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 use tracing::debug;
  23
  24 declare_lint! {
  25     /// The `unused_comparisons` lint detects comparisons made useless by
  26     /// limits of the types involved.
  27     ///
  28     /// ### Example
  29     ///
  30     /// ```rust
  31     /// fn foo(x: u8) {
  32     ///     x >= 0;
  33     /// }
  34     /// ```
  35     ///
  36     /// {{produces}}
  37     ///
  38     /// ### Explanation
  39     ///
  40     /// A useless comparison may indicate a mistake, and should be fixed or
  41     /// removed.
  42     UNUSED_COMPARISONS,
  43     Warn,
  44     "comparisons made useless by limits of the types involved"
  45 }
  46
  47 declare_lint! {
  48     /// The `overflowing_literals` lint detects literal out of range for its
  49     /// type.
  50     ///
  51     /// ### Example
  52     ///
  53     /// ```rust,compile_fail
  54     /// let x: u8 = 1000;
  55     /// ```
  56     ///
  57     /// {{produces}}
  58     ///
  59     /// ### Explanation
  60     ///
  61     /// It is usually a mistake to use a literal that overflows the type where
  62     /// it is used. Either use a literal that is within range, or change the
  63     /// type to be within the range of the literal.
  64     OVERFLOWING_LITERALS,
  65     Deny,
  66     "literal out of range for its type"
  67 }
  68
  69 declare_lint! {
  70     /// The `variant_size_differences` lint detects enums with widely varying
  71     /// variant sizes.
  72     ///
  73     /// ### Example
  74     ///
  75     /// ```rust,compile_fail
  76     /// #![deny(variant_size_differences)]
  77     /// enum En {
  78     ///     V0(u8),
  79     ///     VBig([u8; 1024]),
  80     /// }
  81     /// ```
  82     ///
  83     /// {{produces}}
  84     ///
  85     /// ### Explanation
  86     ///
  87     /// It can be a mistake to add a variant to an enum that is much larger
  88     /// than the other variants, bloating the overall size required for all
  89     /// variants. This can impact performance and memory usage. This is
  90     /// triggered if one variant is more than 3 times larger than the
  91     /// second-largest variant.
  92     ///
  93     /// Consider placing the large variant's contents on the heap (for example
  94     /// via [`Box`]) to keep the overall size of the enum itself down.
  95     ///
  96     /// This lint is "allow" by default because it can be noisy, and may not be
  97     /// an actual problem. Decisions about this should be guided with
  98     /// profiling and benchmarking.
  99     ///
 100     /// [`Box`]: https://doc.rust-lang.org/std/boxed/index.html
 101     VARIANT_SIZE_DIFFERENCES,
 102     Allow,
 103     "detects enums with widely varying variant sizes"
 104 }
 105
 106 #[derive(Copy, Clone)]
 107 pub struct TypeLimits {
 108     /// Id of the last visited negated expression
 109     negated_expr_id: Option<hir::HirId>,
 110 }
 111
 112 impl_lint_pass!(TypeLimits => [UNUSED_COMPARISONS, OVERFLOWING_LITERALS]);
 113
 114 impl TypeLimits {
 115     pub fn new() -> TypeLimits {
 116         TypeLimits { negated_expr_id: None }
 117     }
 118 }
 119
 120 /// Attempts to special-case the overflowing literal lint when it occurs as a range endpoint.
 121 /// Returns `true` iff the lint was overridden.
 122 fn lint_overflowing_range_endpoint<'tcx>(
 123     cx: &LateContext<'tcx>,
 124     lit: &hir::Lit,
 125     lit_val: u128,
 126     max: u128,
 127     expr: &'tcx hir::Expr<'tcx>,
 128     parent_expr: &'tcx hir::Expr<'tcx>,
 129     ty: &str,
 130 ) -> bool {
 131     // We only want to handle exclusive (`..`) ranges,
 132     // which are represented as `ExprKind::Struct`.
 133     let mut overwritten = false;
 134     if let ExprKind::Struct(_, eps, _) = &parent_expr.kind {
 135         if eps.len() != 2 {
 136             return false;
 137         }
 138         // We can suggest using an inclusive range
 139         // (`..=`) instead only if it is the `end` that is
 140         // overflowing and only by 1.
 141         if eps[1].expr.hir_id == expr.hir_id && lit_val - 1 == max {
 142             cx.struct_span_lint(OVERFLOWING_LITERALS, parent_expr.span, |lint| {
 143                 let mut err = lint.build(fluent::lint::range_endpoint_out_of_range);
 144                 err.set_arg("ty", ty);
 145                 if let Ok(start) = cx.sess().source_map().span_to_snippet(eps[0].span) {
 146                     use ast::{LitIntType, LitKind};
 147                     // We need to preserve the literal's suffix,
 148                     // as it may determine typing information.
 149                     let suffix = match lit.node {
 150                         LitKind::Int(_, LitIntType::Signed(s)) => s.name_str(),
 151                         LitKind::Int(_, LitIntType::Unsigned(s)) => s.name_str(),
 152                         LitKind::Int(_, LitIntType::Unsuffixed) => "",
 153                         _ => bug!(),
 154                     };
 155                     let suggestion = format!("{}..={}{}", start, lit_val - 1, suffix);
 156                     err.span_suggestion(
 157                         parent_expr.span,
 158                         fluent::lint::suggestion,
 159                         suggestion,
 160                         Applicability::MachineApplicable,
 161                     );
 162                     err.emit();
 163                     overwritten = true;
 164                 }
 165             });
 166         }
 167     }
 168     overwritten
 169 }
 170
 171 // For `isize` & `usize`, be conservative with the warnings, so that the
 172 // warnings are consistent between 32- and 64-bit platforms.
 173 fn int_ty_range(int_ty: ty::IntTy) -> (i128, i128) {
 174     match int_ty {
 175         ty::IntTy::Isize => (i64::MIN.into(), i64::MAX.into()),
 176         ty::IntTy::I8 => (i8::MIN.into(), i8::MAX.into()),
 177         ty::IntTy::I16 => (i16::MIN.into(), i16::MAX.into()),
 178         ty::IntTy::I32 => (i32::MIN.into(), i32::MAX.into()),
 179         ty::IntTy::I64 => (i64::MIN.into(), i64::MAX.into()),
 180         ty::IntTy::I128 => (i128::MIN, i128::MAX),
 181     }
 182 }
 183
 184 fn uint_ty_range(uint_ty: ty::UintTy) -> (u128, u128) {
 185     let max = match uint_ty {
 186         ty::UintTy::Usize => u64::MAX.into(),
 187         ty::UintTy::U8 => u8::MAX.into(),
 188         ty::UintTy::U16 => u16::MAX.into(),
 189         ty::UintTy::U32 => u32::MAX.into(),
 190         ty::UintTy::U64 => u64::MAX.into(),
 191         ty::UintTy::U128 => u128::MAX,
 192     };
 193     (0, max)
 194 }
 195
 196 fn get_bin_hex_repr(cx: &LateContext<'_>, lit: &hir::Lit) -> Option<String> {
 197     let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?;
 198     let firstch = src.chars().next()?;
 199
 200     if firstch == '0' {
 201         match src.chars().nth(1) {
 202             Some('x' | 'b') => return Some(src),
 203             _ => return None,
 204         }
 205     }
 206
 207     None
 208 }
 209
 210 fn report_bin_hex_error(
 211     cx: &LateContext<'_>,
 212     expr: &hir::Expr<'_>,
 213     ty: attr::IntType,
 214     repr_str: String,
 215     val: u128,
 216     negative: bool,
 217 ) {
 218     let size = Integer::from_attr(&cx.tcx, ty).size();
 219     cx.struct_span_lint(OVERFLOWING_LITERALS, expr.span, |lint| {
 220         let (t, actually) = match ty {
 221             attr::IntType::SignedInt(t) => {
 222                 let actually = if negative {
 223                     -(size.sign_extend(val) as i128)
 224                 } else {
 225                     size.sign_extend(val) as i128
 226                 };
 227                 (t.name_str(), actually.to_string())
 228             }
 229             attr::IntType::UnsignedInt(t) => {
 230                 let actually = size.truncate(val);
 231                 (t.name_str(), actually.to_string())
 232             }
 233         };
 234         let mut err = lint.build(fluent::lint::overflowing_bin_hex);
 235         if negative {
 236             // If the value is negative,
 237             // emits a note about the value itself, apart from the literal.
