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, DUMMY_SP};
  15 use rustc_target::abi::{Abi, 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.
 120 /// Returns `true` iff the lint was overridden.
 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     let mut overwritten = false;
 144     // We can suggest using an inclusive range
 145     // (`..=`) instead only if it is the `end` that is
 146     // overflowing and only by 1.
 147     if eps[1].expr.hir_id == expr.hir_id && lit_val - 1 == max {
 148         cx.struct_span_lint(OVERFLOWING_LITERALS, struct_expr.span, |lint| {
 149             let mut err = lint.build(fluent::lint::range_endpoint_out_of_range);
 150             err.set_arg("ty", ty);
 151             if let Ok(start) = cx.sess().source_map().span_to_snippet(eps[0].span) {
 152                 use ast::{LitIntType, LitKind};
 153                 // We need to preserve the literal's suffix,
 154                 // as it may determine typing information.
 155                 let suffix = match lit.node {
 156                     LitKind::Int(_, LitIntType::Signed(s)) => s.name_str(),
 157                     LitKind::Int(_, LitIntType::Unsigned(s)) => s.name_str(),
 158                     LitKind::Int(_, LitIntType::Unsuffixed) => "",
 159                     _ => bug!(),
 160                 };
 161                 let suggestion = format!("{}..={}{}", start, lit_val - 1, suffix);
 162                 err.span_suggestion(
 163                     struct_expr.span,
 164                     fluent::lint::suggestion,
 165                     suggestion,
 166                     Applicability::MachineApplicable,
 167                 );
 168                 err.emit();
 169                 overwritten = true;
 170             }
 171         });
 172     }
 173     overwritten
 174 }
 175
 176 // For `isize` & `usize`, be conservative with the warnings, so that the
 177 // warnings are consistent between 32- and 64-bit platforms.
 178 fn int_ty_range(int_ty: ty::IntTy) -> (i128, i128) {
 179     match int_ty {
 180         ty::IntTy::Isize => (i64::MIN.into(), i64::MAX.into()),
 181         ty::IntTy::I8 => (i8::MIN.into(), i8::MAX.into()),
 182         ty::IntTy::I16 => (i16::MIN.into(), i16::MAX.into()),
 183         ty::IntTy::I32 => (i32::MIN.into(), i32::MAX.into()),
 184         ty::IntTy::I64 => (i64::MIN.into(), i64::MAX.into()),
 185         ty::IntTy::I128 => (i128::MIN, i128::MAX),
 186     }
 187 }
 188
 189 fn uint_ty_range(uint_ty: ty::UintTy) -> (u128, u128) {
 190     let max = match uint_ty {
 191         ty::UintTy::Usize => u64::MAX.into(),
 192         ty::UintTy::U8 => u8::MAX.into(),
 193         ty::UintTy::U16 => u16::MAX.into(),
 194         ty::UintTy::U32 => u32::MAX.into(),
 195         ty::UintTy::U64 => u64::MAX.into(),
 196         ty::UintTy::U128 => u128::MAX,
 197     };
 198     (0, max)
 199 }
 200
 201 fn get_bin_hex_repr(cx: &LateContext<'_>, lit: &hir::Lit) -> Option<String> {
 202     let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?;
 203     let firstch = src.chars().next()?;
 204
 205     if firstch == '0' {
 206         match src.chars().nth(1) {
 207             Some('x' | 'b') => return Some(src),
 208             _ => return None,
 209         }
 210     }
 211
 212     None
 213 }
 214
 215 fn report_bin_hex_error(
 216     cx: &LateContext<'_>,
 217     expr: &hir::Expr<'_>,
 218     ty: attr::IntType,
 219     repr_str: String,
 220     val: u128,
 221     negative: bool,
 222 ) {
 223     let size = Integer::from_attr(&cx.tcx, ty).size();
 224     cx.struct_span_lint(OVERFLOWING_LITERALS, expr.span, |lint| {
 225         let (t, actually) = match ty {
 226             attr::IntType::SignedInt(t) => {
 227                 let actually = if negative {
 228                     -(size.sign_extend(val) as i128)
 229                 } else {
 230                     size.sign_extend(val) as i128
 231                 };
 232                 (t.name_str(), actually.to_string())
 233             }
 234             attr::IntType::UnsignedInt(t) => {
 235                 let actually = size.truncate(val);
 236                 (t.name_str(), actually.to_string())
 237             }
 238         };
 239         let mut err = lint.build(fluent::lint::overflowing_bin_hex);
 240         if negative {
 241             // If the value is negative,
 242             // emits a note about the value itself, apart from the literal.
 243             err.note(fluent::lint::negative_note);
 244             err.note(fluent::lint::negative_becomes_note);
 245         } else {
 246             err.note(fluent::lint::positive_note);
 247         }
 248         if let Some(sugg_ty) =
 249             get_type_suggestion(cx.typeck_results().node_type(expr.hir_id), val, negative)
 250         {
 251             err.set_arg("suggestion_ty", sugg_ty);
 252             if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') {
 253                 let (sans_suffix, _) = repr_str.split_at(pos);
 254                 err.span_suggestion(
 255                     expr.span,
 256                     fluent::lint::suggestion,
 257                     format!("{}{}", sans_suffix, sugg_ty),
 258                     Applicability::MachineApplicable,
 259                 );
 260             } else {
 261                 err.help(fluent::lint::help);
 262             }
 263         }
 264         err.set_arg("ty", t);
 265         err.set_arg("lit", repr_str);
 266         err.set_arg("dec", val);
 267         err.set_arg("actually", actually);
 268         err.emit();
 269     });
 270 }
 271
 272 // This function finds the next fitting type and generates a suggestion string.
 273 // It searches for fitting types in the following way (`X < Y`):
 274 //  - `iX`: if literal fits in `uX` => `uX`, else => `iY`
 275 //  - `-iX` => `iY`
 276 //  - `uX` => `uY`
 277 //
 278 // No suggestion for: `isize`, `usize`.
