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::iter;
  20 use std::ops::ControlFlow;
  21
  22 declare_lint! {
  23     /// The `unused_comparisons` lint detects comparisons made useless by
  24     /// limits of the types involved.
  25     ///
  26     /// ### Example
  27     ///
  28     /// ```rust
  29     /// fn foo(x: u8) {
  30     ///     x >= 0;
  31     /// }
  32     /// ```
  33     ///
  34     /// {{produces}}
  35     ///
  36     /// ### Explanation
  37     ///
  38     /// A useless comparison may indicate a mistake, and should be fixed or
  39     /// removed.
  40     UNUSED_COMPARISONS,
  41     Warn,
  42     "comparisons made useless by limits of the types involved"
  43 }
  44
  45 declare_lint! {
  46     /// The `overflowing_literals` lint detects literal out of range for its
  47     /// type.
  48     ///
  49     /// ### Example
  50     ///
  51     /// ```rust,compile_fail
  52     /// let x: u8 = 1000;
  53     /// ```
  54     ///
  55     /// {{produces}}
  56     ///
  57     /// ### Explanation
  58     ///
  59     /// It is usually a mistake to use a literal that overflows the type where
  60     /// it is used. Either use a literal that is within range, or change the
  61     /// type to be within the range of the literal.
  62     OVERFLOWING_LITERALS,
  63     Deny,
  64     "literal out of range for its type"
  65 }
  66
  67 declare_lint! {
  68     /// The `variant_size_differences` lint detects enums with widely varying
  69     /// variant sizes.
  70     ///
  71     /// ### Example
  72     ///
  73     /// ```rust,compile_fail
  74     /// #![deny(variant_size_differences)]
  75     /// enum En {
  76     ///     V0(u8),
  77     ///     VBig([u8; 1024]),
  78     /// }
  79     /// ```
  80     ///
  81     /// {{produces}}
  82     ///
  83     /// ### Explanation
  84     ///
  85     /// It can be a mistake to add a variant to an enum that is much larger
  86     /// than the other variants, bloating the overall size required for all
  87     /// variants. This can impact performance and memory usage. This is
  88     /// triggered if one variant is more than 3 times larger than the
  89     /// second-largest variant.
  90     ///
  91     /// Consider placing the large variant's contents on the heap (for example
  92     /// via [`Box`]) to keep the overall size of the enum itself down.
  93     ///
  94     /// This lint is "allow" by default because it can be noisy, and may not be
  95     /// an actual problem. Decisions about this should be guided with
  96     /// profiling and benchmarking.
  97     ///
  98     /// [`Box`]: https://doc.rust-lang.org/std/boxed/index.html
  99     VARIANT_SIZE_DIFFERENCES,
 100     Allow,
 101     "detects enums with widely varying variant sizes"
 102 }
 103
 104 #[derive(Copy, Clone)]
 105 pub struct TypeLimits {
 106     /// Id of the last visited negated expression
 107     negated_expr_id: Option<hir::HirId>,
 108 }
 109
 110 impl_lint_pass!(TypeLimits => [UNUSED_COMPARISONS, OVERFLOWING_LITERALS]);
 111
 112 impl TypeLimits {
 113     pub fn new() -> TypeLimits {
 114         TypeLimits { negated_expr_id: None }
 115     }
 116 }
 117
 118 /// Attempts to special-case the overflowing literal lint when it occurs as a range endpoint (`expr..MAX+1`).
 119 /// Returns `true` iff the lint was emitted.
 120 fn lint_overflowing_range_endpoint<'tcx>(
 121     cx: &LateContext<'tcx>,
 122     lit: &hir::Lit,
 123     lit_val: u128,
 124     max: u128,
 125     expr: &'tcx hir::Expr<'tcx>,
 126     ty: &str,
 127 ) -> bool {
 128     // We only want to handle exclusive (`..`) ranges,
 129     // which are represented as `ExprKind::Struct`.
 130     let par_id = cx.tcx.hir().get_parent_node(expr.hir_id);
 131     let Node::ExprField(field) = cx.tcx.hir().get(par_id) else { return false };
 132     let field_par_id = cx.tcx.hir().get_parent_node(field.hir_id);
 133     let Node::Expr(struct_expr) = cx.tcx.hir().get(field_par_id) else { return false };
 134     if !is_range_literal(struct_expr) {
 135         return false;
 136     };
 137     let ExprKind::Struct(_, eps, _) = &struct_expr.kind else { return false };
 138     if eps.len() != 2 {
 139         return false;
 140     }
 141
 142     // We can suggest using an inclusive range
 143     // (`..=`) instead only if it is the `end` that is
 144     // overflowing and only by 1.
 145     if !(eps[1].expr.hir_id == expr.hir_id && lit_val - 1 == max) {
 146         return false;
 147     };
 148     let Ok(start) = cx.sess().source_map().span_to_snippet(eps[0].span) else { return false };
 149
 150     cx.struct_span_lint(
 151         OVERFLOWING_LITERALS,
 152         struct_expr.span,
 153         fluent::lint_range_endpoint_out_of_range,
 154         |lint| {
 155             use ast::{LitIntType, LitKind};
 156
 157             lint.set_arg("ty", ty);
 158
 159             // We need to preserve the literal's suffix,
 160             // as it may determine typing information.
 161             let suffix = match lit.node {
 162                 LitKind::Int(_, LitIntType::Signed(s)) => s.name_str(),
 163                 LitKind::Int(_, LitIntType::Unsigned(s)) => s.name_str(),
 164                 LitKind::Int(_, LitIntType::Unsuffixed) => "",
 165                 _ => bug!(),
 166             };
 167             let suggestion = format!("{}..={}{}", start, lit_val - 1, suffix);
 168             lint.span_suggestion(
 169                 struct_expr.span,
 170                 fluent::suggestion,
 171                 suggestion,
 172                 Applicability::MachineApplicable,
 173             );
 174
 175             lint
 176         },
 177     );
 178
 179     // We've just emitted a lint, special cased for `(...)..MAX+1` ranges,
 180     // return `true` so the callers don't also emit a lint
 181     true
 182 }
 183
 184 // For `isize` & `usize`, be conservative with the warnings, so that the
 185 // warnings are consistent between 32- and 64-bit platforms.
 186 fn int_ty_range(int_ty: ty::IntTy) -> (i128, i128) {
 187     match int_ty {
 188         ty::IntTy::Isize => (i64::MIN.into(), i64::MAX.into()),
 189         ty::IntTy::I8 => (i8::MIN.into(), i8::MAX.into()),
 190         ty::IntTy::I16 => (i16::MIN.into(), i16::MAX.into()),
 191         ty::IntTy::I32 => (i32::MIN.into(), i32::MAX.into()),
 192         ty::IntTy::I64 => (i64::MIN.into(), i64::MAX.into()),
 193         ty::IntTy::I128 => (i128::MIN, i128::MAX),
 194     }
 195 }
 196
 197 fn uint_ty_range(uint_ty: ty::UintTy) -> (u128, u128) {
 198     let max = match uint_ty {
 199         ty::UintTy::Usize => u64::MAX.into(),
 200         ty::UintTy::U8 => u8::MAX.into(),
 201         ty::UintTy::U16 => u16::MAX.into(),
 202         ty::UintTy::U32 => u32::MAX.into(),
 203         ty::UintTy::U64 => u64::MAX.into(),
 204         ty::UintTy::U128 => u128::MAX,
 205     };
 206     (0, max)
 207 }
 208
 209 fn get_bin_hex_repr(cx: &LateContext<'_>, lit: &hir::Lit) -> Option<String> {
 210     let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?;
 211     let firstch = src.chars().next()?;
 212
 213     if firstch == '0' {
 214         match src.chars().nth(1) {
 215             Some('x' | 'b') => return Some(src),
 216             _ => return None,
 217         }
 218     }
 219
 220     None
 221 }
 222
 223 fn report_bin_hex_error(
 224     cx: &LateContext<'_>,
 225     expr: &hir::Expr<'_>,
 226     ty: attr::IntType,
 227     size: Size,
 228     repr_str: String,
 229     val: u128,
 230     negative: bool,
 231 ) {
 232     cx.struct_span_lint(
 233         OVERFLOWING_LITERALS,
 234         expr.span,
 235         fluent::lint_overflowing_bin_hex,
 236         |lint| {
 237             let (t, actually) = match ty {
 238                 attr::IntType::SignedInt(t) => {
 239                     let actually = if negative {
 240                         -(size.sign_extend(val) as i128)
 241                     } else {
 242                         size.sign_extend(val) as i128
 243                     };
 244                     (t.name_str(), actually.to_string())
 245                 }
 246                 attr::IntType::UnsignedInt(t) => {
 247                     let actually = size.truncate(val);
 248                     (t.name_str(), actually.to_string())
 249                 }
 250             };
 251
 252             if negative {
 253                 // If the value is negative,
 254                 // emits a note about the value itself, apart from the literal.