 238             err.note(fluent::lint::negative_note);
 239             err.note(fluent::lint::negative_becomes_note);
 240         } else {
 241             err.note(fluent::lint::positive_note);
 242         }
 243         if let Some(sugg_ty) =
 244             get_type_suggestion(cx.typeck_results().node_type(expr.hir_id), val, negative)
 245         {
 246             err.set_arg("suggestion_ty", sugg_ty);
 247             if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') {
 248                 let (sans_suffix, _) = repr_str.split_at(pos);
 249                 err.span_suggestion(
 250                     expr.span,
 251                     fluent::lint::suggestion,
 252                     format!("{}{}", sans_suffix, sugg_ty),
 253                     Applicability::MachineApplicable,
 254                 );
 255             } else {
 256                 err.help(fluent::lint::help);
 257             }
 258         }
 259         err.set_arg("ty", t);
 260         err.set_arg("lit", repr_str);
 261         err.set_arg("dec", val);
 262         err.set_arg("actually", actually);
 263         err.emit();
 264     });
 265 }
 266
 267 // This function finds the next fitting type and generates a suggestion string.
 268 // It searches for fitting types in the following way (`X < Y`):
 269 //  - `iX`: if literal fits in `uX` => `uX`, else => `iY`
 270 //  - `-iX` => `iY`
 271 //  - `uX` => `uY`
 272 //
 273 // No suggestion for: `isize`, `usize`.
 274 fn get_type_suggestion(t: Ty<'_>, val: u128, negative: bool) -> Option<&'static str> {
 275     use ty::IntTy::*;
 276     use ty::UintTy::*;
 277     macro_rules! find_fit {
 278         ($ty:expr, $val:expr, $negative:expr,
 279          $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => {
 280             {
 281                 let _neg = if negative { 1 } else { 0 };
 282                 match $ty {
 283                     $($type => {
 284                         $(if !negative && val <= uint_ty_range($utypes).1 {
 285                             return Some($utypes.name_str())
 286                         })*
 287                         $(if val <= int_ty_range($itypes).1 as u128 + _neg {
 288                             return Some($itypes.name_str())
 289                         })*
 290                         None
 291                     },)+
 292                     _ => None
 293                 }
 294             }
 295         }
 296     }
 297     match t.kind() {
 298         ty::Int(i) => find_fit!(i, val, negative,
 299                       I8 => [U8] => [I16, I32, I64, I128],
 300                       I16 => [U16] => [I32, I64, I128],
 301                       I32 => [U32] => [I64, I128],
 302                       I64 => [U64] => [I128],
 303                       I128 => [U128] => []),
 304         ty::Uint(u) => find_fit!(u, val, negative,
 305                       U8 => [U8, U16, U32, U64, U128] => [],
 306                       U16 => [U16, U32, U64, U128] => [],
 307                       U32 => [U32, U64, U128] => [],
 308                       U64 => [U64, U128] => [],
 309                       U128 => [U128] => []),
 310         _ => None,
 311     }
 312 }
 313
 314 fn lint_int_literal<'tcx>(
 315     cx: &LateContext<'tcx>,
 316     type_limits: &TypeLimits,
 317     e: &'tcx hir::Expr<'tcx>,
 318     lit: &hir::Lit,
 319     t: ty::IntTy,
 320     v: u128,
 321 ) {
 322     let int_type = t.normalize(cx.sess().target.pointer_width);
 323     let (min, max) = int_ty_range(int_type);
 324     let max = max as u128;
 325     let negative = type_limits.negated_expr_id == Some(e.hir_id);
 326
 327     // Detect literal value out of range [min, max] inclusive
 328     // avoiding use of -min to prevent overflow/panic
 329     if (negative && v > max + 1) || (!negative && v > max) {
 330         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 331             report_bin_hex_error(
 332                 cx,
 333                 e,
 334                 attr::IntType::SignedInt(ty::ast_int_ty(t)),
 335                 repr_str,
 336                 v,
 337                 negative,
 338             );
 339             return;
 340         }
 341
 342         let par_id = cx.tcx.hir().get_parent_node(e.hir_id);
 343         if let Node::Expr(par_e) = cx.tcx.hir().get(par_id) {
 344             if let hir::ExprKind::Struct(..) = par_e.kind {
 345                 if is_range_literal(par_e)
 346                     && lint_overflowing_range_endpoint(cx, lit, v, max, e, par_e, t.name_str())
 347                 {
 348                     // The overflowing literal lint was overridden.
 349                     return;
 350                 }
 351             }
 352         }
 353
 354         cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
 355             let mut err = lint.build(fluent::lint::overflowing_int);
 356             err.set_arg("ty", t.name_str());
 357             err.set_arg(
 358                 "lit",
 359                 cx.sess()
 360                     .source_map()
 361                     .span_to_snippet(lit.span)
 362                     .expect("must get snippet from literal"),
 363             );
 364             err.set_arg("min", min);
 365             err.set_arg("max", max);
 366             err.note(fluent::lint::note);
 367             if let Some(sugg_ty) =
 368                 get_type_suggestion(cx.typeck_results().node_type(e.hir_id), v, negative)
 369             {
 370                 err.set_arg("suggestion_ty", sugg_ty);
 371                 err.help(fluent::lint::help);
 372             }
 373             err.emit();
 374         });
 375     }
 376 }
 377
 378 fn lint_uint_literal<'tcx>(
 379     cx: &LateContext<'tcx>,
 380     e: &'tcx hir::Expr<'tcx>,
 381     lit: &hir::Lit,
 382     t: ty::UintTy,
 383 ) {
 384     let uint_type = t.normalize(cx.sess().target.pointer_width);
 385     let (min, max) = uint_ty_range(uint_type);
 386     let lit_val: u128 = match lit.node {
 387         // _v is u8, within range by definition
 388         ast::LitKind::Byte(_v) => return,
 389         ast::LitKind::Int(v, _) => v,
 390         _ => bug!(),
 391     };
 392     if lit_val < min || lit_val > max {
 393         let parent_id = cx.tcx.hir().get_parent_node(e.hir_id);
 394         if let Node::Expr(par_e) = cx.tcx.hir().get(parent_id) {
 395             match par_e.kind {
 396                 hir::ExprKind::Cast(..) => {
 397                     if let ty::Char = cx.typeck_results().expr_ty(par_e).kind() {
 398                         cx.struct_span_lint(OVERFLOWING_LITERALS, par_e.span, |lint| {
 399                             lint.build(fluent::lint::only_cast_u8_to_char)
 400                                 .span_suggestion(
 401                                     par_e.span,
 402                                     fluent::lint::suggestion,
 403                                     format!("'\\u{{{:X}}}'", lit_val),
 404                                     Applicability::MachineApplicable,
 405                                 )
 406                                 .emit();
 407                         });
 408                         return;
 409                     }
 410                 }
 411                 hir::ExprKind::Struct(..) if is_range_literal(par_e) => {
 412                     let t = t.name_str();
 413                     if lint_overflowing_range_endpoint(cx, lit, lit_val, max, e, par_e, t) {
 414                         // The overflowing literal lint was overridden.
