull, and #[repr(transparent)] newtypes.
 533 /// FIXME: This duplicates code in codegen.
 534 fn is_repr_nullable_ptr<'tcx>(
 535     tcx: TyCtxt<'tcx>,
 536     ty: Ty<'tcx>,
 537     ty_def: &'tcx ty::AdtDef,
 538     substs: SubstsRef<'tcx>,
 539 ) -> bool {
 540     if ty_def.variants.len() != 2 {
 541         return false;
 542     }
 543
 544     let get_variant_fields = |index| &ty_def.variants[VariantIdx::new(index)].fields;
 545     let variant_fields = [get_variant_fields(0), get_variant_fields(1)];
 546     let fields = if variant_fields[0].is_empty() {
 547         &variant_fields[1]
 548     } else if variant_fields[1].is_empty() {
 549         &variant_fields[0]
 550     } else {
 551         return false;
 552     };
 553
 554     if fields.len() != 1 {
 555         return false;
 556     }
 557
 558     let field_ty = fields[0].ty(tcx, substs);
 559     if !ty_is_known_nonnull(tcx, field_ty) {
 560         return false;
 561     }
 562
 563     // At this point, the field's type is known to be nonnull and the parent enum is Option-like.
 564     // If the computed size for the field and the enum are different, the nonnull optimization isn't
 565     // being applied (and we've got a problem somewhere).
 566     let compute_size_skeleton = |t| SizeSkeleton::compute(t, tcx, ParamEnv::reveal_all()).unwrap();
 567     if !compute_size_skeleton(ty).same_size(compute_size_skeleton(field_ty)) {
 568         bug!("improper_ctypes: Option nonnull optimization not applied?");
 569     }
 570
 571     true
 572 }
 573
 574 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
 575     /// Check if the type is array and emit an unsafe type lint.
 576     fn check_for_array_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
 577         if let ty::Array(..) = ty.kind {
 578             self.emit_ffi_unsafe_type_lint(
 579                 ty,
 580                 sp,
 581                 "passing raw arrays by value is not FFI-safe",
 582                 Some("consider passing a pointer to the array"),
 583             );
 584             true
 585         } else {
 586             false
 587         }
 588     }
 589
 590     /// Checks if the given type is "ffi-safe" (has a stable, well-defined
 591     /// representation which can be exported to C code).
 592     fn check_type_for_ffi(&self, cache: &mut FxHashSet<Ty<'tcx>>, ty: Ty<'tcx>) -> FfiResult<'tcx> {
 593         use FfiResult::*;
 594
 595         let cx = self.cx.tcx;
 596
 597         // Protect against infinite recursion, for example
 598         // `struct S(*mut S);`.
 599         // FIXME: A recursion limit is necessary as well, for irregular
 600         // recursive types.
 601         if !cache.insert(ty) {
 602             return FfiSafe;
 603         }
 604
 605         match ty.kind {
 606             ty::Adt(def, substs) => {
 607                 if def.is_phantom_data() {
 608                     return FfiPhantom(ty);
 609                 }
 610                 match def.adt_kind() {
 611                     AdtKind::Struct => {
 612                         if !def.repr.c() && !def.repr.transparent() {
 613                             return FfiUnsafe {
 614                                 ty,
 615                                 reason: "this struct has unspecified layout",
 616                                 help: Some(
 617                                     "consider adding a `#[repr(C)]` or \
 618                                             `#[repr(transparent)]` attribute to this struct",
 619                                 ),
 620                             };
 621                         }
 622
 623                         let is_non_exhaustive =
 624                             def.non_enum_variant().is_field_list_non_exhaustive();
 625                         if is_non_exhaustive && !def.did.is_local() {
 626                             return FfiUnsafe {
 627                                 ty,
 628                                 reason: "this struct is non-exhaustive",
 629                                 help: None,
 630                             };
 631                         }
 632
 633                         if def.non_enum_variant().fields.is_empty() {
 634                             return FfiUnsafe {
 635                                 ty,
 636                                 reason: "this struct has no fields",
 637                                 help: Some("consider adding a member to this struct"),
 638                             };
 639                         }
 640
 641                         // We can't completely trust repr(C) and repr(transparent) markings;
 642                         // make sure the fields are actually safe.