 255                 lint.note(fluent::negative_note);
 256                 lint.note(fluent::negative_becomes_note);
 257             } else {
 258                 lint.note(fluent::positive_note);
 259             }
 260             if let Some(sugg_ty) =
 261                 get_type_suggestion(cx.typeck_results().node_type(expr.hir_id), val, negative)
 262             {
 263                 lint.set_arg("suggestion_ty", sugg_ty);
 264                 if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') {
 265                     let (sans_suffix, _) = repr_str.split_at(pos);
 266                     lint.span_suggestion(
 267                         expr.span,
 268                         fluent::suggestion,
 269                         format!("{}{}", sans_suffix, sugg_ty),
 270                         Applicability::MachineApplicable,
 271                     );
 272                 } else {
 273                     lint.help(fluent::help);
 274                 }
 275             }
 276             lint.set_arg("ty", t)
 277                 .set_arg("lit", repr_str)
 278                 .set_arg("dec", val)
 279                 .set_arg("actually", actually);
 280
 281             lint
 282         },
 283     );
 284 }
 285
 286 // This function finds the next fitting type and generates a suggestion string.
 287 // It searches for fitting types in the following way (`X < Y`):
 288 //  - `iX`: if literal fits in `uX` => `uX`, else => `iY`
 289 //  - `-iX` => `iY`
 290 //  - `uX` => `uY`
 291 //
 292 // No suggestion for: `isize`, `usize`.
 293 fn get_type_suggestion(t: Ty<'_>, val: u128, negative: bool) -> Option<&'static str> {
 294     use ty::IntTy::*;
 295     use ty::UintTy::*;
 296     macro_rules! find_fit {
 297         ($ty:expr, $val:expr, $negative:expr,
 298          $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => {
 299             {
 300                 let _neg = if negative { 1 } else { 0 };
 301                 match $ty {
 302                     $($type => {
 303                         $(if !negative && val <= uint_ty_range($utypes).1 {
 304                             return Some($utypes.name_str())
 305                         })*
 306                         $(if val <= int_ty_range($itypes).1 as u128 + _neg {
 307                             return Some($itypes.name_str())
 308                         })*
 309                         None
 310                     },)+
 311                     _ => None
 312                 }
 313             }
 314         }
 315     }
 316     match t.kind() {
 317         ty::Int(i) => find_fit!(i, val, negative,
 318                       I8 => [U8] => [I16, I32, I64, I128],
 319                       I16 => [U16] => [I32, I64, I128],
 320                       I32 => [U32] => [I64, I128],
 321                       I64 => [U64] => [I128],
 322                       I128 => [U128] => []),
 323         ty::Uint(u) => find_fit!(u, val, negative,
 324                       U8 => [U8, U16, U32, U64, U128] => [],
 325                       U16 => [U16, U32, U64, U128] => [],
 326                       U32 => [U32, U64, U128] => [],
 327                       U64 => [U64, U128] => [],
 328                       U128 => [U128] => []),
 329         _ => None,
 330     }
 331 }
 332
 333 fn lint_int_literal<'tcx>(
 334     cx: &LateContext<'tcx>,
 335     type_limits: &TypeLimits,
 336     e: &'tcx hir::Expr<'tcx>,
 337     lit: &hir::Lit,
 338     t: ty::IntTy,
 339     v: u128,
 340 ) {
 341     let int_type = t.normalize(cx.sess().target.pointer_width);
 342     let (min, max) = int_ty_range(int_type);
 343     let max = max as u128;
 344     let negative = type_limits.negated_expr_id == Some(e.hir_id);
 345
 346     // Detect literal value out of range [min, max] inclusive
 347     // avoiding use of -min to prevent overflow/panic
 348     if (negative && v > max + 1) || (!negative && v > max) {
 349         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 350             report_bin_hex_error(
 351                 cx,
 352                 e,
 353                 attr::IntType::SignedInt(ty::ast_int_ty(t)),
 354                 Integer::from_int_ty(cx, t).size(),
 355                 repr_str,
 356                 v,
 357                 negative,
 358             );
 359             return;
 360         }
 361
 362         if lint_overflowing_range_endpoint(cx, lit, v, max, e, t.name_str()) {
 363             // The overflowing literal lint was emitted by `lint_overflowing_range_endpoint`.
 364             return;
 365         }
 366
 367         cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, fluent::lint_overflowing_int, |lint| {
 368             lint.set_arg("ty", t.name_str())
 369                 .set_arg(
 370                     "lit",
 371                     cx.sess()
 372                         .source_map()
 373                         .span_to_snippet(lit.span)
 374                         .expect("must get snippet from literal"),
 375                 )
 376                 .set_arg("min", min)
 377                 .set_arg("max", max)
 378                 .note(fluent::note);
 379
 380             if let Some(sugg_ty) =
 381                 get_type_suggestion(cx.typeck_results().node_type(e.hir_id), v, negative)
 382             {
 383                 lint.set_arg("suggestion_ty", sugg_ty);
 384                 lint.help(fluent::help);
 385             }
 386
 387             lint
 388         });
 389     }
 390 }
 391
 392 fn lint_uint_literal<'tcx>(
 393     cx: &LateContext<'tcx>,
 394     e: &'tcx hir::Expr<'tcx>,
 395     lit: &hir::Lit,
 396     t: ty::UintTy,
 397 ) {
 398     let uint_type = t.normalize(cx.sess().target.pointer_width);
 399     let (min, max) = uint_ty_range(uint_type);
 400     let lit_val: u128 = match lit.node {
 401         // _v is u8, within range by definition
 402         ast::LitKind::Byte(_v) => return,
 403         ast::LitKind::Int(v, _) => v,
 404         _ => bug!(),
 405     };
 406     if lit_val < min || lit_val > max {
 407         let parent_id = cx.tcx.hir().get_parent_node(e.hir_id);
 408         if let Node::Expr(par_e) = cx.tcx.hir().get(parent_id) {
 409             match par_e.kind {
 410                 hir::ExprKind::Cast(..) => {
 411                     if let ty::Char = cx.typeck_results().expr_ty(par_e).kind() {
 412                         cx.struct_span_lint(
 413                             OVERFLOWING_LITERALS,
 414                             par_e.span,
 415                             fluent::lint_only_cast_u8_to_char,
 416                             |lint| {
 417                                 lint.span_suggestion(
 418                                     par_e.span,
 419                                     fluent::suggestion,
 420                                     format!("'\\u{{{:X}}}'", lit_val),
 421                                     Applicability::MachineApplicable,
 422                                 )
 423                             },
 424                         );
 425                         return;
 426                     }
 427                 }
 428                 _ => {}
 429             }
 430         }
 431         if lint_overflowing_range_endpoint(cx, lit, lit_val, max, e, t.name_str()) {
 432             // The overflowing literal lint was emitted by `lint_overflowing_range_endpoint`.
