1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_data_structures::stack::ensure_sufficient_stack;
use rustc_hir as hir;
use rustc_hir::def::DefKind;
use rustc_middle::query::Providers;
use rustc_middle::ty::layout::LayoutError;
use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
use rustc_span::{sym, Span, Symbol};
use rustc_target::abi::FIRST_VARIANT;
use crate::lints::{BuiltinClashingExtern, BuiltinClashingExternSub};
use crate::{types, LintVec};
pub(crate) fn provide(providers: &mut Providers) {
*providers = Providers { clashing_extern_declarations, ..*providers };
}
pub(crate) fn get_lints() -> LintVec {
vec![CLASHING_EXTERN_DECLARATIONS]
}
fn clashing_extern_declarations(tcx: TyCtxt<'_>, (): ()) {
let mut lint = ClashingExternDeclarations::new();
for id in tcx.hir_crate_items(()).foreign_items() {
lint.check_foreign_item(tcx, id);
}
}
declare_lint! {
/// The `clashing_extern_declarations` lint detects when an `extern fn`
/// has been declared with the same name but different types.
///
/// ### Example
///
/// ```rust
/// mod m {
/// extern "C" {
/// fn foo();
/// }
/// }
///
/// extern "C" {
/// fn foo(_: u32);
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Because two symbols of the same name cannot be resolved to two
/// different functions at link time, and one function cannot possibly
/// have two types, a clashing extern declaration is almost certainly a
/// mistake. Check to make sure that the `extern` definitions are correct
/// and equivalent, and possibly consider unifying them in one location.
///
/// This lint does not run between crates because a project may have
/// dependencies which both rely on the same extern function, but declare
/// it in a different (but valid) way. For example, they may both declare
/// an opaque type for one or more of the arguments (which would end up
/// distinct types), or use types that are valid conversions in the
/// language the `extern fn` is defined in. In these cases, the compiler
/// can't say that the clashing declaration is incorrect.
pub CLASHING_EXTERN_DECLARATIONS,
Warn,
"detects when an extern fn has been declared with the same name but different types"
}
struct ClashingExternDeclarations {
/// Map of function symbol name to the first-seen hir id for that symbol name.. If seen_decls
/// contains an entry for key K, it means a symbol with name K has been seen by this lint and
/// the symbol should be reported as a clashing declaration.
// FIXME: Technically, we could just store a &'tcx str here without issue; however, the
// `impl_lint_pass` macro doesn't currently support lints parametric over a lifetime.
seen_decls: FxHashMap<Symbol, hir::OwnerId>,
}
/// Differentiate between whether the name for an extern decl came from the link_name attribute or
/// just from declaration itself. This is important because we don't want to report clashes on
/// symbol name if they don't actually clash because one or the other links against a symbol with a
/// different name.
enum SymbolName {
/// The name of the symbol + the span of the annotation which introduced the link name.
Link(Symbol, Span),
/// No link name, so just the name of the symbol.
Normal(Symbol),
}
impl SymbolName {
fn get_name(&self) -> Symbol {
match self {
SymbolName::Link(s, _) | SymbolName::Normal(s) => *s,
}
}
}
impl ClashingExternDeclarations {
pub(crate) fn new() -> Self {
ClashingExternDeclarations { seen_decls: FxHashMap::default() }
}
/// Insert a new foreign item into the seen set. If a symbol with the same name already exists
/// for the item, return its HirId without updating the set.
fn insert(&mut self, tcx: TyCtxt<'_>, fi: hir::ForeignItemId) -> Option<hir::OwnerId> {
let did = fi.owner_id.to_def_id();
let instance = Instance::new(did, ty::List::identity_for_item(tcx, did));
let name = Symbol::intern(tcx.symbol_name(instance).name);
if let Some(&existing_id) = self.seen_decls.get(&name) {
// Avoid updating the map with the new entry when we do find a collision. We want to
// make sure we're always pointing to the first definition as the previous declaration.
// This lets us avoid emitting "knock-on" diagnostics.
