5 Within the check phase of type check, we check each item one at a time
6 (bodies of function expressions are checked as part of the containing
7 function). Inference is used to supply types wherever they are unknown.
9 By far the most complex case is checking the body of a function. This
10 can be broken down into several distinct phases:
12 - gather: creates type variables to represent the type of each local
13 variable and pattern binding.
15 - main: the main pass does the lion's share of the work: it
16 determines the types of all expressions, resolves
17 methods, checks for most invalid conditions, and so forth. In
18 some cases, where a type is unknown, it may create a type or region
19 variable and use that as the type of an expression.
21 In the process of checking, various constraints will be placed on
22 these type variables through the subtyping relationships requested
23 through the `demand` module. The `infer` module is in charge
24 of resolving those constraints.
26 - regionck: after main is complete, the regionck pass goes over all
27 types looking for regions and making sure that they did not escape
28 into places where they are not in scope. This may also influence the
29 final assignments of the various region variables if there is some
32 - writeback: writes the final types within a function body, replacing
33 type variables with their final inferred types. These final types
34 are written into the `tcx.node_types` table, which should *never* contain
35 any reference to a type variable.
39 While type checking a function, the intermediate types for the
40 expressions, blocks, and so forth contained within the function are
41 stored in `fcx.node_types` and `fcx.node_substs`. These types
42 may contain unresolved type variables. After type checking is
43 complete, the functions in the writeback module are used to take the
44 types from this table, resolve them, and then write them into their
45 permanent home in the type context `tcx`.
47 This means that during inferencing you should use `fcx.write_ty()`
48 and `fcx.expr_ty()` / `fcx.node_ty()` to write/obtain the types of
49 nodes within the function.
51 The types of top-level items, which never contain unbound type
52 variables, are stored directly into the `tcx` typeck_results.
54 N.B., a type variable is not the same thing as a type parameter. A
55 type variable is an instance of a type parameter. That is,
56 given a generic function `fn foo<T>(t: T)`, while checking the
57 function `foo`, the type `ty_param(0)` refers to the type `T`, which
58 is treated in abstract. However, when `foo()` is called, `T` will be
59 substituted for a fresh type variable `N`. This variable will
60 eventually be resolved to some concrete type (which might itself be
66 mod compare_impl_item
;
73 pub use check
::check_abi
;
75 use check
::check_mod_item_types
;
76 use rustc_data_structures
::fx
::{FxHashMap, FxHashSet}
;
77 use rustc_errors
::{pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder}
;
78 use rustc_hir
::def_id
::{DefId, LocalDefId}
;
79 use rustc_hir
::intravisit
::Visitor
;
80 use rustc_index
::bit_set
::BitSet
;
81 use rustc_middle
::ty
::query
::Providers
;
82 use rustc_middle
::ty
::{self, Ty, TyCtxt}
;
83 use rustc_middle
::ty
::{InternalSubsts, SubstsRef}
;
84 use rustc_session
::parse
::feature_err
;
85 use rustc_span
::source_map
::DUMMY_SP
;
86 use rustc_span
::symbol
::{kw, Ident}
;
87 use rustc_span
::{self, BytePos, Span, Symbol}
;
88 use rustc_target
::abi
::VariantIdx
;
89 use rustc_target
::spec
::abi
::Abi
;
90 use rustc_trait_selection
::traits
::error_reporting
::suggestions
::ReturnsVisitor
;
91 use std
::num
::NonZeroU32
;
93 use crate::require_c_abi_if_c_variadic
;
94 use crate::util
::common
::indenter
;
96 use self::compare_impl_item
::collect_return_position_impl_trait_in_trait_tys
;
97 use self::region
::region_scope_tree
;
99 pub fn provide(providers
: &mut Providers
) {
100 wfcheck
::provide(providers
);
101 *providers
= Providers
{
103 check_mod_item_types
,
105 collect_return_position_impl_trait_in_trait_tys
,
106 compare_impl_const
: compare_impl_item
::compare_impl_const_raw
,
107 check_generator_obligations
: check
::check_generator_obligations
,
112 fn adt_destructor(tcx
: TyCtxt
<'_
>, def_id
: DefId
) -> Option
<ty
::Destructor
> {
113 tcx
.calculate_dtor(def_id
, dropck
::check_drop_impl
)
116 /// Given a `DefId` for an opaque type in return position, find its parent item's return
118 fn get_owner_return_paths(
121 ) -> Option
<(LocalDefId
, ReturnsVisitor
<'_
>)> {
122 let hir_id
= tcx
.hir().local_def_id_to_hir_id(def_id
);
123 let parent_id
= tcx
.hir().get_parent_item(hir_id
).def_id
;
124 tcx
.hir().find_by_def_id(parent_id
).and_then(|node
| node
.body_id()).map(|body_id
| {
125 let body
= tcx
.hir().body(body_id
);
126 let mut visitor
= ReturnsVisitor
::default();
127 visitor
.visit_body(body
);
132 /// Forbid defining intrinsics in Rust code,
133 /// as they must always be defined by the compiler.