 279 fn get_type_suggestion(t: Ty<'_>, val: u128, negative: bool) -> Option<&'static str> {
 280     use ty::IntTy::*;
 281     use ty::UintTy::*;
 282     macro_rules! find_fit {
 283         ($ty:expr, $val:expr, $negative:expr,
 284          $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => {
 285             {
 286                 let _neg = if negative { 1 } else { 0 };
 287                 match $ty {
 288                     $($type => {
 289                         $(if !negative && val <= uint_ty_range($utypes).1 {
 290                             return Some($utypes.name_str())
 291                         })*
 292                         $(if val <= int_ty_range($itypes).1 as u128 + _neg {
 293                             return Some($itypes.name_str())
 294                         })*
 295                         None
 296                     },)+
 297                     _ => None
 298                 }
 299             }
 300         }
 301     }
 302     match t.kind() {
 303         ty::Int(i) => find_fit!(i, val, negative,
 304                       I8 => [U8] => [I16, I32, I64, I128],
 305                       I16 => [U16] => [I32, I64, I128],
 306                       I32 => [U32] => [I64, I128],
 307                       I64 => [U64] => [I128],
 308                       I128 => [U128] => []),
 309         ty::Uint(u) => find_fit!(u, val, negative,
 310                       U8 => [U8, U16, U32, U64, U128] => [],
 311                       U16 => [U16, U32, U64, U128] => [],
 312                       U32 => [U32, U64, U128] => [],
 313                       U64 => [U64, U128] => [],
 314                       U128 => [U128] => []),
 315         _ => None,
 316     }
 317 }
 318
 319 fn lint_int_literal<'tcx>(
 320     cx: &LateContext<'tcx>,
 321     type_limits: &TypeLimits,
 322     e: &'tcx hir::Expr<'tcx>,
 323     lit: &hir::Lit,
 324     t: ty::IntTy,
 325     v: u128,
 326 ) {
 327     let int_type = t.normalize(cx.sess().target.pointer_width);
 328     let (min, max) = int_ty_range(int_type);
 329     let max = max as u128;
 330     let negative = type_limits.negated_expr_id == Some(e.hir_id);
 331
 332     // Detect literal value out of range [min, max] inclusive
 333     // avoiding use of -min to prevent overflow/panic
 334     if (negative && v > max + 1) || (!negative && v > max) {
 335         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 336             report_bin_hex_error(
 337                 cx,
 338                 e,
 339                 attr::IntType::SignedInt(ty::ast_int_ty(t)),
 340                 repr_str,
 341                 v,
 342                 negative,
 343             );
 344             return;
 345         }
 346
 347         if lint_overflowing_range_endpoint(cx, lit, v, max, e, t.name_str()) {
 348             // The overflowing literal lint was overridden.
 349             return;
 350         }
 351
 352         cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
 353             let mut err = lint.build(fluent::lint::overflowing_int);
 354             err.set_arg("ty", t.name_str());
 355             err.set_arg(
 356                 "lit",
 357                 cx.sess()
 358                     .source_map()
 359                     .span_to_snippet(lit.span)
 360                     .expect("must get snippet from literal"),
 361             );
 362             err.set_arg("min", min);
 363             err.set_arg("max", max);
 364             err.note(fluent::lint::note);
 365             if let Some(sugg_ty) =
 366                 get_type_suggestion(cx.typeck_results().node_type(e.hir_id), v, negative)
 367             {
 368                 err.set_arg("suggestion_ty", sugg_ty);
 369                 err.help(fluent::lint::help);
 370             }
 371             err.emit();
 372         });
 373     }
 374 }
 375
 376 fn lint_uint_literal<'tcx>(
 377     cx: &LateContext<'tcx>,
 378     e: &'tcx hir::Expr<'tcx>,
 379     lit: &hir::Lit,
 380     t: ty::UintTy,
 381 ) {
 382     let uint_type = t.normalize(cx.sess().target.pointer_width);
 383     let (min, max) = uint_ty_range(uint_type);
 384     let lit_val: u128 = match lit.node {
 385         // _v is u8, within range by definition
 386         ast::LitKind::Byte(_v) => return,
 387         ast::LitKind::Int(v, _) => v,
 388         _ => bug!(),
 389     };
 390     if lit_val < min || lit_val > max {
 391         let parent_id = cx.tcx.hir().get_parent_node(e.hir_id);
 392         if let Node::Expr(par_e) = cx.tcx.hir().get(parent_id) {
 393             match par_e.kind {
 394                 hir::ExprKind::Cast(..) => {
 395                     if let ty::Char = cx.typeck_results().expr_ty(par_e).kind() {
 396                         cx.struct_span_lint(OVERFLOWING_LITERALS, par_e.span, |lint| {
 397                             lint.build(fluent::lint::only_cast_u8_to_char)
 398                                 .span_suggestion(
 399                                     par_e.span,
 400                                     fluent::lint::suggestion,
 401                                     format!("'\\u{{{:X}}}'", lit_val),
 402                                     Applicability::MachineApplicable,
 403                                 )
 404                                 .emit();
 405                         });
 406                         return;
 407                     }
 408                 }
 409                 _ => {}
 410             }
 411         }
 412         if lint_overflowing_range_endpoint(cx, lit, lit_val, max, e, t.name_str()) {
 413             // The overflowing literal lint was overridden.
 414             return;
 415         }
 416         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 417             report_bin_hex_error(
 418                 cx,
 419                 e,
 420                 attr::IntType::UnsignedInt(ty::ast_uint_ty(t)),
 421                 repr_str,
 422                 lit_val,
 423                 false,
 424             );
 425             return;
 426         }
 427         cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
 428             lint.build(fluent::lint::overflowing_uint)
 429                 .set_arg("ty", t.name_str())
 430                 .set_arg(
 431                     "lit",
 432                     cx.sess()
 433                         .source_map()
 434                         .span_to_snippet(lit.span)
 435                         .expect("must get snippet from literal"),
 436                 )
 437                 .set_arg("min", min)
 438                 .set_arg("max", max)
 439                 .note(fluent::lint::note)
 440                 .emit();
 441         });
 442     }
 443 }
 444
 445 fn lint_literal<'tcx>(
 446     cx: &LateContext<'tcx>,
 447     type_limits: &TypeLimits,
 448     e: &'tcx hir::Expr<'tcx>,
 449     lit: &hir::Lit,
 450 ) {
 451     match *cx.typeck_results().node_type(e.hir_id).kind() {
 452         ty::Int(t) => {
 453             match lit.node {
 454                 ast::LitKind::Int(v, ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed) => {
 455                     lint_int_literal(cx, type_limits, e, lit, t, v)
 456                 }
 457                 _ => bug!(),
 458             };
 459         }
 460         ty::Uint(t) => lint_uint_literal(cx, e, lit, t),
 461         ty::Float(t) => {
 462             let is_infinite = match lit.node {
 463                 ast::LitKind::Float(v, _) => match t {
 464                     ty::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
 465                     ty::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
 466                 },
 467                 _ => bug!(),
 468             };
 469             if is_infinite == Ok(true) {
 470                 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
 471                     lint.build(fluent::lint::overflowing_literal)
 472                         .set_arg("ty", t.name_str())
 473                         .set_arg(
 474                             "lit",
 475                             cx.sess()
 476                                 .source_map()
 477                                 .span_to_snippet(lit.span)
