compiler/rustc_lint/src/types.rs

   1 use crate::lints::{
   2     AtomicOrderingFence, AtomicOrderingLoad, AtomicOrderingStore, ImproperCTypes,
   3     InvalidAtomicOrderingDiag, OnlyCastu8ToChar, OverflowingBinHex, OverflowingBinHexSign,
   4     OverflowingBinHexSub, OverflowingInt, OverflowingIntHelp, OverflowingLiteral, OverflowingUInt,
   5     RangeEndpointOutOfRange, UnusedComparisons, VariantSizeDifferencesDiag,
   6 };
   7 use crate::{LateContext, LateLintPass, LintContext};
   8 use rustc_ast as ast;
   9 use rustc_attr as attr;
  10 use rustc_data_structures::fx::FxHashSet;
  11 use rustc_errors::{fluent, DiagnosticMessage};
  12 use rustc_hir as hir;
  13 use rustc_hir::{is_range_literal, Expr, ExprKind, Node};
  14 use rustc_middle::ty::layout::{IntegerExt, LayoutOf, SizeSkeleton};
  15 use rustc_middle::ty::subst::SubstsRef;
  16 use rustc_middle::ty::{self, AdtKind, DefIdTree, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable};
  17 use rustc_span::source_map;
  18 use rustc_span::symbol::sym;
  19 use rustc_span::{Span, Symbol};
  20 use rustc_target::abi::{Abi, Size, WrappingRange};
  21 use rustc_target::abi::{Integer, TagEncoding, Variants};
  22 use rustc_target::spec::abi::Abi as SpecAbi;
  23
  24 use std::iter;
  25 use std::ops::ControlFlow;
  26
  27 declare_lint! {
  28     /// The `unused_comparisons` lint detects comparisons made useless by
  29     /// limits of the types involved.
  30     ///
  31     /// ### Example
  32     ///
  33     /// ```rust
  34     /// fn foo(x: u8) {
  35     ///     x >= 0;
  36     /// }
  37     /// ```
  38     ///
  39     /// {{produces}}
  40     ///
  41     /// ### Explanation
  42     ///
  43     /// A useless comparison may indicate a mistake, and should be fixed or
  44     /// removed.
  45     UNUSED_COMPARISONS,
  46     Warn,
  47     "comparisons made useless by limits of the types involved"
  48 }
  49
  50 declare_lint! {
  51     /// The `overflowing_literals` lint detects literal out of range for its
  52     /// type.
  53     ///
  54     /// ### Example
  55     ///
  56     /// ```rust,compile_fail
  57     /// let x: u8 = 1000;
  58     /// ```
  59     ///
  60     /// {{produces}}
  61     ///
  62     /// ### Explanation
  63     ///
  64     /// It is usually a mistake to use a literal that overflows the type where
  65     /// it is used. Either use a literal that is within range, or change the
  66     /// type to be within the range of the literal.
  67     OVERFLOWING_LITERALS,
  68     Deny,
  69     "literal out of range for its type"
  70 }
  71
  72 declare_lint! {
  73     /// The `variant_size_differences` lint detects enums with widely varying
  74     /// variant sizes.
  75     ///
  76     /// ### Example
  77     ///
  78     /// ```rust,compile_fail
  79     /// #![deny(variant_size_differences)]
  80     /// enum En {
  81     ///     V0(u8),
  82     ///     VBig([u8; 1024]),
  83     /// }
  84     /// ```
  85     ///
  86     /// {{produces}}
  87     ///
  88     /// ### Explanation
  89     ///
  90     /// It can be a mistake to add a variant to an enum that is much larger
  91     /// than the other variants, bloating the overall size required for all
  92     /// variants. This can impact performance and memory usage. This is
  93     /// triggered if one variant is more than 3 times larger than the
  94     /// second-largest variant.
  95     ///
  96     /// Consider placing the large variant's contents on the heap (for example
  97     /// via [`Box`]) to keep the overall size of the enum itself down.
  98     ///
  99     /// This lint is "allow" by default because it can be noisy, and may not be
 100     /// an actual problem. Decisions about this should be guided with
 101     /// profiling and benchmarking.
 102     ///
 103     /// [`Box`]: https://doc.rust-lang.org/std/boxed/index.html
 104     VARIANT_SIZE_DIFFERENCES,
 105     Allow,
 106     "detects enums with widely varying variant sizes"
 107 }
 108
 109 #[derive(Copy, Clone)]
 110 pub struct TypeLimits {
 111     /// Id of the last visited negated expression
 112     negated_expr_id: Option<hir::HirId>,
 113 }
 114
 115 impl_lint_pass!(TypeLimits => [UNUSED_COMPARISONS, OVERFLOWING_LITERALS]);
 116
 117 impl TypeLimits {
 118     pub fn new() -> TypeLimits {
 119         TypeLimits { negated_expr_id: None }
 120     }
 121 }
 122
 123 /// Attempts to special-case the overflowing literal lint when it occurs as a range endpoint (`expr..MAX+1`).
 124 /// Returns `true` iff the lint was emitted.
 125 fn lint_overflowing_range_endpoint<'tcx>(
 126     cx: &LateContext<'tcx>,
 127     lit: &hir::Lit,
 128     lit_val: u128,
 129     max: u128,
 130     expr: &'tcx hir::Expr<'tcx>,
 131     ty: &str,
 132 ) -> bool {
 133     // We only want to handle exclusive (`..`) ranges,
 134     // which are represented as `ExprKind::Struct`.
 135     let par_id = cx.tcx.hir().parent_id(expr.hir_id);
 136     let Node::ExprField(field) = cx.tcx.hir().get(par_id) else { return false };
 137     let Node::Expr(struct_expr) = cx.tcx.hir().get_parent(field.hir_id) else { return false };
 138     if !is_range_literal(struct_expr) {
 139         return false;
 140     };
 141     let ExprKind::Struct(_, eps, _) = &struct_expr.kind else { return false };
 142     if eps.len() != 2 {
 143         return false;
 144     }
 145
 146     // We can suggest using an inclusive range
 147     // (`..=`) instead only if it is the `end` that is
 148     // overflowing and only by 1.
 149     if !(eps[1].expr.hir_id == expr.hir_id && lit_val - 1 == max) {
 150         return false;
 151     };
 152     let Ok(start) = cx.sess().source_map().span_to_snippet(eps[0].span) else { return false };
 153
 154     use rustc_ast::{LitIntType, LitKind};
 155     let suffix = match lit.node {
 156         LitKind::Int(_, LitIntType::Signed(s)) => s.name_str(),
 157         LitKind::Int(_, LitIntType::Unsigned(s)) => s.name_str(),
 158         LitKind::Int(_, LitIntType::Unsuffixed) => "",
 159         _ => bug!(),
 160     };
 161     cx.emit_spanned_lint(
 162         OVERFLOWING_LITERALS,
 163         struct_expr.span,
 164         RangeEndpointOutOfRange {
 165             ty,
 166             suggestion: struct_expr.span,
 167             start,
 168             literal: lit_val - 1,
 169             suffix,
 170         },
 171     );
 172
 173     // We've just emitted a lint, special cased for `(...)..MAX+1` ranges,
 174     // return `true` so the callers don't also emit a lint
 175     true
 176 }
 177
 178 // For `isize` & `usize`, be conservative with the warnings, so that the
 179 // warnings are consistent between 32- and 64-bit platforms.
