use crate::{LateContext, LateLintPass, LintContext}; use rustc_ast as ast; use rustc_attr as attr; use rustc_data_structures::fx::FxHashSet; use rustc_errors::Applicability; use rustc_hir as hir; use rustc_hir::{is_range_literal, ExprKind, Node}; use rustc_index::vec::Idx; use rustc_middle::mir::interpret::{sign_extend, truncate}; use rustc_middle::ty::layout::{IntegerExt, SizeSkeleton}; use rustc_middle::ty::subst::SubstsRef; use rustc_middle::ty::{self, AdtKind, Ty, TyCtxt, TypeFoldable}; use rustc_span::source_map; use rustc_span::symbol::sym; use rustc_span::{Span, DUMMY_SP}; use rustc_target::abi::Abi; use rustc_target::abi::{Integer, LayoutOf, TagEncoding, VariantIdx, Variants}; use rustc_target::spec::abi::Abi as SpecAbi; use std::cmp; use tracing::debug; declare_lint! { /// The `unused_comparisons` lint detects comparisons made useless by /// limits of the types involved. /// /// ### Example /// /// ```rust /// fn foo(x: u8) { /// x >= 0; /// } /// ``` /// /// {{produces}} /// /// ### Explanation /// /// A useless comparison may indicate a mistake, and should be fixed or /// removed. UNUSED_COMPARISONS, Warn, "comparisons made useless by limits of the types involved" } declare_lint! { /// The `overflowing_literals` lint detects literal out of range for its /// type. /// /// ### Example /// /// ```rust,compile_fail /// let x: u8 = 1000; /// ``` /// /// {{produces}} /// /// ### Explanation /// /// It is usually a mistake to use a literal that overflows the type where /// it is used. Either use a literal that is within range, or change the /// type to be within the range of the literal. OVERFLOWING_LITERALS, Deny, "literal out of range for its type" } declare_lint! { /// The `variant_size_differences` lint detects enums with widely varying /// variant sizes. /// /// ### Example /// /// ```rust,compile_fail /// #![deny(variant_size_differences)] /// enum En { /// V0(u8), /// VBig([u8; 1024]), /// } /// ``` /// /// {{produces}} /// /// ### Explanation /// /// It can be a mistake to add a variant to an enum that is much larger /// than the other variants, bloating the overall size required for all /// variants. This can impact performance and memory usage. This is /// triggered if one variant is more than 3 times larger than the /// second-largest variant. /// /// Consider placing the large variant's contents on the heap (for example /// via [`Box`]) to keep the overall size of the enum itself down. /// /// This lint is "allow" by default because it can be noisy, and may not be /// an actual problem. Decisions about this should be guided with /// profiling and benchmarking. /// /// [`Box`]: https://doc.rust-lang.org/std/boxed/index.html VARIANT_SIZE_DIFFERENCES, Allow, "detects enums with widely varying variant sizes" } #[derive(Copy, Clone)] pub struct TypeLimits { /// Id of the last visited negated expression negated_expr_id: Option, } impl_lint_pass!(TypeLimits => [UNUSED_COMPARISONS, OVERFLOWING_LITERALS]); impl TypeLimits { pub fn new() -> TypeLimits { TypeLimits { negated_expr_id: None } } } /// Attempts to special-case the overflowing literal lint when it occurs as a range endpoint. /// Returns `true` iff the lint was overridden. fn lint_overflowing_range_endpoint<'tcx>( cx: &LateContext<'tcx>, lit: &hir::Lit, lit_val: u128, max: u128, expr: &'tcx hir::Expr<'tcx>, parent_expr: &'tcx hir::Expr<'tcx>, ty: &str, ) -> bool { // We only want to handle exclusive (`..`) ranges, // which are represented as `ExprKind::Struct`. let mut overwritten = false; if let ExprKind::Struct(_, eps, _) = &parent_expr.kind { if eps.len() != 2 { return false; } // We can suggest using an inclusive range // (`..=`) instead only if it is the `end` that is // overflowing and only by 1. if eps[1].expr.hir_id == expr.hir_id && lit_val - 1 == max { cx.struct_span_lint(OVERFLOWING_LITERALS, parent_expr.span, |lint| { let mut err = lint.build(&format!("range endpoint is out of range for `{}`", ty)); if let Ok(start) = cx.sess().source_map().span_to_snippet(eps[0].span) { use ast::{LitIntType, LitKind}; // We need to preserve the literal's suffix, // as it may determine typing information. let suffix = match lit.node { LitKind::Int(_, LitIntType::Signed(s)) => s.name_str().to_string(), LitKind::Int(_, LitIntType::Unsigned(s)) => s.name_str().to_string(), LitKind::Int(_, LitIntType::Unsuffixed) => "".to_string(), _ => bug!(), }; let suggestion = format!("{}..