 478                                 .expect("must get snippet from literal"),
 479                         )
 480                         .note(fluent::lint::note)
 481                         .emit();
 482                 });
 483             }
 484         }
 485         _ => {}
 486     }
 487 }
 488
 489 impl<'tcx> LateLintPass<'tcx> for TypeLimits {
 490     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx hir::Expr<'tcx>) {
 491         match e.kind {
 492             hir::ExprKind::Unary(hir::UnOp::Neg, ref expr) => {
 493                 // propagate negation, if the negation itself isn't negated
 494                 if self.negated_expr_id != Some(e.hir_id) {
 495                     self.negated_expr_id = Some(expr.hir_id);
 496                 }
 497             }
 498             hir::ExprKind::Binary(binop, ref l, ref r) => {
 499                 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
 500                     cx.struct_span_lint(UNUSED_COMPARISONS, e.span, |lint| {
 501                         lint.build(fluent::lint::unused_comparisons).emit();
 502                     });
 503                 }
 504             }
 505             hir::ExprKind::Lit(ref lit) => lint_literal(cx, self, e, lit),
 506             _ => {}
 507         };
 508
 509         fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
 510             match binop.node {
 511                 hir::BinOpKind::Lt => v > min && v <= max,
 512                 hir::BinOpKind::Le => v >= min && v < max,
 513                 hir::BinOpKind::Gt => v >= min && v < max,
 514                 hir::BinOpKind::Ge => v > min && v <= max,
 515                 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
 516                 _ => bug!(),
 517             }
 518         }
 519
 520         fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
 521             source_map::respan(
 522                 binop.span,
 523                 match binop.node {
 524                     hir::BinOpKind::Lt => hir::BinOpKind::Gt,
 525                     hir::BinOpKind::Le => hir::BinOpKind::Ge,
 526                     hir::BinOpKind::Gt => hir::BinOpKind::Lt,
 527                     hir::BinOpKind::Ge => hir::BinOpKind::Le,
 528                     _ => return binop,
 529                 },
 530             )
 531         }
 532
 533         fn check_limits(
 534             cx: &LateContext<'_>,
 535             binop: hir::BinOp,
 536             l: &hir::Expr<'_>,
 537             r: &hir::Expr<'_>,
 538         ) -> bool {
 539             let (lit, expr, swap) = match (&l.kind, &r.kind) {
 540                 (&hir::ExprKind::Lit(_), _) => (l, r, true),
 541                 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
 542                 _ => return true,
 543             };
 544             // Normalize the binop so that the literal is always on the RHS in
 545             // the comparison
 546             let norm_binop = if swap { rev_binop(binop) } else { binop };
 547             match *cx.typeck_results().node_type(expr.hir_id).kind() {
 548                 ty::Int(int_ty) => {
 549                     let (min, max) = int_ty_range(int_ty);
 550                     let lit_val: i128 = match lit.kind {
 551                         hir::ExprKind::Lit(ref li) => match li.node {
 552                             ast::LitKind::Int(
 553                                 v,
 554                                 ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed,
 555                             ) => v as i128,
 556                             _ => return true,
 557                         },
 558                         _ => bug!(),
 559                     };
 560                     is_valid(norm_binop, lit_val, min, max)
 561                 }
 562                 ty::Uint(uint_ty) => {
 563                     let (min, max): (u128, u128) = uint_ty_range(uint_ty);
 564                     let lit_val: u128 = match lit.kind {
 565                         hir::ExprKind::Lit(ref li) => match li.node {
 566                             ast::LitKind::Int(v, _) => v,
 567                             _ => return true,
 568                         },
 569                         _ => bug!(),
 570                     };
 571                     is_valid(norm_binop, lit_val, min, max)
 572                 }
 573                 _ => true,
 574             }
 575         }
 576
 577         fn is_comparison(binop: hir::BinOp) -> bool {
 578             matches!(
 579                 binop.node,
 580                 hir::BinOpKind::Eq
 581                     | hir::BinOpKind::Lt
 582                     | hir::BinOpKind::Le
 583                     | hir::BinOpKind::Ne
 584                     | hir::BinOpKind::Ge
 585                     | hir::BinOpKind::Gt
 586             )
 587         }
 588     }
 589 }
 590
 591 declare_lint! {
 592     /// The `improper_ctypes` lint detects incorrect use of types in foreign
 593     /// modules.
 594     ///
 595     /// ### Example
 596     ///
 597     /// ```rust
 598     /// extern "C" {
 599     ///     static STATIC: String;
 600     /// }
 601     /// ```
 602     ///
 603     /// {{produces}}
 604     ///
 605     /// ### Explanation
 606     ///
 607     /// The compiler has several checks to verify that types used in `extern`
 608     /// blocks are safe and follow certain rules to ensure proper
 609     /// compatibility with the foreign interfaces. This lint is issued when it
 610     /// detects a probable mistake in a definition. The lint usually should
 611     /// provide a description of the issue, along with possibly a hint on how
 612     /// to resolve it.
 613     IMPROPER_CTYPES,
 614     Warn,
 615     "proper use of libc types in foreign modules"
 616 }
 617
 618 declare_lint_pass!(ImproperCTypesDeclarations => [IMPROPER_CTYPES]);
 619
 620 declare_lint! {
 621     /// The `improper_ctypes_definitions` lint detects incorrect use of
 622     /// [`extern` function] definitions.
 623     ///
 624     /// [`extern` function]: https://doc.rust-lang.org/reference/items/functions.html#extern-function-qualifier
 625     ///
 626     /// ### Example
 627     ///
 628     /// ```rust
 629     /// # #![allow(unused)]
 630     /// pub extern "C" fn str_type(p: &str) { }
 631     /// ```
 632     ///
 633     /// {{produces}}
 634     ///
 635     /// ### Explanation
 636     ///
 637     /// There are many parameter and return types that may be specified in an
 638     /// `extern` function that are not compatible with the given ABI. This
 639     /// lint is an alert that these types should not be used. The lint usually
 640     /// should provide a description of the issue, along with possibly a hint
 641     /// on how to resolve it.
 642     IMPROPER_CTYPES_DEFINITIONS,
 643     Warn,
 644     "proper use of libc types in foreign item definitions"
 645 }
 646
 647 declare_lint_pass!(ImproperCTypesDefinitions => [IMPROPER_CTYPES_DEFINITIONS]);
 648
 649 #[derive(Clone, Copy)]
 650 pub(crate) enum CItemKind {
 651     Declaration,
 652     Definition,
 653 }
 654
 655 struct ImproperCTypesVisitor<'a, 'tcx> {
 656     cx: &'a LateContext<'tcx>,
 657     mode: CItemKind,
 658 }
 659
 660 enum FfiResult<'tcx> {
 661     FfiSafe,
 662     FfiPhantom(Ty<'tcx>),
 663     FfiUnsafe { ty: Ty<'tcx>, reason: DiagnosticMessage, help: Option<DiagnosticMessage> },
 664 }
 665
 666 pub(crate) fn nonnull_optimization_guaranteed<'tcx>(
 667     tcx: TyCtxt<'tcx>,
 668     def: ty::AdtDef<'tcx>,
 669 ) -> bool {
 670     tcx.has_attr(def.did(), sym::rustc_nonnull_optimization_guaranteed)
 671 }
 672
 673 /// `repr(transparent)` structs can have a single non-ZST field, this function returns that
 674 /// field.
 675 pub fn transparent_newtype_field<'a, 'tcx>(
 676     tcx: TyCtxt<'tcx>,
 677     variant: &'a ty::VariantDef,
 678 ) -> Option<&'a ty::FieldDef> {
 679     let param_env = tcx.param_env(variant.def_id);
 680     variant.fields.iter().find(|field| {
 681         let field_ty = tcx.type_of(field.did);
 682         let is_zst = tcx.layout_of(param_env.and(field_ty)).map_or(false, |layout| layout.is_zst());
 683         !is_zst
 684     })
 685 }
 686
 687 /// Is type known to be non-null?