 180 fn int_ty_range(int_ty: ty::IntTy) -> (i128, i128) {
 181     match int_ty {
 182         ty::IntTy::Isize => (i64::MIN.into(), i64::MAX.into()),
 183         ty::IntTy::I8 => (i8::MIN.into(), i8::MAX.into()),
 184         ty::IntTy::I16 => (i16::MIN.into(), i16::MAX.into()),
 185         ty::IntTy::I32 => (i32::MIN.into(), i32::MAX.into()),
 186         ty::IntTy::I64 => (i64::MIN.into(), i64::MAX.into()),
 187         ty::IntTy::I128 => (i128::MIN, i128::MAX),
 188     }
 189 }
 190
 191 fn uint_ty_range(uint_ty: ty::UintTy) -> (u128, u128) {
 192     let max = match uint_ty {
 193         ty::UintTy::Usize => u64::MAX.into(),
 194         ty::UintTy::U8 => u8::MAX.into(),
 195         ty::UintTy::U16 => u16::MAX.into(),
 196         ty::UintTy::U32 => u32::MAX.into(),
 197         ty::UintTy::U64 => u64::MAX.into(),
 198         ty::UintTy::U128 => u128::MAX,
 199     };
 200     (0, max)
 201 }
 202
 203 fn get_bin_hex_repr(cx: &LateContext<'_>, lit: &hir::Lit) -> Option<String> {
 204     let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?;
 205     let firstch = src.chars().next()?;
 206
 207     if firstch == '0' {
 208         match src.chars().nth(1) {
 209             Some('x' | 'b') => return Some(src),
 210             _ => return None,
 211         }
 212     }
 213
 214     None
 215 }
 216
 217 fn report_bin_hex_error(
 218     cx: &LateContext<'_>,
 219     expr: &hir::Expr<'_>,
 220     ty: attr::IntType,
 221     size: Size,
 222     repr_str: String,
 223     val: u128,
 224     negative: bool,
 225 ) {
 226     let (t, actually) = match ty {
 227         attr::IntType::SignedInt(t) => {
 228             let actually = if negative {
 229                 -(size.sign_extend(val) as i128)
 230             } else {
 231                 size.sign_extend(val) as i128
 232             };
 233             (t.name_str(), actually.to_string())
 234         }
 235         attr::IntType::UnsignedInt(t) => {
 236             let actually = size.truncate(val);
 237             (t.name_str(), actually.to_string())
 238         }
 239     };
 240     let sign =
 241         if negative { OverflowingBinHexSign::Negative } else { OverflowingBinHexSign::Positive };
 242     let sub = get_type_suggestion(cx.typeck_results().node_type(expr.hir_id), val, negative).map(
 243         |suggestion_ty| {
 244             if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') {
 245                 let (sans_suffix, _) = repr_str.split_at(pos);
 246                 OverflowingBinHexSub::Suggestion { span: expr.span, suggestion_ty, sans_suffix }
 247             } else {
 248                 OverflowingBinHexSub::Help { suggestion_ty }
 249             }
 250         },
 251     );
 252     cx.emit_spanned_lint(
 253         OVERFLOWING_LITERALS,
 254         expr.span,
 255         OverflowingBinHex { ty: t, lit: repr_str.clone(), dec: val, actually, sign, sub },
 256     )
 257 }
 258
 259 // This function finds the next fitting type and generates a suggestion string.
 260 // It searches for fitting types in the following way (`X < Y`):
 261 //  - `iX`: if literal fits in `uX` => `uX`, else => `iY`
 262 //  - `-iX` => `iY`
 263 //  - `uX` => `uY`
 264 //
 265 // No suggestion for: `isize`, `usize`.
 266 fn get_type_suggestion(t: Ty<'_>, val: u128, negative: bool) -> Option<&'static str> {
 267     use ty::IntTy::*;
 268     use ty::UintTy::*;
 269     macro_rules! find_fit {
 270         ($ty:expr, $val:expr, $negative:expr,
 271          $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => {
 272             {
 273                 let _neg = if negative { 1 } else { 0 };
 274                 match $ty {
 275                     $($type => {
 276                         $(if !negative && val <= uint_ty_range($utypes).1 {
 277                             return Some($utypes.name_str())
 278                         })*
 279                         $(if val <= int_ty_range($itypes).1 as u128 + _neg {
 280                             return Some($itypes.name_str())
 281                         })*
 282                         None
 283                     },)+
 284                     _ => None
 285                 }
 286             }
 287         }
 288     }
 289     match t.kind() {
 290         ty::Int(i) => find_fit!(i, val, negative,
 291                       I8 => [U8] => [I16, I32, I64, I128],
 292                       I16 => [U16] => [I32, I64, I128],
 293                       I32 => [U32] => [I64, I128],
 294                       I64 => [U64] => [I128],
 295                       I128 => [U128] => []),
 296         ty::Uint(u) => find_fit!(u, val, negative,
 297                       U8 => [U8, U16, U32, U64, U128] => [],
 298                       U16 => [U16, U32, U64, U128] => [],
 299                       U32 => [U32, U64, U128] => [],
 300                       U64 => [U64, U128] => [],
 301                       U128 => [U128] => []),
 302         _ => None,
 303     }
 304 }
 305
 306 fn lint_int_literal<'tcx>(
 307     cx: &LateContext<'tcx>,
 308     type_limits: &TypeLimits,
 309     e: &'tcx hir::Expr<'tcx>,
 310     lit: &hir::Lit,
 311     t: ty::IntTy,
 312     v: u128,
 313 ) {
 314     let int_type = t.normalize(cx.sess().target.pointer_width);
 315     let (min, max) = int_ty_range(int_type);
 316     let max = max as u128;
 317     let negative = type_limits.negated_expr_id == Some(e.hir_id);
 318
 319     // Detect literal value out of range [min, max] inclusive
 320     // avoiding use of -min to prevent overflow/panic
 321     if (negative && v > max + 1) || (!negative && v > max) {
 322         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 323             report_bin_hex_error(
 324                 cx,
 325                 e,
 326                 attr::IntType::SignedInt(ty::ast_int_ty(t)),
 327                 Integer::from_int_ty(cx, t).size(),
 328                 repr_str,
 329                 v,
 330                 negative,
 331             );
 332             return;
 333         }
 334
 335         if lint_overflowing_range_endpoint(cx, lit, v, max, e, t.name_str()) {
 336             // The overflowing literal lint was emitted by `lint_overflowing_range_endpoint`.
 337             return;
 338         }
 339
 340         let lit = cx
 341             .sess()
 342             .source_map()
 343             .span_to_snippet(lit.span)
 344             .expect("must get snippet from literal");
 345         let help = get_type_suggestion(cx.typeck_results().node_type(e.hir_id), v, negative)
 346             .map(|suggestion_ty| OverflowingIntHelp { suggestion_ty });
 347
 348         cx.emit_spanned_lint(
 349             OVERFLOWING_LITERALS,
 350             e.span,
 351             OverflowingInt { ty: t.name_str(), lit, min, max, help },
 352         );
 353     }
 354 }
 355
 356 fn lint_uint_literal<'tcx>(
 357     cx: &LateContext<'tcx>,
 358     e: &'tcx hir::Expr<'tcx>,
 359     lit: &hir::Lit,
 360     t: ty::UintTy,
 361 ) {
 362     let uint_type = t.normalize(cx.sess().target.pointer_width);
 363     let (min, max) = uint_ty_range(uint_type);
 364     let lit_val: u128 = match lit.node {
 365         // _v is u8, within range by definition
 366         ast::LitKind::Byte(_v) => return,
 367         ast::LitKind::Int(v, _) => v,
 368         _ => bug!(),
 369     };
 370     if lit_val < min || lit_val > max {
 371         let parent_id = cx.tcx.hir().parent_id(e.hir_id);
 372         if let Node::Expr(par_e) = cx.tcx.hir().get(parent_id) {
 373             match par_e.kind {
 374                 hir::ExprKind::Cast(..) => {
 375                     if let ty::Char = cx.typeck_results().expr_ty(par_e).kind() {
 376                         cx.emit_spanned_lint(
 377                             OVERFLOWING_LITERALS,
 378                             par_e.span,
 379                             OnlyCastu8ToChar { span: par_e.span, literal: lit_val },
 380                         );
 381                         return;
 382                     }
 383                 }
 384                 _ => {}
 385             }
 386         }
 387         if lint_overflowing_range_endpoint(cx, lit, lit_val, max, e, t.name_str()) {
 388             // The overflowing literal lint was emitted by `lint_overflowing_range_endpoint`.