={}{}", start, lit_val - 1, suffix); err.span_suggestion( parent_expr.span, &"use an inclusive range instead", suggestion, Applicability::MachineApplicable, ); err.emit(); overwritten = true; } }); } } overwritten } // For `isize` & `usize`, be conservative with the warnings, so that the // warnings are consistent between 32- and 64-bit platforms. fn int_ty_range(int_ty: ast::IntTy) -> (i128, i128) { match int_ty { ast::IntTy::Isize => (i64::MIN as i128, i64::MAX as i128), ast::IntTy::I8 => (i8::MIN as i64 as i128, i8::MAX as i128), ast::IntTy::I16 => (i16::MIN as i64 as i128, i16::MAX as i128), ast::IntTy::I32 => (i32::MIN as i64 as i128, i32::MAX as i128), ast::IntTy::I64 => (i64::MIN as i128, i64::MAX as i128), ast::IntTy::I128 => (i128::MIN as i128, i128::MAX), } } fn uint_ty_range(uint_ty: ast::UintTy) -> (u128, u128) { match uint_ty { ast::UintTy::Usize => (u64::MIN as u128, u64::MAX as u128), ast::UintTy::U8 => (u8::MIN as u128, u8::MAX as u128), ast::UintTy::U16 => (u16::MIN as u128, u16::MAX as u128), ast::UintTy::U32 => (u32::MIN as u128, u32::MAX as u128), ast::UintTy::U64 => (u64::MIN as u128, u64::MAX as u128), ast::UintTy::U128 => (u128::MIN, u128::MAX), } } fn get_bin_hex_repr(cx: &LateContext<'_>, lit: &hir::Lit) -> Option { let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?; let firstch = src.chars().next()?; if firstch == '0' { match src.chars().nth(1) { Some('x' | 'b') => return Some(src), _ => return None, } } None } fn report_bin_hex_error( cx: &LateContext<'_>, expr: &hir::Expr<'_>, ty: attr::IntType, repr_str: String, val: u128, negative: bool, ) { let size = Integer::from_attr(&cx.tcx, ty).size(); cx.struct_span_lint(OVERFLOWING_LITERALS, expr.span, |lint| { let (t, actually) = match ty { attr::IntType::SignedInt(t) => { let actually = sign_extend(val, size) as i128; (t.name_str(), actually.to_string()) } attr::IntType::UnsignedInt(t) => { let actually = truncate(val, size); (t.name_str(), actually.to_string()) } }; let mut err = lint.build(&format!("literal out of range for {}", t)); err.note(&format!( "the literal `{}` (decimal `{}`) does not fit into \ the type `{}` and will become `{}{}`", repr_str, val, t, actually, t )); if let Some(sugg_ty) = get_type_suggestion(&cx.typeck_results().node_type(expr.hir_id), val, negative) { if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') { let (sans_suffix, _) = repr_str.split_at(pos); err.span_suggestion( expr.span, &format!("consider using `{}` instead", sugg_ty), format!("{}{}", sans_suffix, sugg_ty), Applicability::MachineApplicable, ); } else { err.help(&format!("consider using `{}` instead", sugg_ty)); } } err.emit(); }); } // This function finds the next fitting type and generates a suggestion string. // It searches for fitting types in the following way (`X < Y`): // - `iX`: if literal fits in `uX` => `uX`, else => `iY` // - `-iX` => `iY` // - `uX` => `uY` // // No suggestion for: `isize`, `usize`. fn get_type_suggestion(t: Ty<'_>, val: u128, negative: bool) -> Option<&'static str> { use rustc_ast::IntTy::*; use rustc_ast::UintTy::*; macro_rules! find_fit { ($ty:expr, $val:expr, $negative:expr, $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => { { let _neg = if negative { 1 } else { 0 }; match $ty { $($type => { $(if !negative && val <= uint_ty_range($utypes).1 { return Some($utypes.name_str()) })* $(if val <= int_ty_range($itypes).1 as u128 + _neg { return Some($itypes.name_str()) })* None },)+ _ => None } } } } match t.kind() { ty::Int(i) => find_fit!(i, val, negative, I8 => [U8] => [I16, I32, I64, I128], I16 => [U16] => [I32, I64, I128], I32 => [U32] => [I64, I128], I64 => [U64] => [I128], I128 => [U128] => []), ty::Uint(u) => find_fit!(u, val, negative, U8 => [U8, U16, U32, U64, U128] => [], U16 => [U16, U32, U64, U128] => [], U32 => [U32, U64, U128] => [], U64 => [U64, U128] => [], U128 => [U128] => []), _ => None, } } fn lint_int_literal<'tcx>( cx: &LateContext<'tcx>, type_limits: &TypeLimits, e: &'tcx hir::Expr<'tcx>, lit: &hir::Lit, t: ast::IntTy, v: u128, ) { let int_type = t.normalize(cx.sess().target.ptr_width); let (min, max) = int_ty_range(int_type); let max = max as u128; let negative = type_limits.negated_expr_id == Some(e.hir_id); // Detect literal value out of range [min, max] inclusive // avoiding use of -min to prevent overflow/panic if (negative && v > max + 1) || (!negative && v > max) { if let Some(repr_str) = get_bin_hex_repr(cx, lit) { report_bin_hex_error(cx, e, attr::IntType::SignedInt(t), repr_str, v, negative); return; } let par_id = cx.tcx.hir().get_parent_node(e.hir_id); if let Node::Expr(par_e) = cx.tcx.hir().get(par_id) { if let hir::ExprKind::Struct(..) = par_e.kind { if is_range_literal(par_e) && lint_overflowing_range_endpoint(cx, lit, v, max, e, par_e, t.name_str()) { // The overflowing literal lint was overridden. return; } } } cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| { lint.build(&format!