 433             return;
 434         }
 435         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 436             report_bin_hex_error(
 437                 cx,
 438                 e,
 439                 attr::IntType::UnsignedInt(ty::ast_uint_ty(t)),
 440                 Integer::from_uint_ty(cx, t).size(),
 441                 repr_str,
 442                 lit_val,
 443                 false,
 444             );
 445             return;
 446         }
 447         cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, fluent::lint_overflowing_uint, |lint| {
 448             lint.set_arg("ty", t.name_str())
 449                 .set_arg(
 450                     "lit",
 451                     cx.sess()
 452                         .source_map()
 453                         .span_to_snippet(lit.span)
 454                         .expect("must get snippet from literal"),
 455                 )
 456                 .set_arg("min", min)
 457                 .set_arg("max", max)
 458                 .note(fluent::note)
 459         });
 460     }
 461 }
 462
 463 fn lint_literal<'tcx>(
 464     cx: &LateContext<'tcx>,
 465     type_limits: &TypeLimits,
 466     e: &'tcx hir::Expr<'tcx>,
 467     lit: &hir::Lit,
 468 ) {
 469     match *cx.typeck_results().node_type(e.hir_id).kind() {
 470         ty::Int(t) => {
 471             match lit.node {
 472                 ast::LitKind::Int(v, ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed) => {
 473                     lint_int_literal(cx, type_limits, e, lit, t, v)
 474                 }
 475                 _ => bug!(),
 476             };
 477         }
 478         ty::Uint(t) => lint_uint_literal(cx, e, lit, t),
 479         ty::Float(t) => {
 480             let is_infinite = match lit.node {
 481                 ast::LitKind::Float(v, _) => match t {
 482                     ty::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
 483                     ty::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
 484                 },
 485                 _ => bug!(),
 486             };
 487             if is_infinite == Ok(true) {
 488                 cx.struct_span_lint(
 489                     OVERFLOWING_LITERALS,
 490                     e.span,
 491                     fluent::lint_overflowing_literal,
 492                     |lint| {
 493                         lint.set_arg("ty", t.name_str())
 494                             .set_arg(
 495                                 "lit",
 496                                 cx.sess()
 497                                     .source_map()
 498                                     .span_to_snippet(lit.span)
 499                                     .expect("must get snippet from literal"),
 500                             )
 501                             .note(fluent::note)
 502                     },
 503                 );
 504             }
 505         }
 506         _ => {}
 507     }
 508 }
 509
 510 impl<'tcx> LateLintPass<'tcx> for TypeLimits {
 511     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx hir::Expr<'tcx>) {
 512         match e.kind {
 513             hir::ExprKind::Unary(hir::UnOp::Neg, ref expr) => {
 514                 // propagate negation, if the negation itself isn't negated
 515                 if self.negated_expr_id != Some(e.hir_id) {
 516                     self.negated_expr_id = Some(expr.hir_id);
 517                 }
 518             }
 519             hir::ExprKind::Binary(binop, ref l, ref r) => {
 520                 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
 521                     cx.struct_span_lint(
 522                         UNUSED_COMPARISONS,
 523                         e.span,
 524                         fluent::lint_unused_comparisons,
 525                         |lint| lint,
 526                     );
 527                 }
 528             }
 529             hir::ExprKind::Lit(ref lit) => lint_literal(cx, self, e, lit),
 530             _ => {}
 531         };
 532
 533         fn is_valid<T: PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
 534             match binop.node {
 535                 hir::BinOpKind::Lt => v > min && v <= max,
 536                 hir::BinOpKind::Le => v >= min && v < max,
 537                 hir::BinOpKind::Gt => v >= min && v < max,
 538                 hir::BinOpKind::Ge => v > min && v <= max,
 539                 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
 540                 _ => bug!(),
 541             }
 542         }
 543
 544         fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
 545             source_map::respan(
 546                 binop.span,
 547                 match binop.node {
 548                     hir::BinOpKind::Lt => hir::BinOpKind::Gt,
 549                     hir::BinOpKind::Le => hir::BinOpKind::Ge,
 550                     hir::BinOpKind::Gt => hir::BinOpKind::Lt,
 551                     hir::BinOpKind::Ge => hir::BinOpKind::Le,
 552                     _ => return binop,
 553                 },
 554             )
 555         }
 556
 557         fn check_limits(
 558             cx: &LateContext<'_>,
 559             binop: hir::BinOp,
 560             l: &hir::Expr<'_>,
 561             r: &hir::Expr<'_>,
 562         ) -> bool {
 563             let (lit, expr, swap) = match (&l.kind, &r.kind) {
 564                 (&hir::ExprKind::Lit(_), _) => (l, r, true),
 565                 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
 566                 _ => return true,
 567             };
 568             // Normalize the binop so that the literal is always on the RHS in
 569             // the comparison
 570             let norm_binop = if swap { rev_binop(binop) } else { binop };
 571             match *cx.typeck_results().node_type(expr.hir_id).kind() {
 572                 ty::Int(int_ty) => {
 573                     let (min, max) = int_ty_range(int_ty);
 574                     let lit_val: i128 = match lit.kind {
 575                         hir::ExprKind::Lit(ref li) => match li.node {
 576                             ast::LitKind::Int(
 577                                 v,
 578                                 ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed,
 579                             ) => v as i128,
 580                             _ => return true,
 581                         },
 582                         _ => bug!(),
 583                     };
 584                     is_valid(norm_binop, lit_val, min, max)
 585                 }
 586                 ty::Uint(uint_ty) => {
 587                     let (min, max): (u128, u128) = uint_ty_range(uint_ty);
 588                     let lit_val: u128 = match lit.kind {
 589                         hir::ExprKind::Lit(ref li) => match li.node {
 590                             ast::LitKind::Int(v, _) => v,
 591                             _ => return true,
 592                         },
 593                         _ => bug!(),
 594                     };
 595                     is_valid(norm_binop, lit_val, min, max)
 596                 }
 597                 _ => true,
 598             }
 599         }
 600
 601         fn is_comparison(binop: hir::BinOp) -> bool {
 602             matches!(
 603                 binop.node,
 604                 hir::BinOpKind::Eq
 605                     | hir::BinOpKind::Lt
 606                     | hir::BinOpKind::Le
 607                     | hir::BinOpKind::Ne
 608                     | hir::BinOpKind::Ge
 609                     | hir::BinOpKind::Gt
 610             )
 611         }
 612     }
 613 }
 614
 615 declare_lint! {
 616     /// The `improper_ctypes` lint detects incorrect use of types in foreign
 617     /// modules.
 618     ///
 619     /// ### Example
 620     ///
 621     /// ```rust
 622     /// extern "C" {
 623     ///     static STATIC: String;
 624     /// }
 625     /// ```
 626     ///
 627     /// {{produces}}
 628     ///
 629     /// ### Explanation
 630     ///
 631     /// The compiler has several checks to verify that types used in `extern`
 632     /// blocks are safe and follow certain rules to ensure proper
 633     /// compatibility with the foreign interfaces. This lint is issued when it
 634     /// detects a probable mistake in a definition. The lint usually should
 635     /// provide a description of the issue, along with possibly a hint on how
 636     /// to resolve it.