 389             return;
 390         }
 391         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 392             report_bin_hex_error(
 393                 cx,
 394                 e,
 395                 attr::IntType::UnsignedInt(ty::ast_uint_ty(t)),
 396                 Integer::from_uint_ty(cx, t).size(),
 397                 repr_str,
 398                 lit_val,
 399                 false,
 400             );
 401             return;
 402         }
 403         cx.emit_spanned_lint(
 404             OVERFLOWING_LITERALS,
 405             e.span,
 406             OverflowingUInt {
 407                 ty: t.name_str(),
 408                 lit: cx
 409                     .sess()
 410                     .source_map()
 411                     .span_to_snippet(lit.span)
 412                     .expect("must get snippet from literal"),
 413                 min,
 414                 max,
 415             },
 416         );
 417     }
 418 }
 419
 420 fn lint_literal<'tcx>(
 421     cx: &LateContext<'tcx>,
 422     type_limits: &TypeLimits,
 423     e: &'tcx hir::Expr<'tcx>,
 424     lit: &hir::Lit,
 425 ) {
 426     match *cx.typeck_results().node_type(e.hir_id).kind() {
 427         ty::Int(t) => {
 428             match lit.node {
 429                 ast::LitKind::Int(v, ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed) => {
 430                     lint_int_literal(cx, type_limits, e, lit, t, v)
 431                 }
 432                 _ => bug!(),
 433             };
 434         }
 435         ty::Uint(t) => lint_uint_literal(cx, e, lit, t),
 436         ty::Float(t) => {
 437             let is_infinite = match lit.node {
 438                 ast::LitKind::Float(v, _) => match t {
 439                     ty::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
 440                     ty::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
 441                 },
 442                 _ => bug!(),
 443             };
 444             if is_infinite == Ok(true) {
 445                 cx.emit_spanned_lint(
 446                     OVERFLOWING_LITERALS,
 447                     e.span,
 448                     OverflowingLiteral {
 449                         ty: t.name_str(),
 450                         lit: cx
 451                             .sess()
 452                             .source_map()
 453                             .span_to_snippet(lit.span)
 454                             .expect("must get snippet from literal"),
 455                     },
 456                 );
 457             }
 458         }
 459         _ => {}
 460     }
 461 }
 462
 463 impl<'tcx> LateLintPass<'tcx> for TypeLimits {
 464     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx hir::Expr<'tcx>) {
 465         match e.kind {
 466             hir::ExprKind::Unary(hir::UnOp::Neg, ref expr) => {
 467                 // propagate negation, if the negation itself isn't negated
 468                 if self.negated_expr_id != Some(e.hir_id) {
 469                     self.negated_expr_id = Some(expr.hir_id);
 470                 }
 471             }
 472             hir::ExprKind::Binary(binop, ref l, ref r) => {
 473                 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
 474                     cx.emit_spanned_lint(UNUSED_COMPARISONS, e.span, UnusedComparisons);
 475                 }
 476             }
 477             hir::ExprKind::Lit(ref lit) => lint_literal(cx, self, e, lit),
 478             _ => {}
 479         };
 480
 481         fn is_valid<T: PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
 482             match binop.node {
 483                 hir::BinOpKind::Lt => v > min && v <= max,
 484                 hir::BinOpKind::Le => v >= min && v < max,
 485                 hir::BinOpKind::Gt => v >= min && v < max,
 486                 hir::BinOpKind::Ge => v > min && v <= max,
 487                 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
 488                 _ => bug!(),
 489             }
 490         }
 491
 492         fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
 493             source_map::respan(
 494                 binop.span,
 495                 match binop.node {
 496                     hir::BinOpKind::Lt => hir::BinOpKind::Gt,
 497                     hir::BinOpKind::Le => hir::BinOpKind::Ge,
 498                     hir::BinOpKind::Gt => hir::BinOpKind::Lt,
 499                     hir::BinOpKind::Ge => hir::BinOpKind::Le,
 500                     _ => return binop,
 501                 },
 502             )
 503         }
 504
 505         fn check_limits(
 506             cx: &LateContext<'_>,
 507             binop: hir::BinOp,
 508             l: &hir::Expr<'_>,
 509             r: &hir::Expr<'_>,
 510         ) -> bool {
 511             let (lit, expr, swap) = match (&l.kind, &r.kind) {
 512                 (&hir::ExprKind::Lit(_), _) => (l, r, true),
 513                 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
 514                 _ => return true,
 515             };
 516             // Normalize the binop so that the literal is always on the RHS in
 517             // the comparison
 518             let norm_binop = if swap { rev_binop(binop) } else { binop };
 519             match *cx.typeck_results().node_type(expr.hir_id).kind() {
 520                 ty::Int(int_ty) => {
 521                     let (min, max) = int_ty_range(int_ty);
 522                     let lit_val: i128 = match lit.kind {
 523                         hir::ExprKind::Lit(ref li) => match li.node {
 524                             ast::LitKind::Int(
 525                                 v,
 526                                 ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed,
 527                             ) => v as i128,
 528                             _ => return true,
 529                         },
 530                         _ => bug!(),
 531                     };
 532                     is_valid(norm_binop, lit_val, min, max)
 533                 }
 534                 ty::Uint(uint_ty) => {
 535                     let (min, max): (u128, u128) = uint_ty_range(uint_ty);
 536                     let lit_val: u128 = match lit.kind {
 537                         hir::ExprKind::Lit(ref li) => match li.node {
 538                             ast::LitKind::Int(v, _) => v,
 539                             _ => return true,
 540                         },
 541                         _ => bug!(),
 542                     };
 543                     is_valid(norm_binop, lit_val, min, max)
 544                 }
 545                 _ => true,
 546             }
 547         }
 548
 549         fn is_comparison(binop: hir::BinOp) -> bool {
 550             matches!(
 551                 binop.node,
 552                 hir::BinOpKind::Eq
 553                     | hir::BinOpKind::Lt
 554                     | hir::BinOpKind::Le
 555                     | hir::BinOpKind::Ne
 556                     | hir::BinOpKind::Ge
 557                     | hir::BinOpKind::Gt
 558             )
 559         }
 560     }
 561 }
 562
 563 declare_lint! {
 564     /// The `improper_ctypes` lint detects incorrect use of types in foreign
 565     /// modules.
 566     ///
 567     /// ### Example
 568     ///
 569     /// ```rust
 570     /// extern "C" {
 571     ///     static STATIC: String;
 572     /// }
 573     /// ```
 574     ///
 575     /// {{produces}}
 576     ///
 577     /// ### Explanation
 578     ///
 579     /// The compiler has several checks to verify that types used in `extern`
 580     /// blocks are safe and follow certain rules to ensure proper
 581     /// compatibility with the foreign interfaces. This lint is issued when it
 582     /// detects a probable mistake in a definition. The lint usually should
 583     /// provide a description of the issue, along with possibly a hint on how
 584     /// to resolve it.