134 // FIXME: Move this to a more appropriate place.
135 pub fn fn_maybe_err(tcx
: TyCtxt
<'_
>, sp
: Span
, abi
: Abi
) {
136 if let Abi
::RustIntrinsic
| Abi
::PlatformIntrinsic
= abi
{
137 tcx
.sess
.span_err(sp
, "intrinsic must be in `extern \"rust-intrinsic\" { ... }` block");
141 fn maybe_check_static_with_link_section(tcx
: TyCtxt
<'_
>, id
: LocalDefId
) {
142 // Only restricted on wasm target for now
143 if !tcx
.sess
.target
.is_like_wasm
{
147 // If `#[link_section]` is missing, then nothing to verify
148 let attrs
= tcx
.codegen_fn_attrs(id
);
149 if attrs
.link_section
.is_none() {
153 // For the wasm32 target statics with `#[link_section]` are placed into custom
154 // sections of the final output file, but this isn't link custom sections of
155 // other executable formats. Namely we can only embed a list of bytes,
156 // nothing with provenance (pointers to anything else). If any provenance
157 // show up, reject it here.
158 // `#[link_section]` may contain arbitrary, or even undefined bytes, but it is
159 // the consumer's responsibility to ensure all bytes that have been read
160 // have defined values.
161 if let Ok(alloc
) = tcx
.eval_static_initializer(id
.to_def_id())
162 && alloc
.inner().provenance().ptrs().len() != 0
164 let msg
= "statics with a custom `#[link_section]` must be a \
165 simple list of bytes on the wasm target with no \
166 extra levels of indirection such as references";
167 tcx
.sess
.span_err(tcx
.def_span(id
), msg
);
171 fn report_forbidden_specialization(tcx
: TyCtxt
<'_
>, impl_item
: DefId
, parent_impl
: DefId
) {
172 let span
= tcx
.def_span(impl_item
);
173 let ident
= tcx
.item_name(impl_item
);
174 let mut err
= struct_span_err
!(
178 "`{}` specializes an item from a parent `impl`, but that item is not marked `default`",
181 err
.span_label(span
, format
!("cannot specialize default item `{}`", ident
));
183 match tcx
.span_of_impl(parent_impl
) {
185 err
.span_label(span
, "parent `impl` is here");
187 "to specialize, `{}` in the parent `impl` must be marked `default`",
192 err
.note(&format
!("parent implementation is in crate `{cname}`"));
199 fn missing_items_err(
202 missing_items
: &[ty
::AssocItem
],
203 full_impl_span
: Span
,
205 let missing_items_msg
= missing_items
207 .map(|trait_item
| trait_item
.name
.to_string())
211 let mut err
= struct_span_err
!(
215 "not all trait items implemented, missing: `{missing_items_msg}`",
217 err
.span_label(impl_span
, format
!("missing `{missing_items_msg}` in implementation"));
219 // `Span` before impl block closing brace.
220 let hi
= full_impl_span
.hi() - BytePos(1);
221 // Point at the place right before the closing brace of the relevant `impl` to suggest
222 // adding the associated item at the end of its body.
223 let sugg_sp
= full_impl_span
.with_lo(hi
).with_hi(hi
);
224 // Obtain the level of indentation ending in `sugg_sp`.
