src/librustc_lint/types.rs

   1 #![allow(non_snake_case)]
   2
   3 use crate::{LateContext, LateLintPass, LintContext};
   4 use rustc_ast::ast;
   5 use rustc_attr as attr;
   6 use rustc_data_structures::fx::FxHashSet;
   7 use rustc_errors::Applicability;
   8 use rustc_hir as hir;
   9 use rustc_hir::def_id::DefId;
  10 use rustc_hir::{is_range_literal, ExprKind, Node};
  11 use rustc_index::vec::Idx;
  12 use rustc_middle::mir::interpret::{sign_extend, truncate};
  13 use rustc_middle::ty::layout::{IntegerExt, SizeSkeleton};
  14 use rustc_middle::ty::subst::SubstsRef;
  15 use rustc_middle::ty::{self, AdtKind, ParamEnv, Ty, TyCtxt};
  16 use rustc_span::source_map;
  17 use rustc_span::symbol::sym;
  18 use rustc_span::Span;
  19 use rustc_target::abi::{DiscriminantKind, Integer, LayoutOf, VariantIdx, Variants};
  20 use rustc_target::spec::abi::Abi;
  21
  22 use log::debug;
  23 use std::cmp;
  24
  25 declare_lint! {
  26     UNUSED_COMPARISONS,
  27     Warn,
  28     "comparisons made useless by limits of the types involved"
  29 }
  30
  31 declare_lint! {
  32     OVERFLOWING_LITERALS,
  33     Deny,
  34     "literal out of range for its type"
  35 }
  36
  37 declare_lint! {
  38     VARIANT_SIZE_DIFFERENCES,
  39     Allow,
  40     "detects enums with widely varying variant sizes"
  41 }
  42
  43 #[derive(Copy, Clone)]
  44 pub struct TypeLimits {
  45     /// Id of the last visited negated expression
  46     negated_expr_id: Option<hir::HirId>,
  47 }
  48
  49 impl_lint_pass!(TypeLimits => [UNUSED_COMPARISONS, OVERFLOWING_LITERALS]);
  50
  51 impl TypeLimits {
  52     pub fn new() -> TypeLimits {
  53         TypeLimits { negated_expr_id: None }
  54     }
  55 }
  56
  57 /// Attempts to special-case the overflowing literal lint when it occurs as a range endpoint.
  58 /// Returns `true` iff the lint was overridden.
  59 fn lint_overflowing_range_endpoint<'a, 'tcx>(
  60     cx: &LateContext<'a, 'tcx>,
  61     lit: &hir::Lit,
  62     lit_val: u128,
  63     max: u128,
  64     expr: &'tcx hir::Expr<'tcx>,
  65     parent_expr: &'tcx hir::Expr<'tcx>,
  66     ty: &str,
  67 ) -> bool {
  68     // We only want to handle exclusive (`..`) ranges,
  69     // which are represented as `ExprKind::Struct`.
  70     let mut overwritten = false;
  71     if let ExprKind::Struct(_, eps, _) = &parent_expr.kind {
  72         if eps.len() != 2 {
  73             return false;
  74         }
  75         // We can suggest using an inclusive range
  76         // (`..=`) instead only if it is the `end` that is
  77         // overflowing and only by 1.
  78         if eps[1].expr.hir_id == expr.hir_id && lit_val - 1 == max {
  79             cx.struct_span_lint(OVERFLOWING_LITERALS, parent_expr.span, |lint| {
  80                 let mut err = lint.build(&format!("range endpoint is out of range for `{}`", ty));
  81                 if let Ok(start) = cx.sess().source_map().span_to_snippet(eps[0].span) {
  82                     use ast::{LitIntType, LitKind};
  83                     // We need to preserve the literal's suffix,
  84                     // as it may determine typing information.
  85                     let suffix = match lit.node {
  86                         LitKind::Int(_, LitIntType::Signed(s)) => s.name_str().to_string(),
  87                         LitKind::Int(_, LitIntType::Unsigned(s)) => s.name_str().to_string(),
  88                         LitKind::Int(_, LitIntType::Unsuffixed) => "".to_string(),
  89                         _ => bug!(),
  90                     };
  91                     let suggestion = format!("{}..={}{}", start, lit_val - 1, suffix);
  92                     err.span_suggestion(
  93                         parent_expr.span,
  94                         &"use an inclusive range instead",
  95                         suggestion,
  96                         Applicability::MachineApplicable,
  97                     );
  98                     err.emit();
  99                     overwritten = true;
 100                 }
 101             });
 102         }
 103     }
 104     overwritten
 105 }
 106
 107 // For `isize` & `usize`, be conservative with the warnings, so that the
 108 // warnings are consistent between 32- and 64-bit platforms.