 585     IMPROPER_CTYPES,
 586     Warn,
 587     "proper use of libc types in foreign modules"
 588 }
 589
 590 declare_lint_pass!(ImproperCTypesDeclarations => [IMPROPER_CTYPES]);
 591
 592 declare_lint! {
 593     /// The `improper_ctypes_definitions` lint detects incorrect use of
 594     /// [`extern` function] definitions.
 595     ///
 596     /// [`extern` function]: https://doc.rust-lang.org/reference/items/functions.html#extern-function-qualifier
 597     ///
 598     /// ### Example
 599     ///
 600     /// ```rust
 601     /// # #![allow(unused)]
 602     /// pub extern "C" fn str_type(p: &str) { }
 603     /// ```
 604     ///
 605     /// {{produces}}
 606     ///
 607     /// ### Explanation
 608     ///
 609     /// There are many parameter and return types that may be specified in an
 610     /// `extern` function that are not compatible with the given ABI. This
 611     /// lint is an alert that these types should not be used. The lint usually
 612     /// should provide a description of the issue, along with possibly a hint
 613     /// on how to resolve it.
 614     IMPROPER_CTYPES_DEFINITIONS,
 615     Warn,
 616     "proper use of libc types in foreign item definitions"
 617 }
 618
 619 declare_lint_pass!(ImproperCTypesDefinitions => [IMPROPER_CTYPES_DEFINITIONS]);
 620
 621 #[derive(Clone, Copy)]
 622 pub(crate) enum CItemKind {
 623     Declaration,
 624     Definition,
 625 }
 626
 627 struct ImproperCTypesVisitor<'a, 'tcx> {
 628     cx: &'a LateContext<'tcx>,
 629     mode: CItemKind,
 630 }
 631
 632 enum FfiResult<'tcx> {
 633     FfiSafe,
 634     FfiPhantom(Ty<'tcx>),
 635     FfiUnsafe { ty: Ty<'tcx>, reason: DiagnosticMessage, help: Option<DiagnosticMessage> },
 636 }
 637
 638 pub(crate) fn nonnull_optimization_guaranteed<'tcx>(
 639     tcx: TyCtxt<'tcx>,
 640     def: ty::AdtDef<'tcx>,
 641 ) -> bool {
 642     tcx.has_attr(def.did(), sym::rustc_nonnull_optimization_guaranteed)
 643 }
 644
 645 /// `repr(transparent)` structs can have a single non-ZST field, this function returns that
 646 /// field.
 647 pub fn transparent_newtype_field<'a, 'tcx>(
 648     tcx: TyCtxt<'tcx>,
 649     variant: &'a ty::VariantDef,
 650 ) -> Option<&'a ty::FieldDef> {
 651     let param_env = tcx.param_env(variant.def_id);
 652     variant.fields.iter().find(|field| {
 653         let field_ty = tcx.type_of(field.did);
 654         let is_zst = tcx.layout_of(param_env.and(field_ty)).map_or(false, |layout| layout.is_zst());
 655         !is_zst
 656     })
 657 }
 658
 659 /// Is type known to be non-null?
 660 fn ty_is_known_nonnull<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, mode: CItemKind) -> bool {
 661     let tcx = cx.tcx;
 662     match ty.kind() {
 663         ty::FnPtr(_) => true,
 664         ty::Ref(..) => true,
 665         ty::Adt(def, _) if def.is_box() && matches!(mode, CItemKind::Definition) => true,
 666         ty::Adt(def, substs) if def.repr().transparent() && !def.is_union() => {
 667             let marked_non_null = nonnull_optimization_guaranteed(tcx, *def);
 668
 669             if marked_non_null {
 670                 return true;
 671             }
 672
 673             // `UnsafeCell` has its niche hidden.
 674             if def.is_unsafe_cell() {
 675                 return false;
 676             }
 677
 678             def.variants()
 679                 .iter()
 680                 .filter_map(|variant| transparent_newtype_field(cx.tcx, variant))
 681                 .any(|field| ty_is_known_nonnull(cx, field.ty(tcx, substs), mode))
 682         }
 683         _ => false,
 684     }
 685 }
 686
 687 /// Given a non-null scalar (or transparent) type `ty`, return the nullable version of that type.
 688 /// If the type passed in was not scalar, returns None.
 689 fn get_nullable_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
 690     let tcx = cx.tcx;
 691     Some(match *ty.kind() {
 692         ty::Adt(field_def, field_substs) => {
 693             let inner_field_ty = {
 694                 let mut first_non_zst_ty = field_def
 695                     .variants()
 696                     .iter()
 697                     .filter_map(|v| transparent_newtype_field(cx.tcx, v));
 698                 debug_assert_eq!(
 699                     first_non_zst_ty.clone().count(),
 700                     1,
 701                     "Wrong number of fields for transparent type"
 702                 );
 703                 first_non_zst_ty
 704                     .next_back()
 705                     .expect("No non-zst fields in transparent type.")
 706                     .ty(tcx, field_substs)
 707             };
 708             return get_nullable_type(cx, inner_field_ty);
 709         }
 710         ty::Int(ty) => tcx.mk_mach_int(ty),
 711         ty::Uint(ty) => tcx.mk_mach_uint(ty),
 712         ty::RawPtr(ty_mut) => tcx.mk_ptr(ty_mut),
 713         // As these types are always non-null, the nullable equivalent of
 714         // Option<T> of these types are their raw pointer counterparts.
 715         ty::Ref(_region, ty, mutbl) => tcx.mk_ptr(ty::TypeAndMut { ty, mutbl }),
 716         ty::FnPtr(..) => {
 717             // There is no nullable equivalent for Rust's function pointers -- you
 718             // must use an Option<fn(..) -> _> to represent it.
 719             ty
 720         }
 721
 722         // We should only ever reach this case if ty_is_known_nonnull is extended
 723         // to other types.
 724         ref unhandled => {
 725             debug!(
 726                 "get_nullable_type: Unhandled scalar kind: {:?} while checking {:?}",
 727                 unhandled, ty
 728             );
 729             return None;
 730         }
 731     })
 732 }
 733
 734 /// Check if this enum can be safely exported based on the "nullable pointer optimization". If it
 735 /// can, return the type that `ty` can be safely converted to, otherwise return `None`.
 736 /// Currently restricted to function pointers, boxes, references, `core::num::NonZero*`,
 737 /// `core::ptr::NonNull`, and `#[repr(transparent)]` newtypes.
 738 /// FIXME: This duplicates code in codegen.
 739 pub(crate) fn repr_nullable_ptr<'tcx>(
 740     cx: &LateContext<'tcx>,
 741     ty: Ty<'tcx>,
 742     ckind: CItemKind,
 743 ) -> Option<Ty<'tcx>> {
 744     debug!("is_repr_nullable_ptr(cx, ty = {:?})", ty);
 745     if let ty::Adt(ty_def, substs) = ty.kind() {
 746         let field_ty = match &ty_def.variants().raw[..] {
 747             [var_one, var_two] => match (&var_one.fields[..], &var_two.fields[..]) {
 748                 ([], [field]) | ([field], []) => field.ty(cx.tcx, substs),
 749                 _ => return None,
 750             },
 751             _ => return None,
 752         };
 753
 754         if !ty_is_known_nonnull(cx, field_ty, ckind) {
 755             return None;
 756         }
 757
 758         // At this point, the field's type is known to be nonnull and the parent enum is Option-like.
 759         // If the computed size for the field and the enum are different, the nonnull optimization isn't
 760         // being applied (and we've got a problem somewhere).