 637     IMPROPER_CTYPES,
 638     Warn,
 639     "proper use of libc types in foreign modules"
 640 }
 641
 642 declare_lint_pass!(ImproperCTypesDeclarations => [IMPROPER_CTYPES]);
 643
 644 declare_lint! {
 645     /// The `improper_ctypes_definitions` lint detects incorrect use of
 646     /// [`extern` function] definitions.
 647     ///
 648     /// [`extern` function]: https://doc.rust-lang.org/reference/items/functions.html#extern-function-qualifier
 649     ///
 650     /// ### Example
 651     ///
 652     /// ```rust
 653     /// # #![allow(unused)]
 654     /// pub extern "C" fn str_type(p: &str) { }
 655     /// ```
 656     ///
 657     /// {{produces}}
 658     ///
 659     /// ### Explanation
 660     ///
 661     /// There are many parameter and return types that may be specified in an
 662     /// `extern` function that are not compatible with the given ABI. This
 663     /// lint is an alert that these types should not be used. The lint usually
 664     /// should provide a description of the issue, along with possibly a hint
 665     /// on how to resolve it.
 666     IMPROPER_CTYPES_DEFINITIONS,
 667     Warn,
 668     "proper use of libc types in foreign item definitions"
 669 }
 670
 671 declare_lint_pass!(ImproperCTypesDefinitions => [IMPROPER_CTYPES_DEFINITIONS]);
 672
 673 #[derive(Clone, Copy)]
 674 pub(crate) enum CItemKind {
 675     Declaration,
 676     Definition,
 677 }
 678
 679 struct ImproperCTypesVisitor<'a, 'tcx> {
 680     cx: &'a LateContext<'tcx>,
 681     mode: CItemKind,
 682 }
 683
 684 enum FfiResult<'tcx> {
 685     FfiSafe,
 686     FfiPhantom(Ty<'tcx>),
 687     FfiUnsafe { ty: Ty<'tcx>, reason: DiagnosticMessage, help: Option<DiagnosticMessage> },
 688 }
 689
 690 pub(crate) fn nonnull_optimization_guaranteed<'tcx>(
 691     tcx: TyCtxt<'tcx>,
 692     def: ty::AdtDef<'tcx>,
 693 ) -> bool {
 694     tcx.has_attr(def.did(), sym::rustc_nonnull_optimization_guaranteed)
 695 }
 696
 697 /// `repr(transparent)` structs can have a single non-ZST field, this function returns that
 698 /// field.
 699 pub fn transparent_newtype_field<'a, 'tcx>(
 700     tcx: TyCtxt<'tcx>,
 701     variant: &'a ty::VariantDef,
 702 ) -> Option<&'a ty::FieldDef> {
 703     let param_env = tcx.param_env(variant.def_id);
 704     variant.fields.iter().find(|field| {
 705         let field_ty = tcx.type_of(field.did);
 706         let is_zst = tcx.layout_of(param_env.and(field_ty)).map_or(false, |layout| layout.is_zst());
 707         !is_zst
 708     })
 709 }
 710
 711 /// Is type known to be non-null?
 712 fn ty_is_known_nonnull<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, mode: CItemKind) -> bool {
 713     let tcx = cx.tcx;
 714     match ty.kind() {
 715         ty::FnPtr(_) => true,
 716         ty::Ref(..) => true,
 717         ty::Adt(def, _) if def.is_box() && matches!(mode, CItemKind::Definition) => true,
 718         ty::Adt(def, substs) if def.repr().transparent() && !def.is_union() => {
 719             let marked_non_null = nonnull_optimization_guaranteed(tcx, *def);
 720
 721             if marked_non_null {
 722                 return true;
 723             }
 724
 725             // `UnsafeCell` has its niche hidden.
 726             if def.is_unsafe_cell() {
 727                 return false;
 728             }
 729
 730             def.variants()
 731                 .iter()
 732                 .filter_map(|variant| transparent_newtype_field(cx.tcx, variant))
 733                 .any(|field| ty_is_known_nonnull(cx, field.ty(tcx, substs), mode))
 734         }
 735         _ => false,
 736     }
 737 }
 738
 739 /// Given a non-null scalar (or transparent) type `ty`, return the nullable version of that type.
 740 /// If the type passed in was not scalar, returns None.
 741 fn get_nullable_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
 742     let tcx = cx.tcx;
 743     Some(match *ty.kind() {
 744         ty::Adt(field_def, field_substs) => {
 745             let inner_field_ty = {
 746                 let mut first_non_zst_ty = field_def
 747                     .variants()
 748                     .iter()
 749                     .filter_map(|v| transparent_newtype_field(cx.tcx, v));
 750                 debug_assert_eq!(
 751                     first_non_zst_ty.clone().count(),
 752                     1,
 753                     "Wrong number of fields for transparent type"
 754                 );
 755                 first_non_zst_ty
 756                     .next_back()
 757                     .expect("No non-zst fields in transparent type.")
 758                     .ty(tcx, field_substs)
 759             };
 760             return get_nullable_type(cx, inner_field_ty);
 761         }
 762         ty::Int(ty) => tcx.mk_mach_int(ty),
 763         ty::Uint(ty) => tcx.mk_mach_uint(ty),
 764         ty::RawPtr(ty_mut) => tcx.mk_ptr(ty_mut),
 765         // As these types are always non-null, the nullable equivalent of
 766         // Option<T> of these types are their raw pointer counterparts.
 767         ty::Ref(_region, ty, mutbl) => tcx.mk_ptr(ty::TypeAndMut { ty, mutbl }),
 768         ty::FnPtr(..) => {
 769             // There is no nullable equivalent for Rust's function pointers -- you
 770             // must use an Option<fn(..) -> _> to represent it.
 771             ty
 772         }
 773
 774         // We should only ever reach this case if ty_is_known_nonnull is extended
 775         // to other types.
 776         ref unhandled => {
 777             debug!(
 778                 "get_nullable_type: Unhandled scalar kind: {:?} while checking {:?}",
 779                 unhandled, ty
 780             );
 781             return None;
 782         }
 783     })
 784 }
 785
 786 /// Check if this enum can be safely exported based on the "nullable pointer optimization". If it
 787 /// can, return the type that `ty` can be safely converted to, otherwise return `None`.
 788 /// Currently restricted to function pointers, boxes, references, `core::num::NonZero*`,
 789 /// `core::ptr::NonNull`, and `#[repr(transparent)]` newtypes.
 790 /// FIXME: This duplicates code in codegen.
 791 pub(crate) fn repr_nullable_ptr<'tcx>(
 792     cx: &LateContext<'tcx>,
 793     ty: Ty<'tcx>,
 794     ckind: CItemKind,
 795 ) -> Option<Ty<'tcx>> {
 796     debug!("is_repr_nullable_ptr(cx, ty = {:?})", ty);
 797     if let ty::Adt(ty_def, substs) = ty.kind() {
 798         let field_ty = match &ty_def.variants().raw[..] {
 799             [var_one, var_two] => match (&var_one.fields[..], &var_two.fields[..]) {
 800                 ([], [field]) | ([field], []) => field.ty(cx.tcx, substs),
 801                 _ => return None,
 802             },
 803             _ => return None,
 804         };
 805
 806         if !ty_is_known_nonnull(cx, field_ty, ckind) {
 807             return None;
 808         }
 809
 810         // At this point, the field's type is known to be nonnull and the parent enum is Option-like.
 811         // If the computed size for the field and the enum are different, the nonnull optimization isn't
 812         // being applied (and we've got a problem somewhere).