("literal out of range for `{}`", t.name_str())) .note(&format!( "the literal `{}` does not fit into the type `{}` whose range is `{}..={}`", cx.sess() .source_map() .span_to_snippet(lit.span) .expect("must get snippet from literal"), t.name_str(), min, max, )) .emit(); }); } } fn lint_uint_literal<'tcx>( cx: &LateContext<'tcx>, e: &'tcx hir::Expr<'tcx>, lit: &hir::Lit, t: ast::UintTy, ) { let uint_type = t.normalize(cx.sess().target.ptr_width); let (min, max) = uint_ty_range(uint_type); let lit_val: u128 = match lit.node { // _v is u8, within range by definition ast::LitKind::Byte(_v) => return, ast::LitKind::Int(v, _) => v, _ => bug!(), }; if lit_val < min || lit_val > max { let parent_id = cx.tcx.hir().get_parent_node(e.hir_id); if let Node::Expr(par_e) = cx.tcx.hir().get(parent_id) { match par_e.kind { hir::ExprKind::Cast(..) => { if let ty::Char = cx.typeck_results().expr_ty(par_e).kind() { cx.struct_span_lint(OVERFLOWING_LITERALS, par_e.span, |lint| { lint.build("only `u8` can be cast into `char`") .span_suggestion( par_e.span, &"use a `char` literal instead", format!("'\\u{{{:X}}}'", lit_val), Applicability::MachineApplicable, ) .emit(); }); return; } } hir::ExprKind::Struct(..) if is_range_literal(par_e) => { let t = t.name_str(); if lint_overflowing_range_endpoint(cx, lit, lit_val, max, e, par_e, t) { // The overflowing literal lint was overridden. return; } } _ => {} } } if let Some(repr_str) = get_bin_hex_repr(cx, lit) { report_bin_hex_error(cx, e, attr::IntType::UnsignedInt(t), repr_str, lit_val, false); return; } cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| { lint.build(&format!("literal out of range for `{}`", t.name_str())) .note(&format!( "the literal `{}` does not fit into the type `{}` whose range is `{}..={}`", cx.sess() .source_map() .span_to_snippet(lit.span) .expect("must get snippet from literal"), t.name_str(), min, max, )) .emit() }); } } fn lint_literal<'tcx>( cx: &LateContext<'tcx>, type_limits: &TypeLimits, e: &'tcx hir::Expr<'tcx>, lit: &hir::Lit, ) { match *cx.typeck_results().node_type(e.hir_id).kind() { ty::Int(t) => { match lit.node { ast::LitKind::Int(v, ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed) => { lint_int_literal(cx, type_limits, e, lit, t, v) } _ => bug!(), }; } ty::Uint(t) => lint_uint_literal(cx, e, lit, t), ty::Float(t) => { let is_infinite = match lit.node { ast::LitKind::Float(v, _) => match t { ast::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite), ast::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite), }, _ => bug!(), }; if is_infinite == Ok(true) { cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| { lint.build(&format!("literal out of range for `{}`", t.name_str())) .note(&format!( "the literal `{}` does not fit into the type `{}` and will be converted to `std::{}::INFINITY`", cx.sess() .source_map() .span_to_snippet(lit.span) .expect("must get snippet from literal"), t.name_str(), t.name_str(), )) .emit(); }); } } _ => {} } } impl<'tcx> LateLintPass<'tcx> for TypeLimits { fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx hir::Expr<'tcx>) { match e.kind { hir::ExprKind::Unary(hir::UnOp::UnNeg, ref expr) => { // propagate negation, if the negation itself isn't negated if self.negated_expr_id != Some(e.hir_id) { self.negated_expr_id = Some(expr.hir_id); } } hir::ExprKind::Binary(binop, ref l, ref r) => { if is_comparison(binop) && !check_limits(cx, binop, &l, &r) { cx.struct_span_lint(UNUSED_COMPARISONS, e.span, |lint| { lint.build("comparison is useless due to type limits").emit() }); } } hir::ExprKind::Lit(ref lit) => lint_literal(cx, self, e, lit), _ => {} }; fn is_valid(binop: hir::BinOp, v: T, min: T, max: T) -> bool { match binop.node { hir::BinOpKind::Lt => v > min && v <= max, hir::BinOpKind::Le => v >= min && v < max, hir::BinOpKind::Gt => v >= min && v < max, hir::BinOpKind::Ge => v > min && v <= max, hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max, _ => bug!