 688 fn ty_is_known_nonnull<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, mode: CItemKind) -> bool {
 689     let tcx = cx.tcx;
 690     match ty.kind() {
 691         ty::FnPtr(_) => true,
 692         ty::Ref(..) => true,
 693         ty::Adt(def, _) if def.is_box() && matches!(mode, CItemKind::Definition) => true,
 694         ty::Adt(def, substs) if def.repr().transparent() && !def.is_union() => {
 695             let marked_non_null = nonnull_optimization_guaranteed(tcx, *def);
 696
 697             if marked_non_null {
 698                 return true;
 699             }
 700
 701             // `UnsafeCell` has its niche hidden.
 702             if def.is_unsafe_cell() {
 703                 return false;
 704             }
 705
 706             def.variants()
 707                 .iter()
 708                 .filter_map(|variant| transparent_newtype_field(cx.tcx, variant))
 709                 .any(|field| ty_is_known_nonnull(cx, field.ty(tcx, substs), mode))
 710         }
 711         _ => false,
 712     }
 713 }
 714
 715 /// Given a non-null scalar (or transparent) type `ty`, return the nullable version of that type.
 716 /// If the type passed in was not scalar, returns None.
 717 fn get_nullable_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
 718     let tcx = cx.tcx;
 719     Some(match *ty.kind() {
 720         ty::Adt(field_def, field_substs) => {
 721             let inner_field_ty = {
 722                 let first_non_zst_ty = field_def
 723                     .variants()
 724                     .iter()
 725                     .filter_map(|v| transparent_newtype_field(cx.tcx, v));
 726                 debug_assert_eq!(
 727                     first_non_zst_ty.clone().count(),
 728                     1,
 729                     "Wrong number of fields for transparent type"
 730                 );
 731                 first_non_zst_ty
 732                     .last()
 733                     .expect("No non-zst fields in transparent type.")
 734                     .ty(tcx, field_substs)
 735             };
 736             return get_nullable_type(cx, inner_field_ty);
 737         }
 738         ty::Int(ty) => tcx.mk_mach_int(ty),
 739         ty::Uint(ty) => tcx.mk_mach_uint(ty),
 740         ty::RawPtr(ty_mut) => tcx.mk_ptr(ty_mut),
 741         // As these types are always non-null, the nullable equivalent of
 742         // Option<T> of these types are their raw pointer counterparts.
 743         ty::Ref(_region, ty, mutbl) => tcx.mk_ptr(ty::TypeAndMut { ty, mutbl }),
 744         ty::FnPtr(..) => {
 745             // There is no nullable equivalent for Rust's function pointers -- you
 746             // must use an Option<fn(..) -> _> to represent it.
 747             ty
 748         }
 749
 750         // We should only ever reach this case if ty_is_known_nonnull is extended
 751         // to other types.
 752         ref unhandled => {
 753             debug!(
 754                 "get_nullable_type: Unhandled scalar kind: {:?} while checking {:?}",
 755                 unhandled, ty
 756             );
 757             return None;
 758         }
 759     })
 760 }
 761
 762 /// Check if this enum can be safely exported based on the "nullable pointer optimization". If it
 763 /// can, return the type that `ty` can be safely converted to, otherwise return `None`.
 764 /// Currently restricted to function pointers, boxes, references, `core::num::NonZero*`,
 765 /// `core::ptr::NonNull`, and `#[repr(transparent)]` newtypes.
 766 /// FIXME: This duplicates code in codegen.
 767 pub(crate) fn repr_nullable_ptr<'tcx>(
 768     cx: &LateContext<'tcx>,
 769     ty: Ty<'tcx>,
 770     ckind: CItemKind,
 771 ) -> Option<Ty<'tcx>> {
 772     debug!("is_repr_nullable_ptr(cx, ty = {:?})", ty);
 773     if let ty::Adt(ty_def, substs) = ty.kind() {
 774         let field_ty = match &ty_def.variants().raw[..] {
 775             [var_one, var_two] => match (&var_one.fields[..], &var_two.fields[..]) {
 776                 ([], [field]) | ([field], []) => field.ty(cx.tcx, substs),
 777                 _ => return None,
 778             },
 779             _ => return None,
 780         };
 781
 782         if !ty_is_known_nonnull(cx, field_ty, ckind) {
 783             return None;
 784         }
 785
 786         // At this point, the field's type is known to be nonnull and the parent enum is Option-like.
 787         // If the computed size for the field and the enum are different, the nonnull optimization isn't
 788         // being applied (and we've got a problem somewhere).
 789         let compute_size_skeleton = |t| SizeSkeleton::compute(t, cx.tcx, cx.param_env).unwrap();
 790         if !compute_size_skeleton(ty).same_size(compute_size_skeleton(field_ty)) {
 791             bug!("improper_ctypes: Option nonnull optimization not applied?");
 792         }
 793
 794         // Return the nullable type this Option-like enum can be safely represented with.
 795         let field_ty_abi = &cx.layout_of(field_ty).unwrap().abi;
 796         if let Abi::Scalar(field_ty_scalar) = field_ty_abi {
 797             match field_ty_scalar.valid_range(cx) {
 798                 WrappingRange { start: 0, end }
 799                     if end == field_ty_scalar.size(&cx.tcx).unsigned_int_max() - 1 =>
 800                 {
 801                     return Some(get_nullable_type(cx, field_ty).unwrap());
 802                 }
 803                 WrappingRange { start: 1, .. } => {
 804                     return Some(get_nullable_type(cx, field_ty).unwrap());
 805                 }
 806                 WrappingRange { start, end } => {
 807                     unreachable!("Unhandled start and end range: ({}, {})", start, end)
 808                 }
 809             };
 810         }
 811     }
 812     None
 813 }
 814
 815 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
 816     /// Check if the type is array and emit an unsafe type lint.
 817     fn check_for_array_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
 818         if let ty::Array(..) = ty.kind() {
 819             self.emit_ffi_unsafe_type_lint(
 820                 ty,
 821                 sp,
 822                 fluent::lint::improper_ctypes_array_reason,
 823                 Some(fluent::lint::improper_ctypes_array_help),
 824             );
 825             true
 826         } else {
 827             false
 828         }
 829     }
 830
 831     /// Checks if the given field's type is "ffi-safe".
 832     fn check_field_type_for_ffi(
 833         &self,
 834         cache: &mut FxHashSet<Ty<'tcx>>,
 835         field: &ty::FieldDef,
 836         substs: SubstsRef<'tcx>,
 837     ) -> FfiResult<'tcx> {
 838         let field_ty = field.ty(self.cx.tcx, substs);
 839         if field_ty.has_opaque_types() {
 840             self.check_type_for_ffi(cache, field_ty)
 841         } else {
 842             let field_ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, field_ty);
 843             self.check_type_for_ffi(cache, field_ty)
 844         }
 845     }
 846
 847     /// Checks if the given `VariantDef`'s field types are "ffi-safe".
 848     fn check_variant_for_ffi(
 849         &self,
 850         cache: &mut FxHashSet<Ty<'tcx>>,
 851         ty: Ty<'tcx>,
 852         def: ty::AdtDef<'tcx>,
 853         variant: &ty::VariantDef,
 854         substs: SubstsRef<'tcx>,
 855     ) -> FfiResult<'tcx> {
 856         use FfiResult::*;
 857
 858         if def.repr().transparent() {
 859             // Can assume that at most one field is not a ZST, so only check
 860             // that field's type for FFI-safety.