 813         let compute_size_skeleton = |t| SizeSkeleton::compute(t, cx.tcx, cx.param_env).unwrap();
 814         if !compute_size_skeleton(ty).same_size(compute_size_skeleton(field_ty)) {
 815             bug!("improper_ctypes: Option nonnull optimization not applied?");
 816         }
 817
 818         // Return the nullable type this Option-like enum can be safely represented with.
 819         let field_ty_abi = &cx.layout_of(field_ty).unwrap().abi;
 820         if let Abi::Scalar(field_ty_scalar) = field_ty_abi {
 821             match field_ty_scalar.valid_range(cx) {
 822                 WrappingRange { start: 0, end }
 823                     if end == field_ty_scalar.size(&cx.tcx).unsigned_int_max() - 1 =>
 824                 {
 825                     return Some(get_nullable_type(cx, field_ty).unwrap());
 826                 }
 827                 WrappingRange { start: 1, .. } => {
 828                     return Some(get_nullable_type(cx, field_ty).unwrap());
 829                 }
 830                 WrappingRange { start, end } => {
 831                     unreachable!("Unhandled start and end range: ({}, {})", start, end)
 832                 }
 833             };
 834         }
 835     }
 836     None
 837 }
 838
 839 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
 840     /// Check if the type is array and emit an unsafe type lint.
 841     fn check_for_array_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
 842         if let ty::Array(..) = ty.kind() {
 843             self.emit_ffi_unsafe_type_lint(
 844                 ty,
 845                 sp,
 846                 fluent::lint_improper_ctypes_array_reason,
 847                 Some(fluent::lint_improper_ctypes_array_help),
 848             );
 849             true
 850         } else {
 851             false
 852         }
 853     }
 854
 855     /// Checks if the given field's type is "ffi-safe".
 856     fn check_field_type_for_ffi(
 857         &self,
 858         cache: &mut FxHashSet<Ty<'tcx>>,
 859         field: &ty::FieldDef,
 860         substs: SubstsRef<'tcx>,
 861     ) -> FfiResult<'tcx> {
 862         let field_ty = field.ty(self.cx.tcx, substs);
 863         if field_ty.has_opaque_types() {
 864             self.check_type_for_ffi(cache, field_ty)
 865         } else {
 866             let field_ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, field_ty);
 867             self.check_type_for_ffi(cache, field_ty)
 868         }
 869     }
 870
 871     /// Checks if the given `VariantDef`'s field types are "ffi-safe".
 872     fn check_variant_for_ffi(
 873         &self,
 874         cache: &mut FxHashSet<Ty<'tcx>>,
 875         ty: Ty<'tcx>,
 876         def: ty::AdtDef<'tcx>,
 877         variant: &ty::VariantDef,
 878         substs: SubstsRef<'tcx>,
 879     ) -> FfiResult<'tcx> {
 880         use FfiResult::*;
 881
 882         if def.repr().transparent() {
 883             // Can assume that at most one field is not a ZST, so only check
 884             // that field's type for FFI-safety.
 885             if let Some(field) = transparent_newtype_field(self.cx.tcx, variant) {
 886                 self.check_field_type_for_ffi(cache, field, substs)
 887             } else {
 888                 // All fields are ZSTs; this means that the type should behave
 889                 // like (), which is FFI-unsafe
 890                 FfiUnsafe { ty, reason: fluent::lint_improper_ctypes_struct_zst, help: None }
 891             }
 892         } else {
 893             // We can't completely trust repr(C) markings; make sure the fields are
 894             // actually safe.
 895             let mut all_phantom = !variant.fields.is_empty();
 896             for field in &variant.fields {
 897                 match self.check_field_type_for_ffi(cache, &field, substs) {
 898                     FfiSafe => {
 899                         all_phantom = false;
 900                     }
 901                     FfiPhantom(..) if def.is_enum() => {
 902                         return FfiUnsafe {
 903                             ty,
 904                             reason: fluent::lint_improper_ctypes_enum_phantomdata,
 905                             help: None,
 906                         };
 907                     }
 908                     FfiPhantom(..) => {}
 909                     r => return r,
 910                 }
 911             }
 912
 913             if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 914         }
 915     }
 916
 917     /// Checks if the given type is "ffi-safe" (has a stable, well-defined
 918     /// representation which can be exported to C code).
 919     fn check_type_for_ffi(&self, cache: &mut FxHashSet<Ty<'tcx>>, ty: Ty<'tcx>) -> FfiResult<'tcx> {
 920         use FfiResult::*;
 921
 922         let tcx = self.cx.tcx;
 923
 924         // Protect against infinite recursion, for example
 925         // `struct S(*mut S);`.
 926         // FIXME: A recursion limit is necessary as well, for irregular
 927         // recursive types.
 928         if !cache.insert(ty) {
 929             return FfiSafe;
 930         }
 931
 932         match *ty.kind() {
 933             ty::Adt(def, substs) => {
 934                 if def.is_box() && matches!(self.mode, CItemKind::Definition) {
 935                     if ty.boxed_ty().is_sized(tcx, self.cx.param_env) {
 936                         return FfiSafe;
 937                     } else {
 938                         return FfiUnsafe {
 939                             ty,
 940                             reason: fluent::lint_improper_ctypes_box,
 941                             help: None,
 942                         };
 943                     }
 944                 }
 945                 if def.is_phantom_data() {
 946                     return FfiPhantom(ty);
 947                 }
 948                 match def.adt_kind() {
 949                     AdtKind::Struct | AdtKind::Union => {
 950                         if !def.repr().c() && !def.repr().transparent() {
 951                             return FfiUnsafe {
 952                                 ty,
 953                                 reason: if def.is_struct() {
 954                                     fluent::lint_improper_ctypes_struct_layout_reason
 955                                 } else {
 956                                     fluent::lint_improper_ctypes_union_layout_reason
 957                                 },
 958                                 help: if def.is_struct() {
 959                                     Some(fluent::lint_improper_ctypes_struct_layout_help)
 960                                 } else {
 961                                     Some(fluent::lint_improper_ctypes_union_layout_help)
 962                                 },
 963                             };
 964                         }
 965
 966                         let is_non_exhaustive =
 967                             def.non_enum_variant().is_field_list_non_exhaustive();
 968                         if is_non_exhaustive && !def.did().is_local() {
 969                             return FfiUnsafe {
 970                                 ty,
 971                                 reason: if def.is_struct() {
 972                                     fluent::lint_improper_ctypes_struct_non_exhaustive
 973                                 } else {
 974                                     fluent::lint_improper_ctypes_union_non_exhaustive
 975                                 },
 976                                 help: None,
 977                             };
 978                         }
 979
 980                         if def.non_enum_variant().fields.is_empty() {
 981                             return FfiUnsafe {
 982                                 ty,
 983                                 reason: if def.is_struct() {
 984                                     fluent::lint_improper_ctypes_struct_fieldless_reason
 985                                 } else {
 986                                     fluent::lint_improper_ctypes_union_fieldless_reason
 987                                 },
 988                                 help: if def.is_struct() {
 989                                     Some(fluent::lint_improper_ctypes_struct_fieldless_help)
 990                                 } else {
 991                                     Some(fluent::lint_improper_ctypes_union_fieldless_help)
 992                                 },
 993                             };
 994                         }
 995
 996                         self.check_variant_for_ffi(cache, ty, def, def.non_enum_variant(), substs)
 997                     }
 998                     AdtKind::Enum => {
 999                         if def.variants().is_empty() {
1000                             // Empty enums are okay... although sort of useless.
1001                             return FfiSafe;
1002                         }
1003
1004                         // Check for a repr() attribute to specify the size of the
1005                         // discriminant.