226 tcx
.sess
.source_map().indentation_before(sugg_sp
).unwrap_or_else(|| String
::new());
228 for &trait_item
in missing_items
{
229 let snippet
= suggestion_signature(trait_item
, tcx
);
230 let code
= format
!("{}{}\n{}", padding
, snippet
, padding
);
231 let msg
= format
!("implement the missing item: `{snippet}`");
232 let appl
= Applicability
::HasPlaceholders
;
233 if let Some(span
) = tcx
.hir().span_if_local(trait_item
.def_id
) {
234 err
.span_label(span
, format
!("`{}` from trait", trait_item
.name
));
235 err
.tool_only_span_suggestion(sugg_sp
, &msg
, code
, appl
);
237 err
.span_suggestion_hidden(sugg_sp
, &msg
, code
, appl
);
243 fn missing_items_must_implement_one_of_err(
246 missing_items
: &[Ident
],
247 annotation_span
: Option
<Span
>,
249 let missing_items_msg
=
250 missing_items
.iter().map(Ident
::to_string
).collect
::<Vec
<_
>>().join("`, `");
252 let mut err
= struct_span_err
!(
256 "not all trait items implemented, missing one of: `{missing_items_msg}`",
258 err
.span_label(impl_span
, format
!("missing one of `{missing_items_msg}` in implementation"));
260 if let Some(annotation_span
) = annotation_span
{
261 err
.span_note(annotation_span
, "required because of this annotation");
267 fn default_body_is_unstable(
272 reason
: Option
<Symbol
>,
273 issue
: Option
<NonZeroU32
>,
275 let missing_item_name
= tcx
.associated_item(item_did
).name
;
276 let use_of_unstable_library_feature_note
= match reason
{
277 Some(r
) => format
!("use of unstable library feature '{feature}': {r}"),
278 None
=> format
!("use of unstable library feature '{feature}'"),
281 let mut err
= struct_span_err
!(
285 "not all trait items implemented, missing: `{missing_item_name}`",
287 err
.note(format
!("default implementation of `{missing_item_name}` is unstable"));
288 err
.note(use_of_unstable_library_feature_note
);
289 rustc_session
::parse
::add_feature_diagnostics_for_issue(
291 &tcx
.sess
.parse_sess
,
293 rustc_feature
::GateIssue
::Library(issue
),
298 /// Re-sugar `ty::GenericPredicates` in a way suitable to be used in structured suggestions.
299 fn bounds_from_generic_predicates
<'tcx
>(
301 predicates
: ty
::GenericPredicates
<'tcx
>,
302 ) -> (String
, String
) {
303 let mut types
: FxHashMap
<Ty
<'tcx
>, Vec
<DefId
>> = FxHashMap
::default();
304 let mut projections
= vec
![];
305 for (predicate
, _
) in predicates
.predicates
{
306 debug
!("predicate {:?}", predicate
);
307 let bound_predicate
= predicate
.kind();
308 match bound_predicate
.skip_binder() {
309 ty
::PredicateKind
::Clause(ty
::Clause
::Trait(trait_predicate
)) => {
310 let entry
= types
.entry(trait_predicate
.self_ty()).or_default();
311 let def_id
= trait_predicate
.def_id();
312 if Some(def_id
) != tcx
.lang_items().sized_trait() {
313 // Type params are `Sized` by default, do not add that restriction to the list
314 // if it is a positive requirement.
315 entry
.push(trait_predicate
.def_id());
318 ty
::PredicateKind
::Clause(ty
::Clause
::Projection(projection_pred
)) => {
319 projections
.push(bound_predicate
.rebind(projection_pred
));
324 let generics
= if types
.is_empty() {
331 .filter_map(|t
| match t
.kind() {
332 ty
::Param(_
) => Some(t
.to_string()),
333 // Avoid suggesting the following:
334 // fn foo<T, <T as Trait>::Bar>(_: T) where T: Trait, <T as Trait>::Bar: Other {}
341 let mut where_clauses
= vec
![];
342 for (ty
, bounds
) in types
{
344 .extend(bounds
.into_iter().map(|bound
| format
!("{}: {}", ty
, tcx
.def_path_str(bound
))));
346 for projection
in &projections
{
347 let p
= projection
.skip_binder();
348 // FIXME: this is not currently supported syntax, we should be looking at the `types` and
349 // insert the associated types where they correspond, but for now let's be "lazy" and
350 // propose this instead of the following valid resugaring:
351 // `T: Trait, Trait::Assoc = K` → `T: Trait<Assoc = K>`
352 where_clauses
.push(format
!("{} = {}", tcx
.def_path_str(p
.projection_ty
.def_id
), p
.term
));
354 let where_clauses
= if where_clauses
.is_empty() {
357 format
!(" where {}", where_clauses
.join(", "))
359 (generics
, where_clauses
)
362 /// Return placeholder code for the given function.