Some(existing_id)
} else {
self.seen_decls.insert(name, fi.owner_id)
}
}
#[instrument(level = "trace", skip(self, tcx))]
fn check_foreign_item<'tcx>(&mut self, tcx: TyCtxt<'tcx>, this_fi: hir::ForeignItemId) {
let DefKind::Fn = tcx.def_kind(this_fi.owner_id) else { return };
let Some(existing_did) = self.insert(tcx, this_fi) else { return };
let existing_decl_ty = tcx.type_of(existing_did).skip_binder();
let this_decl_ty = tcx.type_of(this_fi.owner_id).instantiate_identity();
debug!(
"ClashingExternDeclarations: Comparing existing {:?}: {:?} to this {:?}: {:?}",
existing_did, existing_decl_ty, this_fi.owner_id, this_decl_ty
);
// Check that the declarations match.
if !structurally_same_type(
tcx,
tcx.param_env(this_fi.owner_id),
existing_decl_ty,
this_decl_ty,
types::CItemKind::Declaration,
) {
let orig = name_of_extern_decl(tcx, existing_did);
// Finally, emit the diagnostic.
let this = tcx.item_name(this_fi.owner_id.to_def_id());
let orig = orig.get_name();
let previous_decl_label = get_relevant_span(tcx, existing_did);
let mismatch_label = get_relevant_span(tcx, this_fi.owner_id);
let sub =
BuiltinClashingExternSub { tcx, expected: existing_decl_ty, found: this_decl_ty };
let decorator = if orig == this {
BuiltinClashingExtern::SameName {
this,
orig,
previous_decl_label,
mismatch_label,
sub,
}
} else {
BuiltinClashingExtern::DiffName {
this,
orig,
previous_decl_label,
mismatch_label,
sub,
}
};
tcx.emit_spanned_lint(
CLASHING_EXTERN_DECLARATIONS,
this_fi.hir_id(),
mismatch_label,
decorator,
);
}
}
}
/// Get the name of the symbol that's linked against for a given extern declaration. That is,
/// the name specified in a #[link_name = ...] attribute if one was specified, else, just the
/// symbol's name.
fn name_of_extern_decl(tcx: TyCtxt<'_>, fi: hir::OwnerId) -> SymbolName {
if let Some((overridden_link_name, overridden_link_name_span)) =
tcx.codegen_fn_attrs(fi).link_name.map(|overridden_link_name| {
// FIXME: Instead of searching through the attributes again to get span
// information, we could have codegen_fn_attrs also give span information back for
// where the attribute was defined. However, until this is found to be a
// bottleneck, this does just fine.
(overridden_link_name, tcx.get_attr(fi, sym::link_name).unwrap().span)
})
{
SymbolName::Link(overridden_link_name, overridden_link_name_span)
} else {
SymbolName::Normal(tcx.item_name(fi.to_def_id()))
}
}
/// We want to ensure that we use spans for both decls that include where the
/// name was defined, whether that was from the link_name attribute or not.
fn get_relevant_span(tcx: TyCtxt<'_>, fi: hir::OwnerId) -> Span {
match name_of_extern_decl(tcx, fi) {
SymbolName::Normal(_) => tcx.def_span(fi),
SymbolName::Link(_, annot_span) => annot_span,
}
}
/// 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>(
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
a: Ty<'tcx>,
b: Ty<'tcx>,
ckind: types::CItemKind,
) -> bool {
let mut seen_types = FxHashSet::default();
structurally_same_type_impl(&mut seen_types, tcx, param_env, a, b, ckind)
}
fn structurally_same_type_impl<'tcx>(
seen_types: &mut FxHashSet<(Ty<'tcx>, Ty<'tcx>)>,
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
a: Ty<'tcx>,
b: Ty<'tcx>,
ckind: types::CItemKind,
) -> bool {
debug!("structurally_same_type_impl(tcx, a = {:?}, b = {:?})", a, b);
// Given a transparent newtype, reach through and grab the inner
// type unless the newtype makes the type non-null.
let non_transparent_ty = |mut ty: Ty<'tcx>| -> Ty<'tcx> {
loop {
if let ty::Adt(def, args) = *ty.kind() {
let is_transparent = def.repr().transparent();
let is_non_null = types::nonnull_optimization_guaranteed(tcx, def);
debug!(
"non_transparent_ty({:?}) -- type is transparent? {}, type is non-null? {}",
ty, is_transparent, is_non_null
);
if is_transparent && !is_non_null {
debug_assert_eq!(def.variants().len(), 1);
let v = &def.variant(FIRST_VARIANT);
// continue with `ty`'s non-ZST field,
// otherwise `ty` is a ZST and we can return
if let Some(field) = types::transparent_newtype_field(tcx, v) {
ty = field.ty(tcx, args);
continue;
}
}
}
debug!("non_transparent_ty -> {:?}", ty);
return ty;
}
};
let a = non_transparent_ty(a);
let b = non_transparent_ty(b);
if !seen_types.insert((a, b)) {
// We've encountered a cycle. There's no point going any further -- the types are
// structurally the same.