(), } } fn rev_binop(binop: hir::BinOp) -> hir::BinOp { source_map::respan( binop.span, match binop.node { hir::BinOpKind::Lt => hir::BinOpKind::Gt, hir::BinOpKind::Le => hir::BinOpKind::Ge, hir::BinOpKind::Gt => hir::BinOpKind::Lt, hir::BinOpKind::Ge => hir::BinOpKind::Le, _ => return binop, }, ) } fn check_limits( cx: &LateContext<'_>, binop: hir::BinOp, l: &hir::Expr<'_>, r: &hir::Expr<'_>, ) -> bool { let (lit, expr, swap) = match (&l.kind, &r.kind) { (&hir::ExprKind::Lit(_), _) => (l, r, true), (_, &hir::ExprKind::Lit(_)) => (r, l, false), _ => return true, }; // Normalize the binop so that the literal is always on the RHS in // the comparison let norm_binop = if swap { rev_binop(binop) } else { binop }; match *cx.typeck_results().node_type(expr.hir_id).kind() { ty::Int(int_ty) => { let (min, max) = int_ty_range(int_ty); let lit_val: i128 = match lit.kind { hir::ExprKind::Lit(ref li) => match li.node { ast::LitKind::Int( v, ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed, ) => v as i128, _ => return true, }, _ => bug!(), }; is_valid(norm_binop, lit_val, min, max) } ty::Uint(uint_ty) => { let (min, max): (u128, u128) = uint_ty_range(uint_ty); let lit_val: u128 = match lit.kind { hir::ExprKind::Lit(ref li) => match li.node { ast::LitKind::Int(v, _) => v, _ => return true, }, _ => bug!(), }; is_valid(norm_binop, lit_val, min, max) } _ => true, } } fn is_comparison(binop: hir::BinOp) -> bool { match binop.node { hir::BinOpKind::Eq | hir::BinOpKind::Lt | hir::BinOpKind::Le | hir::BinOpKind::Ne | hir::BinOpKind::Ge | hir::BinOpKind::Gt => true, _ => false, } } } } declare_lint! { /// The `improper_ctypes` lint detects incorrect use of types in foreign /// modules. /// /// ### Example /// /// ```rust /// extern "C" { /// static STATIC: String; /// } /// ``` /// /// {{produces}} /// /// ### Explanation /// /// The compiler has several checks to verify that types used in `extern` /// blocks are safe and follow certain rules to ensure proper /// compatibility with the foreign interfaces. This lint is issued when it /// detects a probable mistake in a definition. The lint usually should /// provide a description of the issue, along with possibly a hint on how /// to resolve it. IMPROPER_CTYPES, Warn, "proper use of libc types in foreign modules" } declare_lint_pass!(ImproperCTypesDeclarations => [IMPROPER_CTYPES]); declare_lint! { /// The `improper_ctypes_definitions` lint detects incorrect use of /// [`extern` function] definitions. /// /// [`extern` function]: https://doc.rust-lang.org/reference/items/functions.html#extern-function-qualifier /// /// ### Example /// /// ```rust /// # #![allow(unused)] /// pub extern "C" fn str_type(p: &str) { } /// ``` /// /// {{produces}} /// /// ### Explanation /// /// There are many parameter and return types that may be specified in an /// `extern` function that are not compatible with the given ABI. This /// lint is an alert that these types should not be used. The lint usually /// should provide a description of the issue, along with possibly a hint /// on how to resolve it. IMPROPER_CTYPES_DEFINITIONS, Warn, "proper use of libc types in foreign item definitions" } declare_lint_pass!(ImproperCTypesDefinitions => [IMPROPER_CTYPES_DEFINITIONS]); #[derive(Clone, Copy)] crate enum CItemKind { Declaration, Definition, } struct ImproperCTypesVisitor<'a, 'tcx> { cx: &'a LateContext<'tcx>, mode: CItemKind, } enum FfiResult<'tcx> { FfiSafe, FfiPhantom(Ty<'tcx>), FfiUnsafe { ty: Ty<'tcx>, reason: String, help: Option }, } crate fn nonnull_optimization_guaranteed<'tcx>(tcx: TyCtxt<'tcx>, def: &ty::AdtDef) -> bool { tcx.get_attrs(def.did) .iter() .any(|a| tcx.sess.check_name(a, sym::rustc_nonnull_optimization_guaranteed)) } /// `repr(transparent)` structs can have a single non-ZST field, this function returns that /// field. pub fn transparent_newtype_field<'a, 'tcx>( tcx: TyCtxt<'tcx>, variant: &'a ty::VariantDef, ) -> Option<&'a ty::FieldDef> { let param_env = tcx.param_env(variant.def_id); for field in &variant.fields { let field_ty = tcx.type_of(field.did); let is_zst = tcx.layout_of(param_env.and(field_ty)).map(|layout| layout.is_zst()).unwrap_or(false); if !is_zst { return Some(field); } } None } /// Is type known to be non-null? crate fn ty_is_known_nonnull<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, mode: CItemKind) -> bool { let tcx = cx.tcx; match ty.kind() { ty::FnPtr(_) => true, ty::Ref(..) => true, ty::Adt(def, _) if def.is_box() && matches!