 109 fn int_ty_range(int_ty: ast::IntTy) -> (i128, i128) {
 110     match int_ty {
 111         ast::IntTy::Isize => (i64::min_value() as i128, i64::max_value() as i128),
 112         ast::IntTy::I8 => (i8::min_value() as i64 as i128, i8::max_value() as i128),
 113         ast::IntTy::I16 => (i16::min_value() as i64 as i128, i16::max_value() as i128),
 114         ast::IntTy::I32 => (i32::min_value() as i64 as i128, i32::max_value() as i128),
 115         ast::IntTy::I64 => (i64::min_value() as i128, i64::max_value() as i128),
 116         ast::IntTy::I128 => (i128::min_value() as i128, i128::max_value()),
 117     }
 118 }
 119
 120 fn uint_ty_range(uint_ty: ast::UintTy) -> (u128, u128) {
 121     match uint_ty {
 122         ast::UintTy::Usize => (u64::min_value() as u128, u64::max_value() as u128),
 123         ast::UintTy::U8 => (u8::min_value() as u128, u8::max_value() as u128),
 124         ast::UintTy::U16 => (u16::min_value() as u128, u16::max_value() as u128),
 125         ast::UintTy::U32 => (u32::min_value() as u128, u32::max_value() as u128),
 126         ast::UintTy::U64 => (u64::min_value() as u128, u64::max_value() as u128),
 127         ast::UintTy::U128 => (u128::min_value(), u128::max_value()),
 128     }
 129 }
 130
 131 fn get_bin_hex_repr(cx: &LateContext<'_, '_>, lit: &hir::Lit) -> Option<String> {
 132     let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?;
 133     let firstch = src.chars().next()?;
 134
 135     if firstch == '0' {
 136         match src.chars().nth(1) {
 137             Some('x' | 'b') => return Some(src),
 138             _ => return None,
 139         }
 140     }
 141
 142     None
 143 }
 144
 145 fn report_bin_hex_error(
 146     cx: &LateContext<'_, '_>,
 147     expr: &hir::Expr<'_>,
 148     ty: attr::IntType,
 149     repr_str: String,
 150     val: u128,
 151     negative: bool,
 152 ) {
 153     let size = Integer::from_attr(&cx.tcx, ty).size();
 154     cx.struct_span_lint(OVERFLOWING_LITERALS, expr.span, |lint| {
 155         let (t, actually) = match ty {
 156             attr::IntType::SignedInt(t) => {
 157                 let actually = sign_extend(val, size) as i128;
 158                 (t.name_str(), actually.to_string())
 159             }
 160             attr::IntType::UnsignedInt(t) => {
 161                 let actually = truncate(val, size);
 162                 (t.name_str(), actually.to_string())
 163             }
 164         };
 165         let mut err = lint.build(&format!("literal out of range for {}", t));
 166         err.note(&format!(
 167             "the literal `{}` (decimal `{}`) does not fit into \
 168              the type `{}` and will become `{}{}`",
 169             repr_str, val, t, actually, t
 170         ));
 171         if let Some(sugg_ty) = get_type_suggestion(&cx.tables.node_type(expr.hir_id), val, negative)
 172         {
 173             if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') {
 174                 let (sans_suffix, _) = repr_str.split_at(pos);
 175                 err.span_suggestion(
 176                     expr.span,
 177                     &format!("consider using `{}` instead", sugg_ty),
 178                     format!("{}{}", sans_suffix, sugg_ty),
 179                     Applicability::MachineApplicable,
 180                 );
 181             } else {
 182                 err.help(&format!("consider using `{}` instead", sugg_ty));
 183             }
 184         }
 185         err.emit();
 186     });
 187 }
 188
 189 // This function finds the next fitting type and generates a suggestion string.
 190 // It searches for fitting types in the following way (`X < Y`):
 191 //  - `iX`: if literal fits in `uX` => `uX`, else => `iY`
 192 //  - `-iX` => `iY`
 193 //  - `uX` => `uY`
 194 //
 195 // No suggestion for: `isize`, `usize`.
 196 fn get_type_suggestion(t: Ty<'_>, val: u128, negative: bool) -> Option<&'static str> {
 197     use rustc_ast::ast::IntTy::*;
 198     use rustc_ast::ast::UintTy::*;
 199     macro_rules! find_fit {
 200         ($ty:expr, $val:expr, $negative:expr,
 201          $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => {
 202             {
 203                 let _neg = if negative { 1 } else { 0 };
 204                 match $ty {
 205                     $($type => {
 206                         $(if !negative && val <= uint_ty_range($utypes).1 {
 207                             return Some($utypes.name_str())
 208                         })*
 209                         $(if val <= int_ty_range($itypes).1 as u128 + _neg {
 210                             return Some($itypes.name_str())
 211                         })*
 212                         None
 213                     },)+
 214                     _ => None
 215                 }
 216             }
 217         }
 218     }
 219     match t.kind {
 220         ty::Int(i) => find_fit!(i, val, negative,
 221                       I8 => [U8] => [I16, I32, I64, I128],
 222                       I16 => [U16] => [I32, I64, I128],
 223                       I32 => [U32] => [I64, I128],
 224                       I64 => [U64] => [I128],
 225                       I128 => [U128] => []),
 226         ty::Uint(u) => find_fit!(u, val, negative,
 227                       U8 => [U8, U16, U32, U64, U128] => [],
 228                       U16 => [U16, U32, U64, U128] => [],
 229                       U32 => [U32, U64, U128] => [],
 230                       U64 => [U64, U128] => [],
 231                       U128 => [U128] => []),
 232         _ => None,
 233     }
 234 }
 235
 236 fn lint_int_literal<'a, 'tcx>(
 237     cx: &LateContext<'a, 'tcx>,
 238     type_limits: &TypeLimits,
 239     e: &'tcx hir::Expr<'tcx>,
 240     lit: &hir::Lit,
 241     t: ast::IntTy,
 242     v: u128,
 243 ) {
 244     let int_type = t.normalize(cx.sess().target.ptr_width);
 245     let (min, max) = int_ty_range(int_type);
 246     let max = max as u128;
 247     let negative = type_limits.negated_expr_id == Some(e.hir_id);
 248
 249     // Detect literal value out of range [min, max] inclusive
 250     // avoiding use of -min to prevent overflow/panic
 251     if (negative && v > max + 1) || (!negative && v > max) {
 252         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 253             report_bin_hex_error(cx, e, attr::IntType::SignedInt(t), repr_str, v, negative);
 254             return;
 255         }
 256
 257         let par_id = cx.tcx.hir().get_parent_node(e.hir_id);
 258         if let Node::Expr(par_e) = cx.tcx.hir().get(par_id) {
 259             if let hir::ExprKind::Struct(..) = par_e.kind {
 260                 if is_range_literal(cx.sess().source_map(), par_e)
 261                     && lint_overflowing_range_endpoint(cx, lit, v, max, e, par_e, t.name_str())
 262                 {
 263                     // The overflowing literal lint was overridden.