 415                         return;
 416                     }
 417                 }
 418                 _ => {}
 419             }
 420         }
 421         if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
 422             report_bin_hex_error(
 423                 cx,
 424                 e,
 425                 attr::IntType::UnsignedInt(ty::ast_uint_ty(t)),
 426                 repr_str,
 427                 lit_val,
 428                 false,
 429             );
 430             return;
 431         }
 432         cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
 433             lint.build(fluent::lint::overflowing_uint)
 434                 .set_arg("ty", t.name_str())
 435                 .set_arg(
 436                     "lit",
 437                     cx.sess()
 438                         .source_map()
 439                         .span_to_snippet(lit.span)
 440                         .expect("must get snippet from literal"),
 441                 )
 442                 .set_arg("min", min)
 443                 .set_arg("max", max)
 444                 .note(fluent::lint::note)
 445                 .emit();
 446         });
 447     }
 448 }
 449
 450 fn lint_literal<'tcx>(
 451     cx: &LateContext<'tcx>,
 452     type_limits: &TypeLimits,
 453     e: &'tcx hir::Expr<'tcx>,
 454     lit: &hir::Lit,
 455 ) {
 456     match *cx.typeck_results().node_type(e.hir_id).kind() {
 457         ty::Int(t) => {
 458             match lit.node {
 459                 ast::LitKind::Int(v, ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed) => {
 460                     lint_int_literal(cx, type_limits, e, lit, t, v)
 461                 }
 462                 _ => bug!(),
 463             };
 464         }
 465         ty::Uint(t) => lint_uint_literal(cx, e, lit, t),
 466         ty::Float(t) => {
 467             let is_infinite = match lit.node {
 468                 ast::LitKind::Float(v, _) => match t {
 469                     ty::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
 470                     ty::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
 471                 },
 472                 _ => bug!(),
 473             };
 474             if is_infinite == Ok(true) {
 475                 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
 476                     lint.build(fluent::lint::overflowing_literal)
 477                         .set_arg("ty", t.name_str())
 478                         .set_arg(
 479                             "lit",
 480                             cx.sess()
 481                                 .source_map()
 482                                 .span_to_snippet(lit.span)
 483                                 .expect("must get snippet from literal"),
 484                         )
 485                         .note(fluent::lint::note)
 486                         .emit();
 487                 });
 488             }
 489         }
 490         _ => {}
 491     }
 492 }
 493
 494 impl<'tcx> LateLintPass<'tcx> for TypeLimits {
 495     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx hir::Expr<'tcx>) {
 496         match e.kind {
 497             hir::ExprKind::Unary(hir::UnOp::Neg, ref expr) => {
 498                 // propagate negation, if the negation itself isn't negated
 499                 if self.negated_expr_id != Some(e.hir_id) {
 500                     self.negated_expr_id = Some(expr.hir_id);
 501                 }
 502             }
 503             hir::ExprKind::Binary(binop, ref l, ref r) => {
 504                 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
 505                     cx.struct_span_lint(UNUSED_COMPARISONS, e.span, |lint| {
 506                         lint.build(fluent::lint::unused_comparisons).emit();
 507                     });
 508                 }
 509             }
 510             hir::ExprKind::Lit(ref lit) => lint_literal(cx, self, e, lit),
 511             _ => {}
 512         };
 513
 514         fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
 515             match binop.node {
 516                 hir::BinOpKind::Lt => v > min && v <= max,
 517                 hir::BinOpKind::Le => v >= min && v < max,
 518                 hir::BinOpKind::Gt => v >= min && v < max,
 519                 hir::BinOpKind::Ge => v > min && v <= max,
 520                 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
 521                 _ => bug!(),
 522             }
 523         }
 524
 525         fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
 526             source_map::respan(
 527                 binop.span,
 528                 match binop.node {
 529                     hir::BinOpKind::Lt => hir::BinOpKind::Gt,
 530                     hir::BinOpKind::Le => hir::BinOpKind::Ge,
 531                     hir::BinOpKind::Gt => hir::BinOpKind::Lt,
 532                     hir::BinOpKind::Ge => hir::BinOpKind::Le,
 533                     _ => return binop,
 534                 },
 535             )
 536         }
 537
 538         fn check_limits(
 539             cx: &LateContext<'_>,
 540             binop: hir::BinOp,
 541             l: &hir::Expr<'_>,
 542             r: &hir::Expr<'_>,
 543         ) -> bool {
 544             let (lit, expr, swap) = match (&l.kind, &r.kind) {
 545                 (&hir::ExprKind::Lit(_), _) => (l, r, true),
 546                 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
 547                 _ => return true,
 548             };
 549             // Normalize the binop so that the literal is always on the RHS in
 550             // the comparison
 551             let norm_binop = if swap { rev_binop(binop) } else { binop };
 552             match *cx.typeck_results().node_type(expr.hir_id).kind() {
 553                 ty::Int(int_ty) => {
 554                     let (min, max) = int_ty_range(int_ty);
 555                     let lit_val: i128 = match lit.kind {
 556                         hir::ExprKind::Lit(ref li) => match li.node {
 557                             ast::LitKind::Int(
 558                                 v,
 559                                 ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed,
 560                             ) => v as i128,
 561                             _ => return true,
 562                         },
 563                         _ => bug!(),
 564                     };
 565                     is_valid(norm_binop, lit_val, min, max)
 566                 }
 567                 ty::Uint(uint_ty) => {
 568                     let (min, max): (u128, u128) = uint_ty_range(uint_ty);
 569                     let lit_val: u128 = match lit.kind {
 570                         hir::ExprKind::Lit(ref li) => match li.node {
 571                             ast::LitKind::Int(v, _) => v,
 572                             _ => return true,
 573                         },
 574                         _ => bug!(),
 575                     };
 576                     is_valid(norm_binop, lit_val, min, max)
 577                 }
 578                 _ => true,
 579             }
 580         }
 581
 582         fn is_comparison(binop: hir::BinOp) -> bool {
 583             matches!(
 584                 binop.node,
 585                 hir::BinOpKind::Eq
 586                     | hir::BinOpKind::Lt
 587                     | hir::BinOpKind::Le
 588                     | hir::BinOpKind::Ne
 589                     | hir::BinOpKind::Ge
 590                     | hir::BinOpKind::Gt
 591             )
 592         }
 593     }
 594 }
 595
 596 declare_lint! {
 597     /// The `improper_ctypes` lint detects incorrect use of types in foreign
 598     /// modules.
 599     ///
 600     /// ### Example
 601     ///
 602     /// ```rust
 603     /// extern "C" {
 604     ///     static STATIC: String;
 605     /// }
 606     /// ```
 607     ///
 608     /// {{produces}}
 609     ///
 610     /// ### Explanation
 611     ///
 612     /// The compiler has several checks to verify that types used in `extern`
 613     /// blocks are safe and follow certain rules to ensure proper
 614     /// compatibility with the foreign interfaces. This lint is issued when it
 615     /// detects a probable mistake in a definition. The lint usually should
 616     /// provide a description of the issue, along with possibly a hint on how
 617     /// to resolve it.
 618     IMPROPER_CTYPES,
 619     Warn,
 620     "proper use of libc types in foreign modules"
 621 }
 622
 623 declare_lint_pass!(ImproperCTypesDeclarations => [IMPROPER_CTYPES]);
 624
 625 declare_lint! {
 626     /// The `improper_ctypes_definitions` lint detects incorrect use of
 627     /// [`extern` function] definitions.