(mode, CItemKind::Definition) => true, ty::Adt(def, substs) if def.repr.transparent() && !def.is_union() => { let marked_non_null = nonnull_optimization_guaranteed(tcx, &def); if marked_non_null { return true; } for variant in &def.variants { if let Some(field) = transparent_newtype_field(cx.tcx, variant) { if ty_is_known_nonnull(cx, field.ty(tcx, substs), mode) { return true; } } } false } _ => false, } } /// Given a non-null scalar (or transparent) type `ty`, return the nullable version of that type. /// If the type passed in was not scalar, returns None. fn get_nullable_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option> { let tcx = cx.tcx; Some(match *ty.kind() { ty::Adt(field_def, field_substs) => { let inner_field_ty = { let first_non_zst_ty = field_def.variants.iter().filter_map(|v| transparent_newtype_field(cx.tcx, v)); debug_assert_eq!( first_non_zst_ty.clone().count(), 1, "Wrong number of fields for transparent type" ); first_non_zst_ty .last() .expect("No non-zst fields in transparent type.") .ty(tcx, field_substs) }; return get_nullable_type(cx, inner_field_ty); } ty::Int(ty) => tcx.mk_mach_int(ty), ty::Uint(ty) => tcx.mk_mach_uint(ty), ty::RawPtr(ty_mut) => tcx.mk_ptr(ty_mut), // As these types are always non-null, the nullable equivalent of // Option of these types are their raw pointer counterparts. ty::Ref(_region, ty, mutbl) => tcx.mk_ptr(ty::TypeAndMut { ty, mutbl }), ty::FnPtr(..) => { // There is no nullable equivalent for Rust's function pointers -- you // must use an Option _> to represent it. ty } // We should only ever reach this case if ty_is_known_nonnull is extended // to other types. ref unhandled => { debug!( "get_nullable_type: Unhandled scalar kind: {:?} while checking {:?}", unhandled, ty ); return None; } }) } /// Check if this enum can be safely exported based on the "nullable pointer optimization". If it /// can, return the type that `ty` can be safely converted to, otherwise return `None`. /// Currently restricted to function pointers, boxes, references, `core::num::NonZero*`, /// `core::ptr::NonNull`, and `#[repr(transparent)]` newtypes. /// FIXME: This duplicates code in codegen. crate fn repr_nullable_ptr<'tcx>( cx: &LateContext<'tcx>, ty: Ty<'tcx>, ckind: CItemKind, ) -> Option> { debug!("is_repr_nullable_ptr(cx, ty = {:?})", ty); if let ty::Adt(ty_def, substs) = ty.kind() { if ty_def.variants.len() != 2 { return None; } let get_variant_fields = |index| &ty_def.variants[VariantIdx::new(index)].fields; let variant_fields = [get_variant_fields(0), get_variant_fields(1)]; let fields = if variant_fields[0].is_empty() { &variant_fields[1] } else if variant_fields[1].is_empty() { &variant_fields[0] } else { return None; }; if fields.len() != 1 { return None; } let field_ty = fields[0].ty(cx.tcx, substs); if !ty_is_known_nonnull(cx, field_ty, ckind) { return None; } // At this point, the field's type is known to be nonnull and the parent enum is Option-like. // If the computed size for the field and the enum are different, the nonnull optimization isn't // being applied (and we've got a problem somewhere). let compute_size_skeleton = |t| SizeSkeleton::compute(t, cx.tcx, cx.param_env).unwrap(); if !compute_size_skeleton(ty).same_size(compute_size_skeleton(field_ty)) { bug!("improper_ctypes: Option nonnull optimization not applied?"); } // Return the nullable type this Option-like enum can be safely represented with. let field_ty_abi = &cx.layout_of(field_ty).unwrap().abi; if let Abi::Scalar(field_ty_scalar) = field_ty_abi { match (field_ty_scalar.valid_range.start(), field_ty_scalar.valid_range.end()) { (0, _) => unreachable!("Non-null optimisation extended to a non-zero value."), (1, _) => { return Some(get_nullable_type(cx, field_ty).unwrap()); } (start, end) => unreachable!("Unhandled start and end range: ({}, {})", start, end), }; } } None } impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> { /// Check if the type is array and emit an unsafe type lint. fn check_for_array_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool { if let ty::Array(..) = ty.kind() { self.emit_ffi_unsafe_type_lint( ty, sp, "passing raw arrays by value is not FFI-safe", Some("consider passing a pointer to the array"), ); true } else { false } } /// Checks if the given field's type is "ffi-safe". fn check_field_type_for_ffi( &self, cache: &mut FxHashSet>, field: &ty::FieldDef, substs: SubstsRef<'tcx>, ) -> FfiResult<'tcx> { let field_ty = field.ty(self.cx.tcx, substs); if field_ty.has_opaque_types() { self.check_type_for_ffi(cache, field_ty) } else { let field_ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, field_ty); self.check_type_for_ffi(cache, field_ty) } } /// Checks if the given `VariantDef`'s field types are "ffi-safe". fn check_variant_for_ffi( &self, cache: &mut FxHashSet>, ty: Ty<'tcx>, def: &ty::AdtDef, variant: &ty::VariantDef, substs: SubstsRef<'tcx>, ) -> FfiResult<'tcx> { use FfiResult::*; if def.repr.transparent() { // Can assume that only one field is not a ZST, so only check // that field's type for FFI-safety. if let Some(field) = transparent_newtype_field(self.cx.tcx, variant) { self.check_field_type_for_ffi(cache, field, substs) } else { bug!