 264                     return;
 265                 }
 266             }
 267         }
 268
 269         cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
 270             lint.build(&format!("literal out of range for `{}`", t.name_str()))
 271                 .note(&format!(
 272                     "the literal `{}` does not fit into the type `{}` whose range is `{}..={}`",
 273                     cx.sess()
 274                         .source_map()
 275                         .span_to_snippet(lit.span)
 276                         .expect("must get snippet from literal"),
 277                     t.name_str(),
 278                     min,
 279                     max,
 280                 ))
 281                 .emit();
 282         });
 283     }
 284 }
 285
 286 fn lint_uint_literal<'a, 'tcx>(
 287     cx: &LateContext<'a, 'tcx>,
 288     e: &'tcx hir::Expr<'tcx>,
 289     lit: &hir::Lit,
 290     t: ast::UintTy,
 291 ) {
 292     let uint_type = t.normalize(cx.sess().target.ptr_width);
 293     let (min, max) = uint_ty_range(uint_type);
 294     let lit_val: u128 = match lit.node {
 295         // _v is u8, within range by definition
 296         ast::LitKind::Byte(_v) => return,
 297         ast::LitKind::Int(v, _) => v,
 298         _ => bug!(),
 299     };
 300     if lit_val < min || lit_val > max {
 301         let parent_id = cx.tcx.hir().get_parent_node(e.hir_id);
 302         if let Node::Expr(par_e) = cx.tcx.hir().get(parent_id) {
 303             match par_e.kind {
 304                 hir::ExprKind::Cast(..) => {
 305                     if let ty::Char = cx.tables.expr_ty(par_e).kind {
 306                         cx.struct_span_lint(OVERFLOWING_LITERALS, par_e.span, |lint| {
 307                             lint.build("only `u8` can be cast into `char`")
 308                                 .span_suggestion(
 309                                     par_e.span,
 310                                     &"use a `char` literal instead",
 311                                     format!("'\\u{{{:X}}}'", lit_val),
 312                                     Applicability::MachineApplicable,
 313                                 )
 314                                 .emit();
 315                         });
 316                         return;
 317                     }
 318                 }
 319                 hir::ExprKind::Struct(..) if is_range_literal(cx.sess().source_map(), par_e) => {
 320                     let t = t.name_str();
 321                     if lint_overflowing_range_endpoint(cx, lit, lit_val, max, e, par_e, t) {
 322                         // The overflowing literal lint was overridden.
 323                         return;
 324                     }
 325                 }
 326                 _ => {}
 327             }
 328         }
 329         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 330             report_bin_hex_error(cx, e, attr::IntType::UnsignedInt(t), repr_str, lit_val, false);
 331             return;
 332         }
 333         cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
 334             lint.build(&format!("literal out of range for `{}`", t.name_str()))
 335                 .note(&format!(
 336                     "the literal `{}` does not fit into the type `{}` whose range is `{}..={}`",
 337                     cx.sess()
 338                         .source_map()
 339                         .span_to_snippet(lit.span)
 340                         .expect("must get snippet from literal"),
 341                     t.name_str(),
 342                     min,
 343                     max,
 344                 ))
 345                 .emit()
 346         });
 347     }
 348 }
 349
 350 fn lint_literal<'a, 'tcx>(
 351     cx: &LateContext<'a, 'tcx>,
 352     type_limits: &TypeLimits,
 353     e: &'tcx hir::Expr<'tcx>,
 354     lit: &hir::Lit,
 355 ) {
 356     match cx.tables.node_type(e.hir_id).kind {
 357         ty::Int(t) => {
 358             match lit.node {
 359                 ast::LitKind::Int(v, ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed) => {
 360                     lint_int_literal(cx, type_limits, e, lit, t, v)
 361                 }
 362                 _ => bug!(),
 363             };
 364         }
 365         ty::Uint(t) => lint_uint_literal(cx, e, lit, t),
 366         ty::Float(t) => {
 367             let is_infinite = match lit.node {
 368                 ast::LitKind::Float(v, _) => match t {
 369                     ast::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
 370                     ast::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
 371                 },
 372                 _ => bug!(),
 373             };
 374             if is_infinite == Ok(true) {
 375                 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
 376                     lint.build(&format!("literal out of range for `{}`", t.name_str()))
 377                         .note(&format!(
 378                             "the literal `{}` does not fit into the type `{}` and will be converted to `std::{}::INFINITY`",
 379                             cx.sess()
 380                                 .source_map()
 381                                 .span_to_snippet(lit.span)
 382                                 .expect("must get snippet from literal"),
 383                             t.name_str(),
 384                             t.name_str(),
 385                         ))
 386                         .emit();
 387                 });
 388             }
 389         }
 390         _ => {}
 391     }
 392 }
 393
 394 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TypeLimits {
 395     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx hir::Expr<'tcx>) {
 396         match e.kind {
 397             hir::ExprKind::Unary(hir::UnOp::UnNeg, ref expr) => {
 398                 // propagate negation, if the negation itself isn't negated
 399                 if self.negated_expr_id != Some(e.hir_id) {
 400                     self.negated_expr_id = Some(expr.hir_id);