 643                         let mut all_phantom = true;
 644                         for field in &def.non_enum_variant().fields {
 645                             let field_ty = cx.normalize_erasing_regions(
 646                                 ParamEnv::reveal_all(),
 647                                 field.ty(cx, substs),
 648                             );
 649                             // repr(transparent) types are allowed to have arbitrary ZSTs, not just
 650                             // PhantomData -- skip checking all ZST fields
 651                             if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 652                                 continue;
 653                             }
 654                             let r = self.check_type_for_ffi(cache, field_ty);
 655                             match r {
 656                                 FfiSafe => {
 657                                     all_phantom = false;
 658                                 }
 659                                 FfiPhantom(..) => {}
 660                                 FfiUnsafe { .. } => {
 661                                     return r;
 662                                 }
 663                             }
 664                         }
 665
 666                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 667                     }
 668                     AdtKind::Union => {
 669                         if !def.repr.c() && !def.repr.transparent() {
 670                             return FfiUnsafe {
 671                                 ty,
 672                                 reason: "this union has unspecified layout",
 673                                 help: Some(
 674                                     "consider adding a `#[repr(C)]` or \
 675                                             `#[repr(transparent)]` attribute to this union",
 676                                 ),
 677                             };
 678                         }
 679
 680                         if def.non_enum_variant().fields.is_empty() {
 681                             return FfiUnsafe {
 682                                 ty,
 683                                 reason: "this union has no fields",
 684                                 help: Some("consider adding a field to this union"),
 685                             };
 686                         }
 687
 688                         let mut all_phantom = true;
 689                         for field in &def.non_enum_variant().fields {
 690                             let field_ty = cx.normalize_erasing_regions(
 691                                 ParamEnv::reveal_all(),
 692                                 field.ty(cx, substs),
 693                             );
 694                             // repr(transparent) types are allowed to have arbitrary ZSTs, not just
 695                             // PhantomData -- skip checking all ZST fields.
 696                             if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 697                                 continue;
 698                             }
 699                             let r = self.check_type_for_ffi(cache, field_ty);
 700                             match r {
 701                                 FfiSafe => {
 702                                     all_phantom = false;
 703                                 }
 704                                 FfiPhantom(..) => {}
 705                                 FfiUnsafe { .. } => {
 706                                     return r;
 707                                 }
 708                             }
 709                         }
 710
 711                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 712                     }
 713                     AdtKind::Enum => {
 714                         if def.variants.is_empty() {
 715                             // Empty enums are okay... although sort of useless.
 716                             return FfiSafe;
 717                         }
 718
 719                         // Check for a repr() attribute to specify the size of the
 720                         // discriminant.
 721                         if !def.repr.c() && !def.repr.transparent() && def.repr.int.is_none() {
 722                             // Special-case types like `Option<extern fn()>`.
 723                             if !is_repr_nullable_ptr(cx, ty, def, substs) {
 724                                 return FfiUnsafe {
 725                                     ty,
 726                                     reason: "enum has no representation hint",
 727                                     help: Some(
 728                                         "consider adding a `#[repr(C)]`, \
 729                                                 `#[repr(transparent)]`, or integer `#[repr(...)]` \
 730                                                 attribute to this enum",
 731                                     ),
 732                                 };
 733                             }
 734                         }
 735
 736                         if def.is_variant_list_non_exhaustive() && !def.did.is_local() {
 737                             return FfiUnsafe {
 738                                 ty,
 739                                 reason: "this enum is non-exhaustive",
 740                                 help: None,
 741                             };
 742                         }
 743
 744                         // Check the contained variants.