 861             if let Some(field) = transparent_newtype_field(self.cx.tcx, variant) {
 862                 self.check_field_type_for_ffi(cache, field, substs)
 863             } else {
 864                 // All fields are ZSTs; this means that the type should behave
 865                 // like (), which is FFI-unsafe
 866                 FfiUnsafe { ty, reason: fluent::lint::improper_ctypes_struct_zst, help: None }
 867             }
 868         } else {
 869             // We can't completely trust repr(C) markings; make sure the fields are
 870             // actually safe.
 871             let mut all_phantom = !variant.fields.is_empty();
 872             for field in &variant.fields {
 873                 match self.check_field_type_for_ffi(cache, &field, substs) {
 874                     FfiSafe => {
 875                         all_phantom = false;
 876                     }
 877                     FfiPhantom(..) if def.is_enum() => {
 878                         return FfiUnsafe {
 879                             ty,
 880                             reason: fluent::lint::improper_ctypes_enum_phantomdata,
 881                             help: None,
 882                         };
 883                     }
 884                     FfiPhantom(..) => {}
 885                     r => return r,
 886                 }
 887             }
 888
 889             if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 890         }
 891     }
 892
 893     /// Checks if the given type is "ffi-safe" (has a stable, well-defined
 894     /// representation which can be exported to C code).
 895     fn check_type_for_ffi(&self, cache: &mut FxHashSet<Ty<'tcx>>, ty: Ty<'tcx>) -> FfiResult<'tcx> {
 896         use FfiResult::*;
 897
 898         let tcx = self.cx.tcx;
 899
 900         // Protect against infinite recursion, for example
 901         // `struct S(*mut S);`.
 902         // FIXME: A recursion limit is necessary as well, for irregular
 903         // recursive types.
 904         if !cache.insert(ty) {
 905             return FfiSafe;
 906         }
 907
 908         match *ty.kind() {
 909             ty::Adt(def, substs) => {
 910                 if def.is_box() && matches!(self.mode, CItemKind::Definition) {
 911                     if ty.boxed_ty().is_sized(tcx.at(DUMMY_SP), self.cx.param_env) {
 912                         return FfiSafe;
 913                     } else {
 914                         return FfiUnsafe {
 915                             ty,
 916                             reason: fluent::lint::improper_ctypes_box,
 917                             help: None,
 918                         };
 919                     }
 920                 }
 921                 if def.is_phantom_data() {
 922                     return FfiPhantom(ty);
 923                 }
 924                 match def.adt_kind() {
 925                     AdtKind::Struct | AdtKind::Union => {
 926                         if !def.repr().c() && !def.repr().transparent() {
 927                             return FfiUnsafe {
 928                                 ty,
 929                                 reason: if def.is_struct() {
 930                                     fluent::lint::improper_ctypes_struct_layout_reason
 931                                 } else {
 932                                     fluent::lint::improper_ctypes_union_layout_reason
 933                                 },
 934                                 help: if def.is_struct() {
 935                                     Some(fluent::lint::improper_ctypes_struct_layout_help)
 936                                 } else {
 937                                     Some(fluent::lint::improper_ctypes_union_layout_help)
 938                                 },
 939                             };
 940                         }
 941
 942                         let is_non_exhaustive =
 943                             def.non_enum_variant().is_field_list_non_exhaustive();
 944                         if is_non_exhaustive && !def.did().is_local() {
 945                             return FfiUnsafe {
 946                                 ty,
 947                                 reason: if def.is_struct() {
 948                                     fluent::lint::improper_ctypes_struct_non_exhaustive
 949                                 } else {
 950                                     fluent::lint::improper_ctypes_union_non_exhaustive
 951                                 },
 952                                 help: None,
 953                             };
 954                         }
 955
 956                         if def.non_enum_variant().fields.is_empty() {
 957                             return FfiUnsafe {
 958                                 ty,
 959                                 reason: if def.is_struct() {
 960                                     fluent::lint::improper_ctypes_struct_fieldless_reason
 961                                 } else {
 962                                     fluent::lint::improper_ctypes_union_fieldless_reason
 963                                 },
 964                                 help: if def.is_struct() {
 965                                     Some(fluent::lint::improper_ctypes_struct_fieldless_help)
 966                                 } else {
 967                                     Some(fluent::lint::improper_ctypes_union_fieldless_help)
 968                                 },
 969                             };
 970                         }
 971
 972                         self.check_variant_for_ffi(cache, ty, def, def.non_enum_variant(), substs)
 973                     }
 974                     AdtKind::Enum => {
 975                         if def.variants().is_empty() {
 976                             // Empty enums are okay... although sort of useless.
 977                             return FfiSafe;
 978                         }
 979
 980                         // Check for a repr() attribute to specify the size of the
 981                         // discriminant.
 982                         if !def.repr().c() && !def.repr().transparent() && def.repr().int.is_none()
 983                         {
 984                             // Special-case types like `Option<extern fn()>`.
 985                             if repr_nullable_ptr(self.cx, ty, self.mode).is_none() {
 986                                 return FfiUnsafe {
 987                                     ty,
 988                                     reason: fluent::lint::improper_ctypes_enum_repr_reason,
 989                                     help: Some(fluent::lint::improper_ctypes_enum_repr_help),
 990                                 };
 991                             }
 992                         }
 993
 994                         if def.is_variant_list_non_exhaustive() && !def.did().is_local() {
 995                             return FfiUnsafe {
 996                                 ty,
 997                                 reason: fluent::lint::improper_ctypes_non_exhaustive,
 998                                 help: None,
 999                             };
1000                         }
1001
1002                         // Check the contained variants.
1003                         for variant in def.variants() {
1004                             let is_non_exhaustive = variant.is_field_list_non_exhaustive();
1005                             if is_non_exhaustive && !variant.def_id.is_local() {
1006                                 return FfiUnsafe {
1007                                     ty,
1008                                     reason: fluent::lint::improper_ctypes_non_exhaustive_variant,
1009                                     help: None,
1010                                 };
1011                             }
1012
1013                             match self.check_variant_for_ffi(cache, ty, def, variant, substs) {
1014                                 FfiSafe => (),
1015                                 r => return r,
1016                             }
1017                         }
1018
1019                         FfiSafe
1020                     }
1021                 }
1022             }
1023
1024             ty::Char => FfiUnsafe {
1025                 ty,
1026                 reason: fluent::lint::improper_ctypes_char_reason,
1027                 help: Some(fluent::lint::improper_ctypes_char_help),
1028             },
1029
1030             ty::Int(ty::IntTy::I128) | ty::Uint(ty::UintTy::U128) => {
1031                 FfiUnsafe { ty, reason: fluent::lint::improper_ctypes_128bit, help: None }
1032             }
1033
1034             // Primitive types with a stable representation.