 628     ///
 629     /// [`extern` function]: https://doc.rust-lang.org/reference/items/functions.html#extern-function-qualifier
 630     ///
 631     /// ### Example
 632     ///
 633     /// ```rust
 634     /// # #![allow(unused)]
 635     /// pub extern "C" fn str_type(p: &str) { }
 636     /// ```
 637     ///
 638     /// {{produces}}
 639     ///
 640     /// ### Explanation
 641     ///
 642     /// There are many parameter and return types that may be specified in an
 643     /// `extern` function that are not compatible with the given ABI. This
 644     /// lint is an alert that these types should not be used. The lint usually
 645     /// should provide a description of the issue, along with possibly a hint
 646     /// on how to resolve it.
 647     IMPROPER_CTYPES_DEFINITIONS,
 648     Warn,
 649     "proper use of libc types in foreign item definitions"
 650 }
 651
 652 declare_lint_pass!(ImproperCTypesDefinitions => [IMPROPER_CTYPES_DEFINITIONS]);
 653
 654 #[derive(Clone, Copy)]
 655 pub(crate) enum CItemKind {
 656     Declaration,
 657     Definition,
 658 }
 659
 660 struct ImproperCTypesVisitor<'a, 'tcx> {
 661     cx: &'a LateContext<'tcx>,
 662     mode: CItemKind,
 663 }
 664
 665 enum FfiResult<'tcx> {
 666     FfiSafe,
 667     FfiPhantom(Ty<'tcx>),
 668     FfiUnsafe { ty: Ty<'tcx>, reason: DiagnosticMessage, help: Option<DiagnosticMessage> },
 669 }
 670
 671 pub(crate) fn nonnull_optimization_guaranteed<'tcx>(
 672     tcx: TyCtxt<'tcx>,
 673     def: ty::AdtDef<'tcx>,
 674 ) -> bool {
 675     tcx.has_attr(def.did(), sym::rustc_nonnull_optimization_guaranteed)
 676 }
 677
 678 /// `repr(transparent)` structs can have a single non-ZST field, this function returns that
 679 /// field.
 680 pub fn transparent_newtype_field<'a, 'tcx>(
 681     tcx: TyCtxt<'tcx>,
 682     variant: &'a ty::VariantDef,
 683 ) -> Option<&'a ty::FieldDef> {
 684     let param_env = tcx.param_env(variant.def_id);
 685     variant.fields.iter().find(|field| {
 686         let field_ty = tcx.type_of(field.did);
 687         let is_zst = tcx.layout_of(param_env.and(field_ty)).map_or(false, |layout| layout.is_zst());
 688         !is_zst
 689     })
 690 }
 691
 692 /// Is type known to be non-null?
 693 fn ty_is_known_nonnull<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, mode: CItemKind) -> bool {
 694     let tcx = cx.tcx;
 695     match ty.kind() {
 696         ty::FnPtr(_) => true,
 697         ty::Ref(..) => true,
 698         ty::Adt(def, _) if def.is_box() && matches!(mode, CItemKind::Definition) => true,
 699         ty::Adt(def, substs) if def.repr().transparent() && !def.is_union() => {
 700             let marked_non_null = nonnull_optimization_guaranteed(tcx, *def);
 701
 702             if marked_non_null {
 703                 return true;
 704             }
 705
 706             // `UnsafeCell` has its niche hidden.
 707             if def.is_unsafe_cell() {
 708                 return false;
 709             }
 710
 711             def.variants()
 712                 .iter()
 713                 .filter_map(|variant| transparent_newtype_field(cx.tcx, variant))
 714                 .any(|field| ty_is_known_nonnull(cx, field.ty(tcx, substs), mode))
 715         }
 716         _ => false,
 717     }
 718 }
 719
 720 /// Given a non-null scalar (or transparent) type `ty`, return the nullable version of that type.
 721 /// If the type passed in was not scalar, returns None.
 722 fn get_nullable_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
 723     let tcx = cx.tcx;
 724     Some(match *ty.kind() {
 725         ty::Adt(field_def, field_substs) => {
 726             let inner_field_ty = {
 727                 let first_non_zst_ty = field_def
 728                     .variants()
 729                     .iter()
 730                     .filter_map(|v| transparent_newtype_field(cx.tcx, v));
 731                 debug_assert_eq!(
 732                     first_non_zst_ty.clone().count(),
 733                     1,
 734                     "Wrong number of fields for transparent type"
 735                 );
 736                 first_non_zst_ty
 737                     .last()
 738                     .expect("No non-zst fields in transparent type.")
 739                     .ty(tcx, field_substs)
 740             };
 741             return get_nullable_type(cx, inner_field_ty);
 742         }
 743         ty::Int(ty) => tcx.mk_mach_int(ty),
 744         ty::Uint(ty) => tcx.mk_mach_uint(ty),
 745         ty::RawPtr(ty_mut) => tcx.mk_ptr(ty_mut),
 746         // As these types are always non-null, the nullable equivalent of
 747         // Option<T> of these types are their raw pointer counterparts.
 748         ty::Ref(_region, ty, mutbl) => tcx.mk_ptr(ty::TypeAndMut { ty, mutbl }),
 749         ty::FnPtr(..) => {
 750             // There is no nullable equivalent for Rust's function pointers -- you
 751             // must use an Option<fn(..) -> _> to represent it.
 752             ty
 753         }
 754
 755         // We should only ever reach this case if ty_is_known_nonnull is extended
 756         // to other types.
 757         ref unhandled => {
 758             debug!(
 759                 "get_nullable_type: Unhandled scalar kind: {:?} while checking {:?}",
 760                 unhandled, ty
 761             );
 762             return None;
 763         }
 764     })
 765 }
 766
 767 /// Check if this enum can be safely exported based on the "nullable pointer optimization". If it
 768 /// can, return the type that `ty` can be safely converted to, otherwise return `None`.
 769 /// Currently restricted to function pointers, boxes, references, `core::num::NonZero*`,
 770 /// `core::ptr::NonNull`, and `#[repr(transparent)]` newtypes.
 771 /// FIXME: This duplicates code in codegen.
 772 pub(crate) fn repr_nullable_ptr<'tcx>(
 773     cx: &LateContext<'tcx>,
 774     ty: Ty<'tcx>,
 775     ckind: CItemKind,
 776 ) -> Option<Ty<'tcx>> {
 777     debug!("is_repr_nullable_ptr(cx, ty = {:?})", ty);
 778     if let ty::Adt(ty_def, substs) = ty.kind() {
 779         let field_ty = match &ty_def.variants().raw[..] {
 780             [var_one, var_two] => match (&var_one.fields[..], &var_two.fields[..]) {
 781                 ([], [field]) | ([field], []) => field.ty(cx.tcx, substs),
 782                 _ => return None,
 783             },
 784             _ => return None,
 785         };
 786
 787         if !ty_is_known_nonnull(cx, field_ty, ckind) {
 788             return None;
 789         }
 790
 791         // At this point, the field's type is known to be nonnull and the parent enum is Option-like.
 792         // If the computed size for the field and the enum are different, the nonnull optimization isn't
 793         // being applied (and we've got a problem somewhere).
 794         let compute_size_skeleton = |t| SizeSkeleton::compute(t, cx.tcx, cx.param_env).unwrap();
 795         if !compute_size_skeleton(ty).same_size(compute_size_skeleton(field_ty)) {
 796             bug!("improper_ctypes: Option nonnull optimization not applied?");
 797         }
 798
 799         // Return the nullable type this Option-like enum can be safely represented with.