 401                 }
 402             }
 403             hir::ExprKind::Binary(binop, ref l, ref r) => {
 404                 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
 405                     cx.struct_span_lint(UNUSED_COMPARISONS, e.span, |lint| {
 406                         lint.build("comparison is useless due to type limits").emit()
 407                     });
 408                 }
 409             }
 410             hir::ExprKind::Lit(ref lit) => lint_literal(cx, self, e, lit),
 411             _ => {}
 412         };
 413
 414         fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
 415             match binop.node {
 416                 hir::BinOpKind::Lt => v > min && v <= max,
 417                 hir::BinOpKind::Le => v >= min && v < max,
 418                 hir::BinOpKind::Gt => v >= min && v < max,
 419                 hir::BinOpKind::Ge => v > min && v <= max,
 420                 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
 421                 _ => bug!(),
 422             }
 423         }
 424
 425         fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
 426             source_map::respan(
 427                 binop.span,
 428                 match binop.node {
 429                     hir::BinOpKind::Lt => hir::BinOpKind::Gt,
 430                     hir::BinOpKind::Le => hir::BinOpKind::Ge,
 431                     hir::BinOpKind::Gt => hir::BinOpKind::Lt,
 432                     hir::BinOpKind::Ge => hir::BinOpKind::Le,
 433                     _ => return binop,
 434                 },
 435             )
 436         }
 437
 438         fn check_limits(
 439             cx: &LateContext<'_, '_>,
 440             binop: hir::BinOp,
 441             l: &hir::Expr<'_>,
 442             r: &hir::Expr<'_>,
 443         ) -> bool {
 444             let (lit, expr, swap) = match (&l.kind, &r.kind) {
 445                 (&hir::ExprKind::Lit(_), _) => (l, r, true),
 446                 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
 447                 _ => return true,
 448             };
 449             // Normalize the binop so that the literal is always on the RHS in
 450             // the comparison
 451             let norm_binop = if swap { rev_binop(binop) } else { binop };
 452             match cx.tables.node_type(expr.hir_id).kind {
 453                 ty::Int(int_ty) => {
 454                     let (min, max) = int_ty_range(int_ty);
 455                     let lit_val: i128 = match lit.kind {
 456                         hir::ExprKind::Lit(ref li) => match li.node {
 457                             ast::LitKind::Int(
 458                                 v,
 459                                 ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed,
 460                             ) => v as i128,
 461                             _ => return true,
 462                         },
 463                         _ => bug!(),
 464                     };
 465                     is_valid(norm_binop, lit_val, min, max)
 466                 }
 467                 ty::Uint(uint_ty) => {
 468                     let (min, max): (u128, u128) = uint_ty_range(uint_ty);
 469                     let lit_val: u128 = match lit.kind {
 470                         hir::ExprKind::Lit(ref li) => match li.node {
 471                             ast::LitKind::Int(v, _) => v,
 472                             _ => return true,
 473                         },
 474                         _ => bug!(),
 475                     };
 476                     is_valid(norm_binop, lit_val, min, max)
 477                 }
 478                 _ => true,
 479             }
 480         }
 481
 482         fn is_comparison(binop: hir::BinOp) -> bool {
 483             match binop.node {
 484                 hir::BinOpKind::Eq
 485                 | hir::BinOpKind::Lt
 486                 | hir::BinOpKind::Le
 487                 | hir::BinOpKind::Ne
 488                 | hir::BinOpKind::Ge
 489                 | hir::BinOpKind::Gt => true,
 490                 _ => false,
 491             }
 492         }
 493     }
 494 }
 495
 496 declare_lint! {
 497     IMPROPER_CTYPES,
 498     Warn,
 499     "proper use of libc types in foreign modules"
 500 }
 501
 502 declare_lint_pass!(ImproperCTypes => [IMPROPER_CTYPES]);
 503
 504 struct ImproperCTypesVisitor<'a, 'tcx> {
 505     cx: &'a LateContext<'a, 'tcx>,
 506 }
 507
 508 enum FfiResult<'tcx> {
 509     FfiSafe,
 510     FfiPhantom(Ty<'tcx>),
 511     FfiUnsafe { ty: Ty<'tcx>, reason: &'static str, help: Option<&'static str> },
 512 }
 513
 514 fn is_zst<'tcx>(tcx: TyCtxt<'tcx>, did: DefId, ty: Ty<'tcx>) -> bool {
 515     tcx.layout_of(tcx.param_env(did).and(ty)).map(|layout| layout.is_zst()).unwrap_or(false)
 516 }
 517
 518 fn ty_is_known_nonnull<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool {
 519     match ty.kind {
 520         ty::FnPtr(_) => true,
 521         ty::Ref(..) => true,
 522         ty::Adt(field_def, substs) if field_def.repr.transparent() && !field_def.is_union() => {
 523             for field in field_def.all_fields() {
 524                 let field_ty =
 525                     tcx.normalize_erasing_regions(ParamEnv::reveal_all(), field.ty(tcx, substs));
 526                 if is_zst(tcx, field.did, field_ty) {
 527                     continue;
 528                 }
 529
 530                 let attrs = tcx.get_attrs(field_def.did);
 531                 if attrs.iter().any(|a| a.check_name(sym::rustc_nonnull_optimization_guaranteed))
 532                     || ty_is_known_nonnull(tcx, field_ty)
 533                 {
 534                     return true;
 535                 }
 536             }
 537
 538             false
 539         }
 540         _ => false,
 541     }
 542 }
 543
 544 /// Check if this enum can be safely exported based on the
 545 /// "nullable pointer optimization". Currently restricted
 546 /// to function pointers, references, core::num::NonZero*,
 547 /// core::ptr::NonNull, and #[repr(transparent)] newtypes.
