src/librustc_lint/types.rs

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