 800         let field_ty_abi = &cx.layout_of(field_ty).unwrap().abi;
 801         if let Abi::Scalar(field_ty_scalar) = field_ty_abi {
 802             match field_ty_scalar.valid_range(cx) {
 803                 WrappingRange { start: 0, end }
 804                     if end == field_ty_scalar.size(&cx.tcx).unsigned_int_max() - 1 =>
 805                 {
 806                     return Some(get_nullable_type(cx, field_ty).unwrap());
 807                 }
 808                 WrappingRange { start: 1, .. } => {
 809                     return Some(get_nullable_type(cx, field_ty).unwrap());
 810                 }
 811                 WrappingRange { start, end } => {
 812                     unreachable!("Unhandled start and end range: ({}, {})", start, end)
 813                 }
 814             };
 815         }
 816     }
 817     None
 818 }
 819
 820 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
 821     /// Check if the type is array and emit an unsafe type lint.
 822     fn check_for_array_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
 823         if let ty::Array(..) = ty.kind() {
 824             self.emit_ffi_unsafe_type_lint(
 825                 ty,
 826                 sp,
 827                 fluent::lint::improper_ctypes_array_reason,
 828                 Some(fluent::lint::improper_ctypes_array_help),
 829             );
 830             true
 831         } else {
 832             false
 833         }
 834     }
 835
 836     /// Checks if the given field's type is "ffi-safe".
 837     fn check_field_type_for_ffi(
 838         &self,
 839         cache: &mut FxHashSet<Ty<'tcx>>,
 840         field: &ty::FieldDef,
 841         substs: SubstsRef<'tcx>,
 842     ) -> FfiResult<'tcx> {
 843         let field_ty = field.ty(self.cx.tcx, substs);
 844         if field_ty.has_opaque_types() {
 845             self.check_type_for_ffi(cache, field_ty)
 846         } else {
 847             let field_ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, field_ty);
 848             self.check_type_for_ffi(cache, field_ty)
 849         }
 850     }
 851
 852     /// Checks if the given `VariantDef`'s field types are "ffi-safe".
 853     fn check_variant_for_ffi(
 854         &self,
 855         cache: &mut FxHashSet<Ty<'tcx>>,
 856         ty: Ty<'tcx>,
 857         def: ty::AdtDef<'tcx>,
 858         variant: &ty::VariantDef,
 859         substs: SubstsRef<'tcx>,
 860     ) -> FfiResult<'tcx> {
 861         use FfiResult::*;
 862
 863         if def.repr().transparent() {
 864             // Can assume that at most one field is not a ZST, so only check
 865             // that field's type for FFI-safety.
 866             if let Some(field) = transparent_newtype_field(self.cx.tcx, variant) {
 867                 self.check_field_type_for_ffi(cache, field, substs)
 868             } else {
 869                 // All fields are ZSTs; this means that the type should behave
 870                 // like (), which is FFI-unsafe
 871                 FfiUnsafe { ty, reason: fluent::lint::improper_ctypes_struct_zst, help: None }
 872             }
 873         } else {
 874             // We can't completely trust repr(C) markings; make sure the fields are
 875             // actually safe.
 876             let mut all_phantom = !variant.fields.is_empty();
 877             for field in &variant.fields {
 878                 match self.check_field_type_for_ffi(cache, &field, substs) {
 879                     FfiSafe => {
 880                         all_phantom = false;
 881                     }
 882                     FfiPhantom(..) if def.is_enum() => {
 883                         return FfiUnsafe {
 884                             ty,
 885                             reason: fluent::lint::improper_ctypes_enum_phantomdata,
 886                             help: None,
 887                         };
 888                     }
 889                     FfiPhantom(..) => {}
 890                     r => return r,
 891                 }
 892             }
 893
 894             if all_phantom { FfiPhantom(ty) } else { FfiSafe }
 895         }
 896     }
 897
 898     /// Checks if the given type is "ffi-safe" (has a stable, well-defined
 899     /// representation which can be exported to C code).
 900     fn check_type_for_ffi(&self, cache: &mut FxHashSet<Ty<'tcx>>, ty: Ty<'tcx>) -> FfiResult<'tcx> {
 901         use FfiResult::*;
 902
 903         let tcx = self.cx.tcx;
 904
 905         // Protect against infinite recursion, for example
 906         // `struct S(*mut S);`.
 907         // FIXME: A recursion limit is necessary as well, for irregular
 908         // recursive types.
 909         if !cache.insert(ty) {
 910             return FfiSafe;
 911         }
 912
 913         match *ty.kind() {
 914             ty::Adt(def, substs) => {
 915                 if def.is_box() && matches!(self.mode, CItemKind::Definition) {
 916                     if ty.boxed_ty().is_sized(tcx.at(DUMMY_SP), self.cx.param_env) {
 917                         return FfiSafe;
 918                     } else {
 919                         return FfiUnsafe {
 920                             ty,
 921                             reason: fluent::lint::improper_ctypes_box,
 922                             help: None,
 923                         };
 924                     }
 925                 }
 926                 if def.is_phantom_data() {
 927                     return FfiPhantom(ty);
 928                 }
 929                 match def.adt_kind() {
 930                     AdtKind::Struct | AdtKind::Union => {
 931                         if !def.repr().c() && !def.repr().transparent() {
 932                             return FfiUnsafe {
 933                                 ty,
 934                                 reason: if def.is_struct() {
 935                                     fluent::lint::improper_ctypes_struct_layout_reason
 936                                 } else {
 937                                     fluent::lint::improper_ctypes_union_layout_reason
 938                                 },
 939                                 help: if def.is_struct() {
 940                                     Some(fluent::lint::improper_ctypes_struct_layout_help)
 941                                 } else {
 942                                     Some(fluent::lint::improper_ctypes_union_layout_help)
 943                                 },
 944                             };
 945                         }
 946
 947                         let is_non_exhaustive =
 948                             def.non_enum_variant().is_field_list_non_exhaustive();
 949                         if is_non_exhaustive && !def.did().is_local() {
 950                             return FfiUnsafe {
 951                                 ty,
 952                                 reason: if def.is_struct() {
 953                                     fluent::lint::improper_ctypes_struct_non_exhaustive
 954                                 } else {
 955                                     fluent::lint::improper_ctypes_union_non_exhaustive
 956                                 },
 957                                 help: None,
 958                             };
 959                         }
 960
 961                         if def.non_enum_variant().fields.is_empty() {
 962                             return FfiUnsafe {
 963                                 ty,
 964                                 reason: if def.is_struct() {
 965                                     fluent::lint::improper_ctypes_struct_fieldless_reason
 966                                 } else {
 967                                     fluent::lint::improper_ctypes_union_fieldless_reason
 968                                 },
 969                                 help: if def.is_struct() {
 970                                     Some(fluent::lint::improper_ctypes_struct_fieldless_help)
 971                                 } else {
 972                                     Some(fluent::lint::improper_ctypes_union_fieldless_help)
 973                                 },
 974                             };
 975                         }
 976
 977                         self.check_variant_for_ffi(cache, ty, def, def.non_enum_variant(), substs)
 978                     }
 979                     AdtKind::Enum => {
 980                         if def.variants().is_empty() {
 981                             // Empty enums are okay... although sort of useless.
 982                             return FfiSafe;
 983                         }
 984
 985                         // Check for a repr() attribute to specify the size of the
 986                         // discriminant.
 987                         if !def.repr().c() && !def.repr().transparent() && def.repr().int.is_none()
 988                         {
 989                             // Special-case types like `Option<extern fn()>`.
 990                             if repr_nullable_ptr(self.cx, ty, self.mode).is_none() {
 991                                 return FfiUnsafe {
 992                                     ty,
 993                                     reason: fluent::lint::improper_ctypes_enum_repr_reason,
 994                                     help: Some(fluent::lint::improper_ctypes_enum_repr_help),
 995                                 };
 996                             }
 997                         }
 998
 999                         if def.is_variant_list_non_exhaustive() && !def.did().is_local() {
1000                             return FfiUnsafe {
1001                                 ty,
1002                                 reason: fluent::lint::improper_ctypes_non_exhaustive,
1003                                 help: None,
1004                             };
1005                         }
1006
1007                         // Check the contained variants.
