compiler/rustc_lint/src/types.rs

   1 use crate::{LateContext, LateLintPass, LintContext};
   2 use rustc_ast as ast;
   3 use rustc_attr as attr;
   4 use rustc_data_structures::fx::FxHashSet;
   5 use rustc_errors::{fluent, Applicability, DiagnosticMessage};
   6 use rustc_hir as hir;
   7 use rustc_hir::{is_range_literal, Expr, ExprKind, Node};
   8 use rustc_macros::LintDiagnostic;
   9 use rustc_middle::ty::layout::{IntegerExt, LayoutOf, SizeSkeleton};
  10 use rustc_middle::ty::subst::SubstsRef;
  11 use rustc_middle::ty::{self, AdtKind, DefIdTree, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable};
  12 use rustc_span::source_map;
  13 use rustc_span::symbol::sym;
  14 use rustc_span::{Span, Symbol};
  15 use rustc_target::abi::{Abi, Size, WrappingRange};
  16 use rustc_target::abi::{Integer, TagEncoding, Variants};
  17 use rustc_target::spec::abi::Abi as SpecAbi;
  18
  19 use std::cmp;
  20 use std::iter;
  21 use std::ops::ControlFlow;
  22
  23 declare_lint! {
  24     /// The `unused_comparisons` lint detects comparisons made useless by
  25     /// limits of the types involved.
  26     ///
  27     /// ### Example
  28     ///
  29     /// ```rust
  30     /// fn foo(x: u8) {
  31     ///     x >= 0;
  32     /// }
  33     /// ```
  34     ///
  35     /// {{produces}}
  36     ///
  37     /// ### Explanation
  38     ///
  39     /// A useless comparison may indicate a mistake, and should be fixed or
  40     /// removed.
  41     UNUSED_COMPARISONS,
  42     Warn,
  43     "comparisons made useless by limits of the types involved"
  44 }
  45
  46 declare_lint! {
  47     /// The `overflowing_literals` lint detects literal out of range for its
  48     /// type.
  49     ///
  50     /// ### Example
  51     ///
  52     /// ```rust,compile_fail
  53     /// let x: u8 = 1000;
  54     /// ```
  55     ///
  56     /// {{produces}}
  57     ///
  58     /// ### Explanation
  59     ///
  60     /// It is usually a mistake to use a literal that overflows the type where
  61     /// it is used. Either use a literal that is within range, or change the
  62     /// type to be within the range of the literal.
  63     OVERFLOWING_LITERALS,
  64     Deny,
  65     "literal out of range for its type"
  66 }
  67
  68 declare_lint! {
  69     /// The `variant_size_differences` lint detects enums with widely varying
  70     /// variant sizes.
  71     ///
  72     /// ### Example
  73     ///
  74     /// ```rust,compile_fail
  75     /// #![deny(variant_size_differences)]
  76     /// enum En {
  77     ///     V0(u8),
  78     ///     VBig([u8; 1024]),
  79     /// }
  80     /// ```
  81     ///
  82     /// {{produces}}
  83     ///
  84     /// ### Explanation
  85     ///
  86     /// It can be a mistake to add a variant to an enum that is much larger
  87     /// than the other variants, bloating the overall size required for all
  88     /// variants. This can impact performance and memory usage. This is
  89     /// triggered if one variant is more than 3 times larger than the
  90     /// second-largest variant.
  91     ///
  92     /// Consider placing the large variant's contents on the heap (for example
  93     /// via [`Box`]) to keep the overall size of the enum itself down.
  94     ///
  95     /// This lint is "allow" by default because it can be noisy, and may not be
  96     /// an actual problem. Decisions about this should be guided with
  97     /// profiling and benchmarking.
  98     ///
  99     /// [`Box`]: https://doc.rust-lang.org/std/boxed/index.html
 100     VARIANT_SIZE_DIFFERENCES,
 101     Allow,
 102     "detects enums with widely varying variant sizes"
 103 }
 104
 105 #[derive(Copy, Clone)]
 106 pub struct TypeLimits {
 107     /// Id of the last visited negated expression
 108     negated_expr_id: Option<hir::HirId>,
 109 }
 110
 111 impl_lint_pass!(TypeLimits => [UNUSED_COMPARISONS, OVERFLOWING_LITERALS]);
 112
 113 impl TypeLimits {
 114     pub fn new() -> TypeLimits {
 115         TypeLimits { negated_expr_id: None }
 116     }
 117 }
 118
 119 /// Attempts to special-case the overflowing literal lint when it occurs as a range endpoint (`expr..MAX+1`).
 120 /// Returns `true` iff the lint was emitted.
 121 fn lint_overflowing_range_endpoint<'tcx>(
 122     cx: &LateContext<'tcx>,
 123     lit: &hir::Lit,
 124     lit_val: u128,
 125     max: u128,
 126     expr: &'tcx hir::Expr<'tcx>,
 127     ty: &str,
 128 ) -> bool {
 129     // We only want to handle exclusive (`..`) ranges,
 130     // which are represented as `ExprKind::Struct`.
 131     let par_id = cx.tcx.hir().get_parent_node(expr.hir_id);
 132     let Node::ExprField(field) = cx.tcx.hir().get(par_id) else { return false };
 133     let field_par_id = cx.tcx.hir().get_parent_node(field.hir_id);
 134     let Node::Expr(struct_expr) = cx.tcx.hir().get(field_par_id) else { return false };
 135     if !is_range_literal(struct_expr) {
 136         return false;
 137     };
 138     let ExprKind::Struct(_, eps, _) = &struct_expr.kind else { return false };
 139     if eps.len() != 2 {
 140         return false;
 141     }
 142
 143     // We can suggest using an inclusive range
 144     // (`..=`) instead only if it is the `end` that is
 145     // overflowing and only by 1.
 146     if !(eps[1].expr.hir_id == expr.hir_id && lit_val - 1 == max) {
 147         return false;
 148     };
 149     let Ok(start) = cx.sess().source_map().span_to_snippet(eps[0].span) else { return false };
 150
 151     cx.struct_span_lint(
 152         OVERFLOWING_LITERALS,
 153         struct_expr.span,
 154         fluent::lint_range_endpoint_out_of_range,
 155         |lint| {
 156             use ast::{LitIntType, LitKind};
 157
 158             lint.set_arg("ty", ty);
 159
 160             // We need to preserve the literal's suffix,
 161             // as it may determine typing information.
 162             let suffix = match lit.node {
 163                 LitKind::Int(_, LitIntType::Signed(s)) => s.name_str(),
 164                 LitKind::Int(_, LitIntType::Unsigned(s)) => s.name_str(),
 165                 LitKind::Int(_, LitIntType::Unsuffixed) => "",
 166                 _ => bug!(),
 167             };
 168             let suggestion = format!("{}..={}{}", start, lit_val - 1, suffix);
 169             lint.span_suggestion(
 170                 struct_expr.span,
 171                 fluent::suggestion,
 172                 suggestion,
 173                 Applicability::MachineApplicable,
 174             );
 175
 176             lint
 177         },
 178     );
 179
 180     // We've just emitted a lint, special cased for `(...)..MAX+1` ranges,
 181     // return `true` so the callers don't also emit a lint
 182     true
 183 }
 184
 185 // For `isize` & `usize`, be conservative with the warnings, so that the
 186 // warnings are consistent between 32- and 64-bit platforms.