 745                         for variant in &def.variants {
 746                             let is_non_exhaustive = variant.is_field_list_non_exhaustive();
 747                             if is_non_exhaustive && !variant.def_id.is_local() {
 748                                 return FfiUnsafe {
 749                                     ty,
 750                                     reason: "this enum has non-exhaustive variants",
 751                                     help: None,
 752                                 };
 753                             }
 754
 755                             for field in &variant.fields {
 756                                 let field_ty = cx.normalize_erasing_regions(
 757                                     ParamEnv::reveal_all(),
 758                                     field.ty(cx, substs),
 759                                 );
 760                                 // repr(transparent) types are allowed to have arbitrary ZSTs, not
 761                                 // just PhantomData -- skip checking all ZST fields.
 762                                 if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 763                                     continue;
 764                                 }
 765                                 let r = self.check_type_for_ffi(cache, field_ty);
 766                                 match r {
 767                                     FfiSafe => {}
 768                                     FfiUnsafe { .. } => {
 769                                         return r;
 770                                     }
 771                                     FfiPhantom(..) => {
 772                                         return FfiUnsafe {
 773                                             ty,
 774                                             reason: "this enum contains a PhantomData field",
 775                                             help: None,
 776                                         };
 777                                     }
 778                                 }
 779                             }
 780                         }
 781                         FfiSafe
 782                     }
 783                 }
 784             }
 785
 786             ty::Char => FfiUnsafe {
 787                 ty,
 788                 reason: "the `char` type has no C equivalent",
 789                 help: Some("consider using `u32` or `libc::wchar_t` instead"),
 790             },
 791
 792             ty::Int(ast::IntTy::I128) | ty::Uint(ast::UintTy::U128) => FfiUnsafe {
 793                 ty,
 794                 reason: "128-bit integers don't currently have a known stable ABI",
 795                 help: None,
 796             },
 797
 798             // Primitive types with a stable representation.
 799             ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
 800
 801             ty::Slice(_) => FfiUnsafe {
 802                 ty,
 803                 reason: "slices have no C equivalent",
 804                 help: Some("consider using a raw pointer instead"),
 805             },
 806
 807             ty::Dynamic(..) => {
 808                 FfiUnsafe { ty, reason: "trait objects have no C equivalent", help: None }
 809             }
 810
 811             ty::Str => FfiUnsafe {
 812                 ty,
 813                 reason: "string slices have no C equivalent",
 814                 help: Some("consider using `*const u8` and a length instead"),
 815             },
 816
 817             ty::Tuple(..) => FfiUnsafe {
 818                 ty,
 819                 reason: "tuples have unspecified layout",
 820                 help: Some("consider using a struct instead"),
 821             },
 822
 823             ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _) => {
 824                 self.check_type_for_ffi(cache, ty)
 825             }
 826
 827             ty::Array(inner_ty, _) => self.check_type_for_ffi(cache, inner_ty),
 828
 829             ty::FnPtr(sig) => {
 830                 match sig.abi() {
 831                     Abi::Rust | Abi::RustIntrinsic | Abi::PlatformIntrinsic | Abi::RustCall => {
 832                         return FfiUnsafe {
 833                             ty,
 834                             reason: "this function pointer has Rust-specific calling convention",
 835                             help: Some(
 836                                 "consider using an `extern fn(...) -> ...` \
 837                                         function pointer instead",
 838                             ),
 839                         };
 840                     }
 841                     _ => {}
 842                 }
 843
 844                 let sig = cx.erase_late_bound_regions(&sig);
 845                 if !sig.output().is_unit() {
 846                     let r = self.check_type_for_ffi(cache, sig.output());
 847                     match r {
 848                         FfiSafe => {}
 849                         _ => {
 850                             return r;
 851                         }
 852                     }
 853                 }
 854                 for arg in sig.inputs() {
 855                     let r = self.check_type_for_ffi(cache, arg);
 856                     match r {
 857                         FfiSafe => {}
 858                         _ => {
 859                             return r;
 860                         }
 861                     }
 862                 }
 863                 FfiSafe
 864             }
 865
 866             ty::Foreign(..) => FfiSafe,
 867
 868             ty::Param(..)