("malformed transparent type"); } } else { // We can't completely trust repr(C) markings; make sure the fields are // actually safe. let mut all_phantom = !variant.fields.is_empty(); for field in &variant.fields { match self.check_field_type_for_ffi(cache, &field, substs) { FfiSafe => { all_phantom = false; } FfiPhantom(..) if def.is_enum() => { return FfiUnsafe { ty, reason: "this enum contains a PhantomData field".into(), help: None, }; } FfiPhantom(..) => {} r => return r, } } if all_phantom { FfiPhantom(ty) } else { FfiSafe } } } /// Checks if the given type is "ffi-safe" (has a stable, well-defined /// representation which can be exported to C code). fn check_type_for_ffi(&self, cache: &mut FxHashSet>, ty: Ty<'tcx>) -> FfiResult<'tcx> { use FfiResult::*; let tcx = self.cx.tcx; // Protect against infinite recursion, for example // `struct S(*mut S);`. // FIXME: A recursion limit is necessary as well, for irregular // recursive types. if !cache.insert(ty) { return FfiSafe; } match ty.kind() { ty::Adt(def, _) if def.is_box() && matches!(self.mode, CItemKind::Definition) => { FfiSafe } ty::Adt(def, substs) => { if def.is_phantom_data() { return FfiPhantom(ty); } match def.adt_kind() { AdtKind::Struct | AdtKind::Union => { let kind = if def.is_struct() { "struct" } else { "union" }; if !def.repr.c() && !def.repr.transparent() { return FfiUnsafe { ty, reason: format!("this {} has unspecified layout", kind), help: Some(format!( "consider adding a `#[repr(C)]` or \ `#[repr(transparent)]` attribute to this {}", kind )), }; } let is_non_exhaustive = def.non_enum_variant().is_field_list_non_exhaustive(); if is_non_exhaustive && !def.did.is_local() { return FfiUnsafe { ty, reason: format!("this {} is non-exhaustive", kind), help: None, }; } if def.non_enum_variant().fields.is_empty() { return FfiUnsafe { ty, reason: format!("this {} has no fields", kind), help: Some(format!("consider adding a member to this {}", kind)), }; } self.check_variant_for_ffi(cache, ty, def, def.non_enum_variant(), substs) } AdtKind::Enum => { if def.variants.is_empty() { // Empty enums are okay... although sort of useless. return FfiSafe; } // Check for a repr() attribute to specify the size of the // discriminant. if !def.repr.c() && !def.repr.transparent() && def.repr.int.is_none() { // Special-case types like `Option`. if repr_nullable_ptr(self.cx, ty, self.mode).is_none() { return FfiUnsafe { ty, reason: "enum has no representation hint".into(), help: Some( "consider adding a `#[repr(C)]`, \ `#[repr(transparent)]`, or integer `#[repr(...)]` \ attribute to this enum" .into(), ), }; } } if def.is_variant_list_non_exhaustive() && !def.did.is_local() { return FfiUnsafe { ty, reason: "this enum is non-exhaustive".into(), help: None, }; } // Check the contained variants. for variant in &def.variants { let is_non_exhaustive = variant.is_field_list_non_exhaustive(); if is_non_exhaustive && !variant.def_id.is_local() { return FfiUnsafe { ty, reason: "this enum has non-exhaustive variants".into(), help: None, }; } match self.check_variant_for_ffi(cache, ty, def, variant, substs) { FfiSafe => (), r => return r, } } FfiSafe } } } ty::Char => FfiUnsafe { ty, reason: "the `char` type has no C equivalent".into(), help: Some("consider using `u32` or `libc::wchar_t` instead".into()), }, ty::Int(ast::IntTy::I128) | ty::Uint(ast::UintTy::U128) => FfiUnsafe { ty, reason: "128-bit integers don't currently have a known stable ABI".into(), help: None, }, // Primitive types with a stable representation. ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe, ty::Slice(_) => FfiUnsafe { ty, reason: "slices have no C equivalent".into(), help: Some("consider using a raw pointer instead".into()), }, ty::Dynamic(..) => { FfiUnsafe { ty, reason: "trait objects have no C equivalent".into(), help: None } } ty::Str => FfiUnsafe { ty, reason: "string slices have no C equivalent".into(), help: Some("consider using `*const u8` and a length instead".into()), }, ty::Tuple(..) => FfiUnsafe { ty, reason: "tuples have unspecified layout".into(), help: Some("consider using a struct instead".into()), }, ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _) if { matches!(self.mode, CItemKind::Definition) && ty.is_sized(self.cx.tcx.at(DUMMY_SP), self.cx.param_env) } => { FfiSafe } ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _) => { self.check_type_for_ffi(cache, ty) } ty::Array(inner_ty, _) => self.check_type_for_ffi(cache, inner_ty), ty::FnPtr(sig) => { if self.is_internal_abi(sig.abi()) { return FfiUnsafe { ty, reason: "this function pointer has Rust-specific calling convention".into(), help: Some( "consider using an `extern fn(...) -> ...` \ function pointer instead" .into(), ), }; } let sig = tcx.erase_late_bound_regions(&sig); if !sig.output().is_unit() { let r = self.check_type_for_ffi(cache, sig.output()); match r { FfiSafe => {} _ => { return r; } } } for arg in sig.inputs() { let r = self.check_type_for_ffi(cache, arg); match r { FfiSafe => {} _ => { return r; } } } FfiSafe } ty::Foreign(..) => FfiSafe, // While opaque types are checked for earlier, if a projection in a struct field // normalizes to an opaque type, then it will reach this branch. ty::Opaque(..) => { FfiUnsafe { ty, reason: "opaque types have no C equivalent".into(), help: None } } // `extern "C" fn` functions can have type parameters, which may or may not be FFI-safe, // so they are currently ignored for the purposes of this lint. ty::Param(..) | ty::Projection(..) if matches!(self.mode, CItemKind::Definition) => { FfiSafe } ty::Param(..) | ty::Projection(..) | ty::Infer(..) | ty::Bound(..) | ty::Error(_) | ty::Closure(..) | ty::Generator(..) | ty::GeneratorWitness(..) | ty::Placeholder(..) | ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty), } } fn emit_ffi_unsafe_type_lint( &mut self, ty: Ty<'tcx>, sp: Span, note: &str, help: Option<&str>, ) { let lint = match self.mode { CItemKind::Declaration => IMPROPER_CTYPES, CItemKind::Definition => IMPROPER_CTYPES_DEFINITIONS, }; self.cx.struct_span_lint(lint, sp, |lint| { let item_description = match self.mode { CItemKind::Declaration => "block", CItemKind::Definition => "fn", }; let mut diag = lint.build(&format!( "`extern` {} uses type `{}`, which is not FFI-safe", item_description, ty )); diag.span_label(sp, "not FFI-safe"); if let Some(help) = help { diag.help(help); } diag.note(note); if let ty::Adt(def, _) = ty.kind() { if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did) { diag.span_note(sp, "the type is defined here"); } } diag.emit(); }); } fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool { struct ProhibitOpaqueTypes<'a, 'tcx> { cx: &'a LateContext<'tcx>, ty: Option>, }; impl<'a, 'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'a, 'tcx> { fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool { match ty.kind() { ty::Opaque(..) => { self.ty = Some(ty); true } // Consider opaque types within projections FFI-safe if they do not normalize // to more opaque types. ty::Projection(..) => { let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty); // If `ty` is a opaque type directly then `super_visit_with` won't invoke // this function again. if ty.has_opaque_types() { self.visit_ty(ty) } else { false } } _ => ty.super_visit_with(self), } } } let mut visitor = ProhibitOpaqueTypes { cx: self.cx, ty: None }; ty.visit_with(&mut visitor); if let Some(ty) = visitor.ty { self.emit_ffi_unsafe_type_lint(ty, sp, "opaque types have no C equivalent", None); true } else { false } } fn check_type_for_ffi_and_report_errors( &mut self, sp: Span, ty: Ty<'tcx>, is_static: bool, is_return_type: bool, ) { // We have to check for opaque types before `normalize_erasing_regions`, // which will replace opaque types with their underlying concrete type. if self.check_for_opaque_ty(sp, ty) { // We've already emitted an error due to an opaque type. return; } // it is only OK to use this function because extern fns cannot have // any generic types right now: let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty); // C doesn't really support passing arrays by value - the only way to pass an array by value // is through a struct. So, first test that the top level isn't an array, and then // recursively check the types inside. if !is_static && self.check_for_array_ty(sp, ty) { return; } // Don't