 548 /// FIXME: This duplicates code in codegen.
 549 fn is_repr_nullable_ptr<'tcx>(
 550     tcx: TyCtxt<'tcx>,
 551     ty: Ty<'tcx>,
 552     ty_def: &'tcx ty::AdtDef,
 553     substs: SubstsRef<'tcx>,
 554 ) -> bool {
 555     if ty_def.variants.len() != 2 {
 556         return false;
 557     }
 558
 559     let get_variant_fields = |index| &ty_def.variants[VariantIdx::new(index)].fields;
 560     let variant_fields = [get_variant_fields(0), get_variant_fields(1)];
 561     let fields = if variant_fields[0].is_empty() {
 562         &variant_fields[1]
 563     } else if variant_fields[1].is_empty() {
 564         &variant_fields[0]
 565     } else {
 566         return false;
 567     };
 568
 569     if fields.len() != 1 {
 570         return false;
 571     }
 572
 573     let field_ty = fields[0].ty(tcx, substs);
 574     if !ty_is_known_nonnull(tcx, field_ty) {
 575         return false;
 576     }
 577
 578     // At this point, the field's type is known to be nonnull and the parent enum is Option-like.
 579     // If the computed size for the field and the enum are different, the nonnull optimization isn't
 580     // being applied (and we've got a problem somewhere).
 581     let compute_size_skeleton = |t| SizeSkeleton::compute(t, tcx, ParamEnv::reveal_all()).unwrap();
 582     if !compute_size_skeleton(ty).same_size(compute_size_skeleton(field_ty)) {
 583         bug!("improper_ctypes: Option nonnull optimization not applied?");
 584     }
 585
 586     true
 587 }
 588
 589 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
 590     /// Check if the type is array and emit an unsafe type lint.
 591     fn check_for_array_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
 592         if let ty::Array(..) = ty.kind {
 593             self.emit_ffi_unsafe_type_lint(
 594                 ty,
 595                 sp,
 596                 "passing raw arrays by value is not FFI-safe",
 597                 Some("consider passing a pointer to the array"),
 598             );
 599             true
 600         } else {
 601             false
 602         }
 603     }
 604
 605     /// Checks if the given type is "ffi-safe" (has a stable, well-defined
 606     /// representation which can be exported to C code).
 607     fn check_type_for_ffi(&self, cache: &mut FxHashSet<Ty<'tcx>>, ty: Ty<'tcx>) -> FfiResult<'tcx> {
 608         use FfiResult::*;
 609
 610         let cx = self.cx.tcx;
 611
 612         // Protect against infinite recursion, for example
 613         // `struct S(*mut S);`.
 614         // FIXME: A recursion limit is necessary as well, for irregular
 615         // recursive types.
 616         if !cache.insert(ty) {
 617             return FfiSafe;
 618         }
 619
 620         match ty.kind {
 621             ty::Adt(def, substs) => {
 622                 if def.is_phantom_data() {
 623                     return FfiPhantom(ty);
 624                 }
 625                 match def.adt_kind() {
 626                     AdtKind::Struct => {
 627                         if !def.repr.c() && !def.repr.transparent() {
 628                             return FfiUnsafe {
 629                                 ty,
 630                                 reason: "this struct has unspecified layout",
 631                                 help: Some(
 632                                     "consider adding a `#[repr(C)]` or \
 633                                             `#[repr(transparent)]` attribute to this struct",
 634                                 ),
 635                             };
 636                         }
 637
 638                         let is_non_exhaustive =
 639                             def.non_enum_variant().is_field_list_non_exhaustive();
 640                         if is_non_exhaustive && !def.did.is_local() {
 641                             return FfiUnsafe {
 642                                 ty,
 643                                 reason: "this struct is non-exhaustive",
 644                                 help: None,
 645                             };
 646                         }
 647
 648                         if def.non_enum_variant().fields.is_empty() {
 649                             return FfiUnsafe {
 650                                 ty,
 651                                 reason: "this struct has no fields",
 652                                 help: Some("consider adding a member to this struct"),
 653                             };
 654                         }
 655
 656                         // We can't completely trust repr(C) and repr(transparent) markings;
 657                         // make sure the fields are actually safe.