 187 fn int_ty_range(int_ty: ty::IntTy) -> (i128, i128) {
 188     match int_ty {
 189         ty::IntTy::Isize => (i64::MIN.into(), i64::MAX.into()),
 190         ty::IntTy::I8 => (i8::MIN.into(), i8::MAX.into()),
 191         ty::IntTy::I16 => (i16::MIN.into(), i16::MAX.into()),
 192         ty::IntTy::I32 => (i32::MIN.into(), i32::MAX.into()),
 193         ty::IntTy::I64 => (i64::MIN.into(), i64::MAX.into()),
 194         ty::IntTy::I128 => (i128::MIN, i128::MAX),
 195     }
 196 }
 197
 198 fn uint_ty_range(uint_ty: ty::UintTy) -> (u128, u128) {
 199     let max = match uint_ty {
 200         ty::UintTy::Usize => u64::MAX.into(),
 201         ty::UintTy::U8 => u8::MAX.into(),
 202         ty::UintTy::U16 => u16::MAX.into(),
 203         ty::UintTy::U32 => u32::MAX.into(),
 204         ty::UintTy::U64 => u64::MAX.into(),
 205         ty::UintTy::U128 => u128::MAX,
 206     };
 207     (0, max)
 208 }
 209
 210 fn get_bin_hex_repr(cx: &LateContext<'_>, lit: &hir::Lit) -> Option<String> {
 211     let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?;
 212     let firstch = src.chars().next()?;
 213
 214     if firstch == '0' {
 215         match src.chars().nth(1) {
 216             Some('x' | 'b') => return Some(src),
 217             _ => return None,
 218         }
 219     }
 220
 221     None
 222 }
 223
 224 fn report_bin_hex_error(
 225     cx: &LateContext<'_>,
 226     expr: &hir::Expr<'_>,
 227     ty: attr::IntType,
 228     size: Size,
 229     repr_str: String,
 230     val: u128,
 231     negative: bool,
 232 ) {
 233     cx.struct_span_lint(
 234         OVERFLOWING_LITERALS,
 235         expr.span,
 236         fluent::lint_overflowing_bin_hex,
 237         |lint| {
 238             let (t, actually) = match ty {
 239                 attr::IntType::SignedInt(t) => {
 240                     let actually = if negative {
 241                         -(size.sign_extend(val) as i128)
 242                     } else {
 243                         size.sign_extend(val) as i128
 244                     };
 245                     (t.name_str(), actually.to_string())
 246                 }
 247                 attr::IntType::UnsignedInt(t) => {
 248                     let actually = size.truncate(val);
 249                     (t.name_str(), actually.to_string())
 250                 }
 251             };
 252
 253             if negative {
 254                 // If the value is negative,
 255                 // emits a note about the value itself, apart from the literal.
 256                 lint.note(fluent::negative_note);
 257                 lint.note(fluent::negative_becomes_note);
 258             } else {
 259                 lint.note(fluent::positive_note);
 260             }
 261             if let Some(sugg_ty) =
 262                 get_type_suggestion(cx.typeck_results().node_type(expr.hir_id), val, negative)
 263             {
 264                 lint.set_arg("suggestion_ty", sugg_ty);
 265                 if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') {
 266                     let (sans_suffix, _) = repr_str.split_at(pos);
 267                     lint.span_suggestion(
 268                         expr.span,
 269                         fluent::suggestion,
 270                         format!("{}{}", sans_suffix, sugg_ty),
 271                         Applicability::MachineApplicable,
 272                     );
 273                 } else {
 274                     lint.help(fluent::help);
 275                 }
 276             }
 277             lint.set_arg("ty", t)
 278                 .set_arg("lit", repr_str)
 279                 .set_arg("dec", val)
 280                 .set_arg("actually", actually);
 281
 282             lint
 283         },
 284     );
 285 }
 286
 287 // This function finds the next fitting type and generates a suggestion string.
 288 // It searches for fitting types in the following way (`X < Y`):
 289 //  - `iX`: if literal fits in `uX` => `uX`, else => `iY`
 290 //  - `-iX` => `iY`
 291 //  - `uX` => `uY`
 292 //
 293 // No suggestion for: `isize`, `usize`.
 294 fn get_type_suggestion(t: Ty<'_>, val: u128, negative: bool) -> Option<&'static str> {
 295     use ty::IntTy::*;
 296     use ty::UintTy::*;
 297     macro_rules! find_fit {
 298         ($ty:expr, $val:expr, $negative:expr,
 299          $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => {
 300             {
 301                 let _neg = if negative { 1 } else { 0 };
 302                 match $ty {
 303                     $($type => {
 304                         $(if !negative && val <= uint_ty_range($utypes).1 {
 305                             return Some($utypes.name_str())
 306                         })*
 307                         $(if val <= int_ty_range($itypes).1 as u128 + _neg {
 308                             return Some($itypes.name_str())
 309                         })*
 310                         None
 311                     },)+
 312                     _ => None
 313                 }
 314             }
 315         }
 316     }
 317     match t.kind() {
 318         ty::Int(i) => find_fit!(i, val, negative,
 319                       I8 => [U8] => [I16, I32, I64, I128],
 320                       I16 => [U16] => [I32, I64, I128],
 321                       I32 => [U32] => [I64, I128],
 322                       I64 => [U64] => [I128],
 323                       I128 => [U128] => []),
 324         ty::Uint(u) => find_fit!(u, val, negative,
 325                       U8 => [U8, U16, U32, U64, U128] => [],
 326                       U16 => [U16, U32, U64, U128] => [],
 327                       U32 => [U32, U64, U128] => [],
 328                       U64 => [U64, U128] => [],
 329                       U128 => [U128] => []),
 330         _ => None,
 331     }
 332 }
 333
 334 fn lint_int_literal<'tcx>(
 335     cx: &LateContext<'tcx>,
 336     type_limits: &TypeLimits,
 337     e: &'tcx hir::Expr<'tcx>,
 338     lit: &hir::Lit,
 339     t: ty::IntTy,
 340     v: u128,
 341 ) {
 342     let int_type = t.normalize(cx.sess().target.pointer_width);
 343     let (min, max) = int_ty_range(int_type);
 344     let max = max as u128;
 345     let negative = type_limits.negated_expr_id == Some(e.hir_id);
 346
 347     // Detect literal value out of range [min, max] inclusive
 348     // avoiding use of -min to prevent overflow/panic
 349     if (negative && v > max + 1) || (!negative && v > max) {
 350         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 351             report_bin_hex_error(
 352                 cx,
 353                 e,
 354                 attr::IntType::SignedInt(ty::ast_int_ty(t)),
 355                 Integer::from_int_ty(cx, t).size(),
 356                 repr_str,
 357                 v,
 358                 negative,
 359             );
 360             return;
 361         }
 362
 363         if lint_overflowing_range_endpoint(cx, lit, v, max, e, t.name_str()) {
 364             // The overflowing literal lint was emitted by `lint_overflowing_range_endpoint`.
