55#include " llvm/ADT/STLExtras.h"
66#include " toolchain/check/context.h"
77#include " toolchain/check/convert.h"
8+ #include " toolchain/diagnostics/diagnostic_emitter.h"
89#include " toolchain/sem_ir/inst.h"
910#include " toolchain/sem_ir/typed_insts.h"
1011
1112namespace Carbon ::Check {
1213
1314// Returns the name scope corresponding to base_id, or nullopt if not a scope.
1415// On invalid scopes, prints a diagnostic and still returns the scope.
15- static auto GetAsNameScope (Context& context, SemIR::InstId base_id)
16+ static auto GetAsNameScope (Context& context, Parse::NodeId node_id,
17+ SemIR::ConstantId base_const_id)
1618 -> std::optional<SemIR::NameScopeId> {
17- auto base_const_id = context.constant_values ().Get (base_id);
18- if (!base_const_id.is_constant ()) {
19- // A name scope must be a constant.
20- return std::nullopt ;
21- }
2219 auto base = context.insts ().Get (base_const_id.inst_id ());
2320 if (auto base_as_namespace = base.TryAs <SemIR::Namespace>()) {
2421 return base_as_namespace->name_scope_id ;
@@ -31,9 +28,9 @@ static auto GetAsNameScope(Context& context, SemIR::InstId base_id)
3128 CARBON_DIAGNOSTIC (QualifiedExprInIncompleteClassScope, Error,
3229 " Member access into incomplete class `{0}`."
3330 std::string);
34- auto builder =
35- context. emitter (). Build (base_id , QualifiedExprInIncompleteClassScope,
36- context.sem_ir ().StringifyTypeExpr (base_id ));
31+ auto builder = context. emitter (). Build (
32+ node_id , QualifiedExprInIncompleteClassScope,
33+ context.sem_ir ().StringifyTypeExpr (base_const_id. inst_id () ));
3734 context.NoteIncompleteClass (base_as_class->class_id , builder);
3835 builder.Emit ();
3936 }
@@ -47,8 +44,8 @@ static auto GetAsNameScope(Context& context, SemIR::InstId base_id)
4744 " Member access into undefined interface `{0}`."
4845 std::string);
4946 auto builder = context.emitter ().Build (
50- base_id , QualifiedExprInUndefinedInterfaceScope,
51- context.sem_ir ().StringifyTypeExpr (base_id ));
47+ node_id , QualifiedExprInUndefinedInterfaceScope,
48+ context.sem_ir ().StringifyTypeExpr (base_const_id. inst_id () ));
5249 context.NoteUndefinedInterface (base_as_interface->interface_id , builder);
5350 builder.Emit ();
5451 }
@@ -93,12 +90,111 @@ static auto IsInstanceMethod(const SemIR::File& sem_ir,
9390 return false ;
9491}
9592
96- // Performs a member name lookup into the specified scope. If the scope is
97- // invalid, assume an error has already been diagnosed, and return BuiltinError.
93+ // Returns whether `name_scope_id` is a scope for which impl lookup should be
94+ // performed if we find an associated entity.
95+ static auto ScopeNeedsImplLookup (Context& context,
96+ SemIR::NameScopeId name_scope_id) -> bool {
97+ auto inst_id = context.name_scopes ().GetInstIdIfValid (name_scope_id);
98+ if (!inst_id.is_valid ()) {
99+ return false ;
100+ }
101+
102+ auto inst = context.insts ().Get (inst_id);
103+ if (inst.Is <SemIR::InterfaceDecl>()) {
104+ // Don't perform impl lookup if an associated entity is named as a member of
105+ // a facet type.
106+ return false ;
107+ }
108+ if (inst.Is <SemIR::Namespace>()) {
109+ // Don't perform impl lookup if an associated entity is named as a namespace
110+ // member.
111+ // TODO: This case is not yet listed in the design.
112+ return false ;
113+ }
114+ // Any other kind of scope is assumed to be a type that implements the
115+ // interface containing the associated entity, and impl lookup is performed.