 658                         let mut all_phantom = true;
 659                         for field in &def.non_enum_variant().fields {
 660                             let field_ty = cx.normalize_erasing_regions(
 661                                 ParamEnv::reveal_all(),
 662                                 field.ty(cx, substs),
 663                             );
 664                             // repr(transparent) types are allowed to have arbitrary ZSTs, not just
 665                             // PhantomData -- skip checking all ZST fields
 666                             if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 667                                 continue;
 668                             }
 669                             let r = self.check_type_for_ffi(cache, field_ty);
 670                             match r {
 671                                 FfiSafe => {
 672                                     all_phantom = false;
 673                                 }
 674                                 FfiPhantom(..) => {}
 675                                 FfiUnsafe { .. } => {
 676                                     return r;
 677                                 }
 678                             }
 679                         }
 680
 681                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 682                     }
 683                     AdtKind::Union => {
 684                         if !def.repr.c() && !def.repr.transparent() {
 685                             return FfiUnsafe {
 686                                 ty,
 687                                 reason: "this union has unspecified layout",
 688                                 help: Some(
 689                                     "consider adding a `#[repr(C)]` or \
 690                                             `#[repr(transparent)]` attribute to this union",
 691                                 ),
 692                             };
 693                         }
 694
 695                         if def.non_enum_variant().fields.is_empty() {
 696                             return FfiUnsafe {
 697                                 ty,
 698                                 reason: "this union has no fields",
 699                                 help: Some("consider adding a field to this union"),
 700                             };
 701                         }
 702
 703                         let mut all_phantom = true;
 704                         for field in &def.non_enum_variant().fields {
 705                             let field_ty = cx.normalize_erasing_regions(
 706                                 ParamEnv::reveal_all(),
 707                                 field.ty(cx, substs),
 708                             );
 709                             // repr(transparent) types are allowed to have arbitrary ZSTs, not just
 710                             // PhantomData -- skip checking all ZST fields.
 711                             if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 712                                 continue;
 713                             }
 714                             let r = self.check_type_for_ffi(cache, field_ty);
 715                             match r {
 716                                 FfiSafe => {
 717                                     all_phantom = false;
 718                                 }
 719                                 FfiPhantom(..) => {}
 720                                 FfiUnsafe { .. } => {
 721                                     return r;
 722                                 }
 723                             }
 724                         }
 725
 726                         if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 727                     }
 728                     AdtKind::Enum => {
 729                         if def.variants.is_empty() {
 730                             // Empty enums are okay... although sort of useless.
 731                             return FfiSafe;
 732                         }
 733
 734                         // Check for a repr() attribute to specify the size of the
 735                         // discriminant.
 736                         if !def.repr.c() && !def.repr.transparent() && def.repr.int.is_none() {
 737                             // Special-case types like `Option<extern fn()>`.
 738                             if !is_repr_nullable_ptr(cx, ty, def, substs) {
 739                                 return FfiUnsafe {
 740                                     ty,
 741                                     reason: "enum has no representation hint",
 742                                     help: Some(
 743                                         "consider adding a `#[repr(C)]`, \
 744                                                 `#[repr(transparent)]`, or integer `#[repr(...)]` \
 745                                                 attribute to this enum",
 746                                     ),
 747                                 };
 748                             }
 749                         }
 750
 751                         if def.is_variant_list_non_exhaustive() && !def.did.is_local() {
 752                             return FfiUnsafe {
 753                                 ty,
 754                                 reason: "this enum is non-exhaustive",
 755                                 help: None,
 756                             };
 757                         }
 758
 759                         // Check the contained variants.
 760                         for variant in &def.variants {
 761                             let is_non_exhaustive = variant.is_field_list_non_exhaustive();
 762                             if is_non_exhaustive && !variant.def_id.is_local() {
 763                                 return FfiUnsafe {
 764                                     ty,
 765                                     reason: "this enum has non-exhaustive variants",
 766                                     help: None,
 767                                 };
 768                             }
 769
 770                             for field in &variant.fields {
 771                                 let field_ty = cx.normalize_erasing_regions(
 772                                     ParamEnv::reveal_all(),
 773                                     field.ty(cx, substs),
 774                                 );
 775                                 // repr(transparent) types are allowed to have arbitrary ZSTs, not
 776                                 // just PhantomData -- skip checking all ZST fields.
 777                                 if def.repr.transparent() && is_zst(cx, field.did, field_ty) {
 778                                     continue;
 779                                 }
 780                                 let r = self.check_type_for_ffi(cache, field_ty);
 781                                 match r {
 782                                     FfiSafe => {}
 783                                     FfiUnsafe { .. } => {
 784                                         return r;
 785                                     }
 786                                     FfiPhantom(..) => {
 787                                         return FfiUnsafe {
 788                                             ty,
 789                                             reason: "this enum contains a PhantomData field",
 790                                             help: None,
 791                                         };
 792                                     }
 793                                 }
 794                             }
 795                         }
 796                         FfiSafe
 797                     }
 798                 }
 799             }
 800
 801             ty::Char => FfiUnsafe {
 802                 ty,
 803                 reason: "the `char` type has no C equivalent",
 804                 help: Some("consider using `u32` or `libc::wchar_t` instead"),
 805             },
 806
 807             ty::Int(ast::IntTy::I128) | ty::Uint(ast::UintTy::U128) => FfiUnsafe {
 808                 ty,
 809                 reason: "128-bit integers don't currently have a known stable ABI",
 810                 help: None,
 811             },
 812
 813             // Primitive types with a stable representation.