1006                         if !def.repr().c() && !def.repr().transparent() && def.repr().int.is_none()
1007                         {
1008                             // Special-case types like `Option<extern fn()>`.
1009                             if repr_nullable_ptr(self.cx, ty, self.mode).is_none() {
1010                                 return FfiUnsafe {
1011                                     ty,
1012                                     reason: fluent::lint_improper_ctypes_enum_repr_reason,
1013                                     help: Some(fluent::lint_improper_ctypes_enum_repr_help),
1014                                 };
1015                             }
1016                         }
1017
1018                         if def.is_variant_list_non_exhaustive() && !def.did().is_local() {
1019                             return FfiUnsafe {
1020                                 ty,
1021                                 reason: fluent::lint_improper_ctypes_non_exhaustive,
1022                                 help: None,
1023                             };
1024                         }
1025
1026                         // Check the contained variants.
1027                         for variant in def.variants() {
1028                             let is_non_exhaustive = variant.is_field_list_non_exhaustive();
1029                             if is_non_exhaustive && !variant.def_id.is_local() {
1030                                 return FfiUnsafe {
1031                                     ty,
1032                                     reason: fluent::lint_improper_ctypes_non_exhaustive_variant,
1033                                     help: None,
1034                                 };
1035                             }
1036
1037                             match self.check_variant_for_ffi(cache, ty, def, variant, substs) {
1038                                 FfiSafe => (),
1039                                 r => return r,
1040                             }
1041                         }
1042
1043                         FfiSafe
1044                     }
1045                 }
1046             }
1047
1048             ty::Char => FfiUnsafe {
1049                 ty,
1050                 reason: fluent::lint_improper_ctypes_char_reason,
1051                 help: Some(fluent::lint_improper_ctypes_char_help),
1052             },
1053
1054             ty::Int(ty::IntTy::I128) | ty::Uint(ty::UintTy::U128) => {
1055                 FfiUnsafe { ty, reason: fluent::lint_improper_ctypes_128bit, help: None }
1056             }
1057
1058             // Primitive types with a stable representation.
1059             ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
1060
1061             ty::Slice(_) => FfiUnsafe {
1062                 ty,
1063                 reason: fluent::lint_improper_ctypes_slice_reason,
1064                 help: Some(fluent::lint_improper_ctypes_slice_help),
1065             },
1066
1067             ty::Dynamic(..) => {
1068                 FfiUnsafe { ty, reason: fluent::lint_improper_ctypes_dyn, help: None }
1069             }
1070
1071             ty::Str => FfiUnsafe {
1072                 ty,
1073                 reason: fluent::lint_improper_ctypes_str_reason,
1074                 help: Some(fluent::lint_improper_ctypes_str_help),
1075             },
1076
1077             ty::Tuple(..) => FfiUnsafe {
1078                 ty,
1079                 reason: fluent::lint_improper_ctypes_tuple_reason,
1080                 help: Some(fluent::lint_improper_ctypes_tuple_help),
1081             },
1082
1083             ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _)
1084                 if {
1085                     matches!(self.mode, CItemKind::Definition)
1086                         && ty.is_sized(self.cx.tcx, self.cx.param_env)
1087                 } =>
1088             {
1089                 FfiSafe
1090             }
1091
1092             ty::RawPtr(ty::TypeAndMut { ty, .. })
1093                 if match ty.kind() {
1094                     ty::Tuple(tuple) => tuple.is_empty(),
1095                     _ => false,
1096                 } =>
1097             {
1098                 FfiSafe
1099             }
1100
1101             ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _) => {
1102                 self.check_type_for_ffi(cache, ty)
1103             }
1104
1105             ty::Array(inner_ty, _) => self.check_type_for_ffi(cache, inner_ty),
1106
1107             ty::FnPtr(sig) => {
1108                 if self.is_internal_abi(sig.abi()) {
1109                     return FfiUnsafe {
1110                         ty,
1111                         reason: fluent::lint_improper_ctypes_fnptr_reason,
1112                         help: Some(fluent::lint_improper_ctypes_fnptr_help),
1113                     };
1114                 }
1115
1116                 let sig = tcx.erase_late_bound_regions(sig);
1117                 if !sig.output().is_unit() {
1118                     let r = self.check_type_for_ffi(cache, sig.output());
1119                     match r {
1120                         FfiSafe => {}
1121                         _ => {
1122                             return r;
1123                         }
1124                     }
1125                 }
1126                 for arg in sig.inputs() {
1127                     let r = self.check_type_for_ffi(cache, *arg);
1128                     match r {
1129                         FfiSafe => {}
1130                         _ => {
1131                             return r;
1132                         }
1133                     }
1134                 }
1135                 FfiSafe
1136             }
1137
1138             ty::Foreign(..) => FfiSafe,
1139
1140             // While opaque types are checked for earlier, if a projection in a struct field
1141             // normalizes to an opaque type, then it will reach this branch.
1142             ty::Alias(ty::Opaque, ..) => {
1143                 FfiUnsafe { ty, reason: fluent::lint_improper_ctypes_opaque, help: None }
1144             }
1145
1146             // `extern "C" fn` functions can have type parameters, which may or may not be FFI-safe,
1147             //  so they are currently ignored for the purposes of this lint.
1148             ty::Param(..) | ty::Alias(ty::Projection, ..)
1149                 if matches!(self.mode, CItemKind::Definition) =>
1150             {
1151                 FfiSafe
1152             }
1153
1154             ty::Param(..)
1155             | ty::Alias(ty::Projection, ..)
1156             | ty::Infer(..)
1157             | ty::Bound(..)
1158             | ty::Error(_)
1159             | ty::Closure(..)
1160             | ty::Generator(..)
1161             | ty::GeneratorWitness(..)
1162             | ty::Placeholder(..)
1163             | ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty),
1164         }
1165     }
1166
1167     fn emit_ffi_unsafe_type_lint(
1168         &mut self,
1169         ty: Ty<'tcx>,
1170         sp: Span,
1171         note: DiagnosticMessage,
1172         help: Option<DiagnosticMessage>,
1173     ) {
1174         let lint = match self.mode {
1175             CItemKind::Declaration => IMPROPER_CTYPES,
1176             CItemKind::Definition => IMPROPER_CTYPES_DEFINITIONS,
1177         };
1178
1179         self.cx.struct_span_lint(lint, sp, fluent::lint_improper_ctypes, |lint| {
1180             let item_description = match self.mode {
1181                 CItemKind::Declaration => "block",
1182                 CItemKind::Definition => "fn",
1183             };
1184             lint.set_arg("ty", ty);
1185             lint.set_arg("desc", item_description);
1186             lint.span_label(sp, fluent::label);
1187             if let Some(help) = help {
1188                 lint.help(help);
1189             }
1190             lint.note(note);
1191             if let ty::Adt(def, _) = ty.kind() {
1192                 if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did()) {
1193                     lint.span_note(sp, fluent::note);
1194                 }
1195             }
1196             lint
1197         });
1198     }
1199
1200     fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
1201         struct ProhibitOpaqueTypes;
1202         impl<'tcx> ty::visit::TypeVisitor<'tcx> for ProhibitOpaqueTypes {
1203             type BreakTy = Ty<'tcx>;
1204
1205             fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1206                 if !ty.has_opaque_types() {
1207                     return ControlFlow::CONTINUE;
1208                 }
1209
1210                 if let ty::Alias(ty::Opaque, ..) = ty.kind() {
1211                     ControlFlow::Break(ty)
1212                 } else {
1213                     ty.super_visit_with(self)
1214                 }
1215             }
1216         }
1217
1218         if let Some(ty) = self
1219             .cx
1220             .tcx
1221             .normalize_erasing_regions(self.cx.param_env, ty)
1222             .visit_with(&mut ProhibitOpaqueTypes)
1223             .break_value()
1224         {
1225             self.emit_ffi_unsafe_type_lint(ty, sp, fluent::lint_improper_ctypes_opaque, None);
1226             true
1227         } else {
1228             false
1229         }
1230     }
1231
1232     fn check_type_for_ffi_and_report_errors(
1233         &mut self,
1234         sp: Span,
1235         ty: Ty<'tcx>,
1236         is_static: bool,
1237         is_return_type: bool,
1238     ) {
1239         // We have to check for opaque types before `normalize_erasing_regions`,
1240         // which will replace opaque types with their underlying concrete type.
