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Auto merge of #73990 - jumbatm:clashing-extern-decl, r=nagisa
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Fix incorrect clashing_extern_declarations warnings.

Fixes #73735, fixes #73872.

Fix clashing_extern_declarations warning for `#[repr(transparent)]` structs and safely-FFI-convertible enums, and not warning for clashes of struct members of different types, but the same size.

r? @nagisa
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@bors
bors committed Jul 30, 2020
2 parents 2186722 + 0bd292d commit 6b09c37
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Showing 6 changed files with 456 additions and 161 deletions.
103 changes: 82 additions & 21 deletions src/librustc_lint/builtin.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -20,7 +20,9 @@
//! If you define a new `LateLintPass`, you will also need to add it to the
//! `late_lint_methods!` invocation in `lib.rs`.
use crate::{EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext};
use crate::{
types::CItemKind, EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext,
};
use rustc_ast::ast::{self, Expr};
use rustc_ast::attr::{self, HasAttrs};
use rustc_ast::tokenstream::{TokenStream, TokenTree};
Expand All @@ -36,14 +38,14 @@ use rustc_hir::def_id::DefId;
use rustc_hir::{ForeignItemKind, GenericParamKind, PatKind};
use rustc_hir::{HirId, HirIdSet, Node};
use rustc_middle::lint::LintDiagnosticBuilder;
use rustc_middle::ty::subst::GenericArgKind;
use rustc_middle::ty::subst::{GenericArgKind, Subst};
use rustc_middle::ty::{self, Ty, TyCtxt};
use rustc_session::lint::FutureIncompatibleInfo;
use rustc_span::edition::Edition;
use rustc_span::source_map::Spanned;
use rustc_span::symbol::{kw, sym, Ident, Symbol};
use rustc_span::{BytePos, Span};
use rustc_target::abi::VariantIdx;
use rustc_target::abi::{LayoutOf, VariantIdx};
use rustc_trait_selection::traits::misc::can_type_implement_copy;

use crate::nonstandard_style::{method_context, MethodLateContext};
Expand Down Expand Up @@ -2144,7 +2146,13 @@ impl ClashingExternDeclarations {
/// Checks whether two types are structurally the same enough that the declarations shouldn't
/// clash. We need this so we don't emit a lint when two modules both declare an extern struct,
/// with the same members (as the declarations shouldn't clash).
fn structurally_same_type<'tcx>(cx: &LateContext<'tcx>, a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
fn structurally_same_type<'tcx>(
cx: &LateContext<'tcx>,
a: Ty<'tcx>,
b: Ty<'tcx>,
ckind: CItemKind,
) -> bool {
debug!("structurally_same_type(cx, a = {:?}, b = {:?})", a, b);
let tcx = cx.tcx;
if a == b || rustc_middle::ty::TyS::same_type(a, b) {
// All nominally-same types are structurally same, too.
Expand All @@ -2155,47 +2163,77 @@ impl ClashingExternDeclarations {
let a_kind = &a.kind;
let b_kind = &b.kind;

let compare_layouts = |a, b| -> bool {
let a_layout = &cx.layout_of(a).unwrap().layout.abi;
let b_layout = &cx.layout_of(b).unwrap().layout.abi;
debug!("{:?} == {:?} = {}", a_layout, b_layout, a_layout == b_layout);
a_layout == b_layout
};

#[allow(rustc::usage_of_ty_tykind)]
let is_primitive_or_pointer =
|kind: &ty::TyKind<'_>| kind.is_primitive() || matches!(kind, RawPtr(..));

match (a_kind, b_kind) {
(Adt(..), Adt(..)) => {
// Adts are pretty straightforward: just compare the layouts.
use rustc_target::abi::LayoutOf;
let a_layout = cx.layout_of(a).unwrap().layout;
let b_layout = cx.layout_of(b).unwrap().layout;
a_layout == b_layout
(Adt(_, a_substs), Adt(_, b_substs)) => {
let a = a.subst(cx.tcx, a_substs);
let b = b.subst(cx.tcx, b_substs);
debug!("Comparing {:?} and {:?}", a, b);