true
} else if a == b {
// All nominally-same types are structurally same, too.
true
} else {
// Do a full, depth-first comparison between the two.
use rustc_type_ir::sty::TyKind::*;
let a_kind = a.kind();
let b_kind = b.kind();
let compare_layouts = |a, b| -> Result<bool, &'tcx LayoutError<'tcx>> {
debug!("compare_layouts({:?}, {:?})", a, b);
let a_layout = &tcx.layout_of(param_env.and(a))?.layout.abi();
let b_layout = &tcx.layout_of(param_env.and(b))?.layout.abi();
debug!(
"comparing layouts: {:?} == {:?} = {}",
a_layout,
b_layout,
a_layout == b_layout
);
Ok(a_layout == b_layout)
};
#[allow(rustc::usage_of_ty_tykind)]
let is_primitive_or_pointer =
|kind: &ty::TyKind<'_>| kind.is_primitive() || matches!(kind, RawPtr(..) | Ref(..));
ensure_sufficient_stack(|| {
match (a_kind, b_kind) {
(Adt(a_def, _), Adt(b_def, _)) => {
// We can immediately rule out these types as structurally same if
// their layouts differ.
match compare_layouts(a, b) {
Ok(false) => return false,
_ => (), // otherwise, continue onto the full, fields comparison
}
// 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());
// Perform a structural comparison for each field.
a_fields.eq_by(
b_fields,
|&ty::FieldDef { did: a_did, .. }, &ty::FieldDef { did: b_did, .. }| {
structurally_same_type_impl(
seen_types,
tcx,
param_env,
tcx.type_of(a_did).instantiate_identity(),
tcx.type_of(b_did).instantiate_identity(),
ckind,
)
},
)
}
(Array(a_ty, a_const), Array(b_ty, b_const)) => {
// For arrays, we also check the constness of the type.
a_const.kind() == b_const.kind()
&& structurally_same_type_impl(
seen_types, tcx, param_env, *a_ty, *b_ty, ckind,
)
}
(Slice(a_ty), Slice(b_ty)) => {
structurally_same_type_impl(seen_types, tcx, param_env, *a_ty, *b_ty, ckind)
}
(RawPtr(a_tymut), RawPtr(b_tymut)) => {
a_tymut.mutbl == b_tymut.mutbl
&& structurally_same_type_impl(
seen_types, tcx, param_env, 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
&& structurally_same_type_impl(
seen_types, tcx, param_env, *a_ty, *b_ty, ckind,
)
}
(FnDef(..), FnDef(..)) => {
let a_poly_sig = a.fn_sig(tcx);
let b_poly_sig = b.fn_sig(tcx);
// We don't compare regions, but leaving bound regions around ICEs, so
// we erase them.
let a_sig = tcx.erase_late_bound_regions(a_poly_sig);
let b_sig = tcx.erase_late_bound_regions(b_poly_sig);
(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| {
structurally_same_type_impl(seen_types, tcx, param_env, *a, *b, ckind)
})
&& structurally_same_type_impl(
seen_types,
tcx,
param_env,
a_sig.output(),
b_sig.output(),
ckind,
)
}
(Tuple(a_args), Tuple(b_args)) => {
a_args.iter().eq_by(b_args.iter(), |a_ty, b_ty| {
structurally_same_type_impl(seen_types, tcx, param_env, a_ty, b_ty, ckind)
})
}
// For these, it's not quite as easy to define structural-sameness quite so easily.
// For the purposes of this lint, take the conservative approach and mark them as
// not structurally same.
(Dynamic(..), Dynamic(..))
| (Error(..), Error(..))
| (Closure(..), Closure(..))
| (Generator(..), Generator(..))
| (GeneratorWitness(..), GeneratorWitness(..))
| (Alias(ty::Projection, ..), Alias(ty::Projection, ..))
| (Alias(ty::Inherent, ..), Alias(ty::Inherent, ..))
| (Alias(ty::Opaque, ..), Alias(ty::Opaque, ..)) => false,
// These definitely should have been caught above.
(Bool, Bool) | (Char, Char) | (Never, Never) | (Str, Str) => unreachable!(),
// An Adt and a primitive or pointer type. This can be FFI-safe if non-null
// enum layout optimisation is being applied.
(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) = types::repr_nullable_ptr(tcx, param_env, adt, ckind) {
ty == primitive
} else {
compare_layouts(a, b).unwrap_or(false)
}
}
// 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).unwrap_or(false),
}
})
}
}