 869             | ty::Infer(..)
 870             | ty::Bound(..)
 871             | ty::Error
 872             | ty::Closure(..)
 873             | ty::Generator(..)
 874             | ty::GeneratorWitness(..)
 875             | ty::Placeholder(..)
 876             | ty::UnnormalizedProjection(..)
 877             | ty::Projection(..)
 878             | ty::Opaque(..)
 879             | ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty),
 880         }
 881     }
 882
 883     fn emit_ffi_unsafe_type_lint(
 884         &mut self,
 885         ty: Ty<'tcx>,
 886         sp: Span,
 887         note: &str,
 888         help: Option<&str>,
 889     ) {
 890         let mut diag = self.cx.struct_span_lint(
 891             IMPROPER_CTYPES,
 892             sp,
 893             &format!("`extern` block uses type `{}`, which is not FFI-safe", ty),
 894         );
 895         diag.span_label(sp, "not FFI-safe");
 896         if let Some(help) = help {
 897             diag.help(help);
 898         }
 899         diag.note(note);
 900         if let ty::Adt(def, _) = ty.kind {
 901             if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did) {
 902                 diag.span_note(sp, "type defined here");
 903             }
 904         }
 905         diag.emit();
 906     }
 907
 908     fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
 909         use crate::rustc::ty::TypeFoldable;
 910
 911         struct ProhibitOpaqueTypes<'tcx> {
 912             ty: Option<Ty<'tcx>>,
 913         };
 914
 915         impl<'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'tcx> {
 916             fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
 917                 if let ty::Opaque(..) = ty.kind {
 918                     self.ty = Some(ty);
 919                     true
 920                 } else {
 921                     ty.super_visit_with(self)
 922                 }
 923             }
 924         }
 925
 926         let mut visitor = ProhibitOpaqueTypes { ty: None };
 927         ty.visit_with(&mut visitor);
 928         if let Some(ty) = visitor.ty {
 929             self.emit_ffi_unsafe_type_lint(ty, sp, "opaque types have no C equivalent", None);
 930             true
 931         } else {
 932             false
 933         }
 934     }
 935
 936     fn check_type_for_ffi_and_report_errors(&mut self, sp: Span, ty: Ty<'tcx>, is_static: bool) {
 937         // We have to check for opaque types before `normalize_erasing_regions`,
 938         // which will replace opaque types with their underlying concrete type.
 939         if self.check_for_opaque_ty(sp, ty) {
 940             // We've already emitted an error due to an opaque type.
 941             return;
 942         }
 943
 944         // it is only OK to use this function because extern fns cannot have
 945         // any generic types right now:
 946         let ty = self.cx.tcx.normalize_erasing_regions(ParamEnv::reveal_all(), ty);
 947         // C doesn't really support passing arrays by value.
 948         // The only way to pass an array by value is through a struct.
 949         // So we first test that the top level isn't an array,
 950         // and then recursively check the types inside.
 951         if !is_static && self.check_for_array_ty(sp, ty) {
 952             return;
 953         }
 954
 955         match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
 956             FfiResult::FfiSafe => {}
 957             FfiResult::FfiPhantom(ty) => {
 958                 self.emit_ffi_unsafe_type_lint(ty, sp, "composed only of `PhantomData`", None);
 959             }
 960             FfiResult::FfiUnsafe { ty, reason, help } => {
 961                 self.emit_ffi_unsafe_type_lint(ty, sp, reason, help);
 962             }
 963         }
 964     }
 965
 966     fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl<'_>) {
 967         let def_id = self.cx.tcx.hir().local_def_id(id);
 968         let sig = self.cx.tcx.fn_sig(def_id);
 969         let sig = self.cx.tcx.erase_late_bound_regions(&sig);
 970
 971         for (input_ty, input_hir) in sig.inputs().iter().zip(decl.inputs) {
 972             self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty, false);
 973         }
 974
 975         if let hir::Return(ref ret_hir) = decl.output {
 976             let ret_ty = sig.output();
 977             if !ret_ty.is_unit() {
 978                 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty, false);
 979             }
 980         }
 981     }
 982
 983     fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
 984         let def_id = self.cx.tcx.hir().local_def_id(id);
 985         let ty = self.cx.tcx.type_of(def_id);
 986         self.check_type_for_ffi_and_report_errors(span, ty, true);
 987     }
 988 }
 989
 990 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImproperCTypes {
 991     fn check_foreign_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::ForeignItem<'_>) {
 992         let mut vis = ImproperCTypesVisitor { cx };
 993         let abi = cx.tcx.hir().get_foreign_abi(it.hir_id);
 994         if let Abi::Rust | Abi::RustCall | Abi::RustIntrinsic | Abi::PlatformIntrinsic = abi {
 995             // Don't worry about types in internal ABIs.