if let (Adt(a_def, ..), Adt(b_def, ..)) = (&a.kind, &b.kind) {
// Grab a flattened representation of all fields.
let a_fields = a_def.variants.iter().flat_map(|v| v.fields.iter());
let b_fields = b_def.variants.iter().flat_map(|v| v.fields.iter());
compare_layouts(a, b)
&& a_fields.eq_by(
b_fields,
|&ty::FieldDef { did: a_did, .. },
&ty::FieldDef { did: b_did, .. }| {
Self::structurally_same_type(
cx,
tcx.type_of(a_did),
tcx.type_of(b_did),
ckind,
)
},
)
} else {
unreachable!()
}
}
(Array(a_ty, a_const), Array(b_ty, b_const)) => {
// For arrays, we also check the constness of the type.
a_const.val == b_const.val
&& Self::structurally_same_type(cx, a_const.ty, b_const.ty)
&& Self::structurally_same_type(cx, a_ty, b_ty)
&& Self::structurally_same_type(cx, a_const.ty, b_const.ty, ckind)
&& Self::structurally_same_type(cx, a_ty, b_ty, ckind)
}
(Slice(a_ty), Slice(b_ty)) => Self::structurally_same_type(cx, a_ty, b_ty),
(Slice(a_ty), Slice(b_ty)) => Self::structurally_same_type(cx, a_ty, b_ty, ckind),
(RawPtr(a_tymut), RawPtr(b_tymut)) => {
a_tymut.mutbl == a_tymut.mutbl
&& Self::structurally_same_type(cx, &a_tymut.ty, &b_tymut.ty)
&& Self::structurally_same_type(cx, &a_tymut.ty, &b_tymut.ty, ckind)
}
(Ref(_a_region, a_ty, a_mut), Ref(_b_region, b_ty, b_mut)) => {
// For structural sameness, we don't need the region to be same.
a_mut == b_mut && Self::structurally_same_type(cx, a_ty, b_ty)
a_mut == b_mut && Self::structurally_same_type(cx, a_ty, b_ty, ckind)
}
(FnDef(..), FnDef(..)) => {
// As we don't compare regions, skip_binder is fine.
let a_poly_sig = a.fn_sig(tcx);
let b_poly_sig = b.fn_sig(tcx);

// As we don't compare regions, skip_binder is fine.
let a_sig = a_poly_sig.skip_binder();
let b_sig = b_poly_sig.skip_binder();

(a_sig.abi, a_sig.unsafety, a_sig.c_variadic)
== (b_sig.abi, b_sig.unsafety, b_sig.c_variadic)
&& a_sig.inputs().iter().eq_by(b_sig.inputs().iter(), |a, b| {
Self::structurally_same_type(cx, a, b)
Self::structurally_same_type(cx, a, b, ckind)
})
&& Self::structurally_same_type(cx, a_sig.output(), b_sig.output())
&& Self::structurally_same_type(cx, a_sig.output(), b_sig.output(), ckind)
}
(Tuple(a_substs), Tuple(b_substs)) => {
a_substs.types().eq_by(b_substs.types(), |a_ty, b_ty| {
Self::structurally_same_type(cx, a_ty, b_ty)
Self::structurally_same_type(cx, a_ty, b_ty, ckind)
})
}
// For these, it's not quite as easy to define structural-sameness quite so easily.
Expand All @@ -2208,9 +2246,27 @@ impl ClashingExternDeclarations {
| (GeneratorWitness(..), GeneratorWitness(..))
| (Projection(..), Projection(..))
| (Opaque(..), Opaque(..)) => false,

// These definitely should have been caught above.
(Bool, Bool) | (Char, Char) | (Never, Never) | (Str, Str) => unreachable!(),
_ => false,

// An Adt and a primitive type. This can be FFI-safe is the ADT is an enum with a
// non-null field.
(Adt(..), other_kind) | (other_kind, Adt(..))
if is_primitive_or_pointer(other_kind) =>
{
let (primitive, adt) =
if is_primitive_or_pointer(&a.kind) { (a, b) } else { (b, a) };
if let Some(ty) = crate::types::repr_nullable_ptr(cx, adt, ckind) {
ty == primitive
} else {
compare_layouts(a, b)
}
}
// Otherwise, just compare the layouts. This may fail to lint for some
// incompatible types, but at the very least, will stop reads into
// uninitialised memory.
_ => compare_layouts(a, b),
}
}
}
Expand All @@ -2231,7 +2287,12 @@ impl<'tcx> LateLintPass<'tcx> for ClashingExternDeclarations {
existing_hid, existing_decl_ty, this_fi.hir_id, this_decl_ty
);
// Check that the declarations match.
if !Self::structurally_same_type(cx, existing_decl_ty, this_decl_ty) {
if !Self::structurally_same_type(
cx,
existing_decl_ty,
this_decl_ty,
CItemKind::Declaration,
) {
let orig_fi = tcx.hir().expect_foreign_item(existing_hid);
let orig = Self::name_of_extern_decl(tcx, orig_fi);

Expand Down
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