 365             return;
 366         }
 367
 368         cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, fluent::lint_overflowing_int, |lint| {
 369             lint.set_arg("ty", t.name_str())
 370                 .set_arg(
 371                     "lit",
 372                     cx.sess()
 373                         .source_map()
 374                         .span_to_snippet(lit.span)
 375                         .expect("must get snippet from literal"),
 376                 )
 377                 .set_arg("min", min)
 378                 .set_arg("max", max)
 379                 .note(fluent::note);
 380
 381             if let Some(sugg_ty) =
 382                 get_type_suggestion(cx.typeck_results().node_type(e.hir_id), v, negative)
 383             {
 384                 lint.set_arg("suggestion_ty", sugg_ty);
 385                 lint.help(fluent::help);
 386             }
 387
 388             lint
 389         });
 390     }
 391 }
 392
 393 fn lint_uint_literal<'tcx>(
 394     cx: &LateContext<'tcx>,
 395     e: &'tcx hir::Expr<'tcx>,
 396     lit: &hir::Lit,
 397     t: ty::UintTy,
 398 ) {
 399     let uint_type = t.normalize(cx.sess().target.pointer_width);
 400     let (min, max) = uint_ty_range(uint_type);
 401     let lit_val: u128 = match lit.node {
 402         // _v is u8, within range by definition
 403         ast::LitKind::Byte(_v) => return,
 404         ast::LitKind::Int(v, _) => v,
 405         _ => bug!(),
 406     };
 407     if lit_val < min || lit_val > max {
 408         let parent_id = cx.tcx.hir().get_parent_node(e.hir_id);
 409         if let Node::Expr(par_e) = cx.tcx.hir().get(parent_id) {
 410             match par_e.kind {
 411                 hir::ExprKind::Cast(..) => {
 412                     if let ty::Char = cx.typeck_results().expr_ty(par_e).kind() {
 413                         cx.struct_span_lint(
 414                             OVERFLOWING_LITERALS,
 415                             par_e.span,
 416                             fluent::lint_only_cast_u8_to_char,
 417                             |lint| {
 418                                 lint.span_suggestion(
 419                                     par_e.span,
 420                                     fluent::suggestion,
 421                                     format!("'\\u{{{:X}}}'", lit_val),
 422                                     Applicability::MachineApplicable,
 423                                 )
 424                             },
 425                         );
 426                         return;
 427                     }
 428                 }
 429                 _ => {}
 430             }
 431         }
 432         if lint_overflowing_range_endpoint(cx, lit, lit_val, max, e, t.name_str()) {
 433             // The overflowing literal lint was emitted by `lint_overflowing_range_endpoint`.
 434             return;
 435         }
 436         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 437             report_bin_hex_error(
 438                 cx,
 439                 e,
 440                 attr::IntType::UnsignedInt(ty::ast_uint_ty(t)),
 441                 Integer::from_uint_ty(cx, t).size(),
 442                 repr_str,
 443                 lit_val,
 444                 false,
 445             );
 446             return;
 447         }
 448         cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, fluent::lint_overflowing_uint, |lint| {
 449             lint.set_arg("ty", t.name_str())
 450                 .set_arg(
 451                     "lit",
 452                     cx.sess()
 453                         .source_map()
 454                         .span_to_snippet(lit.span)
 455                         .expect("must get snippet from literal"),
 456                 )
 457                 .set_arg("min", min)
 458                 .set_arg("max", max)
 459                 .note(fluent::note)
 460         });
 461     }
 462 }
 463
 464 fn lint_literal<'tcx>(
 465     cx: &LateContext<'tcx>,
 466     type_limits: &TypeLimits,
 467     e: &'tcx hir::Expr<'tcx>,
 468     lit: &hir::Lit,
 469 ) {
 470     match *cx.typeck_results().node_type(e.hir_id).kind() {
 471         ty::Int(t) => {
 472             match lit.node {
 473                 ast::LitKind::Int(v, ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed) => {
 474                     lint_int_literal(cx, type_limits, e, lit, t, v)
 475                 }
 476                 _ => bug!(),
 477             };
 478         }
 479         ty::Uint(t) => lint_uint_literal(cx, e, lit, t),
 480         ty::Float(t) => {
 481             let is_infinite = match lit.node {
 482                 ast::LitKind::Float(v, _) => match t {
 483                     ty::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
 484                     ty::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
 485                 },
 486                 _ => bug!(),
 487             };
 488             if is_infinite == Ok(true) {
 489                 cx.struct_span_lint(
 490                     OVERFLOWING_LITERALS,
 491                     e.span,
 492                     fluent::lint_overflowing_literal,
 493                     |lint| {
 494                         lint.set_arg("ty", t.name_str())
 495                             .set_arg(
 496                                 "lit",
 497                                 cx.sess()
 498                                     .source_map()
 499                                     .span_to_snippet(lit.span)
 500                                     .expect("must get snippet from literal"),
 501                             )
 502                             .note(fluent::note)
 503                     },
 504                 );
 505             }
 506         }
 507         _ => {}
 508     }
 509 }
 510
 511 impl<'tcx> LateLintPass<'tcx> for TypeLimits {
 512     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx hir::Expr<'tcx>) {
 513         match e.kind {
 514             hir::ExprKind::Unary(hir::UnOp::Neg, ref expr) => {
 515                 // propagate negation, if the negation itself isn't negated
 516                 if self.negated_expr_id != Some(e.hir_id) {
 517                     self.negated_expr_id = Some(expr.hir_id);
 518                 }
 519             }
 520             hir::ExprKind::Binary(binop, ref l, ref r) => {
 521                 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
 522                     cx.struct_span_lint(
 523                         UNUSED_COMPARISONS,
 524                         e.span,
 525                         fluent::lint_unused_comparisons,
 526                         |lint| lint,
 527                     );
 528                 }
 529             }
 530             hir::ExprKind::Lit(ref lit) => lint_literal(cx, self, e, lit),
 531             _ => {}
 532         };
 533
 534         fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
 535             match binop.node {
 536                 hir::BinOpKind::Lt => v > min && v <= max,
 537                 hir::BinOpKind::Le => v >= min && v < max,
 538                 hir::BinOpKind::Gt => v >= min && v < max,
 539                 hir::BinOpKind::Ge => v > min && v <= max,
 540                 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
 541                 _ => bug!(),
 542             }
 543         }
 544
 545         fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
 546             source_map::respan(
 547                 binop.span,
 548                 match binop.node {
 549                     hir::BinOpKind::Lt => hir::BinOpKind::Gt,
 550                     hir::BinOpKind::Le => hir::BinOpKind::Ge,
 551                     hir::BinOpKind::Gt => hir::BinOpKind::Lt,
 552                     hir::BinOpKind::Ge => hir::BinOpKind::Le,
 553                     _ => return binop,
 554                 },
 555             )
 556         }
 557
 558         fn check_limits(
 559             cx: &LateContext<'_>,
 560             binop: hir::BinOp,
 561             l: &hir::Expr<'_>,
 562             r: &hir::Expr<'_>,
 563         ) -> bool {
 564             let (lit, expr, swap) = match (&l.kind, &r.kind) {
 565                 (&hir::ExprKind::Lit(_), _) => (l, r, true),
 566                 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
 567                 _ => return true,
 568             };
 569             // Normalize the binop so that the literal is always on the RHS in
 570             // the comparison
 571             let norm_binop = if swap { rev_binop(binop) } else { binop };
 572             match *cx.typeck_results().node_type(expr.hir_id).kind() {
 573                 ty::Int(int_ty) => {
 574                     let (min, max) = int_ty_range(int_ty);
 575                     let lit_val: i128 = match lit.kind {
 576                         hir::ExprKind::Lit(ref li) => match li.node {
 577                             ast::LitKind::Int(
 578                                 v,
 579                                 ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed,
 580                             ) => v as i128,
 581                             _ => return true,
 582                         },
 583                         _ => bug!(),
 584                     };
 585                     is_valid(norm_binop, lit_val, min, max)
 586                 }
 587                 ty::Uint(uint_ty) => {
 588                     let (min, max): (u128, u128) = uint_ty_range(uint_ty);
 589                     let lit_val: u128 = match lit.kind {
 590                         hir::ExprKind::Lit(ref li) => match li.node {
 591                             ast::LitKind::Int(v, _) => v,
 592                             _ => return true,
 593                         },
 594                         _ => bug!(),
 595                     };
 596                     is_valid(norm_binop, lit_val, min, max)
 597                 }
 598                 _ => true,
 599             }
 600         }
 601
 602         fn is_comparison(binop: hir::BinOp) -> bool {
 603             matches!(
 604                 binop.node,
 605                 hir::BinOpKind::Eq
 606                     | hir::BinOpKind::Lt
 607                     | hir::BinOpKind::Le
 608                     | hir::BinOpKind::Ne
 609                     | hir::BinOpKind::Ge
 610                     | hir::BinOpKind::Gt
 611             )
 612         }
 613     }
 614 }
 615
 616 declare_lint! {
 617     /// The `improper_ctypes` lint detects incorrect use of types in foreign
 618     /// modules.