report FFI errors for unit return types. This check exists here, and not in // `check_foreign_fn` (where it would make more sense) so that normalization has definitely // happened. if is_return_type && ty.is_unit() { return; } match self.check_type_for_ffi(&mut FxHashSet::default(), ty) { FfiResult::FfiSafe => {} FfiResult::FfiPhantom(ty) => { self.emit_ffi_unsafe_type_lint(ty, sp, "composed only of `PhantomData`", None); } // If `ty` is a `repr(transparent)` newtype, and the non-zero-sized type is a generic // argument, which after substitution, is `()`, then this branch can be hit. FfiResult::FfiUnsafe { ty, .. } if is_return_type && ty.is_unit() => {} FfiResult::FfiUnsafe { ty, reason, help } => { self.emit_ffi_unsafe_type_lint(ty, sp, &reason, help.as_deref()); } } } fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl<'_>) { let def_id = self.cx.tcx.hir().local_def_id(id); let sig = self.cx.tcx.fn_sig(def_id); let sig = self.cx.tcx.erase_late_bound_regions(&sig); for (input_ty, input_hir) in sig.inputs().iter().zip(decl.inputs) { self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty, false, false); } if let hir::FnRetTy::Return(ref ret_hir) = decl.output { let ret_ty = sig.output(); self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty, false, true); } } fn check_foreign_static(&mut self, id: hir::HirId, span: Span) { let def_id = self.cx.tcx.hir().local_def_id(id); let ty = self.cx.tcx.type_of(def_id); self.check_type_for_ffi_and_report_errors(span, ty, true, false); } fn is_internal_abi(&self, abi: SpecAbi) -> bool { if let SpecAbi::Rust | SpecAbi::RustCall | SpecAbi::RustIntrinsic | SpecAbi::PlatformIntrinsic = abi { true } else { false } } } impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDeclarations { fn check_foreign_item(&mut self, cx: &LateContext<'_>, it: &hir::ForeignItem<'_>) { let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Declaration }; let abi = cx.tcx.hir().get_foreign_abi(it.hir_id); if !vis.is_internal_abi(abi) { match it.kind { hir::ForeignItemKind::Fn(ref decl, _, _) => { vis.check_foreign_fn(it.hir_id, decl); } hir::ForeignItemKind::Static(ref ty, _) => { vis.check_foreign_static(it.hir_id, ty.span); } hir::ForeignItemKind::Type => (), } } } } impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDefinitions { fn check_fn( &mut self, cx: &LateContext<'tcx>, kind: hir::intravisit::FnKind<'tcx>, decl: &'tcx hir::FnDecl<'_>, _: &'tcx hir::Body<'_>, _: Span, hir_id: hir::HirId, ) { use hir::intravisit::FnKind; let abi = match kind { FnKind::ItemFn(_, _, header, ..) => header.abi, FnKind::Method(_, sig, ..) => sig.header.abi, _ => return, }; let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Definition }; if !vis.is_internal_abi(abi) { vis.check_foreign_fn(hir_id, decl); } } } declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]); impl<'tcx> LateLintPass<'tcx> for VariantSizeDifferences { fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) { if let hir::ItemKind::Enum(ref enum_definition, _) = it.kind { let item_def_id = cx.tcx.hir().local_def_id(it.hir_id); let t = cx.tcx.type_of(item_def_id); let ty = cx.tcx.erase_regions(&t); let layout = match cx.layout_of(ty) { Ok(layout) => layout, Err( ty::layout::LayoutError::Unknown(_) | ty::layout::LayoutError::SizeOverflow(_), ) => return, }; let (variants, tag) = match layout.variants { Variants::Multiple { tag_encoding: TagEncoding::Direct, ref tag, ref variants, .. } => (variants, tag), _ => return, }; let tag_size = tag.value.size(&cx.tcx).bytes(); debug!( "enum `{}` is {} bytes large with layout:\n{:#?}", t, layout.size.bytes(), layout ); let (largest, slargest, largest_index) = enum_definition .variants .iter() .zip(variants) .map(|(variant, variant_layout)| { // Subtract the size of the enum tag. let bytes = variant_layout.size.bytes().saturating_sub(tag_size); debug!("- variant `{}` is {} bytes large", variant.ident, bytes); bytes }) .enumerate() .fold((0, 0, 0), |(l, s, li), (idx, size)| { if size > l { (size, l, idx) } else if size > s { (l, size, li) } else { (l, s, li) } }); // We only warn if the largest variant is at least thrice as large as // the second-largest. if largest > slargest * 3 && slargest > 0 { cx.struct_span_lint( VARIANT_SIZE_DIFFERENCES, enum_definition.variants[largest_index].span, |lint| { lint.build(&format!( "enum variant is more than three times \ larger ({} bytes) than the next largest", largest )) .emit() }, ); } } } }