src/librustc_lint/types.rs

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