1035             ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
1036
1037             ty::Slice(_) => FfiUnsafe {
1038                 ty,
1039                 reason: fluent::lint::improper_ctypes_slice_reason,
1040                 help: Some(fluent::lint::improper_ctypes_slice_help),
1041             },
1042
1043             ty::Dynamic(..) => {
1044                 FfiUnsafe { ty, reason: fluent::lint::improper_ctypes_dyn, help: None }
1045             }
1046
1047             ty::Str => FfiUnsafe {
1048                 ty,
1049                 reason: fluent::lint::improper_ctypes_str_reason,
1050                 help: Some(fluent::lint::improper_ctypes_str_help),
1051             },
1052
1053             ty::Tuple(..) => FfiUnsafe {
1054                 ty,
1055                 reason: fluent::lint::improper_ctypes_tuple_reason,
1056                 help: Some(fluent::lint::improper_ctypes_tuple_help),
1057             },
1058
1059             ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _)
1060                 if {
1061                     matches!(self.mode, CItemKind::Definition)
1062                         && ty.is_sized(self.cx.tcx.at(DUMMY_SP), self.cx.param_env)
1063                 } =>
1064             {
1065                 FfiSafe
1066             }
1067
1068             ty::RawPtr(ty::TypeAndMut { ty, .. })
1069                 if match ty.kind() {
1070                     ty::Tuple(tuple) => tuple.is_empty(),
1071                     _ => false,
1072                 } =>
1073             {
1074                 FfiSafe
1075             }
1076
1077             ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _) => {
1078                 self.check_type_for_ffi(cache, ty)
1079             }
1080
1081             ty::Array(inner_ty, _) => self.check_type_for_ffi(cache, inner_ty),
1082
1083             ty::FnPtr(sig) => {
1084                 if self.is_internal_abi(sig.abi()) {
1085                     return FfiUnsafe {
1086                         ty,
1087                         reason: fluent::lint::improper_ctypes_fnptr_reason,
1088                         help: Some(fluent::lint::improper_ctypes_fnptr_help),
1089                     };
1090                 }
1091
1092                 let sig = tcx.erase_late_bound_regions(sig);
1093                 if !sig.output().is_unit() {
1094                     let r = self.check_type_for_ffi(cache, sig.output());
1095                     match r {
1096                         FfiSafe => {}
1097                         _ => {
1098                             return r;
1099                         }
1100                     }
1101                 }
1102                 for arg in sig.inputs() {
1103                     let r = self.check_type_for_ffi(cache, *arg);
1104                     match r {
1105                         FfiSafe => {}
1106                         _ => {
1107                             return r;
1108                         }
1109                     }
1110                 }
1111                 FfiSafe
1112             }
1113
1114             ty::Foreign(..) => FfiSafe,
1115
1116             // While opaque types are checked for earlier, if a projection in a struct field
1117             // normalizes to an opaque type, then it will reach this branch.
1118             ty::Opaque(..) => {
1119                 FfiUnsafe { ty, reason: fluent::lint::improper_ctypes_opaque, help: None }
1120             }
1121
1122             // `extern "C" fn` functions can have type parameters, which may or may not be FFI-safe,
1123             //  so they are currently ignored for the purposes of this lint.
1124             ty::Param(..) | ty::Projection(..) if matches!(self.mode, CItemKind::Definition) => {
1125                 FfiSafe
1126             }
1127
1128             ty::Param(..)
1129             | ty::Projection(..)
1130             | ty::Infer(..)
1131             | ty::Bound(..)
1132             | ty::Error(_)
1133             | ty::Closure(..)
1134             | ty::Generator(..)
1135             | ty::GeneratorWitness(..)
1136             | ty::Placeholder(..)
1137             | ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty),
1138         }
1139     }
1140
1141     fn emit_ffi_unsafe_type_lint(
1142         &mut self,
1143         ty: Ty<'tcx>,
1144         sp: Span,
1145         note: DiagnosticMessage,
1146         help: Option<DiagnosticMessage>,
1147     ) {
1148         let lint = match self.mode {
1149             CItemKind::Declaration => IMPROPER_CTYPES,
1150             CItemKind::Definition => IMPROPER_CTYPES_DEFINITIONS,
1151         };
1152
1153         self.cx.struct_span_lint(lint, sp, |lint| {
1154             let item_description = match self.mode {
1155                 CItemKind::Declaration => "block",
1156                 CItemKind::Definition => "fn",
1157             };
1158             let mut diag = lint.build(fluent::lint::improper_ctypes);
1159             diag.set_arg("ty", ty);
1160             diag.set_arg("desc", item_description);
1161             diag.span_label(sp, fluent::lint::label);
1162             if let Some(help) = help {
1163                 diag.help(help);
1164             }
1165             diag.note(note);
1166             if let ty::Adt(def, _) = ty.kind() {
1167                 if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did()) {
1168                     diag.span_note(sp, fluent::lint::note);
1169                 }
1170             }
1171             diag.emit();
1172         });
1173     }
1174
1175     fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
1176         struct ProhibitOpaqueTypes<'a, 'tcx> {
1177             cx: &'a LateContext<'tcx>,
1178         }
1179
1180         impl<'a, 'tcx> ty::visit::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'a, 'tcx> {
1181             type BreakTy = Ty<'tcx>;
1182
1183             fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1184                 match ty.kind() {
1185                     ty::Opaque(..) => ControlFlow::Break(ty),
1186                     // Consider opaque types within projections FFI-safe if they do not normalize
1187                     // to more opaque types.
1188                     ty::Projection(..) => {
1189                         let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
1190
1191                         // If `ty` is an opaque type directly then `super_visit_with` won't invoke
1192                         // this function again.
1193                         if ty.has_opaque_types() {
1194                             self.visit_ty(ty)
1195                         } else {
1196                             ControlFlow::CONTINUE
1197                         }
1198                     }
1199                     _ => ty.super_visit_with(self),
1200                 }
1201             }
1202         }
1203
1204         if let Some(ty) = ty.visit_with(&mut ProhibitOpaqueTypes { cx: self.cx }).break_value() {
1205             self.emit_ffi_unsafe_type_lint(ty, sp, fluent::lint::improper_ctypes_opaque, None);
1206             true
1207         } else {
1208             false
1209         }
1210     }
1211
1212     fn check_type_for_ffi_and_report_errors(
1213         &mut self,
1214         sp: Span,
1215         ty: Ty<'tcx>,
1216         is_static: bool,
1217         is_return_type: bool,
1218     ) {
1219         // We have to check for opaque types before `normalize_erasing_regions`,
1220         // which will replace opaque types with their underlying concrete type.
1221         if self.check_for_opaque_ty(sp, ty) {
1222             // We've already emitted an error due to an opaque type.
1223             return;
1224         }
1225
1226         // it is only OK to use this function because extern fns cannot have
1227         // any generic types right now:
1228         let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
1229
1230         // C doesn't really support passing arrays by value - the only way to pass an array by value
1231         // is through a struct. So, first test that the top level isn't an array, and then
1232         // recursively check the types inside.
1233         if !is_static && self.check_for_array_ty(sp, ty) {
1234             return;
1235         }
1236
1237         // Don't report FFI errors for unit return types. This check exists here, and not in
1238         // `check_foreign_fn` (where it would make more sense) so that normalization has definitely
1239         // happened.