116+ return true ;
117+ }
118+
119+ // Given a type and an interface, searches for an impl that describes how that
120+ // type implements that interface, and returns the corresponding witness.
121+ // Returns an invalid InstId if no matching impl is found.
122+ static auto LookupInterfaceWitness (Context& context,
123+ SemIR::ConstantId type_const_id,
124+ SemIR::InterfaceId interface_id)
125+ -> SemIR::InstId {
126+ // TODO: Add a better impl lookup system. At the very least, we should only be
127+ // considering impls that are for the same interface we're querying. We can
128+ // also skip impls that mention any types that aren't part of our impl query.
129+ for (const auto & impl : context.impls ().array_ref ()) {
130+ if (context.types ().GetInstId (impl.self_id ) != type_const_id.inst_id ()) {
131+ continue ;
132+ }
133+ auto interface_type =
134+ context.types ().TryGetAs <SemIR::InterfaceType>(impl.constraint_id );
135+ if (!interface_type) {
136+ // TODO: An impl of a constraint type should be treated as implementing
137+ // the constraint's interfaces.
138+ continue ;
139+ }
140+ if (interface_type->interface_id != interface_id) {
141+ continue ;
142+ }
143+ // TODO: Diagnose if the impl isn't defined yet?
144+ return impl.witness_id ;
145+ }
146+ return SemIR::InstId::Invalid;
147+ }
148+
149+ // Performs impl lookup for a member name expression. This finds the relevant
150+ // impl witness and extracts the corresponding impl member.
151+ static auto PerformImplLookup (Context& context, SemIR::ConstantId type_const_id,
152+ SemIR::AssociatedEntityType assoc_type,
153+ SemIR::InstId member_id) -> SemIR::InstId {
154+ auto witness_id =
155+ LookupInterfaceWitness (context, type_const_id, assoc_type.interface_id );
156+ if (!witness_id.is_valid ()) {
157+ CARBON_DIAGNOSTIC (MissingImplInMemberAccess, Error,
158+ " Cannot access member of interface {0} in type {1} "
159+ " that does not implement that interface."
160+ SemIR::NameId, std::string);
161+ context.emitter ().Emit (
162+ member_id, MissingImplInMemberAccess,
163+ context.interfaces ().Get (assoc_type.interface_id ).name_id ,
164+ context.sem_ir ().StringifyTypeExpr (type_const_id.inst_id ()));
165+ return SemIR::InstId::BuiltinError;
166+ }
167+
168+ auto const_id = context.constant_values ().Get (member_id);
169+ if (!const_id.is_constant ()) {
170+ if (const_id != SemIR::ConstantId::Error) {
171+ context.TODO (context.insts ().GetNodeId (member_id),
172+ " non-constant associated entity"
173+ }
174+ return SemIR::InstId::BuiltinError;
175+ }
176+
177+ auto assoc_entity =
178+ context.insts ().TryGetAs <SemIR::AssociatedEntity>(const_id.inst_id ());
179+ if (!assoc_entity) {
180+ context.TODO (context.insts ().GetNodeId (member_id),
181+ " unexpected value for associated entity"
182+ return SemIR::InstId::BuiltinError;
183+ }
184+
185+ // TODO: Substitute interface arguments and `Self` into `entity_type_id`.
186+ return context.AddInst (SemIR::InterfaceWitnessAccess{
187+ assoc_type.entity_type_id , witness_id, assoc_entity->index });
188+ }
189+
190+ // Performs a member name lookup into the specified scope, including performing
191+ // impl lookup if necessary. If the scope is invalid, assume an error has
192+ // already been diagnosed, and return BuiltinError.