1008                         for variant in def.variants() {
1009                             let is_non_exhaustive = variant.is_field_list_non_exhaustive();
1010                             if is_non_exhaustive && !variant.def_id.is_local() {
1011                                 return FfiUnsafe {
1012                                     ty,
1013                                     reason: fluent::lint::improper_ctypes_non_exhaustive_variant,
1014                                     help: None,
1015                                 };
1016                             }
1017
1018                             match self.check_variant_for_ffi(cache, ty, def, variant, substs) {
1019                                 FfiSafe => (),
1020                                 r => return r,
1021                             }
1022                         }
1023
1024                         FfiSafe
1025                     }
1026                 }
1027             }
1028
1029             ty::Char => FfiUnsafe {
1030                 ty,
1031                 reason: fluent::lint::improper_ctypes_char_reason,
1032                 help: Some(fluent::lint::improper_ctypes_char_help),
1033             },
1034
1035             ty::Int(ty::IntTy::I128) | ty::Uint(ty::UintTy::U128) => {
1036                 FfiUnsafe { ty, reason: fluent::lint::improper_ctypes_128bit, help: None }
1037             }
1038
1039             // Primitive types with a stable representation.
1040             ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
1041
1042             ty::Slice(_) => FfiUnsafe {
1043                 ty,
1044                 reason: fluent::lint::improper_ctypes_slice_reason,
1045                 help: Some(fluent::lint::improper_ctypes_slice_help),
1046             },
1047
1048             ty::Dynamic(..) => {
1049                 FfiUnsafe { ty, reason: fluent::lint::improper_ctypes_dyn, help: None }
1050             }
1051
1052             ty::Str => FfiUnsafe {
1053                 ty,
1054                 reason: fluent::lint::improper_ctypes_str_reason,
1055                 help: Some(fluent::lint::improper_ctypes_str_help),
1056             },
1057
1058             ty::Tuple(..) => FfiUnsafe {
1059                 ty,
1060                 reason: fluent::lint::improper_ctypes_tuple_reason,
1061                 help: Some(fluent::lint::improper_ctypes_tuple_help),
1062             },
1063
1064             ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _)
1065                 if {
1066                     matches!(self.mode, CItemKind::Definition)
1067                         && ty.is_sized(self.cx.tcx.at(DUMMY_SP), self.cx.param_env)
1068                 } =>
1069             {
1070                 FfiSafe
1071             }
1072
1073             ty::RawPtr(ty::TypeAndMut { ty, .. })
1074                 if match ty.kind() {
1075                     ty::Tuple(tuple) => tuple.is_empty(),
1076                     _ => false,
1077                 } =>
1078             {
1079                 FfiSafe
1080             }
1081
1082             ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _) => {
1083                 self.check_type_for_ffi(cache, ty)
1084             }
1085
1086             ty::Array(inner_ty, _) => self.check_type_for_ffi(cache, inner_ty),
1087
1088             ty::FnPtr(sig) => {
1089                 if self.is_internal_abi(sig.abi()) {
1090                     return FfiUnsafe {
1091                         ty,
1092                         reason: fluent::lint::improper_ctypes_fnptr_reason,
1093                         help: Some(fluent::lint::improper_ctypes_fnptr_help),
1094                     };
1095                 }
1096
1097                 let sig = tcx.erase_late_bound_regions(sig);
1098                 if !sig.output().is_unit() {
1099                     let r = self.check_type_for_ffi(cache, sig.output());
1100                     match r {
1101                         FfiSafe => {}
1102                         _ => {
1103                             return r;
1104                         }
1105                     }
1106                 }
1107                 for arg in sig.inputs() {
1108                     let r = self.check_type_for_ffi(cache, *arg);
1109                     match r {
1110                         FfiSafe => {}
1111                         _ => {
1112                             return r;
1113                         }
1114                     }
1115                 }
1116                 FfiSafe
1117             }
1118
1119             ty::Foreign(..) => FfiSafe,
1120
1121             // While opaque types are checked for earlier, if a projection in a struct field
1122             // normalizes to an opaque type, then it will reach this branch.
1123             ty::Opaque(..) => {
1124                 FfiUnsafe { ty, reason: fluent::lint::improper_ctypes_opaque, help: None }
1125             }
1126
1127             // `extern "C" fn` functions can have type parameters, which may or may not be FFI-safe,
1128             //  so they are currently ignored for the purposes of this lint.
1129             ty::Param(..) | ty::Projection(..) if matches!(self.mode, CItemKind::Definition) => {
1130                 FfiSafe
1131             }
1132
1133             ty::Param(..)
1134             | ty::Projection(..)
1135             | ty::Infer(..)
1136             | ty::Bound(..)
1137             | ty::Error(_)
1138             | ty::Closure(..)
1139             | ty::Generator(..)
1140             | ty::GeneratorWitness(..)
1141             | ty::Placeholder(..)
1142             | ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty),
1143         }
1144     }
1145
1146     fn emit_ffi_unsafe_type_lint(
1147         &mut self,
1148         ty: Ty<'tcx>,
1149         sp: Span,
1150         note: DiagnosticMessage,
1151         help: Option<DiagnosticMessage>,
1152     ) {
1153         let lint = match self.mode {
1154             CItemKind::Declaration => IMPROPER_CTYPES,
1155             CItemKind::Definition => IMPROPER_CTYPES_DEFINITIONS,
1156         };
1157
1158         self.cx.struct_span_lint(lint, sp, |lint| {
1159             let item_description = match self.mode {
1160                 CItemKind::Declaration => "block",
1161                 CItemKind::Definition => "fn",
1162             };
1163             let mut diag = lint.build(fluent::lint::improper_ctypes);
1164             diag.set_arg("ty", ty);
1165             diag.set_arg("desc", item_description);
1166             diag.span_label(sp, fluent::lint::label);
1167             if let Some(help) = help {
1168                 diag.help(help);
1169             }
1170             diag.note(note);
1171             if let ty::Adt(def, _) = ty.kind() {
1172                 if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did()) {
1173                     diag.span_note(sp, fluent::lint::note);
1174                 }
1175             }
1176             diag.emit();
1177         });
1178     }
1179
1180     fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
1181         struct ProhibitOpaqueTypes<'a, 'tcx> {
1182             cx: &'a LateContext<'tcx>,
1183         }
1184
1185         impl<'a, 'tcx> ty::visit::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'a, 'tcx> {
1186             type BreakTy = Ty<'tcx>;
1187
1188             fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1189                 match ty.kind() {
1190                     ty::Opaque(..) => ControlFlow::Break(ty),
1191                     // Consider opaque types within projections FFI-safe if they do not normalize
1192                     // to more opaque types.
1193                     ty::Projection(..) => {
1194                         let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
1195
1196                         // If `ty` is an opaque type directly then `super_visit_with` won't invoke
1197                         // this function again.
1198                         if ty.has_opaque_types() {
1199                             self.visit_ty(ty)
1200                         } else {
1201                             ControlFlow::CONTINUE
1202                         }
1203                     }
1204                     _ => ty.super_visit_with(self),
1205                 }
1206             }
1207         }
1208
1209         if let Some(ty) = ty.visit_with(&mut ProhibitOpaqueTypes { cx: self.cx }).break_value() {
1210             self.emit_ffi_unsafe_type_lint(ty, sp, fluent::lint::improper_ctypes_opaque, None);
1211             true
1212         } else {
1213             false
1214         }
1215     }
1216
1217     fn check_type_for_ffi_and_report_errors(
1218         &mut self,
1219         sp: Span,
1220         ty: Ty<'tcx>,
1221         is_static: bool,
1222         is_return_type: bool,
1223     ) {
1224         // We have to check for opaque types before `normalize_erasing_regions`,
1225         // which will replace opaque types with their underlying concrete type.