 814             ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
 815
 816             ty::Slice(_) => FfiUnsafe {
 817                 ty,
 818                 reason: "slices have no C equivalent",
 819                 help: Some("consider using a raw pointer instead"),
 820             },
 821
 822             ty::Dynamic(..) => {
 823                 FfiUnsafe { ty, reason: "trait objects have no C equivalent", help: None }
 824             }
 825
 826             ty::Str => FfiUnsafe {
 827                 ty,
 828                 reason: "string slices have no C equivalent",
 829                 help: Some("consider using `*const u8` and a length instead"),
 830             },
 831
 832             ty::Tuple(..) => FfiUnsafe {
 833                 ty,
 834                 reason: "tuples have unspecified layout",
 835                 help: Some("consider using a struct instead"),
 836             },
 837
 838             ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _) => {
 839                 self.check_type_for_ffi(cache, ty)
 840             }
 841
 842             ty::Array(inner_ty, _) => self.check_type_for_ffi(cache, inner_ty),
 843
 844             ty::FnPtr(sig) => {
 845                 match sig.abi() {
 846                     Abi::Rust | Abi::RustIntrinsic | Abi::PlatformIntrinsic | Abi::RustCall => {
 847                         return FfiUnsafe {
 848                             ty,
 849                             reason: "this function pointer has Rust-specific calling convention",
 850                             help: Some(
 851                                 "consider using an `extern fn(...) -> ...` \
 852                                         function pointer instead",
 853                             ),
 854                         };
 855                     }
 856                     _ => {}
 857                 }
 858
 859                 let sig = cx.erase_late_bound_regions(&sig);
 860                 if !sig.output().is_unit() {
 861                     let r = self.check_type_for_ffi(cache, sig.output());
 862                     match r {
 863                         FfiSafe => {}
 864                         _ => {
 865                             return r;
 866                         }
 867                     }
 868                 }
 869                 for arg in sig.inputs() {
 870                     let r = self.check_type_for_ffi(cache, arg);
 871                     match r {
 872                         FfiSafe => {}
 873                         _ => {
 874                             return r;
 875                         }
 876                     }
 877                 }
 878                 FfiSafe
 879             }
 880
 881             ty::Foreign(..) => FfiSafe,
 882
 883             ty::Param(..)
 884             | ty::Infer(..)
 885             | ty::Bound(..)
 886             | ty::Error
 887             | ty::Closure(..)
 888             | ty::Generator(..)
 889             | ty::GeneratorWitness(..)
 890             | ty::Placeholder(..)
 891             | ty::Projection(..)
 892             | ty::Opaque(..)
 893             | ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty),
 894         }
 895     }
 896
 897     fn emit_ffi_unsafe_type_lint(
 898         &mut self,
 899         ty: Ty<'tcx>,
 900         sp: Span,
 901         note: &str,
 902         help: Option<&str>,
 903     ) {
 904         self.cx.struct_span_lint(IMPROPER_CTYPES, sp, |lint| {
 905             let mut diag =
 906                 lint.build(&format!("`extern` block uses type `{}`, which is not FFI-safe", ty));
 907             diag.span_label(sp, "not FFI-safe");
 908             if let Some(help) = help {
 909                 diag.help(help);
 910             }
 911             diag.note(note);
 912             if let ty::Adt(def, _) = ty.kind {
 913                 if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did) {
 914                     diag.span_note(sp, "the type is defined here");
 915                 }
 916             }
 917             diag.emit();
 918         });
 919     }
 920
 921     fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
 922         use rustc_middle::ty::TypeFoldable;
 923
 924         struct ProhibitOpaqueTypes<'tcx> {
 925             ty: Option<Ty<'tcx>>,
 926         };
 927
 928         impl<'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'tcx> {
 929             fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
 930                 if let ty::Opaque(..) = ty.kind {
 931                     self.ty = Some(ty);
 932                     true
 933                 } else {
 934                     ty.super_visit_with(self)
 935                 }
 936             }
 937         }
 938
 939         let mut visitor = ProhibitOpaqueTypes { ty: None };
 940         ty.visit_with(&mut visitor);
 941         if let Some(ty) = visitor.ty {
 942             self.emit_ffi_unsafe_type_lint(ty, sp, "opaque types have no C equivalent", None);
 943             true
 944         } else {
 945             false
 946         }
 947     }
 948
 949     fn check_type_for_ffi_and_report_errors(&mut self, sp: Span, ty: Ty<'tcx>, is_static: bool) {
 950         // We have to check for opaque types before `normalize_erasing_regions`,
 951         // which will replace opaque types with their underlying concrete type.
 952         if self.check_for_opaque_ty(sp, ty) {
 953             // We've already emitted an error due to an opaque type.