 761         let compute_size_skeleton = |t| SizeSkeleton::compute(t, cx.tcx, cx.param_env).unwrap();
 762         if !compute_size_skeleton(ty).same_size(compute_size_skeleton(field_ty)) {
 763             bug!("improper_ctypes: Option nonnull optimization not applied?");
 764         }
 765
 766         // Return the nullable type this Option-like enum can be safely represented with.
 767         let field_ty_abi = &cx.layout_of(field_ty).unwrap().abi;
 768         if let Abi::Scalar(field_ty_scalar) = field_ty_abi {
 769             match field_ty_scalar.valid_range(cx) {
 770                 WrappingRange { start: 0, end }
 771                     if end == field_ty_scalar.size(&cx.tcx).unsigned_int_max() - 1 =>
 772                 {
 773                     return Some(get_nullable_type(cx, field_ty).unwrap());
 774                 }
 775                 WrappingRange { start: 1, .. } => {
 776                     return Some(get_nullable_type(cx, field_ty).unwrap());
 777                 }
 778                 WrappingRange { start, end } => {
 779                     unreachable!("Unhandled start and end range: ({}, {})", start, end)
 780                 }
 781             };
 782         }
 783     }
 784     None
 785 }
 786
 787 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
 788     /// Check if the type is array and emit an unsafe type lint.
 789     fn check_for_array_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
 790         if let ty::Array(..) = ty.kind() {
 791             self.emit_ffi_unsafe_type_lint(
 792                 ty,
 793                 sp,
 794                 fluent::lint_improper_ctypes_array_reason,
 795                 Some(fluent::lint_improper_ctypes_array_help),
 796             );
 797             true
 798         } else {
 799             false
 800         }
 801     }
 802
 803     /// Checks if the given field's type is "ffi-safe".
 804     fn check_field_type_for_ffi(
 805         &self,
 806         cache: &mut FxHashSet<Ty<'tcx>>,
 807         field: &ty::FieldDef,
 808         substs: SubstsRef<'tcx>,
 809     ) -> FfiResult<'tcx> {
 810         let field_ty = field.ty(self.cx.tcx, substs);
 811         if field_ty.has_opaque_types() {
 812             self.check_type_for_ffi(cache, field_ty)
 813         } else {
 814             let field_ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, field_ty);
 815             self.check_type_for_ffi(cache, field_ty)
 816         }
 817     }
 818
 819     /// Checks if the given `VariantDef`'s field types are "ffi-safe".
 820     fn check_variant_for_ffi(
 821         &self,
 822         cache: &mut FxHashSet<Ty<'tcx>>,
 823         ty: Ty<'tcx>,
 824         def: ty::AdtDef<'tcx>,
 825         variant: &ty::VariantDef,
 826         substs: SubstsRef<'tcx>,
 827     ) -> FfiResult<'tcx> {
 828         use FfiResult::*;
 829
 830         let transparent_safety = def.repr().transparent().then(|| {
 831             // Can assume that at most one field is not a ZST, so only check
 832             // that field's type for FFI-safety.
 833             if let Some(field) = transparent_newtype_field(self.cx.tcx, variant) {
 834                 return self.check_field_type_for_ffi(cache, field, substs);
 835             } else {
 836                 // All fields are ZSTs; this means that the type should behave
 837                 // like (), which is FFI-unsafe... except if all fields are PhantomData,
 838                 // which is tested for below
 839                 FfiUnsafe { ty, reason: fluent::lint_improper_ctypes_struct_zst, help: None }
 840             }
 841         });
 842         // We can't completely trust repr(C) markings; make sure the fields are
 843         // actually safe.
 844         let mut all_phantom = !variant.fields.is_empty();
 845         for field in &variant.fields {
 846             match self.check_field_type_for_ffi(cache, &field, substs) {
 847                 FfiSafe => {
 848                     all_phantom = false;
 849                 }
 850                 FfiPhantom(..) if !def.repr().transparent() && def.is_enum() => {
 851                     return FfiUnsafe {
 852                         ty,
 853                         reason: fluent::lint_improper_ctypes_enum_phantomdata,
 854                         help: None,
 855                     };
 856                 }
 857                 FfiPhantom(..) => {}
 858                 r => return transparent_safety.unwrap_or(r),
 859             }
 860         }
 861
 862         if all_phantom { FfiPhantom(ty) } else { transparent_safety.unwrap_or(FfiSafe) }
 863     }
 864
 865     /// Checks if the given type is "ffi-safe" (has a stable, well-defined
 866     /// representation which can be exported to C code).
 867     fn check_type_for_ffi(&self, cache: &mut FxHashSet<Ty<'tcx>>, ty: Ty<'tcx>) -> FfiResult<'tcx> {
 868         use FfiResult::*;
 869
 870         let tcx = self.cx.tcx;
 871
 872         // Protect against infinite recursion, for example
 873         // `struct S(*mut S);`.
 874         // FIXME: A recursion limit is necessary as well, for irregular
 875         // recursive types.
 876         if !cache.insert(ty) {
 877             return FfiSafe;
 878         }
 879
 880         match *ty.kind() {
 881             ty::Adt(def, substs) => {
 882                 if def.is_box() && matches!(self.mode, CItemKind::Definition) {
 883                     if ty.boxed_ty().is_sized(tcx, self.cx.param_env) {
 884                         return FfiSafe;
 885                     } else {
 886                         return FfiUnsafe {
 887                             ty,
 888                             reason: fluent::lint_improper_ctypes_box,
 889                             help: None,
 890                         };
 891                     }
 892                 }
 893                 if def.is_phantom_data() {
 894                     return FfiPhantom(ty);
 895                 }
 896                 match def.adt_kind() {
 897                     AdtKind::Struct | AdtKind::Union => {
 898                         if !def.repr().c() && !def.repr().transparent() {
 899                             return FfiUnsafe {
 900                                 ty,
 901                                 reason: if def.is_struct() {
 902                                     fluent::lint_improper_ctypes_struct_layout_reason
 903                                 } else {
 904                                     fluent::lint_improper_ctypes_union_layout_reason
 905                                 },
 906                                 help: if def.is_struct() {
 907                                     Some(fluent::lint_improper_ctypes_struct_layout_help)
 908                                 } else {
 909                                     Some(fluent::lint_improper_ctypes_union_layout_help)
 910                                 },
 911                             };
 912                         }
 913
 914                         let is_non_exhaustive =
 915                             def.non_enum_variant().is_field_list_non_exhaustive();
 916                         if is_non_exhaustive && !def.did().is_local() {
 917                             return FfiUnsafe {
 918                                 ty,
 919                                 reason: if def.is_struct() {
 920                                     fluent::lint_improper_ctypes_struct_non_exhaustive
 921                                 } else {
 922                                     fluent::lint_improper_ctypes_union_non_exhaustive
 923                                 },
 924                                 help: None,
 925                             };
 926                         }
 927
 928                         if def.non_enum_variant().fields.is_empty() {
 929                             return FfiUnsafe {
 930                                 ty,
 931                                 reason: if def.is_struct() {
 932                                     fluent::lint_improper_ctypes_struct_fieldless_reason
 933                                 } else {
 934                                     fluent::lint_improper_ctypes_union_fieldless_reason
 935                                 },
 936                                 help: if def.is_struct() {
 937                                     Some(fluent::lint_improper_ctypes_struct_fieldless_help)
 938                                 } else {
 939                                     Some(fluent::lint_improper_ctypes_union_fieldless_help)
 940                                 },
 941                             };
 942                         }
 943
 944                         self.check_variant_for_ffi(cache, ty, def, def.non_enum_variant(), substs)
 945                     }
 946                     AdtKind::Enum => {
 947                         if def.variants().is_empty() {
 948                             // Empty enums are okay... although sort of useless.