1226         if self.check_for_opaque_ty(sp, ty) {
1227             // We've already emitted an error due to an opaque type.
1228             return;
1229         }
1230
1231         // it is only OK to use this function because extern fns cannot have
1232         // any generic types right now:
1233         let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
1234
1235         // C doesn't really support passing arrays by value - the only way to pass an array by value
1236         // is through a struct. So, first test that the top level isn't an array, and then
1237         // recursively check the types inside.
1238         if !is_static && self.check_for_array_ty(sp, ty) {
1239             return;
1240         }
1241
1242         // Don't report FFI errors for unit return types. This check exists here, and not in
1243         // `check_foreign_fn` (where it would make more sense) so that normalization has definitely
1244         // happened.
1245         if is_return_type && ty.is_unit() {
1246             return;
1247         }
1248
1249         match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
1250             FfiResult::FfiSafe => {}
1251             FfiResult::FfiPhantom(ty) => {
1252                 self.emit_ffi_unsafe_type_lint(
1253                     ty,
1254                     sp,
1255                     fluent::lint::improper_ctypes_only_phantomdata,
1256                     None,
1257                 );
1258             }
1259             // If `ty` is a `repr(transparent)` newtype, and the non-zero-sized type is a generic
1260             // argument, which after substitution, is `()`, then this branch can be hit.
1261             FfiResult::FfiUnsafe { ty, .. } if is_return_type && ty.is_unit() => {}
1262             FfiResult::FfiUnsafe { ty, reason, help } => {
1263                 self.emit_ffi_unsafe_type_lint(ty, sp, reason, help);
1264             }
1265         }
1266     }
1267
1268     fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl<'_>) {
1269         let def_id = self.cx.tcx.hir().local_def_id(id);
1270         let sig = self.cx.tcx.fn_sig(def_id);
1271         let sig = self.cx.tcx.erase_late_bound_regions(sig);
1272
1273         for (input_ty, input_hir) in iter::zip(sig.inputs(), decl.inputs) {
1274             self.check_type_for_ffi_and_report_errors(input_hir.span, *input_ty, false, false);
1275         }
1276
1277         if let hir::FnRetTy::Return(ref ret_hir) = decl.output {
1278             let ret_ty = sig.output();
1279             self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty, false, true);
1280         }
1281     }
1282
1283     fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
1284         let def_id = self.cx.tcx.hir().local_def_id(id);
1285         let ty = self.cx.tcx.type_of(def_id);
1286         self.check_type_for_ffi_and_report_errors(span, ty, true, false);
1287     }
1288
1289     fn is_internal_abi(&self, abi: SpecAbi) -> bool {
1290         matches!(
1291             abi,
1292             SpecAbi::Rust | SpecAbi::RustCall | SpecAbi::RustIntrinsic | SpecAbi::PlatformIntrinsic
1293         )
1294     }
1295 }
1296
1297 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDeclarations {
1298     fn check_foreign_item(&mut self, cx: &LateContext<'_>, it: &hir::ForeignItem<'_>) {
1299         let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Declaration };
1300         let abi = cx.tcx.hir().get_foreign_abi(it.hir_id());
1301
1302         if !vis.is_internal_abi(abi) {
1303             match it.kind {
1304                 hir::ForeignItemKind::Fn(ref decl, _, _) => {
1305                     vis.check_foreign_fn(it.hir_id(), decl);
1306                 }
1307                 hir::ForeignItemKind::Static(ref ty, _) => {
1308                     vis.check_foreign_static(it.hir_id(), ty.span);
1309                 }
1310                 hir::ForeignItemKind::Type => (),
1311             }
1312         }
1313     }
1314 }
1315
1316 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDefinitions {
1317     fn check_fn(
1318         &mut self,
1319         cx: &LateContext<'tcx>,
1320         kind: hir::intravisit::FnKind<'tcx>,
1321         decl: &'tcx hir::FnDecl<'_>,
1322         _: &'tcx hir::Body<'_>,
1323         _: Span,
1324         hir_id: hir::HirId,
1325     ) {
1326         use hir::intravisit::FnKind;
1327
1328         let abi = match kind {
1329             FnKind::ItemFn(_, _, header, ..) => header.abi,
1330             FnKind::Method(_, sig, ..) => sig.header.abi,
1331             _ => return,
1332         };
1333
1334         let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Definition };
1335         if !vis.is_internal_abi(abi) {
1336             vis.check_foreign_fn(hir_id, decl);
1337         }
1338     }
1339 }
1340
1341 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
1342
1343 impl<'tcx> LateLintPass<'tcx> for VariantSizeDifferences {
1344     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1345         if let hir::ItemKind::Enum(ref enum_definition, _) = it.kind {
1346             let t = cx.tcx.type_of(it.def_id);
1347             let ty = cx.tcx.erase_regions(t);
1348             let Ok(layout) = cx.layout_of(ty) else { return };
1349             let Variants::Multiple {
1350                     tag_encoding: TagEncoding::Direct, tag, ref variants, ..
1351                 } = &layout.variants else {
1352                 return
1353             };
1354
1355             let tag_size = tag.size(&cx.tcx).bytes();
1356
1357             debug!(
1358                 "enum `{}` is {} bytes large with layout:\n{:#?}",
1359                 t,
1360                 layout.size.bytes(),
1361                 layout
1362             );
1363
1364             let (largest, slargest, largest_index) = iter::zip(enum_definition.variants, variants)
1365                 .map(|(variant, variant_layout)| {
1366                     // Subtract the size of the enum tag.
1367                     let bytes = variant_layout.size().bytes().saturating_sub(tag_size);
1368
1369                     debug!("- variant `{}` is {} bytes large", variant.ident, bytes);
1370                     bytes
1371                 })
1372                 .enumerate()
1373                 .fold((0, 0, 0), |(l, s, li), (idx, size)| {
1374                     if size > l {
1375                         (size, l, idx)
1376                     } else if size > s {
1377                         (l, size, li)
1378                     } else {
1379                         (l, s, li)
1380                     }
1381                 });
1382
1383             // We only warn if the largest variant is at least thrice as large as
1384             // the second-largest.
1385             if largest > slargest * 3 && slargest > 0 {
1386                 cx.struct_span_lint(
1387                     VARIANT_SIZE_DIFFERENCES,
1388                     enum_definition.variants[largest_index].span,
1389                     |lint| {
1390                         lint.build(fluent::lint::variant_size_differences)
1391                             .set_arg("largest", largest)
1392                             .emit();
1393                     },
1394                 );
1395             }
1396         }
1397     }
1398 }
1399
1400 declare_lint! {
1401     /// The `invalid_atomic_ordering` lint detects passing an `Ordering`
1402     /// to an atomic operation that does not support that ordering.
1403     ///
1404     /// ### Example
1405     ///
1406     /// ```rust,compile_fail
1407     /// # use core::sync::atomic::{AtomicU8, Ordering};
1408     /// let atom = AtomicU8::new(0);
1409     /// let value = atom.load(Ordering::Release);
1410     /// # let _ = value;
1411     /// ```
1412     ///
1413     /// {{produces}}
1414     ///
1415     /// ### Explanation
1416     ///
1417     /// Some atomic operations are only supported for a subset of the
1418     /// `atomic::Ordering` variants. Passing an unsupported variant will cause
1419     /// an unconditional panic at runtime, which is detected by this lint.