 619     ///
 620     /// ### Example
 621     ///
 622     /// ```rust
 623     /// extern "C" {
 624     ///     static STATIC: String;
 625     /// }
 626     /// ```
 627     ///
 628     /// {{produces}}
 629     ///
 630     /// ### Explanation
 631     ///
 632     /// The compiler has several checks to verify that types used in `extern`
 633     /// blocks are safe and follow certain rules to ensure proper
 634     /// compatibility with the foreign interfaces. This lint is issued when it
 635     /// detects a probable mistake in a definition. The lint usually should
 636     /// provide a description of the issue, along with possibly a hint on how
 637     /// to resolve it.
 638     IMPROPER_CTYPES,
 639     Warn,
 640     "proper use of libc types in foreign modules"
 641 }
 642
 643 declare_lint_pass!(ImproperCTypesDeclarations => [IMPROPER_CTYPES]);
 644
 645 declare_lint! {
 646     /// The `improper_ctypes_definitions` lint detects incorrect use of
 647     /// [`extern` function] definitions.
 648     ///
 649     /// [`extern` function]: https://doc.rust-lang.org/reference/items/functions.html#extern-function-qualifier
 650     ///
 651     /// ### Example
 652     ///
 653     /// ```rust
 654     /// # #![allow(unused)]
 655     /// pub extern "C" fn str_type(p: &str) { }
 656     /// ```
 657     ///
 658     /// {{produces}}
 659     ///
 660     /// ### Explanation
 661     ///
 662     /// There are many parameter and return types that may be specified in an
 663     /// `extern` function that are not compatible with the given ABI. This
 664     /// lint is an alert that these types should not be used. The lint usually
 665     /// should provide a description of the issue, along with possibly a hint
 666     /// on how to resolve it.
 667     IMPROPER_CTYPES_DEFINITIONS,
 668     Warn,
 669     "proper use of libc types in foreign item definitions"
 670 }
 671
 672 declare_lint_pass!(ImproperCTypesDefinitions => [IMPROPER_CTYPES_DEFINITIONS]);
 673
 674 #[derive(Clone, Copy)]
 675 pub(crate) enum CItemKind {
 676     Declaration,
 677     Definition,
 678 }
 679
 680 struct ImproperCTypesVisitor<'a, 'tcx> {
 681     cx: &'a LateContext<'tcx>,
 682     mode: CItemKind,
 683 }
 684
 685 enum FfiResult<'tcx> {
 686     FfiSafe,
 687     FfiPhantom(Ty<'tcx>),
 688     FfiUnsafe { ty: Ty<'tcx>, reason: DiagnosticMessage, help: Option<DiagnosticMessage> },
 689 }
 690
 691 pub(crate) fn nonnull_optimization_guaranteed<'tcx>(
 692     tcx: TyCtxt<'tcx>,
 693     def: ty::AdtDef<'tcx>,
 694 ) -> bool {
 695     tcx.has_attr(def.did(), sym::rustc_nonnull_optimization_guaranteed)
 696 }
 697
 698 /// `repr(transparent)` structs can have a single non-ZST field, this function returns that
 699 /// field.
 700 pub fn transparent_newtype_field<'a, 'tcx>(
 701     tcx: TyCtxt<'tcx>,
 702     variant: &'a ty::VariantDef,
 703 ) -> Option<&'a ty::FieldDef> {
 704     let param_env = tcx.param_env(variant.def_id);
 705     variant.fields.iter().find(|field| {
 706         let field_ty = tcx.type_of(field.did);
 707         let is_zst = tcx.layout_of(param_env.and(field_ty)).map_or(false, |layout| layout.is_zst());
 708         !is_zst
 709     })
 710 }
 711
 712 /// Is type known to be non-null?
 713 fn ty_is_known_nonnull<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, mode: CItemKind) -> bool {
 714     let tcx = cx.tcx;
 715     match ty.kind() {
 716         ty::FnPtr(_) => true,
 717         ty::Ref(..) => true,
 718         ty::Adt(def, _) if def.is_box() && matches!(mode, CItemKind::Definition) => true,
 719         ty::Adt(def, substs) if def.repr().transparent() && !def.is_union() => {
 720             let marked_non_null = nonnull_optimization_guaranteed(tcx, *def);
 721
 722             if marked_non_null {
 723                 return true;
 724             }
 725
 726             // `UnsafeCell` has its niche hidden.
 727             if def.is_unsafe_cell() {
 728                 return false;
 729             }
 730
 731             def.variants()
 732                 .iter()
 733                 .filter_map(|variant| transparent_newtype_field(cx.tcx, variant))
 734                 .any(|field| ty_is_known_nonnull(cx, field.ty(tcx, substs), mode))
 735         }
 736         _ => false,
 737     }
 738 }
 739
 740 /// Given a non-null scalar (or transparent) type `ty`, return the nullable version of that type.
 741 /// If the type passed in was not scalar, returns None.
 742 fn get_nullable_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
 743     let tcx = cx.tcx;
 744     Some(match *ty.kind() {
 745         ty::Adt(field_def, field_substs) => {
 746             let inner_field_ty = {
 747                 let mut first_non_zst_ty = field_def
 748                     .variants()
 749                     .iter()
 750                     .filter_map(|v| transparent_newtype_field(cx.tcx, v));
 751                 debug_assert_eq!(
 752                     first_non_zst_ty.clone().count(),
 753                     1,
 754                     "Wrong number of fields for transparent type"
 755                 );
 756                 first_non_zst_ty
 757                     .next_back()
 758                     .expect("No non-zst fields in transparent type.")
 759                     .ty(tcx, field_substs)
 760             };
 761             return get_nullable_type(cx, inner_field_ty);
 762         }
 763         ty::Int(ty) => tcx.mk_mach_int(ty),
 764         ty::Uint(ty) => tcx.mk_mach_uint(ty),
 765         ty::RawPtr(ty_mut) => tcx.mk_ptr(ty_mut),
 766         // As these types are always non-null, the nullable equivalent of
 767         // Option<T> of these types are their raw pointer counterparts.
 768         ty::Ref(_region, ty, mutbl) => tcx.mk_ptr(ty::TypeAndMut { ty, mutbl }),
 769         ty::FnPtr(..) => {
 770             // There is no nullable equivalent for Rust's function pointers -- you
 771             // must use an Option<fn(..) -> _> to represent it.
 772             ty
 773         }
 774
 775         // We should only ever reach this case if ty_is_known_nonnull is extended
 776         // to other types.
 777         ref unhandled => {
 778             debug!(
 779                 "get_nullable_type: Unhandled scalar kind: {:?} while checking {:?}",
 780                 unhandled, ty
 781             );
 782             return None;
 783         }
 784     })
 785 }
 786
 787 /// Check if this enum can be safely exported based on the "nullable pointer optimization". If it
 788 /// can, return the type that `ty` can be safely converted to, otherwise return `None`.
 789 /// Currently restricted to function pointers, boxes, references, `core::num::NonZero*`,
 790 /// `core::ptr::NonNull`, and `#[repr(transparent)]` newtypes.
 791 /// FIXME: This duplicates code in codegen.
 792 pub(crate) fn repr_nullable_ptr<'tcx>(
 793     cx: &LateContext<'tcx>,
 794     ty: Ty<'tcx>,
 795     ckind: CItemKind,
 796 ) -> Option<Ty<'tcx>> {
 797     debug!("is_repr_nullable_ptr(cx, ty = {:?})", ty);
 798     if let ty::Adt(ty_def, substs) = ty.kind() {
 799         let field_ty = match &ty_def.variants().raw[..] {
 800             [var_one, var_two] => match (&var_one.fields[..], &var_two.fields[..]) {
 801                 ([], [field]) | ([field], []) => field.ty(cx.tcx, substs),
 802                 _ => return None,
 803             },
 804             _ => return None,
 805         };
 806
 807         if !ty_is_known_nonnull(cx, field_ty, ckind) {
 808             return None;
 809         }
 810
 811         // At this point, the field's type is known to be nonnull and the parent enum is Option-like.