 949                             return FfiSafe;
 950                         }
 951
 952                         // Check for a repr() attribute to specify the size of the
 953                         // discriminant.
 954                         if !def.repr().c() && !def.repr().transparent() && def.repr().int.is_none()
 955                         {
 956                             // Special-case types like `Option<extern fn()>`.
 957                             if repr_nullable_ptr(self.cx, ty, self.mode).is_none() {
 958                                 return FfiUnsafe {
 959                                     ty,
 960                                     reason: fluent::lint_improper_ctypes_enum_repr_reason,
 961                                     help: Some(fluent::lint_improper_ctypes_enum_repr_help),
 962                                 };
 963                             }
 964                         }
 965
 966                         if def.is_variant_list_non_exhaustive() && !def.did().is_local() {
 967                             return FfiUnsafe {
 968                                 ty,
 969                                 reason: fluent::lint_improper_ctypes_non_exhaustive,
 970                                 help: None,
 971                             };
 972                         }
 973
 974                         // Check the contained variants.
 975                         for variant in def.variants() {
 976                             let is_non_exhaustive = variant.is_field_list_non_exhaustive();
 977                             if is_non_exhaustive && !variant.def_id.is_local() {
 978                                 return FfiUnsafe {
 979                                     ty,
 980                                     reason: fluent::lint_improper_ctypes_non_exhaustive_variant,
 981                                     help: None,
 982                                 };
 983                             }
 984
 985                             match self.check_variant_for_ffi(cache, ty, def, variant, substs) {
 986                                 FfiSafe => (),
 987                                 r => return r,
 988                             }
 989                         }
 990
 991                         FfiSafe
 992                     }
 993                 }
 994             }
 995
 996             ty::Char => FfiUnsafe {
 997                 ty,
 998                 reason: fluent::lint_improper_ctypes_char_reason,
 999                 help: Some(fluent::lint_improper_ctypes_char_help),
1000             },
1001
1002             ty::Int(ty::IntTy::I128) | ty::Uint(ty::UintTy::U128) => {
1003                 FfiUnsafe { ty, reason: fluent::lint_improper_ctypes_128bit, help: None }
1004             }
1005
1006             // Primitive types with a stable representation.
1007             ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
1008
1009             ty::Slice(_) => FfiUnsafe {
1010                 ty,
1011                 reason: fluent::lint_improper_ctypes_slice_reason,
1012                 help: Some(fluent::lint_improper_ctypes_slice_help),
1013             },
1014
1015             ty::Dynamic(..) => {
1016                 FfiUnsafe { ty, reason: fluent::lint_improper_ctypes_dyn, help: None }
1017             }
1018
1019             ty::Str => FfiUnsafe {
1020                 ty,
1021                 reason: fluent::lint_improper_ctypes_str_reason,
1022                 help: Some(fluent::lint_improper_ctypes_str_help),
1023             },
1024
1025             ty::Tuple(..) => FfiUnsafe {
1026                 ty,
1027                 reason: fluent::lint_improper_ctypes_tuple_reason,
1028                 help: Some(fluent::lint_improper_ctypes_tuple_help),
1029             },
1030
1031             ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _)
1032                 if {
1033                     matches!(self.mode, CItemKind::Definition)
1034                         && ty.is_sized(self.cx.tcx, self.cx.param_env)
1035                 } =>
1036             {
1037                 FfiSafe
1038             }
1039
1040             ty::RawPtr(ty::TypeAndMut { ty, .. })
1041                 if match ty.kind() {
1042                     ty::Tuple(tuple) => tuple.is_empty(),
1043                     _ => false,
1044                 } =>
1045             {
1046                 FfiSafe
1047             }
1048
1049             ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _) => {
1050                 self.check_type_for_ffi(cache, ty)
1051             }
1052
1053             ty::Array(inner_ty, _) => self.check_type_for_ffi(cache, inner_ty),
1054
1055             ty::FnPtr(sig) => {
1056                 if self.is_internal_abi(sig.abi()) {
1057                     return FfiUnsafe {
1058                         ty,
1059                         reason: fluent::lint_improper_ctypes_fnptr_reason,
1060                         help: Some(fluent::lint_improper_ctypes_fnptr_help),
1061                     };
1062                 }
1063
1064                 let sig = tcx.erase_late_bound_regions(sig);
1065                 if !sig.output().is_unit() {
1066                     let r = self.check_type_for_ffi(cache, sig.output());
1067                     match r {
1068                         FfiSafe => {}
1069                         _ => {
1070                             return r;
1071                         }
1072                     }
1073                 }
1074                 for arg in sig.inputs() {
1075                     let r = self.check_type_for_ffi(cache, *arg);
1076                     match r {
1077                         FfiSafe => {}
1078                         _ => {
1079                             return r;
1080                         }
1081                     }
1082                 }
1083                 FfiSafe
1084             }
1085
1086             ty::Foreign(..) => FfiSafe,
1087
1088             // While opaque types are checked for earlier, if a projection in a struct field
1089             // normalizes to an opaque type, then it will reach this branch.
1090             ty::Alias(ty::Opaque, ..) => {
1091                 FfiUnsafe { ty, reason: fluent::lint_improper_ctypes_opaque, help: None }
1092             }
1093
1094             // `extern "C" fn` functions can have type parameters, which may or may not be FFI-safe,
1095             //  so they are currently ignored for the purposes of this lint.
1096             ty::Param(..) | ty::Alias(ty::Projection, ..)
1097                 if matches!(self.mode, CItemKind::Definition) =>
1098             {
1099                 FfiSafe
1100             }
1101
1102             ty::Param(..)
1103             | ty::Alias(ty::Projection, ..)
1104             | ty::Infer(..)
1105             | ty::Bound(..)
1106             | ty::Error(_)
1107             | ty::Closure(..)
1108             | ty::Generator(..)
1109             | ty::GeneratorWitness(..)
1110             | ty::Placeholder(..)
1111             | ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty),
1112         }
1113     }
1114
1115     fn emit_ffi_unsafe_type_lint(
1116         &mut self,
1117         ty: Ty<'tcx>,
1118         sp: Span,
1119         note: DiagnosticMessage,
1120         help: Option<DiagnosticMessage>,
1121     ) {
1122         let lint = match self.mode {
1123             CItemKind::Declaration => IMPROPER_CTYPES,
1124             CItemKind::Definition => IMPROPER_CTYPES_DEFINITIONS,
1125         };
1126         let desc = match self.mode {
1127             CItemKind::Declaration => "block",
1128             CItemKind::Definition => "fn",
1129         };
1130         let span_note = if let ty::Adt(def, _) = ty.kind()
1131             && let Some(sp) = self.cx.tcx.hir().span_if_local(def.did()) {
1132                 Some(sp)
1133             } else {
1134                 None
1135             };
1136         self.cx.emit_spanned_lint(
1137             lint,
1138             sp,
1139             ImproperCTypes { ty, desc, label: sp, help, note, span_note },
1140         );
1141     }
1142
1143     fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
1144         struct ProhibitOpaqueTypes;
1145         impl<'tcx> ty::visit::TypeVisitor<'tcx> for ProhibitOpaqueTypes {
1146             type BreakTy = Ty<'tcx>;
1147
1148             fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1149                 if !ty.has_opaque_types() {
1150                     return ControlFlow::Continue(());
1151                 }
1152
1153                 if let ty::Alias(ty::Opaque, ..) = ty.kind() {
1154                     ControlFlow::Break(ty)
1155                 } else {
1156                     ty.super_visit_with(self)
1157                 }
1158             }
1159         }
1160
1161         if let Some(ty) = self
1162             .cx
1163             .tcx
1164             .normalize_erasing_regions(self.cx.param_env, ty)
1165             .visit_with(&mut ProhibitOpaqueTypes)
1166             .break_value()
1167         {
1168             self.emit_ffi_unsafe_type_lint(ty, sp, fluent::lint_improper_ctypes_opaque, None);
1169             true
1170         } else {
1171             false
1172         }
1173     }
1174
1175     fn check_type_for_ffi_and_report_errors(
1176         &mut self,
1177         sp: Span,
1178         ty: Ty<'tcx>,
1179         is_static: bool,
1180         is_return_type: bool,
1181     ) {
1182         // We have to check for opaque types before `normalize_erasing_regions`,
1183         // which will replace opaque types with their underlying concrete type.