1420     ///
1421     /// This lint will trigger in the following cases: (where `AtomicType` is an
1422     /// atomic type from `core::sync::atomic`, such as `AtomicBool`,
1423     /// `AtomicPtr`, `AtomicUsize`, or any of the other integer atomics).
1424     ///
1425     /// - Passing `Ordering::Acquire` or `Ordering::AcqRel` to
1426     ///   `AtomicType::store`.
1427     ///
1428     /// - Passing `Ordering::Release` or `Ordering::AcqRel` to
1429     ///   `AtomicType::load`.
1430     ///
1431     /// - Passing `Ordering::Relaxed` to `core::sync::atomic::fence` or
1432     ///   `core::sync::atomic::compiler_fence`.
1433     ///
1434     /// - Passing `Ordering::Release` or `Ordering::AcqRel` as the failure
1435     ///   ordering for any of `AtomicType::compare_exchange`,
1436     ///   `AtomicType::compare_exchange_weak`, or `AtomicType::fetch_update`.
1437     INVALID_ATOMIC_ORDERING,
1438     Deny,
1439     "usage of invalid atomic ordering in atomic operations and memory fences"
1440 }
1441
1442 declare_lint_pass!(InvalidAtomicOrdering => [INVALID_ATOMIC_ORDERING]);
1443
1444 impl InvalidAtomicOrdering {
1445     fn inherent_atomic_method_call<'hir>(
1446         cx: &LateContext<'_>,
1447         expr: &Expr<'hir>,
1448         recognized_names: &[Symbol], // used for fast path calculation
1449     ) -> Option<(Symbol, &'hir [Expr<'hir>])> {
1450         const ATOMIC_TYPES: &[Symbol] = &[
1451             sym::AtomicBool,
1452             sym::AtomicPtr,
1453             sym::AtomicUsize,
1454             sym::AtomicU8,
1455             sym::AtomicU16,
1456             sym::AtomicU32,
1457             sym::AtomicU64,
1458             sym::AtomicU128,
1459             sym::AtomicIsize,
1460             sym::AtomicI8,
1461             sym::AtomicI16,
1462             sym::AtomicI32,
1463             sym::AtomicI64,
1464             sym::AtomicI128,
1465         ];
1466         if let ExprKind::MethodCall(ref method_path, args, _) = &expr.kind
1467             && recognized_names.contains(&method_path.ident.name)
1468             && let Some(m_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id)
1469             && let Some(impl_did) = cx.tcx.impl_of_method(m_def_id)
1470             && let Some(adt) = cx.tcx.type_of(impl_did).ty_adt_def()
1471             // skip extension traits, only lint functions from the standard library
1472             && cx.tcx.trait_id_of_impl(impl_did).is_none()
1473             && let parent = cx.tcx.parent(adt.did())
1474             && cx.tcx.is_diagnostic_item(sym::atomic_mod, parent)
1475             && ATOMIC_TYPES.contains(&cx.tcx.item_name(adt.did()))
1476         {
1477             return Some((method_path.ident.name, args));
1478         }
1479         None
1480     }
1481
1482     fn match_ordering(cx: &LateContext<'_>, ord_arg: &Expr<'_>) -> Option<Symbol> {
1483         let ExprKind::Path(ref ord_qpath) = ord_arg.kind else { return None };
1484         let did = cx.qpath_res(ord_qpath, ord_arg.hir_id).opt_def_id()?;
1485         let tcx = cx.tcx;
1486         let atomic_ordering = tcx.get_diagnostic_item(sym::Ordering);
1487         let name = tcx.item_name(did);
1488         let parent = tcx.parent(did);
1489         [sym::Relaxed, sym::Release, sym::Acquire, sym::AcqRel, sym::SeqCst].into_iter().find(
1490             |&ordering| {
1491                 name == ordering
1492                     && (Some(parent) == atomic_ordering
1493                             // needed in case this is a ctor, not a variant
1494                             || tcx.opt_parent(parent) == atomic_ordering)
1495             },
1496         )
1497     }
1498
1499     fn check_atomic_load_store(cx: &LateContext<'_>, expr: &Expr<'_>) {
1500         if let Some((method, args)) = Self::inherent_atomic_method_call(cx, expr, &[sym::load, sym::store])
1501             && let Some((ordering_arg, invalid_ordering)) = match method {
1502                 sym::load => Some((&args[1], sym::Release)),
1503                 sym::store => Some((&args[2], sym::Acquire)),
1504                 _ => None,
1505             }
1506             && let Some(ordering) = Self::match_ordering(cx, ordering_arg)
1507             && (ordering == invalid_ordering || ordering == sym::AcqRel)
1508         {
1509             cx.struct_span_lint(INVALID_ATOMIC_ORDERING, ordering_arg.span, |diag| {
1510                 if method == sym::load {
1511                     diag.build(fluent::lint::atomic_ordering_load)
1512                         .help(fluent::lint::help)
1513                         .emit()
1514                 } else {
1515                     debug_assert_eq!(method, sym::store);
1516                     diag.build(fluent::lint::atomic_ordering_store)
1517                         .help(fluent::lint::help)
1518                         .emit();
1519                 }
1520             });
1521         }
1522     }
1523
1524     fn check_memory_fence(cx: &LateContext<'_>, expr: &Expr<'_>) {
1525         if let ExprKind::Call(ref func, ref args) = expr.kind
1526             && let ExprKind::Path(ref func_qpath) = func.kind
1527             && let Some(def_id) = cx.qpath_res(func_qpath, func.hir_id).opt_def_id()
1528             && matches!(cx.tcx.get_diagnostic_name(def_id), Some(sym::fence | sym::compiler_fence))
1529             && Self::match_ordering(cx, &args[0]) == Some(sym::Relaxed)
1530         {
1531             cx.struct_span_lint(INVALID_ATOMIC_ORDERING, args[0].span, |diag| {
1532                 diag.build(fluent::lint::atomic_ordering_fence)
1533                     .help(fluent::lint::help)
1534                     .emit();
1535             });
1536         }
1537     }
1538
1539     fn check_atomic_compare_exchange(cx: &LateContext<'_>, expr: &Expr<'_>) {
1540         let Some((method, args)) = Self::inherent_atomic_method_call(cx, expr, &[sym::fetch_update, sym::compare_exchange, sym::compare_exchange_weak])
1541             else {return };
1542
1543         let fail_order_arg = match method {
1544             sym::fetch_update => &args[2],
1545             sym::compare_exchange | sym::compare_exchange_weak => &args[4],
1546             _ => return,
1547         };
1548
1549         let Some(fail_ordering) = Self::match_ordering(cx, fail_order_arg) else { return };
1550
1551         if matches!(fail_ordering, sym::Release | sym::AcqRel) {
1552             #[derive(LintDiagnostic)]
1553             #[lint(lint::atomic_ordering_invalid)]
1554             #[help]
1555             struct InvalidAtomicOrderingDiag {
1556                 method: Symbol,
1557                 #[label]
1558                 fail_order_arg_span: Span,
1559             }
1560
1561             cx.emit_spanned_lint(
1562                 INVALID_ATOMIC_ORDERING,
1563                 fail_order_arg.span,
1564                 InvalidAtomicOrderingDiag { method, fail_order_arg_span: fail_order_arg.span },
1565             );
1566         }
1567     }
1568 }
1569
1570 impl<'tcx> LateLintPass<'tcx> for InvalidAtomicOrdering {
1571     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
1572         Self::check_atomic_load_store(cx, expr);
1573         Self::check_memory_fence(cx, expr);
1574         Self::check_atomic_compare_exchange(cx, expr);
1575     }
1576 }