 996         } else {
 997             match it.kind {
 998                 hir::ForeignItemKind::Fn(ref decl, _, _) => {
 999                     vis.check_foreign_fn(it.hir_id, decl);
1000                 }
1001                 hir::ForeignItemKind::Static(ref ty, _) => {
1002                     vis.check_foreign_static(it.hir_id, ty.span);
1003                 }
1004                 hir::ForeignItemKind::Type => (),
1005             }
1006         }
1007     }
1008 }
1009
1010 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
1011
1012 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for VariantSizeDifferences {
1013     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item<'_>) {
1014         if let hir::ItemKind::Enum(ref enum_definition, _) = it.kind {
1015             let item_def_id = cx.tcx.hir().local_def_id(it.hir_id);
1016             let t = cx.tcx.type_of(item_def_id);
1017             let ty = cx.tcx.erase_regions(&t);
1018             let layout = match cx.layout_of(ty) {
1019                 Ok(layout) => layout,
1020                 Err(ty::layout::LayoutError::Unknown(_)) => return,
1021                 Err(err @ ty::layout::LayoutError::SizeOverflow(_)) => {
1022                     bug!("failed to get layout for `{}`: {}", t, err);
1023                 }
1024             };
1025             let (variants, tag) = match layout.variants {
1026                 layout::Variants::Multiple {
1027                     discr_kind: layout::DiscriminantKind::Tag,
1028                     ref discr,
1029                     ref variants,
1030                     ..
1031                 } => (variants, discr),
1032                 _ => return,
1033             };
1034
1035             let discr_size = tag.value.size(&cx.tcx).bytes();
1036
1037             debug!(
1038                 "enum `{}` is {} bytes large with layout:\n{:#?}",
1039                 t,
1040                 layout.size.bytes(),
1041                 layout
1042             );
1043
1044             let (largest, slargest, largest_index) = enum_definition
1045                 .variants
1046                 .iter()
1047                 .zip(variants)
1048                 .map(|(variant, variant_layout)| {
1049                     // Subtract the size of the enum discriminant.
1050                     let bytes = variant_layout.size.bytes().saturating_sub(discr_size);
1051
1052                     debug!("- variant `{}` is {} bytes large", variant.ident, bytes);
1053                     bytes
1054                 })
1055                 .enumerate()
1056                 .fold((0, 0, 0), |(l, s, li), (idx, size)| {
1057                     if size > l {
1058                         (size, l, idx)
1059                     } else if size > s {
1060                         (l, size, li)
1061                     } else {
1062                         (l, s, li)
1063                     }
1064                 });
1065
1066             // We only warn if the largest variant is at least thrice as large as
1067             // the second-largest.
1068             if largest > slargest * 3 && slargest > 0 {
1069                 cx.span_lint(
1070                     VARIANT_SIZE_DIFFERENCES,
1071                     enum_definition.variants[largest_index].span,
1072                     &format!(
1073                         "enum variant is more than three times \
1074                                           larger ({} bytes) than the next largest",
1075                         largest
1076                     ),
1077                 );
1078             }
1079         }
1080     }
1081 }