1184         if self.check_for_opaque_ty(sp, ty) {
1185             // We've already emitted an error due to an opaque type.
1186             return;
1187         }
1188
1189         // it is only OK to use this function because extern fns cannot have
1190         // any generic types right now:
1191         let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
1192
1193         // C doesn't really support passing arrays by value - the only way to pass an array by value
1194         // is through a struct. So, first test that the top level isn't an array, and then
1195         // recursively check the types inside.
1196         if !is_static && self.check_for_array_ty(sp, ty) {
1197             return;
1198         }
1199
1200         // Don't report FFI errors for unit return types. This check exists here, and not in
1201         // `check_foreign_fn` (where it would make more sense) so that normalization has definitely
1202         // happened.
1203         if is_return_type && ty.is_unit() {
1204             return;
1205         }
1206
1207         match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
1208             FfiResult::FfiSafe => {}
1209             FfiResult::FfiPhantom(ty) => {
1210                 self.emit_ffi_unsafe_type_lint(
1211                     ty,
1212                     sp,
1213                     fluent::lint_improper_ctypes_only_phantomdata,
1214                     None,
1215                 );
1216             }
1217             // If `ty` is a `repr(transparent)` newtype, and the non-zero-sized type is a generic
1218             // argument, which after substitution, is `()`, then this branch can be hit.
1219             FfiResult::FfiUnsafe { ty, .. } if is_return_type && ty.is_unit() => {}
1220             FfiResult::FfiUnsafe { ty, reason, help } => {
1221                 self.emit_ffi_unsafe_type_lint(ty, sp, reason, help);
1222             }
1223         }
1224     }
1225
1226     fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl<'_>) {
1227         let def_id = self.cx.tcx.hir().local_def_id(id);
1228         let sig = self.cx.tcx.fn_sig(def_id);
1229         let sig = self.cx.tcx.erase_late_bound_regions(sig);
1230
1231         for (input_ty, input_hir) in iter::zip(sig.inputs(), decl.inputs) {
1232             self.check_type_for_ffi_and_report_errors(input_hir.span, *input_ty, false, false);
1233         }
1234
1235         if let hir::FnRetTy::Return(ref ret_hir) = decl.output {
1236             let ret_ty = sig.output();
1237             self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty, false, true);
1238         }
1239     }
1240
1241     fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
1242         let def_id = self.cx.tcx.hir().local_def_id(id);
1243         let ty = self.cx.tcx.type_of(def_id);
1244         self.check_type_for_ffi_and_report_errors(span, ty, true, false);
1245     }
1246
1247     fn is_internal_abi(&self, abi: SpecAbi) -> bool {
1248         matches!(
1249             abi,
1250             SpecAbi::Rust | SpecAbi::RustCall | SpecAbi::RustIntrinsic | SpecAbi::PlatformIntrinsic
1251         )
1252     }
1253 }
1254
1255 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDeclarations {
1256     fn check_foreign_item(&mut self, cx: &LateContext<'_>, it: &hir::ForeignItem<'_>) {
1257         let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Declaration };
1258         let abi = cx.tcx.hir().get_foreign_abi(it.hir_id());
1259
1260         if !vis.is_internal_abi(abi) {
1261             match it.kind {
1262                 hir::ForeignItemKind::Fn(ref decl, _, _) => {
1263                     vis.check_foreign_fn(it.hir_id(), decl);
1264                 }
1265                 hir::ForeignItemKind::Static(ref ty, _) => {
1266                     vis.check_foreign_static(it.hir_id(), ty.span);
1267                 }
1268                 hir::ForeignItemKind::Type => (),
1269             }
1270         }
1271     }
1272 }
1273
1274 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDefinitions {
1275     fn check_fn(
1276         &mut self,
1277         cx: &LateContext<'tcx>,
1278         kind: hir::intravisit::FnKind<'tcx>,
1279         decl: &'tcx hir::FnDecl<'_>,
1280         _: &'tcx hir::Body<'_>,
1281         _: Span,
1282         hir_id: hir::HirId,
1283     ) {
1284         use hir::intravisit::FnKind;
1285
1286         let abi = match kind {
1287             FnKind::ItemFn(_, _, header, ..) => header.abi,
1288             FnKind::Method(_, sig, ..) => sig.header.abi,
1289             _ => return,
1290         };
1291
1292         let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Definition };
1293         if !vis.is_internal_abi(abi) {
1294             vis.check_foreign_fn(hir_id, decl);
1295         }
1296     }
1297 }
1298
1299 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
1300
1301 impl<'tcx> LateLintPass<'tcx> for VariantSizeDifferences {
1302     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1303         if let hir::ItemKind::Enum(ref enum_definition, _) = it.kind {
1304             let t = cx.tcx.type_of(it.owner_id);
1305             let ty = cx.tcx.erase_regions(t);
1306             let Ok(layout) = cx.layout_of(ty) else { return };
1307             let Variants::Multiple {
1308                     tag_encoding: TagEncoding::Direct, tag, ref variants, ..
1309                 } = &layout.variants else {
1310                 return
1311             };
1312
1313             let tag_size = tag.size(&cx.tcx).bytes();
1314
1315             debug!(
1316                 "enum `{}` is {} bytes large with layout:\n{:#?}",
1317                 t,
1318                 layout.size.bytes(),
1319                 layout
1320             );
1321
1322             let (largest, slargest, largest_index) = iter::zip(enum_definition.variants, variants)
1323                 .map(|(variant, variant_layout)| {
1324                     // Subtract the size of the enum tag.
1325                     let bytes = variant_layout.size.bytes().saturating_sub(tag_size);
1326
1327                     debug!("- variant `{}` is {} bytes large", variant.ident, bytes);
1328                     bytes
1329                 })
1330                 .enumerate()
1331                 .fold((0, 0, 0), |(l, s, li), (idx, size)| {
1332                     if size > l {
1333                         (size, l, idx)
1334                     } else if size > s {
1335                         (l, size, li)
1336                     } else {
1337                         (l, s, li)
1338                     }
1339                 });
1340
1341             // We only warn if the largest variant is at least thrice as large as
1342             // the second-largest.
1343             if largest > slargest * 3 && slargest > 0 {
1344                 cx.emit_spanned_lint(
1345                     VARIANT_SIZE_DIFFERENCES,
1346                     enum_definition.variants[largest_index].span,
1347                     VariantSizeDifferencesDiag { largest },
1348                 );
1349             }
1350         }
1351     }
1352 }
1353
1354 declare_lint! {
1355     /// The `invalid_atomic_ordering` lint detects passing an `Ordering`
1356     /// to an atomic operation that does not support that ordering.