 812         // If the computed size for the field and the enum are different, the nonnull optimization isn't
 813         // being applied (and we've got a problem somewhere).
 814         let compute_size_skeleton = |t| SizeSkeleton::compute(t, cx.tcx, cx.param_env).unwrap();
 815         if !compute_size_skeleton(ty).same_size(compute_size_skeleton(field_ty)) {
 816             bug!("improper_ctypes: Option nonnull optimization not applied?");
 817         }
 818
 819         // Return the nullable type this Option-like enum can be safely represented with.
 820         let field_ty_abi = &cx.layout_of(field_ty).unwrap().abi;
 821         if let Abi::Scalar(field_ty_scalar) = field_ty_abi {
 822             match field_ty_scalar.valid_range(cx) {
 823                 WrappingRange { start: 0, end }
 824                     if end == field_ty_scalar.size(&cx.tcx).unsigned_int_max() - 1 =>
 825                 {
 826                     return Some(get_nullable_type(cx, field_ty).unwrap());
 827                 }
 828                 WrappingRange { start: 1, .. } => {
 829                     return Some(get_nullable_type(cx, field_ty).unwrap());
 830                 }
 831                 WrappingRange { start, end } => {
 832                     unreachable!("Unhandled start and end range: ({}, {})", start, end)
 833                 }
 834             };
 835         }
 836     }
 837     None
 838 }
 839
 840 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
 841     /// Check if the type is array and emit an unsafe type lint.
 842     fn check_for_array_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
 843         if let ty::Array(..) = ty.kind() {
 844             self.emit_ffi_unsafe_type_lint(
 845                 ty,
 846                 sp,
 847                 fluent::lint_improper_ctypes_array_reason,
 848                 Some(fluent::lint_improper_ctypes_array_help),
 849             );
 850             true
 851         } else {
 852             false
 853         }
 854     }
 855
 856     /// Checks if the given field's type is "ffi-safe".
 857     fn check_field_type_for_ffi(
 858         &self,
 859         cache: &mut FxHashSet<Ty<'tcx>>,
 860         field: &ty::FieldDef,
 861         substs: SubstsRef<'tcx>,
 862     ) -> FfiResult<'tcx> {
 863         let field_ty = field.ty(self.cx.tcx, substs);
 864         if field_ty.has_opaque_types() {
 865             self.check_type_for_ffi(cache, field_ty)
 866         } else {
 867             let field_ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, field_ty);
 868             self.check_type_for_ffi(cache, field_ty)
 869         }
 870     }
 871
 872     /// Checks if the given `VariantDef`'s field types are "ffi-safe".
 873     fn check_variant_for_ffi(
 874         &self,
 875         cache: &mut FxHashSet<Ty<'tcx>>,
 876         ty: Ty<'tcx>,
 877         def: ty::AdtDef<'tcx>,
 878         variant: &ty::VariantDef,
 879         substs: SubstsRef<'tcx>,
 880     ) -> FfiResult<'tcx> {
 881         use FfiResult::*;
 882
 883         if def.repr().transparent() {
 884             // Can assume that at most one field is not a ZST, so only check
 885             // that field's type for FFI-safety.
 886             if let Some(field) = transparent_newtype_field(self.cx.tcx, variant) {
 887                 self.check_field_type_for_ffi(cache, field, substs)
 888             } else {
 889                 // All fields are ZSTs; this means that the type should behave
 890                 // like (), which is FFI-unsafe
 891                 FfiUnsafe { ty, reason: fluent::lint_improper_ctypes_struct_zst, help: None }
 892             }
 893         } else {
 894             // We can't completely trust repr(C) markings; make sure the fields are
 895             // actually safe.
 896             let mut all_phantom = !variant.fields.is_empty();
 897             for field in &variant.fields {
 898                 match self.check_field_type_for_ffi(cache, &field, substs) {
 899                     FfiSafe => {
 900                         all_phantom = false;
 901                     }
 902                     FfiPhantom(..) if def.is_enum() => {
 903                         return FfiUnsafe {
 904                             ty,
 905                             reason: fluent::lint_improper_ctypes_enum_phantomdata,
 906                             help: None,
 907                         };
 908                     }
 909                     FfiPhantom(..) => {}
 910                     r => return r,
 911                 }
 912             }
 913
 914             if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 915         }
 916     }
 917
 918     /// Checks if the given type is "ffi-safe" (has a stable, well-defined
 919     /// representation which can be exported to C code).
 920     fn check_type_for_ffi(&self, cache: &mut FxHashSet<Ty<'tcx>>, ty: Ty<'tcx>) -> FfiResult<'tcx> {
 921         use FfiResult::*;
 922
 923         let tcx = self.cx.tcx;
 924
 925         // Protect against infinite recursion, for example
 926         // `struct S(*mut S);`.
 927         // FIXME: A recursion limit is necessary as well, for irregular
 928         // recursive types.
 929         if !cache.insert(ty) {
 930             return FfiSafe;
 931         }
 932
 933         match *ty.kind() {
 934             ty::Adt(def, substs) => {
 935                 if def.is_box() && matches!(self.mode, CItemKind::Definition) {
 936                     if ty.boxed_ty().is_sized(tcx, self.cx.param_env) {
 937                         return FfiSafe;
 938                     } else {
 939                         return FfiUnsafe {
 940                             ty,
 941                             reason: fluent::lint_improper_ctypes_box,
 942                             help: None,
 943                         };
 944                     }
 945                 }
 946                 if def.is_phantom_data() {
 947                     return FfiPhantom(ty);
 948                 }
 949                 match def.adt_kind() {
 950                     AdtKind::Struct | AdtKind::Union => {
 951                         if !def.repr().c() && !def.repr().transparent() {
 952                             return FfiUnsafe {
 953                                 ty,
 954                                 reason: if def.is_struct() {
 955                                     fluent::lint_improper_ctypes_struct_layout_reason
 956                                 } else {
 957                                     fluent::lint_improper_ctypes_union_layout_reason
 958                                 },
 959                                 help: if def.is_struct() {
 960                                     Some(fluent::lint_improper_ctypes_struct_layout_help)
 961                                 } else {
 962                                     Some(fluent::lint_improper_ctypes_union_layout_help)
 963                                 },
 964                             };
 965                         }
 966
 967                         let is_non_exhaustive =
 968                             def.non_enum_variant().is_field_list_non_exhaustive();
 969                         if is_non_exhaustive && !def.did().is_local() {
 970                             return FfiUnsafe {
 971                                 ty,
 972                                 reason: if def.is_struct() {
 973                                     fluent::lint_improper_ctypes_struct_non_exhaustive
 974                                 } else {
 975                                     fluent::lint_improper_ctypes_union_non_exhaustive
 976                                 },
 977                                 help: None,
 978                             };
 979                         }
 980
 981                         if def.non_enum_variant().fields.is_empty() {
 982                             return FfiUnsafe {
 983                                 ty,
 984                                 reason: if def.is_struct() {
 985                                     fluent::lint_improper_ctypes_struct_fieldless_reason
 986                                 } else {
 987                                     fluent::lint_improper_ctypes_union_fieldless_reason
 988                                 },
 989                                 help: if def.is_struct() {
 990                                     Some(fluent::lint_improper_ctypes_struct_fieldless_help)
 991                                 } else {
 992                                     Some(fluent::lint_improper_ctypes_union_fieldless_help)
 993                                 },
 994                             };
 995                         }
 996
 997                         self.check_variant_for_ffi(cache, ty, def, def.non_enum_variant(), substs)
 998                     }
 999                     AdtKind::Enum => {
1000                         if def.variants().is_empty() {
1001                             // Empty enums are okay... although sort of useless.