1240         if is_return_type && ty.is_unit() {
1241             return;
1242         }
1243
1244         match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
1245             FfiResult::FfiSafe => {}
1246             FfiResult::FfiPhantom(ty) => {
1247                 self.emit_ffi_unsafe_type_lint(
1248                     ty,
1249                     sp,
1250                     fluent::lint::improper_ctypes_only_phantomdata,
1251                     None,
1252                 );
1253             }
1254             // If `ty` is a `repr(transparent)` newtype, and the non-zero-sized type is a generic
1255             // argument, which after substitution, is `()`, then this branch can be hit.
1256             FfiResult::FfiUnsafe { ty, .. } if is_return_type && ty.is_unit() => {}
1257             FfiResult::FfiUnsafe { ty, reason, help } => {
1258                 self.emit_ffi_unsafe_type_lint(ty, sp, reason, help);
1259             }
1260         }
1261     }
1262
1263     fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl<'_>) {
1264         let def_id = self.cx.tcx.hir().local_def_id(id);
1265         let sig = self.cx.tcx.fn_sig(def_id);
1266         let sig = self.cx.tcx.erase_late_bound_regions(sig);
1267
1268         for (input_ty, input_hir) in iter::zip(sig.inputs(), decl.inputs) {
1269             self.check_type_for_ffi_and_report_errors(input_hir.span, *input_ty, false, false);
1270         }
1271
1272         if let hir::FnRetTy::Return(ref ret_hir) = decl.output {
1273             let ret_ty = sig.output();
1274             self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty, false, true);
1275         }
1276     }
1277
1278     fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
1279         let def_id = self.cx.tcx.hir().local_def_id(id);
1280         let ty = self.cx.tcx.type_of(def_id);
1281         self.check_type_for_ffi_and_report_errors(span, ty, true, false);
1282     }
1283
1284     fn is_internal_abi(&self, abi: SpecAbi) -> bool {
1285         matches!(
1286             abi,
1287             SpecAbi::Rust | SpecAbi::RustCall | SpecAbi::RustIntrinsic | SpecAbi::PlatformIntrinsic
1288         )
1289     }
1290 }
1291
1292 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDeclarations {
1293     fn check_foreign_item(&mut self, cx: &LateContext<'_>, it: &hir::ForeignItem<'_>) {
1294         let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Declaration };
1295         let abi = cx.tcx.hir().get_foreign_abi(it.hir_id());
1296
1297         if !vis.is_internal_abi(abi) {
1298             match it.kind {
1299                 hir::ForeignItemKind::Fn(ref decl, _, _) => {
1300                     vis.check_foreign_fn(it.hir_id(), decl);
1301                 }
1302                 hir::ForeignItemKind::Static(ref ty, _) => {
1303                     vis.check_foreign_static(it.hir_id(), ty.span);
1304                 }
1305                 hir::ForeignItemKind::Type => (),
1306             }
1307         }
1308     }
1309 }
1310
1311 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDefinitions {
1312     fn check_fn(
1313         &mut self,
1314         cx: &LateContext<'tcx>,
1315         kind: hir::intravisit::FnKind<'tcx>,
1316         decl: &'tcx hir::FnDecl<'_>,
1317         _: &'tcx hir::Body<'_>,
1318         _: Span,
1319         hir_id: hir::HirId,
1320     ) {
1321         use hir::intravisit::FnKind;
1322
1323         let abi = match kind {
1324             FnKind::ItemFn(_, _, header, ..) => header.abi,
1325             FnKind::Method(_, sig, ..) => sig.header.abi,
1326             _ => return,
1327         };
1328
1329         let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Definition };
1330         if !vis.is_internal_abi(abi) {
1331             vis.check_foreign_fn(hir_id, decl);
1332         }
1333     }
1334 }
1335
1336 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
1337
1338 impl<'tcx> LateLintPass<'tcx> for VariantSizeDifferences {
1339     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1340         if let hir::ItemKind::Enum(ref enum_definition, _) = it.kind {
1341             let t = cx.tcx.type_of(it.def_id);
1342             let ty = cx.tcx.erase_regions(t);
1343             let Ok(layout) = cx.layout_of(ty) else { return };
1344             let Variants::Multiple {
1345                     tag_encoding: TagEncoding::Direct, tag, ref variants, ..
1346                 } = &layout.variants else {
1347                 return
1348             };
1349
1350             let tag_size = tag.size(&cx.tcx).bytes();
1351
1352             debug!(
1353                 "enum `{}` is {} bytes large with layout:\n{:#?}",
1354                 t,
1355                 layout.size.bytes(),
1356                 layout
1357             );
1358
1359             let (largest, slargest, largest_index) = iter::zip(enum_definition.variants, variants)
1360                 .map(|(variant, variant_layout)| {
1361                     // Subtract the size of the enum tag.
1362                     let bytes = variant_layout.size().bytes().saturating_sub(tag_size);
1363
1364                     debug!("- variant `{}` is {} bytes large", variant.ident, bytes);
1365                     bytes
1366                 })
1367                 .enumerate()
1368                 .fold((0, 0, 0), |(l, s, li), (idx, size)| {
1369                     if size > l {
1370                         (size, l, idx)
1371                     } else if size > s {
1372                         (l, size, li)
1373                     } else {
1374                         (l, s, li)
1375                     }
1376                 });
1377
1378             // We only warn if the largest variant is at least thrice as large as
1379             // the second-largest.
1380             if largest > slargest * 3 && slargest > 0 {
1381                 cx.struct_span_lint(
1382                     VARIANT_SIZE_DIFFERENCES,
1383                     enum_definition.variants[largest_index].span,
1384                     |lint| {
1385                         lint.build(fluent::lint::variant_size_differences)
1386                             .set_arg("largest", largest)
1387                             .emit();
1388                     },
1389                 );
1390             }
1391         }
1392     }
1393 }
1394
1395 declare_lint! {
1396     /// The `invalid_atomic_ordering` lint detects passing an `Ordering`
1397     /// to an atomic operation that does not support that ordering.
1398     ///
1399     /// ### Example
1400     ///
1401     /// ```rust,compile_fail
1402     /// # use core::sync::atomic::{AtomicU8, Ordering};
1403     /// let atom = AtomicU8::new(0);
1404     /// let value = atom.load(Ordering::Release);
1405     /// # let _ = value;
1406     /// ```
1407     ///
1408     /// {{produces}}
1409     ///
1410     /// ### Explanation
1411     ///
1412     /// Some atomic operations are only supported for a subset of the
1413     /// `atomic::Ordering` variants. Passing an unsupported variant will cause
1414     /// an unconditional panic at runtime, which is detected by this lint.
1415     ///
1416     /// This lint will trigger in the following cases: (where `AtomicType` is an
1417     /// atomic type from `core::sync::atomic`, such as `AtomicBool`,
1418     /// `AtomicPtr`, `AtomicUsize`, or any of the other integer atomics).
1419     ///
1420     /// - Passing `Ordering::Acquire` or `Ordering::AcqRel` to
1421     ///   `AtomicType::store`.
1422     ///
1423     /// - Passing `Ordering::Release` or `Ordering::AcqRel` to
1424     ///   `AtomicType::load`.