1357     ///
1358     /// ### Example
1359     ///
1360     /// ```rust,compile_fail
1361     /// # use core::sync::atomic::{AtomicU8, Ordering};
1362     /// let atom = AtomicU8::new(0);
1363     /// let value = atom.load(Ordering::Release);
1364     /// # let _ = value;
1365     /// ```
1366     ///
1367     /// {{produces}}
1368     ///
1369     /// ### Explanation
1370     ///
1371     /// Some atomic operations are only supported for a subset of the
1372     /// `atomic::Ordering` variants. Passing an unsupported variant will cause
1373     /// an unconditional panic at runtime, which is detected by this lint.
1374     ///
1375     /// This lint will trigger in the following cases: (where `AtomicType` is an
1376     /// atomic type from `core::sync::atomic`, such as `AtomicBool`,
1377     /// `AtomicPtr`, `AtomicUsize`, or any of the other integer atomics).
1378     ///
1379     /// - Passing `Ordering::Acquire` or `Ordering::AcqRel` to
1380     ///   `AtomicType::store`.
1381     ///
1382     /// - Passing `Ordering::Release` or `Ordering::AcqRel` to
1383     ///   `AtomicType::load`.
1384     ///
1385     /// - Passing `Ordering::Relaxed` to `core::sync::atomic::fence` or
1386     ///   `core::sync::atomic::compiler_fence`.
1387     ///
1388     /// - Passing `Ordering::Release` or `Ordering::AcqRel` as the failure
1389     ///   ordering for any of `AtomicType::compare_exchange`,
1390     ///   `AtomicType::compare_exchange_weak`, or `AtomicType::fetch_update`.
1391     INVALID_ATOMIC_ORDERING,
1392     Deny,
1393     "usage of invalid atomic ordering in atomic operations and memory fences"
1394 }
1395
1396 declare_lint_pass!(InvalidAtomicOrdering => [INVALID_ATOMIC_ORDERING]);
1397
1398 impl InvalidAtomicOrdering {
1399     fn inherent_atomic_method_call<'hir>(
1400         cx: &LateContext<'_>,
1401         expr: &Expr<'hir>,
1402         recognized_names: &[Symbol], // used for fast path calculation
1403     ) -> Option<(Symbol, &'hir [Expr<'hir>])> {
1404         const ATOMIC_TYPES: &[Symbol] = &[
1405             sym::AtomicBool,
1406             sym::AtomicPtr,
1407             sym::AtomicUsize,
1408             sym::AtomicU8,
1409             sym::AtomicU16,
1410             sym::AtomicU32,
1411             sym::AtomicU64,
1412             sym::AtomicU128,
1413             sym::AtomicIsize,
1414             sym::AtomicI8,
1415             sym::AtomicI16,
1416             sym::AtomicI32,
1417             sym::AtomicI64,
1418             sym::AtomicI128,
1419         ];
1420         if let ExprKind::MethodCall(ref method_path, _, args, _) = &expr.kind
1421             && recognized_names.contains(&method_path.ident.name)
1422             && let Some(m_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id)
1423             && let Some(impl_did) = cx.tcx.impl_of_method(m_def_id)
1424             && let Some(adt) = cx.tcx.type_of(impl_did).ty_adt_def()
1425             // skip extension traits, only lint functions from the standard library
1426             && cx.tcx.trait_id_of_impl(impl_did).is_none()
1427             && let parent = cx.tcx.parent(adt.did())
1428             && cx.tcx.is_diagnostic_item(sym::atomic_mod, parent)
1429             && ATOMIC_TYPES.contains(&cx.tcx.item_name(adt.did()))
1430         {
1431             return Some((method_path.ident.name, args));
1432         }
1433         None
1434     }
1435
1436     fn match_ordering(cx: &LateContext<'_>, ord_arg: &Expr<'_>) -> Option<Symbol> {
1437         let ExprKind::Path(ref ord_qpath) = ord_arg.kind else { return None };
1438         let did = cx.qpath_res(ord_qpath, ord_arg.hir_id).opt_def_id()?;
1439         let tcx = cx.tcx;
1440         let atomic_ordering = tcx.get_diagnostic_item(sym::Ordering);
1441         let name = tcx.item_name(did);
1442         let parent = tcx.parent(did);
1443         [sym::Relaxed, sym::Release, sym::Acquire, sym::AcqRel, sym::SeqCst].into_iter().find(
1444             |&ordering| {
1445                 name == ordering
1446                     && (Some(parent) == atomic_ordering
1447                             // needed in case this is a ctor, not a variant
1448                             || tcx.opt_parent(parent) == atomic_ordering)
1449             },
1450         )
1451     }
1452
1453     fn check_atomic_load_store(cx: &LateContext<'_>, expr: &Expr<'_>) {
1454         if let Some((method, args)) = Self::inherent_atomic_method_call(cx, expr, &[sym::load, sym::store])
1455             && let Some((ordering_arg, invalid_ordering)) = match method {
1456                 sym::load => Some((&args[0], sym::Release)),
1457                 sym::store => Some((&args[1], sym::Acquire)),
1458                 _ => None,
1459             }
1460             && let Some(ordering) = Self::match_ordering(cx, ordering_arg)
1461             && (ordering == invalid_ordering || ordering == sym::AcqRel)
1462         {
1463             if method == sym::load {
1464                 cx.emit_spanned_lint(INVALID_ATOMIC_ORDERING, ordering_arg.span, AtomicOrderingLoad);
1465             } else {
1466                 cx.emit_spanned_lint(INVALID_ATOMIC_ORDERING, ordering_arg.span, AtomicOrderingStore);
1467             };
1468         }
1469     }
1470
1471     fn check_memory_fence(cx: &LateContext<'_>, expr: &Expr<'_>) {
1472         if let ExprKind::Call(ref func, ref args) = expr.kind
1473             && let ExprKind::Path(ref func_qpath) = func.kind
1474             && let Some(def_id) = cx.qpath_res(func_qpath, func.hir_id).opt_def_id()
1475             && matches!(cx.tcx.get_diagnostic_name(def_id), Some(sym::fence | sym::compiler_fence))
1476             && Self::match_ordering(cx, &args[0]) == Some(sym::Relaxed)
1477         {
1478             cx.emit_spanned_lint(INVALID_ATOMIC_ORDERING, args[0].span, AtomicOrderingFence);
1479         }
1480     }
1481
1482     fn check_atomic_compare_exchange(cx: &LateContext<'_>, expr: &Expr<'_>) {
1483         let Some((method, args)) = Self::inherent_atomic_method_call(cx, expr, &[sym::fetch_update, sym::compare_exchange, sym::compare_exchange_weak])
1484             else {return };
1485
1486         let fail_order_arg = match method {
1487             sym::fetch_update => &args[1],
1488             sym::compare_exchange | sym::compare_exchange_weak => &args[3],
1489             _ => return,
1490         };
1491
1492         let Some(fail_ordering) = Self::match_ordering(cx, fail_order_arg) else { return };
1493
1494         if matches!(fail_ordering, sym::Release | sym::AcqRel) {
1495             cx.emit_spanned_lint(
1496                 INVALID_ATOMIC_ORDERING,
1497                 fail_order_arg.span,
1498                 InvalidAtomicOrderingDiag { method, fail_order_arg_span: fail_order_arg.span },
1499             );
1500         }
1501     }
1502 }
1503
1504 impl<'tcx> LateLintPass<'tcx> for InvalidAtomicOrdering {
1505     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
1506         Self::check_atomic_load_store(cx, expr);
1507         Self::check_memory_fence(cx, expr);
1508         Self::check_atomic_compare_exchange(cx, expr);
1509     }
1510 }