98193static auto LookupMemberNameInScope (Context& context,
99194 Parse::MemberAccessExprId node_id,
100195 SemIR::InstId /* base_id*/
101196 SemIR::NameId name_id,
197+ SemIR::ConstantId name_scope_const_id,
102198 SemIR::NameScopeId name_scope_id)
103199 -> SemIR::InstId {
104200 auto inst_id = name_scope_id.is_valid () ? context.LookupQualifiedName (
@@ -107,8 +203,24 @@ static auto LookupMemberNameInScope(Context& context,
107203 auto inst = context.insts ().Get (inst_id);
108204 // TODO: Use a different kind of instruction that also references the
109205 // `base_id` so that `SemIR` consumers can find it.
110- return context.AddInst (
206+ auto member_id = context.AddInst (
111207 {node_id, SemIR::NameRef{inst.type_id (), name_id, inst_id}});
208+
209+ // If member name lookup finds an associated entity name, and the scope is not
210+ // a facet type, perform impl lookup.
211+ //
212+ // TODO: We need to do this as part of searching extended scopes, because a
213+ // lookup that finds an associated entity and also finds the corresponding
214+ // impl member is not supposed to be treated as ambiguous.
215+ if (auto assoc_type = context.types ().TryGetAs <SemIR::AssociatedEntityType>(
216+ inst.type_id ())) {
217+ if (ScopeNeedsImplLookup (context, name_scope_id)) {
218+ member_id = PerformImplLookup (context, name_scope_const_id, *assoc_type,
219+ member_id);
220+ }
221+ }
222+
223+ return member_id;
112224}
113225
114226// Performs the instance binding step in member access. If the found member is a
@@ -180,9 +292,12 @@ auto PerformMemberAccess(Context& context, Parse::MemberAccessExprId node_id,
180292 -> SemIR::InstId {
181293 // If the base is a name scope, such as a class or namespace, perform lookup
182294 // into that scope.
183- if (auto name_scope_id = GetAsNameScope (context, base_id)) {
184- return LookupMemberNameInScope (context, node_id, base_id, name_id,
185- *name_scope_id);
295+ if (auto base_const_id = context.constant_values ().Get (base_id);
296+ base_const_id.is_constant ()) {
297+ if (auto name_scope_id = GetAsNameScope (context, node_id, base_const_id)) {
298+ return LookupMemberNameInScope (context, node_id, base_id, name_id,
299+ base_const_id, *name_scope_id);
300+ }
186301 }
187302
188303 // If the base isn't a scope, it must have a complete type.
@@ -200,14 +315,14 @@ auto PerformMemberAccess(Context& context, Parse::MemberAccessExprId node_id,
200315 // Materialize a temporary for the base expression if necessary.
201316 base_id = ConvertToValueOrRefExpr (context, base_id);
202317 base_type_id = context.insts ().Get (base_id).type_id ();
203- auto base_type_inst_id = context.types ().GetInstId (base_type_id);
318+ auto base_type_const_id = context.types ().GetConstantId (base_type_id);
204319
205320 // Find the scope corresponding to the base type.
206- auto name_scope_id = GetAsNameScope (context, base_type_inst_id );
321+ auto name_scope_id = GetAsNameScope (context, node_id, base_type_const_id );
207322 if (!name_scope_id) {
208323 // The base type is not a name scope. Try some fallback options.
209- if (auto struct_type =
210- context. insts (). TryGetAs <SemIR::StructType>(base_type_inst_id )) {
324+ if (auto struct_type = context. insts (). TryGetAs <SemIR::StructType>(
325+ base_type_const_id. inst_id () )) {
211326 // TODO: Do we need to optimize this with a lookup table for O(1)?
212327 for (auto [i, ref_id] :
213328 llvm::enumerate (context.inst_blocks ().Get (struct_type->fields_id ))) {
@@ -239,7 +354,7 @@ auto PerformMemberAccess(Context& context, Parse::MemberAccessExprId node_id,
239354
240355 // Perform lookup into the base type.
241356 auto member_id = LookupMemberNameInScope (context, node_id, base_id, name_id,
242- *name_scope_id);
357+ base_type_const_id, *name_scope_id);
243358
244359 // Perform instance binding if we found an instance member.
245360 member_id = PerformInstanceBinding (context, node_id, base_id, member_id);
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