1425     ///
1426     /// - Passing `Ordering::Relaxed` to `core::sync::atomic::fence` or
1427     ///   `core::sync::atomic::compiler_fence`.
1428     ///
1429     /// - Passing `Ordering::Release` or `Ordering::AcqRel` as the failure
1430     ///   ordering for any of `AtomicType::compare_exchange`,
1431     ///   `AtomicType::compare_exchange_weak`, or `AtomicType::fetch_update`.
1432     INVALID_ATOMIC_ORDERING,
1433     Deny,
1434     "usage of invalid atomic ordering in atomic operations and memory fences"
1435 }
1436
1437 declare_lint_pass!(InvalidAtomicOrdering => [INVALID_ATOMIC_ORDERING]);
1438
1439 impl InvalidAtomicOrdering {
1440     fn inherent_atomic_method_call<'hir>(
1441         cx: &LateContext<'_>,
1442         expr: &Expr<'hir>,
1443         recognized_names: &[Symbol], // used for fast path calculation
1444     ) -> Option<(Symbol, &'hir [Expr<'hir>])> {
1445         const ATOMIC_TYPES: &[Symbol] = &[
1446             sym::AtomicBool,
1447             sym::AtomicPtr,
1448             sym::AtomicUsize,
1449             sym::AtomicU8,
1450             sym::AtomicU16,
1451             sym::AtomicU32,
1452             sym::AtomicU64,
1453             sym::AtomicU128,
1454             sym::AtomicIsize,
1455             sym::AtomicI8,
1456             sym::AtomicI16,
1457             sym::AtomicI32,
1458             sym::AtomicI64,
1459             sym::AtomicI128,
1460         ];
1461         if let ExprKind::MethodCall(ref method_path, _, args, _) = &expr.kind
1462             && recognized_names.contains(&method_path.ident.name)
1463             && let Some(m_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id)
1464             && let Some(impl_did) = cx.tcx.impl_of_method(m_def_id)
1465             && let Some(adt) = cx.tcx.type_of(impl_did).ty_adt_def()
1466             // skip extension traits, only lint functions from the standard library
1467             && cx.tcx.trait_id_of_impl(impl_did).is_none()
1468             && let parent = cx.tcx.parent(adt.did())
1469             && cx.tcx.is_diagnostic_item(sym::atomic_mod, parent)
1470             && ATOMIC_TYPES.contains(&cx.tcx.item_name(adt.did()))
1471         {
1472             return Some((method_path.ident.name, args));
1473         }
1474         None
1475     }
1476
1477     fn match_ordering(cx: &LateContext<'_>, ord_arg: &Expr<'_>) -> Option<Symbol> {
1478         let ExprKind::Path(ref ord_qpath) = ord_arg.kind else { return None };
1479         let did = cx.qpath_res(ord_qpath, ord_arg.hir_id).opt_def_id()?;
1480         let tcx = cx.tcx;
1481         let atomic_ordering = tcx.get_diagnostic_item(sym::Ordering);
1482         let name = tcx.item_name(did);
1483         let parent = tcx.parent(did);
1484         [sym::Relaxed, sym::Release, sym::Acquire, sym::AcqRel, sym::SeqCst].into_iter().find(
1485             |&ordering| {
1486                 name == ordering
1487                     && (Some(parent) == atomic_ordering
1488                             // needed in case this is a ctor, not a variant
1489                             || tcx.opt_parent(parent) == atomic_ordering)
1490             },
1491         )
1492     }
1493
1494     fn check_atomic_load_store(cx: &LateContext<'_>, expr: &Expr<'_>) {
1495         if let Some((method, args)) = Self::inherent_atomic_method_call(cx, expr, &[sym::load, sym::store])
1496             && let Some((ordering_arg, invalid_ordering)) = match method {
1497                 sym::load => Some((&args[0], sym::Release)),
1498                 sym::store => Some((&args[1], sym::Acquire)),
1499                 _ => None,
1500             }
1501             && let Some(ordering) = Self::match_ordering(cx, ordering_arg)
1502             && (ordering == invalid_ordering || ordering == sym::AcqRel)
1503         {
1504             cx.struct_span_lint(INVALID_ATOMIC_ORDERING, ordering_arg.span, |diag| {
1505                 if method == sym::load {
1506                     diag.build(fluent::lint::atomic_ordering_load)
1507                         .help(fluent::lint::help)
1508                         .emit()
1509                 } else {
1510                     debug_assert_eq!(method, sym::store);
1511                     diag.build(fluent::lint::atomic_ordering_store)
1512                         .help(fluent::lint::help)
1513                         .emit();
1514                 }
1515             });
1516         }
1517     }
1518
1519     fn check_memory_fence(cx: &LateContext<'_>, expr: &Expr<'_>) {
1520         if let ExprKind::Call(ref func, ref args) = expr.kind
1521             && let ExprKind::Path(ref func_qpath) = func.kind
1522             && let Some(def_id) = cx.qpath_res(func_qpath, func.hir_id).opt_def_id()
1523             && matches!(cx.tcx.get_diagnostic_name(def_id), Some(sym::fence | sym::compiler_fence))
1524             && Self::match_ordering(cx, &args[0]) == Some(sym::Relaxed)
1525         {
1526             cx.struct_span_lint(INVALID_ATOMIC_ORDERING, args[0].span, |diag| {
1527                 diag.build(fluent::lint::atomic_ordering_fence)
1528                     .help(fluent::lint::help)
1529                     .emit();
1530             });
1531         }
1532     }
1533
1534     fn check_atomic_compare_exchange(cx: &LateContext<'_>, expr: &Expr<'_>) {
1535         let Some((method, args)) = Self::inherent_atomic_method_call(cx, expr, &[sym::fetch_update, sym::compare_exchange, sym::compare_exchange_weak])
1536             else {return };
1537
1538         let fail_order_arg = match method {
1539             sym::fetch_update => &args[1],
1540             sym::compare_exchange | sym::compare_exchange_weak => &args[3],
1541             _ => return,
1542         };
1543
1544         let Some(fail_ordering) = Self::match_ordering(cx, fail_order_arg) else { return };
1545
1546         if matches!(fail_ordering, sym::Release | sym::AcqRel) {
1547             #[derive(LintDiagnostic)]
1548             #[diag(lint::atomic_ordering_invalid)]
1549             #[help]
1550             struct InvalidAtomicOrderingDiag {
1551                 method: Symbol,
1552                 #[label]
1553                 fail_order_arg_span: Span,
1554             }
1555
1556             cx.emit_spanned_lint(
1557                 INVALID_ATOMIC_ORDERING,
1558                 fail_order_arg.span,
1559                 InvalidAtomicOrderingDiag { method, fail_order_arg_span: fail_order_arg.span },
1560             );
1561         }
1562     }
1563 }
1564
1565 impl<'tcx> LateLintPass<'tcx> for InvalidAtomicOrdering {
1566     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
1567         Self::check_atomic_load_store(cx, expr);
1568         Self::check_memory_fence(cx, expr);
1569         Self::check_atomic_compare_exchange(cx, expr);
1570     }
1571 }