1002                             return FfiSafe;
1003                         }
1004
1005                         // Check for a repr() attribute to specify the size of the
1006                         // discriminant.
1007                         if !def.repr().c() && !def.repr().transparent() && def.repr().int.is_none()
1008                         {
1009                             // Special-case types like `Option<extern fn()>`.
1010                             if repr_nullable_ptr(self.cx, ty, self.mode).is_none() {
1011                                 return FfiUnsafe {
1012                                     ty,
1013                                     reason: fluent::lint_improper_ctypes_enum_repr_reason,
1014                                     help: Some(fluent::lint_improper_ctypes_enum_repr_help),
1015                                 };
1016                             }
1017                         }
1018
1019                         if def.is_variant_list_non_exhaustive() && !def.did().is_local() {
1020                             return FfiUnsafe {
1021                                 ty,
1022                                 reason: fluent::lint_improper_ctypes_non_exhaustive,
1023                                 help: None,
1024                             };
1025                         }
1026
1027                         // Check the contained variants.
1028                         for variant in def.variants() {
1029                             let is_non_exhaustive = variant.is_field_list_non_exhaustive();
1030                             if is_non_exhaustive && !variant.def_id.is_local() {
1031                                 return FfiUnsafe {
1032                                     ty,
1033                                     reason: fluent::lint_improper_ctypes_non_exhaustive_variant,
1034                                     help: None,
1035                                 };
1036                             }
1037
1038                             match self.check_variant_for_ffi(cache, ty, def, variant, substs) {
1039                                 FfiSafe => (),
1040                                 r => return r,
1041                             }
1042                         }
1043
1044                         FfiSafe
1045                     }
1046                 }
1047             }
1048
1049             ty::Char => FfiUnsafe {
1050                 ty,
1051                 reason: fluent::lint_improper_ctypes_char_reason,
1052                 help: Some(fluent::lint_improper_ctypes_char_help),
1053             },
1054
1055             ty::Int(ty::IntTy::I128) | ty::Uint(ty::UintTy::U128) => {
1056                 FfiUnsafe { ty, reason: fluent::lint_improper_ctypes_128bit, help: None }
1057             }
1058
1059             // Primitive types with a stable representation.
1060             ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
1061
1062             ty::Slice(_) => FfiUnsafe {
1063                 ty,
1064                 reason: fluent::lint_improper_ctypes_slice_reason,
1065                 help: Some(fluent::lint_improper_ctypes_slice_help),
1066             },
1067
1068             ty::Dynamic(..) => {
1069                 FfiUnsafe { ty, reason: fluent::lint_improper_ctypes_dyn, help: None }
1070             }
1071
1072             ty::Str => FfiUnsafe {
1073                 ty,
1074                 reason: fluent::lint_improper_ctypes_str_reason,
1075                 help: Some(fluent::lint_improper_ctypes_str_help),
1076             },
1077
1078             ty::Tuple(..) => FfiUnsafe {
1079                 ty,
1080                 reason: fluent::lint_improper_ctypes_tuple_reason,
1081                 help: Some(fluent::lint_improper_ctypes_tuple_help),
1082             },
1083
1084             ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _)
1085                 if {
1086                     matches!(self.mode, CItemKind::Definition)
1087                         && ty.is_sized(self.cx.tcx, self.cx.param_env)
1088                 } =>
1089             {
1090                 FfiSafe
1091             }
1092
1093             ty::RawPtr(ty::TypeAndMut { ty, .. })
1094                 if match ty.kind() {
1095                     ty::Tuple(tuple) => tuple.is_empty(),
1096                     _ => false,
1097                 } =>
1098             {
1099                 FfiSafe
1100             }
1101
1102             ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _) => {
1103                 self.check_type_for_ffi(cache, ty)
1104             }
1105
1106             ty::Array(inner_ty, _) => self.check_type_for_ffi(cache, inner_ty),
1107
1108             ty::FnPtr(sig) => {
1109                 if self.is_internal_abi(sig.abi()) {
1110                     return FfiUnsafe {
1111                         ty,
1112                         reason: fluent::lint_improper_ctypes_fnptr_reason,
1113                         help: Some(fluent::lint_improper_ctypes_fnptr_help),
1114                     };
1115                 }
1116
1117                 let sig = tcx.erase_late_bound_regions(sig);
1118                 if !sig.output().is_unit() {
1119                     let r = self.check_type_for_ffi(cache, sig.output());
1120                     match r {
1121                         FfiSafe => {}
1122                         _ => {
1123                             return r;
1124                         }
1125                     }
1126                 }
1127                 for arg in sig.inputs() {
1128                     let r = self.check_type_for_ffi(cache, *arg);
1129                     match r {
1130                         FfiSafe => {}
1131                         _ => {
1132                             return r;
1133                         }
1134                     }
1135                 }
1136                 FfiSafe
1137             }
1138
1139             ty::Foreign(..) => FfiSafe,
1140
1141             // While opaque types are checked for earlier, if a projection in a struct field
1142             // normalizes to an opaque type, then it will reach this branch.
1143             ty::Opaque(..) => {
1144                 FfiUnsafe { ty, reason: fluent::lint_improper_ctypes_opaque, help: None }
1145             }
1146
1147             // `extern "C" fn` functions can have type parameters, which may or may not be FFI-safe,
1148             //  so they are currently ignored for the purposes of this lint.
1149             ty::Param(..) | ty::Projection(..) if matches!(self.mode, CItemKind::Definition) => {
1150                 FfiSafe
1151             }
1152
1153             ty::Param(..)
1154             | ty::Projection(..)
1155             | ty::Infer(..)
1156             | ty::Bound(..)
1157             | ty::Error(_)
1158             | ty::Closure(..)
1159             | ty::Generator(..)
1160             | ty::GeneratorWitness(..)
1161             | ty::Placeholder(..)
1162             | ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty),
1163         }
1164     }
1165
1166     fn emit_ffi_unsafe_type_lint(
1167         &mut self,
1168         ty: Ty<'tcx>,
1169         sp: Span,
1170         note: DiagnosticMessage,
1171         help: Option<DiagnosticMessage>,
1172     ) {
1173         let lint = match self.mode {
1174             CItemKind::Declaration => IMPROPER_CTYPES,
1175             CItemKind::Definition => IMPROPER_CTYPES_DEFINITIONS,
1176         };
1177
1178         self.cx.struct_span_lint(lint, sp, fluent::lint_improper_ctypes, |lint| {
1179             let item_description = match self.mode {
1180                 CItemKind::Declaration => "block",
1181                 CItemKind::Definition => "fn",
1182             };
1183             lint.set_arg("ty", ty);
1184             lint.set_arg("desc", item_description);
1185             lint.span_label(sp, fluent::label);
1186             if let Some(help) = help {
1187                 lint.help(help);
1188             }
1189             lint.note(note);
1190             if let ty::Adt(def, _) = ty.kind() {
1191                 if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did()) {
1192                     lint.span_note(sp, fluent::note);
1193                 }
1194             }
1195             lint
1196         });
1197     }
1198
1199     fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
1200         struct ProhibitOpaqueTypes;
1201         impl<'tcx> ty::visit::TypeVisitor<'tcx> for ProhibitOpaqueTypes {
1202             type BreakTy = Ty<'tcx>;
1203
1204             fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1205                 if !ty.has_opaque_types() {
1206                     return ControlFlow::CONTINUE;
1207                 }
1208
1209                 if let ty::Opaque(..) = ty.kind() {
1210                     ControlFlow::Break(ty)
1211                 } else {
1212                     ty.super_visit_with(self)
1213                 }
1214             }
1215         }
1216
1217         if let Some(ty) = self
1218             .cx
1219             .tcx
1220             .normalize_erasing_regions(self.cx.param_env, ty)
1221             .visit_with(&mut ProhibitOpaqueTypes)
1222             .break_value()
1223         {
1224             self.emit_ffi_unsafe_type_lint(ty, sp, fluent::lint_improper_ctypes_opaque, None);
1225             true
1226         } else {
1227             false
1228         }
1229     }
1230
1231     fn check_type_for_ffi_and_report_errors(
1232         &mut self,
1233         sp: Span,
1234         ty: Ty<'tcx>,
1235         is_static: bool,
1236         is_return_type: bool,
1237     ) {
1238         // We have to check for opaque types before `normalize_erasing_regions`,
1239         // which will replace opaque types with their underlying concrete type.