 954             return;
 955         }
 956
 957         // it is only OK to use this function because extern fns cannot have
 958         // any generic types right now:
 959         let ty = self.cx.tcx.normalize_erasing_regions(ParamEnv::reveal_all(), ty);
 960         // C doesn't really support passing arrays by value.
 961         // The only way to pass an array by value is through a struct.
 962         // So we first test that the top level isn't an array,
 963         // and then recursively check the types inside.
 964         if !is_static && self.check_for_array_ty(sp, ty) {
 965             return;
 966         }
 967
 968         match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
 969             FfiResult::FfiSafe => {}
 970             FfiResult::FfiPhantom(ty) => {
 971                 self.emit_ffi_unsafe_type_lint(ty, sp, "composed only of `PhantomData`", None);
 972             }
 973             FfiResult::FfiUnsafe { ty, reason, help } => {
 974                 self.emit_ffi_unsafe_type_lint(ty, sp, reason, help);
 975             }
 976         }
 977     }
 978
 979     fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl<'_>) {
 980         let def_id = self.cx.tcx.hir().local_def_id(id);
 981         let sig = self.cx.tcx.fn_sig(def_id);
 982         let sig = self.cx.tcx.erase_late_bound_regions(&sig);
 983
 984         for (input_ty, input_hir) in sig.inputs().iter().zip(decl.inputs) {
 985             self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty, false);
 986         }
 987
 988         if let hir::FnRetTy::Return(ref ret_hir) = decl.output {
 989             let ret_ty = sig.output();
 990             if !ret_ty.is_unit() {
 991                 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty, false);
 992             }
 993         }
 994     }
 995
 996     fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
 997         let def_id = self.cx.tcx.hir().local_def_id(id);
 998         let ty = self.cx.tcx.type_of(def_id);
 999         self.check_type_for_ffi_and_report_errors(span, ty, true);
1000     }
1001 }
1002
1003 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImproperCTypes {
1004     fn check_foreign_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::ForeignItem<'_>) {
1005         let mut vis = ImproperCTypesVisitor { cx };
1006         let abi = cx.tcx.hir().get_foreign_abi(it.hir_id);
1007         if let Abi::Rust | Abi::RustCall | Abi::RustIntrinsic | Abi::PlatformIntrinsic = abi {
1008             // Don't worry about types in internal ABIs.
1009         } else {
1010             match it.kind {
1011                 hir::ForeignItemKind::Fn(ref decl, _, _) => {
1012                     vis.check_foreign_fn(it.hir_id, decl);
1013                 }
1014                 hir::ForeignItemKind::Static(ref ty, _) => {
1015                     vis.check_foreign_static(it.hir_id, ty.span);
1016                 }
1017                 hir::ForeignItemKind::Type => (),
1018             }
1019         }
1020     }
1021 }
1022
1023 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
1024
1025 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for VariantSizeDifferences {
1026     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item<'_>) {
1027         if let hir::ItemKind::Enum(ref enum_definition, _) = it.kind {
1028             let item_def_id = cx.tcx.hir().local_def_id(it.hir_id);
1029             let t = cx.tcx.type_of(item_def_id);
1030             let ty = cx.tcx.erase_regions(&t);
1031             let layout = match cx.layout_of(ty) {
1032                 Ok(layout) => layout,
1033                 Err(
1034                     ty::layout::LayoutError::Unknown(_) | ty::layout::LayoutError::SizeOverflow(_),
1035                 ) => return,
1036             };
1037             let (variants, tag) = match layout.variants {
1038                 Variants::Multiple {
1039                     discr_kind: DiscriminantKind::Tag,
1040                     ref discr,
1041                     ref variants,
1042                     ..
1043                 } => (variants, discr),
1044                 _ => return,
1045             };
1046
1047             let discr_size = tag.value.size(&cx.tcx).bytes();
1048
1049             debug!(
1050                 "enum `{}` is {} bytes large with layout:\n{:#?}",
1051                 t,
1052                 layout.size.bytes(),
1053                 layout
1054             );
1055
1056             let (largest, slargest, largest_index) = enum_definition
1057                 .variants
1058                 .iter()
1059                 .zip(variants)
1060                 .map(|(variant, variant_layout)| {
1061                     // Subtract the size of the enum discriminant.
1062                     let bytes = variant_layout.size.bytes().saturating_sub(discr_size);
1063
1064                     debug!("- variant `{}` is {} bytes large", variant.ident, bytes);
1065                     bytes
1066                 })
1067                 .enumerate()
1068                 .fold((0, 0, 0), |(l, s, li), (idx, size)| {
1069                     if size > l {
1070                         (size, l, idx)
1071                     } else if size > s {
1072                         (l, size, li)
1073                     } else {
1074                         (l, s, li)
1075                     }
1076                 });
1077
1078             // We only warn if the largest variant is at least thrice as large as
1079             // the second-largest.
1080             if largest > slargest * 3 && slargest > 0 {
1081                 cx.struct_span_lint(
1082                     VARIANT_SIZE_DIFFERENCES,
1083                     enum_definition.variants[largest_index].span,
1084                     |lint| {
1085                         lint.build(&format!(
1086                             "enum variant is more than three times \
1087                                           larger ({} bytes) than the next largest",
1088                             largest
1089                         ))
1090                         .emit()
1091                     },
1092                 );
1093             }
1094         }
1095     }
1096 }