1241         if self.check_for_opaque_ty(sp, ty) {
1242             // We've already emitted an error due to an opaque type.
1243             return;
1244         }
1245
1246         // it is only OK to use this function because extern fns cannot have
1247         // any generic types right now:
1248         let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
1249
1250         // C doesn't really support passing arrays by value - the only way to pass an array by value
1251         // is through a struct. So, first test that the top level isn't an array, and then
1252         // recursively check the types inside.
1253         if !is_static && self.check_for_array_ty(sp, ty) {
1254             return;
1255         }
1256
1257         // Don't report FFI errors for unit return types. This check exists here, and not in
1258         // `check_foreign_fn` (where it would make more sense) so that normalization has definitely
1259         // happened.
1260         if is_return_type && ty.is_unit() {
1261             return;
1262         }
1263
1264         match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
1265             FfiResult::FfiSafe => {}
1266             FfiResult::FfiPhantom(ty) => {
1267                 self.emit_ffi_unsafe_type_lint(
1268                     ty,
1269                     sp,
1270                     fluent::lint_improper_ctypes_only_phantomdata,
1271                     None,
1272                 );
1273             }
1274             // If `ty` is a `repr(transparent)` newtype, and the non-zero-sized type is a generic
1275             // argument, which after substitution, is `()`, then this branch can be hit.
1276             FfiResult::FfiUnsafe { ty, .. } if is_return_type && ty.is_unit() => {}
1277             FfiResult::FfiUnsafe { ty, reason, help } => {
1278                 self.emit_ffi_unsafe_type_lint(ty, sp, reason, help);
1279             }
1280         }
1281     }
1282
1283     fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl<'_>) {
1284         let def_id = self.cx.tcx.hir().local_def_id(id);
1285         let sig = self.cx.tcx.fn_sig(def_id);
1286         let sig = self.cx.tcx.erase_late_bound_regions(sig);
1287
1288         for (input_ty, input_hir) in iter::zip(sig.inputs(), decl.inputs) {
1289             self.check_type_for_ffi_and_report_errors(input_hir.span, *input_ty, false, false);
1290         }
1291
1292         if let hir::FnRetTy::Return(ref ret_hir) = decl.output {
1293             let ret_ty = sig.output();
1294             self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty, false, true);
1295         }
1296     }
1297
1298     fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
1299         let def_id = self.cx.tcx.hir().local_def_id(id);
1300         let ty = self.cx.tcx.type_of(def_id);
1301         self.check_type_for_ffi_and_report_errors(span, ty, true, false);
1302     }
1303
1304     fn is_internal_abi(&self, abi: SpecAbi) -> bool {
1305         matches!(
1306             abi,
1307             SpecAbi::Rust | SpecAbi::RustCall | SpecAbi::RustIntrinsic | SpecAbi::PlatformIntrinsic
1308         )
1309     }
1310 }
1311
1312 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDeclarations {
1313     fn check_foreign_item(&mut self, cx: &LateContext<'_>, it: &hir::ForeignItem<'_>) {
1314         let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Declaration };
1315         let abi = cx.tcx.hir().get_foreign_abi(it.hir_id());
1316
1317         if !vis.is_internal_abi(abi) {
1318             match it.kind {
1319                 hir::ForeignItemKind::Fn(ref decl, _, _) => {
1320                     vis.check_foreign_fn(it.hir_id(), decl);
1321                 }
1322                 hir::ForeignItemKind::Static(ref ty, _) => {
1323                     vis.check_foreign_static(it.hir_id(), ty.span);
1324                 }
1325                 hir::ForeignItemKind::Type => (),
1326             }
1327         }
1328     }
1329 }
1330
1331 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDefinitions {
1332     fn check_fn(
1333         &mut self,
1334         cx: &LateContext<'tcx>,
1335         kind: hir::intravisit::FnKind<'tcx>,
1336         decl: &'tcx hir::FnDecl<'_>,
1337         _: &'tcx hir::Body<'_>,
1338         _: Span,
1339         hir_id: hir::HirId,
1340     ) {
1341         use hir::intravisit::FnKind;
1342
1343         let abi = match kind {
1344             FnKind::ItemFn(_, _, header, ..) => header.abi,
1345             FnKind::Method(_, sig, ..) => sig.header.abi,
1346             _ => return,
1347         };
1348
1349         let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Definition };
1350         if !vis.is_internal_abi(abi) {
1351             vis.check_foreign_fn(hir_id, decl);
1352         }
1353     }
1354 }
1355
1356 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
1357
1358 impl<'tcx> LateLintPass<'tcx> for VariantSizeDifferences {
1359     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1360         if let hir::ItemKind::Enum(ref enum_definition, _) = it.kind {
1361             let t = cx.tcx.type_of(it.owner_id);
1362             let ty = cx.tcx.erase_regions(t);
1363             let Ok(layout) = cx.layout_of(ty) else { return };
1364             let Variants::Multiple {
1365                     tag_encoding: TagEncoding::Direct, tag, ref variants, ..
1366                 } = &layout.variants else {
1367                 return
1368             };
1369
1370             let tag_size = tag.size(&cx.tcx).bytes();
1371
1372             debug!(
1373                 "enum `{}` is {} bytes large with layout:\n{:#?}",
1374                 t,
1375                 layout.size.bytes(),
1376                 layout
1377             );
1378
1379             let (largest, slargest, largest_index) = iter::zip(enum_definition.variants, variants)
1380                 .map(|(variant, variant_layout)| {
1381                     // Subtract the size of the enum tag.
1382                     let bytes = variant_layout.size.bytes().saturating_sub(tag_size);
1383
1384                     debug!("- variant `{}` is {} bytes large", variant.ident, bytes);
1385                     bytes
1386                 })
1387                 .enumerate()
1388                 .fold((0, 0, 0), |(l, s, li), (idx, size)| {
1389                     if size > l {
1390                         (size, l, idx)
1391                     } else if size > s {
1392                         (l, size, li)
1393                     } else {
1394                         (l, s, li)
1395                     }
1396                 });
1397
1398             // We only warn if the largest variant is at least thrice as large as
1399             // the second-largest.
1400             if largest > slargest * 3 && slargest > 0 {
1401                 cx.struct_span_lint(
1402                     VARIANT_SIZE_DIFFERENCES,
1403                     enum_definition.variants[largest_index].span,
1404                     fluent::lint_variant_size_differences,
1405                     |lint| lint.set_arg("largest", largest),
1406                 );
1407             }
1408         }
1409     }
1410 }
1411
1412 declare_lint! {
1413     /// The `invalid_atomic_ordering` lint detects passing an `Ordering`
1414     /// to an atomic operation that does not support that ordering.
1415     ///
1416     /// ### Example
1417     ///
1418     /// ```rust,compile_fail
1419     /// # use core::sync::atomic::{AtomicU8, Ordering};
1420     /// let atom = AtomicU8::new(0);
1421     /// let value = atom.load(Ordering::Release);
1422     /// # let _ = value;
1423     /// ```
1424     ///
1425     /// {{produces}}
1426     ///
1427     /// ### Explanation
1428     ///
1429     /// Some atomic operations are only supported for a subset of the
1430     /// `atomic::Ordering` variants. Passing an unsupported variant will cause
1431     /// an unconditional panic at runtime, which is detected by this lint.