363 fn fn_sig_suggestion
<'tcx
>(
365 sig
: ty
::FnSig
<'tcx
>,
367 predicates
: ty
::GenericPredicates
<'tcx
>,
368 assoc
: ty
::AssocItem
,
375 Some(match ty
.kind() {
376 ty
::Param(_
) if assoc
.fn_has_self_parameter
&& i
== 0 => "self".to_string(),
377 ty
::Ref(reg
, ref_ty
, mutability
) if i
== 0 => {
378 let reg
= format
!("{reg} ");
379 let reg
= match ®
[..] {
383 if assoc
.fn_has_self_parameter
{
384 match ref_ty
.kind() {
385 ty
::Param(param
) if param
.name
== kw
::SelfUpper
=> {
386 format
!("&{}{}self", reg
, mutability
.prefix_str())
389 _
=> format
!("self: {ty}"),
396 if assoc
.fn_has_self_parameter
&& i
== 0 {
397 format
!("self: {ty}")
404 .chain(std
::iter
::once(if sig
.c_variadic { Some("...".to_string()) }
else { None }
))
406 .collect
::<Vec
<String
>>()
408 let output
= sig
.output();
409 let output
= if !output
.is_unit() { format!(" -> {output}
") } else { String::new() };
411 let unsafety = sig.unsafety.prefix_str();
412 let (generics, where_clauses) = bounds_from_generic_predicates(tcx, predicates);
414 // FIXME: this is not entirely correct, as the lifetimes from borrowed params will
415 // not be present in the `fn` definition, not will we account for renamed
416 // lifetimes between the `impl` and the `trait`, but this should be good enough to
417 // fill in a significant portion of the missing code, and other subsequent
418 // suggestions can help the user fix the code.
419 format!("{unsafety}
fn {ident}{generics}
({args}
){output}{where_clauses} {{ todo!() }
}")
422 pub fn ty_kind_suggestion(ty: Ty<'_>) -> Option<&'static str> {
423 Some(match ty.kind() {
426 ty::Int(_) | ty::Uint(_) => "42",
427 ty::Float(_) => "3.14159",
428 ty::Error(_) | ty::Never => return None,
433 /// Return placeholder code for the given associated item.
434 /// Similar to `ty::AssocItem::suggestion`, but appropriate for use as the code snippet of a
435 /// structured suggestion.
436 fn suggestion_signature(assoc: ty::AssocItem, tcx: TyCtxt<'_>) -> String {
438 ty::AssocKind::Fn => {
439 // We skip the binder here because the binder would deanonymize all
440 // late-bound regions, and we don't want method signatures to show up
441 // `as for<'r> fn(&'r MyType)`. Pretty-printing handles late-bound
442 // regions just fine, showing `fn(&MyType)`.
445 tcx.fn_sig(assoc.def_id).subst_identity().skip_binder(),
447 tcx.predicates_of(assoc.def_id),
451 ty::AssocKind::Type => format!("type {}
= Type
;", assoc.name),
452 ty::AssocKind::Const => {
453 let ty = tcx.type_of(assoc.def_id).subst_identity();
454 let val = ty_kind_suggestion(ty).unwrap_or("value
");
455 format!("const {}
: {}
= {}
;", assoc.name, ty, val)
460 /// Emit an error when encountering two or more variants in a transparent enum.
461 fn bad_variant_count<'tcx>(tcx: TyCtxt<'tcx>, adt: ty::AdtDef<'tcx>, sp: Span, did: DefId) {
462 let variant_spans: Vec<_> = adt
465 .map(|variant| tcx.hir().span_if_local(variant.def_id).unwrap())
467 let msg = format!("needs exactly one variant
, but has {}
", adt.variants().len(),);
468 let mut err = struct_span_err!(tcx.sess, sp, E0731, "transparent
enum {msg}
");
469 err.span_label(sp, &msg);
470 if let [start @ .., end] = &*variant_spans {
471 for variant_span in start {
472 err.span_label(*variant_span, "");
474 err.span_label(*end, &format!("too many variants
in `{}`
", tcx.def_path_str(did)));
479 /// Emit an error when encountering two or more non-zero-sized fields in a transparent
481 fn bad_non_zero_sized_fields<'tcx>(
483 adt: ty::AdtDef<'tcx>,
485 field_spans: impl Iterator<Item = Span>,
488 let msg = format!("needs at most one non
-zero
-sized field
, but has {field_count}
");
489 let mut err = struct_span_err!(
493 "{}transparent {} {}
",
494 if adt.is_enum() { "the variant of a " } else { "" },
498 err.span_label(sp, &msg);
499 for sp in field_spans {
500 err.span_label(sp, "this field is non
-zero
-sized
");
505 // FIXME: Consider moving this method to a more fitting place.
506 pub fn potentially_plural_count(count: usize, word: &str) -> String {
507 format!("{} {}{}
", count, word, pluralize!(count))