1240         if self.check_for_opaque_ty(sp, ty) {
1241             // We've already emitted an error due to an opaque type.
1242             return;
1243         }
1244
1245         // it is only OK to use this function because extern fns cannot have
1246         // any generic types right now:
1247         let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
1248
1249         // C doesn't really support passing arrays by value - the only way to pass an array by value
1250         // is through a struct. So, first test that the top level isn't an array, and then
1251         // recursively check the types inside.
1252         if !is_static && self.check_for_array_ty(sp, ty) {
1253             return;
1254         }
1255
1256         // Don't report FFI errors for unit return types. This check exists here, and not in
1257         // `check_foreign_fn` (where it would make more sense) so that normalization has definitely
1258         // happened.
1259         if is_return_type && ty.is_unit() {
1260             return;
1261         }
1262
1263         match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
1264             FfiResult::FfiSafe => {}
1265             FfiResult::FfiPhantom(ty) => {
1266                 self.emit_ffi_unsafe_type_lint(
1267                     ty,
1268                     sp,
1269                     fluent::lint_improper_ctypes_only_phantomdata,
1270                     None,
1271                 );
1272             }
1273             // If `ty` is a `repr(transparent)` newtype, and the non-zero-sized type is a generic
1274             // argument, which after substitution, is `()`, then this branch can be hit.
1275             FfiResult::FfiUnsafe { ty, .. } if is_return_type && ty.is_unit() => {}
1276             FfiResult::FfiUnsafe { ty, reason, help } => {
1277                 self.emit_ffi_unsafe_type_lint(ty, sp, reason, help);
1278             }
1279         }
1280     }
1281
1282     fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl<'_>) {
1283         let def_id = self.cx.tcx.hir().local_def_id(id);
1284         let sig = self.cx.tcx.fn_sig(def_id);
1285         let sig = self.cx.tcx.erase_late_bound_regions(sig);
1286
1287         for (input_ty, input_hir) in iter::zip(sig.inputs(), decl.inputs) {
1288             self.check_type_for_ffi_and_report_errors(input_hir.span, *input_ty, false, false);
1289         }
1290
1291         if let hir::FnRetTy::Return(ref ret_hir) = decl.output {
1292             let ret_ty = sig.output();
1293             self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty, false, true);
1294         }
1295     }
1296
1297     fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
1298         let def_id = self.cx.tcx.hir().local_def_id(id);
1299         let ty = self.cx.tcx.type_of(def_id);
1300         self.check_type_for_ffi_and_report_errors(span, ty, true, false);
1301     }
1302
1303     fn is_internal_abi(&self, abi: SpecAbi) -> bool {
1304         matches!(
1305             abi,
1306             SpecAbi::Rust | SpecAbi::RustCall | SpecAbi::RustIntrinsic | SpecAbi::PlatformIntrinsic
1307         )
1308     }
1309 }
1310
1311 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDeclarations {
1312     fn check_foreign_item(&mut self, cx: &LateContext<'_>, it: &hir::ForeignItem<'_>) {
1313         let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Declaration };
1314         let abi = cx.tcx.hir().get_foreign_abi(it.hir_id());
1315
1316         if !vis.is_internal_abi(abi) {
1317             match it.kind {
1318                 hir::ForeignItemKind::Fn(ref decl, _, _) => {
1319                     vis.check_foreign_fn(it.hir_id(), decl);
1320                 }
1321                 hir::ForeignItemKind::Static(ref ty, _) => {
1322                     vis.check_foreign_static(it.hir_id(), ty.span);
1323                 }
1324                 hir::ForeignItemKind::Type => (),
1325             }
1326         }
1327     }
1328 }
1329
1330 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDefinitions {
1331     fn check_fn(
1332         &mut self,
1333         cx: &LateContext<'tcx>,
1334         kind: hir::intravisit::FnKind<'tcx>,
1335         decl: &'tcx hir::FnDecl<'_>,
1336         _: &'tcx hir::Body<'_>,
1337         _: Span,
1338         hir_id: hir::HirId,
1339     ) {
1340         use hir::intravisit::FnKind;
1341
1342         let abi = match kind {
1343             FnKind::ItemFn(_, _, header, ..) => header.abi,
1344             FnKind::Method(_, sig, ..) => sig.header.abi,
1345             _ => return,
1346         };
1347
1348         let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Definition };
1349         if !vis.is_internal_abi(abi) {
1350             vis.check_foreign_fn(hir_id, decl);
1351         }
1352     }
1353 }
1354
1355 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
1356
1357 impl<'tcx> LateLintPass<'tcx> for VariantSizeDifferences {
1358     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1359         if let hir::ItemKind::Enum(ref enum_definition, _) = it.kind {
1360             let t = cx.tcx.type_of(it.owner_id);
1361             let ty = cx.tcx.erase_regions(t);
1362             let Ok(layout) = cx.layout_of(ty) else { return };
1363             let Variants::Multiple {
1364                     tag_encoding: TagEncoding::Direct, tag, ref variants, ..
1365                 } = &layout.variants else {
1366                 return
1367             };
1368
1369             let tag_size = tag.size(&cx.tcx).bytes();
1370
1371             debug!(
1372                 "enum `{}` is {} bytes large with layout:\n{:#?}",
1373                 t,
1374                 layout.size.bytes(),
1375                 layout
1376             );
1377
1378             let (largest, slargest, largest_index) = iter::zip(enum_definition.variants, variants)
1379                 .map(|(variant, variant_layout)| {
1380                     // Subtract the size of the enum tag.
1381                     let bytes = variant_layout.size.bytes().saturating_sub(tag_size);
1382
1383                     debug!("- variant `{}` is {} bytes large", variant.ident, bytes);
1384                     bytes
1385                 })
1386                 .enumerate()
1387                 .fold((0, 0, 0), |(l, s, li), (idx, size)| {
1388                     if size > l {
1389                         (size, l, idx)
1390                     } else if size > s {
1391                         (l, size, li)
1392                     } else {
1393                         (l, s, li)
1394                     }
1395                 });
1396
1397             // We only warn if the largest variant is at least thrice as large as
1398             // the second-largest.
1399             if largest > slargest * 3 && slargest > 0 {
1400                 cx.struct_span_lint(
1401                     VARIANT_SIZE_DIFFERENCES,
1402                     enum_definition.variants[largest_index].span,
1403                     fluent::lint_variant_size_differences,
1404                     |lint| lint.set_arg("largest", largest),
1405                 );
1406             }
1407         }
1408     }
1409 }
1410
1411 declare_lint! {
1412     /// The `invalid_atomic_ordering` lint detects passing an `Ordering`
1413     /// to an atomic operation that does not support that ordering.