1432     ///
1433     /// This lint will trigger in the following cases: (where `AtomicType` is an
1434     /// atomic type from `core::sync::atomic`, such as `AtomicBool`,
1435     /// `AtomicPtr`, `AtomicUsize`, or any of the other integer atomics).
1436     ///
1437     /// - Passing `Ordering::Acquire` or `Ordering::AcqRel` to
1438     ///   `AtomicType::store`.
1439     ///
1440     /// - Passing `Ordering::Release` or `Ordering::AcqRel` to
1441     ///   `AtomicType::load`.
1442     ///
1443     /// - Passing `Ordering::Relaxed` to `core::sync::atomic::fence` or
1444     ///   `core::sync::atomic::compiler_fence`.
1445     ///
1446     /// - Passing `Ordering::Release` or `Ordering::AcqRel` as the failure
1447     ///   ordering for any of `AtomicType::compare_exchange`,
1448     ///   `AtomicType::compare_exchange_weak`, or `AtomicType::fetch_update`.
1449     INVALID_ATOMIC_ORDERING,
1450     Deny,
1451     "usage of invalid atomic ordering in atomic operations and memory fences"
1452 }
1453
1454 declare_lint_pass!(InvalidAtomicOrdering => [INVALID_ATOMIC_ORDERING]);
1455
1456 impl InvalidAtomicOrdering {
1457     fn inherent_atomic_method_call<'hir>(
1458         cx: &LateContext<'_>,
1459         expr: &Expr<'hir>,
1460         recognized_names: &[Symbol], // used for fast path calculation
1461     ) -> Option<(Symbol, &'hir [Expr<'hir>])> {
1462         const ATOMIC_TYPES: &[Symbol] = &[
1463             sym::AtomicBool,
1464             sym::AtomicPtr,
1465             sym::AtomicUsize,
1466             sym::AtomicU8,
1467             sym::AtomicU16,
1468             sym::AtomicU32,
1469             sym::AtomicU64,
1470             sym::AtomicU128,
1471             sym::AtomicIsize,
1472             sym::AtomicI8,
1473             sym::AtomicI16,
1474             sym::AtomicI32,
1475             sym::AtomicI64,
1476             sym::AtomicI128,
1477         ];
1478         if let ExprKind::MethodCall(ref method_path, _, args, _) = &expr.kind
1479             && recognized_names.contains(&method_path.ident.name)
1480             && let Some(m_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id)
1481             && let Some(impl_did) = cx.tcx.impl_of_method(m_def_id)
1482             && let Some(adt) = cx.tcx.type_of(impl_did).ty_adt_def()
1483             // skip extension traits, only lint functions from the standard library
1484             && cx.tcx.trait_id_of_impl(impl_did).is_none()
1485             && let parent = cx.tcx.parent(adt.did())
1486             && cx.tcx.is_diagnostic_item(sym::atomic_mod, parent)
1487             && ATOMIC_TYPES.contains(&cx.tcx.item_name(adt.did()))
1488         {
1489             return Some((method_path.ident.name, args));
1490         }
1491         None
1492     }
1493
1494     fn match_ordering(cx: &LateContext<'_>, ord_arg: &Expr<'_>) -> Option<Symbol> {
1495         let ExprKind::Path(ref ord_qpath) = ord_arg.kind else { return None };
1496         let did = cx.qpath_res(ord_qpath, ord_arg.hir_id).opt_def_id()?;
1497         let tcx = cx.tcx;
1498         let atomic_ordering = tcx.get_diagnostic_item(sym::Ordering);
1499         let name = tcx.item_name(did);
1500         let parent = tcx.parent(did);
1501         [sym::Relaxed, sym::Release, sym::Acquire, sym::AcqRel, sym::SeqCst].into_iter().find(
1502             |&ordering| {
1503                 name == ordering
1504                     && (Some(parent) == atomic_ordering
1505                             // needed in case this is a ctor, not a variant
1506                             || tcx.opt_parent(parent) == atomic_ordering)
1507             },
1508         )
1509     }
1510
1511     fn check_atomic_load_store(cx: &LateContext<'_>, expr: &Expr<'_>) {
1512         if let Some((method, args)) = Self::inherent_atomic_method_call(cx, expr, &[sym::load, sym::store])
1513             && let Some((ordering_arg, invalid_ordering, msg)) = match method {
1514                 sym::load => Some((&args[0], sym::Release, fluent::lint_atomic_ordering_load)),
1515                 sym::store => Some((&args[1], sym::Acquire, fluent::lint_atomic_ordering_store)),
1516                 _ => None,
1517             }
1518             && let Some(ordering) = Self::match_ordering(cx, ordering_arg)
1519             && (ordering == invalid_ordering || ordering == sym::AcqRel)
1520         {
1521             cx.struct_span_lint(INVALID_ATOMIC_ORDERING, ordering_arg.span, msg, |lint| {
1522                 lint.help(fluent::help)
1523             });
1524         }
1525     }
1526
1527     fn check_memory_fence(cx: &LateContext<'_>, expr: &Expr<'_>) {
1528         if let ExprKind::Call(ref func, ref args) = expr.kind
1529             && let ExprKind::Path(ref func_qpath) = func.kind
1530             && let Some(def_id) = cx.qpath_res(func_qpath, func.hir_id).opt_def_id()
1531             && matches!(cx.tcx.get_diagnostic_name(def_id), Some(sym::fence | sym::compiler_fence))
1532             && Self::match_ordering(cx, &args[0]) == Some(sym::Relaxed)
1533         {
1534             cx.struct_span_lint(INVALID_ATOMIC_ORDERING, args[0].span, fluent::lint_atomic_ordering_fence, |lint| {
1535                 lint
1536                     .help(fluent::help)
1537             });
1538         }
1539     }
1540
1541     fn check_atomic_compare_exchange(cx: &LateContext<'_>, expr: &Expr<'_>) {
1542         let Some((method, args)) = Self::inherent_atomic_method_call(cx, expr, &[sym::fetch_update, sym::compare_exchange, sym::compare_exchange_weak])
1543             else {return };
1544
1545         let fail_order_arg = match method {
1546             sym::fetch_update => &args[1],
1547             sym::compare_exchange | sym::compare_exchange_weak => &args[3],
1548             _ => return,
1549         };
1550
1551         let Some(fail_ordering) = Self::match_ordering(cx, fail_order_arg) else { return };
1552
1553         if matches!(fail_ordering, sym::Release | sym::AcqRel) {
1554             #[derive(LintDiagnostic)]
1555             #[diag(lint_atomic_ordering_invalid)]
1556             #[help]
1557             struct InvalidAtomicOrderingDiag {
1558                 method: Symbol,
1559                 #[label]
1560                 fail_order_arg_span: Span,
1561             }
1562
1563             cx.emit_spanned_lint(
1564                 INVALID_ATOMIC_ORDERING,
1565                 fail_order_arg.span,
1566                 InvalidAtomicOrderingDiag { method, fail_order_arg_span: fail_order_arg.span },
1567             );
1568         }
1569     }
1570 }
1571
1572 impl<'tcx> LateLintPass<'tcx> for InvalidAtomicOrdering {
1573     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
1574         Self::check_atomic_load_store(cx, expr);
1575         Self::check_memory_fence(cx, expr);
1576         Self::check_atomic_compare_exchange(cx, expr);
1577     }
1578 }