1414     ///
1415     /// ### Example
1416     ///
1417     /// ```rust,compile_fail
1418     /// # use core::sync::atomic::{AtomicU8, Ordering};
1419     /// let atom = AtomicU8::new(0);
1420     /// let value = atom.load(Ordering::Release);
1421     /// # let _ = value;
1422     /// ```
1423     ///
1424     /// {{produces}}
1425     ///
1426     /// ### Explanation
1427     ///
1428     /// Some atomic operations are only supported for a subset of the
1429     /// `atomic::Ordering` variants. Passing an unsupported variant will cause
1430     /// an unconditional panic at runtime, which is detected by this lint.
1431     ///
1432     /// This lint will trigger in the following cases: (where `AtomicType` is an
1433     /// atomic type from `core::sync::atomic`, such as `AtomicBool`,
1434     /// `AtomicPtr`, `AtomicUsize`, or any of the other integer atomics).
1435     ///
1436     /// - Passing `Ordering::Acquire` or `Ordering::AcqRel` to
1437     ///   `AtomicType::store`.
1438     ///
1439     /// - Passing `Ordering::Release` or `Ordering::AcqRel` to
1440     ///   `AtomicType::load`.
1441     ///
1442     /// - Passing `Ordering::Relaxed` to `core::sync::atomic::fence` or
1443     ///   `core::sync::atomic::compiler_fence`.
1444     ///
1445     /// - Passing `Ordering::Release` or `Ordering::AcqRel` as the failure
1446     ///   ordering for any of `AtomicType::compare_exchange`,
1447     ///   `AtomicType::compare_exchange_weak`, or `AtomicType::fetch_update`.
1448     INVALID_ATOMIC_ORDERING,
1449     Deny,
1450     "usage of invalid atomic ordering in atomic operations and memory fences"
1451 }
1452
1453 declare_lint_pass!(InvalidAtomicOrdering => [INVALID_ATOMIC_ORDERING]);
1454
1455 impl InvalidAtomicOrdering {
1456     fn inherent_atomic_method_call<'hir>(
1457         cx: &LateContext<'_>,
1458         expr: &Expr<'hir>,
1459         recognized_names: &[Symbol], // used for fast path calculation
1460     ) -> Option<(Symbol, &'hir [Expr<'hir>])> {
1461         const ATOMIC_TYPES: &[Symbol] = &[
1462             sym::AtomicBool,
1463             sym::AtomicPtr,
1464             sym::AtomicUsize,
1465             sym::AtomicU8,
1466             sym::AtomicU16,
1467             sym::AtomicU32,
1468             sym::AtomicU64,
1469             sym::AtomicU128,
1470             sym::AtomicIsize,
1471             sym::AtomicI8,
1472             sym::AtomicI16,
1473             sym::AtomicI32,
1474             sym::AtomicI64,
1475             sym::AtomicI128,
1476         ];
1477         if let ExprKind::MethodCall(ref method_path, _, args, _) = &expr.kind
1478             && recognized_names.contains(&method_path.ident.name)
1479             && let Some(m_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id)
1480             && let Some(impl_did) = cx.tcx.impl_of_method(m_def_id)
1481             && let Some(adt) = cx.tcx.type_of(impl_did).ty_adt_def()
1482             // skip extension traits, only lint functions from the standard library
1483             && cx.tcx.trait_id_of_impl(impl_did).is_none()
1484             && let parent = cx.tcx.parent(adt.did())
1485             && cx.tcx.is_diagnostic_item(sym::atomic_mod, parent)
1486             && ATOMIC_TYPES.contains(&cx.tcx.item_name(adt.did()))
1487         {
1488             return Some((method_path.ident.name, args));
1489         }
1490         None
1491     }
1492
1493     fn match_ordering(cx: &LateContext<'_>, ord_arg: &Expr<'_>) -> Option<Symbol> {
1494         let ExprKind::Path(ref ord_qpath) = ord_arg.kind else { return None };
1495         let did = cx.qpath_res(ord_qpath, ord_arg.hir_id).opt_def_id()?;
1496         let tcx = cx.tcx;
1497         let atomic_ordering = tcx.get_diagnostic_item(sym::Ordering);
1498         let name = tcx.item_name(did);
1499         let parent = tcx.parent(did);
1500         [sym::Relaxed, sym::Release, sym::Acquire, sym::AcqRel, sym::SeqCst].into_iter().find(
1501             |&ordering| {
1502                 name == ordering
1503                     && (Some(parent) == atomic_ordering
1504                             // needed in case this is a ctor, not a variant
1505                             || tcx.opt_parent(parent) == atomic_ordering)
1506             },
1507         )
1508     }
1509
1510     fn check_atomic_load_store(cx: &LateContext<'_>, expr: &Expr<'_>) {
1511         if let Some((method, args)) = Self::inherent_atomic_method_call(cx, expr, &[sym::load, sym::store])
1512             && let Some((ordering_arg, invalid_ordering, msg)) = match method {
1513                 sym::load => Some((&args[0], sym::Release, fluent::lint_atomic_ordering_load)),
1514                 sym::store => Some((&args[1], sym::Acquire, fluent::lint_atomic_ordering_store)),
1515                 _ => None,
1516             }
1517             && let Some(ordering) = Self::match_ordering(cx, ordering_arg)
1518             && (ordering == invalid_ordering || ordering == sym::AcqRel)
1519         {
1520             cx.struct_span_lint(INVALID_ATOMIC_ORDERING, ordering_arg.span, msg, |lint| {
1521                 lint.help(fluent::help)
1522             });
1523         }
1524     }
1525
1526     fn check_memory_fence(cx: &LateContext<'_>, expr: &Expr<'_>) {
1527         if let ExprKind::Call(ref func, ref args) = expr.kind
1528             && let ExprKind::Path(ref func_qpath) = func.kind
1529             && let Some(def_id) = cx.qpath_res(func_qpath, func.hir_id).opt_def_id()
1530             && matches!(cx.tcx.get_diagnostic_name(def_id), Some(sym::fence | sym::compiler_fence))
1531             && Self::match_ordering(cx, &args[0]) == Some(sym::Relaxed)
1532         {
1533             cx.struct_span_lint(INVALID_ATOMIC_ORDERING, args[0].span, fluent::lint_atomic_ordering_fence, |lint| {
1534                 lint
1535                     .help(fluent::help)
1536             });
1537         }
1538     }
1539
1540     fn check_atomic_compare_exchange(cx: &LateContext<'_>, expr: &Expr<'_>) {
1541         let Some((method, args)) = Self::inherent_atomic_method_call(cx, expr, &[sym::fetch_update, sym::compare_exchange, sym::compare_exchange_weak])
1542             else {return };
1543
1544         let fail_order_arg = match method {
1545             sym::fetch_update => &args[1],
1546             sym::compare_exchange | sym::compare_exchange_weak => &args[3],
1547             _ => return,
1548         };
1549
1550         let Some(fail_ordering) = Self::match_ordering(cx, fail_order_arg) else { return };
1551
1552         if matches!(fail_ordering, sym::Release | sym::AcqRel) {
1553             #[derive(LintDiagnostic)]
1554             #[diag(lint_atomic_ordering_invalid)]
1555             #[help]
1556             struct InvalidAtomicOrderingDiag {
1557                 method: Symbol,
1558                 #[label]
1559                 fail_order_arg_span: Span,
1560             }
1561
1562             cx.emit_spanned_lint(
1563                 INVALID_ATOMIC_ORDERING,
1564                 fail_order_arg.span,
1565                 InvalidAtomicOrderingDiag { method, fail_order_arg_span: fail_order_arg.span },
1566             );
1567         }
1568     }
1569 }
1570
1571 impl<'tcx> LateLintPass<'tcx> for InvalidAtomicOrdering {
1572     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
1573         Self::check_atomic_load_store(cx, expr);
1574         Self::check_memory_fence(cx, expr);
1575         Self::check_atomic_compare_exchange(cx, expr);
1576     }
1577 }