Superficial support for template modifier on symbolic bindings.

toolchain/check/deduce.cpp

@@ -357,7 +357,7 @@ auto DeductionContext::Deduce() -> bool {
       // compile-time constant.
       case CARBON_KIND(SemIR::SymbolicBindingPattern bind): {
         auto& entity_name = context().entity_names().Get(bind.entity_name_id);
-        auto index = entity_name.bind_index;
+        auto index = entity_name.bind_index();
         if (!index.has_value()) {
           break;
         }
@@ -396,7 +396,7 @@ auto DeductionContext::Deduce() -> bool {
       // deducing `[T:! type](x: T)` against `("foo")` deduces `T` as `String`.
       case CARBON_KIND(SemIR::BindSymbolicName bind): {
         auto& entity_name = context().entity_names().Get(bind.entity_name_id);
-        auto index = entity_name.bind_index;
+        auto index = entity_name.bind_index();
         if (!index.has_value() || index < first_deduced_index_ ||
             non_deduced_indexes_[index.index - first_deduced_index_.index]) {
           break;

toolchain/check/eval.cpp

@@ -1862,7 +1862,7 @@ static auto TryEvalInstInContext(EvalContext& eval_context,
       // argument of that specific, its constant value is the corresponding
       // argument value.
       if (auto value =
-              eval_context.GetCompileTimeBindValue(bind_name.bind_index);
+              eval_context.GetCompileTimeBindValue(bind_name.bind_index());
           value.has_value()) {
         return value;
       }
@@ -1871,6 +1871,7 @@ static auto TryEvalInstInContext(EvalContext& eval_context,
       // original, with no equivalent value.
       bind.entity_name_id =
           eval_context.entity_names().MakeCanonical(bind.entity_name_id);
+      // TODO: Propagate the `is_template` flag into the phase.
       return MakeConstantResult(eval_context.context(), bind, Phase::Symbolic);
     }
     case CARBON_KIND(SemIR::BindSymbolicName bind): {
@@ -1885,10 +1886,11 @@ static auto TryEvalInstInContext(EvalContext& eval_context,
         // argument of that specific, its constant value is the corresponding
         // argument value.
         if (auto value =
-                eval_context.GetCompileTimeBindValue(bind_name.bind_index);
+                eval_context.GetCompileTimeBindValue(bind_name.bind_index());
             value.has_value()) {
           return value;
         }
+        // TODO: Propagate the `is_template` flag into the phase.
         phase = Phase::Symbolic;
       }
       // The constant form of a symbolic binding is an idealized form of the

toolchain/check/generic.cpp

@@ -115,7 +115,8 @@ class RebuildGenericConstantInEvalBlockCallbacks final
             context_.insts().TryGetAs<SemIR::BindSymbolicName>(inst_id)) {
       if (context_.entity_names()
               .Get(binding->entity_name_id)
-              .bind_index.has_value()) {
+              .bind_index()
+              .has_value()) {
         inst_id = Rebuild(inst_id, *binding);
         return true;
       }

toolchain/check/handle_alias.cpp

@@ -36,8 +36,7 @@ auto HandleParseNode(Context& context, Parse::AliasId /*node_id*/) -> bool {
 
   auto entity_name_id = context.entity_names().Add(
       {.name_id = name_context.name_id_for_new_inst(),
-       .parent_scope_id = name_context.parent_scope_id,
-       .bind_index = SemIR::CompileTimeBindIndex::None});
+       .parent_scope_id = name_context.parent_scope_id});
 
   auto alias_type_id = SemIR::TypeId::None;
   auto alias_value_id = SemIR::InstId::None;

toolchain/check/handle_binding_pattern.cpp

@@ -28,22 +28,16 @@ static auto HandleAnyBindingPattern(Context& context, Parse::NodeId node_id,
   SemIR::ExprRegionId type_expr_region_id =
       EndSubpatternAsExpr(context, cast_type_inst_id);
 
-  // Every other kind of pattern binding has a name.
-  auto [name_node, name_id] = context.node_stack().PopNameWithNodeId();
-
-  // Determine whether we're handling an associated constant. These share the
-  // syntax for a compile-time binding, but don't behave like other compile-time
-  // bindings.
-  // TODO: Consider using a different parse node kind to make this easier.
-  bool is_associated_constant = false;
+  // The name in a template binding may be wrapped in `template`.
   bool is_generic = node_kind == Parse::NodeKind::CompileTimeBindingPattern;
-  if (is_generic) {
-    auto inst_id = context.scope_stack().PeekInstId();
-    is_associated_constant = inst_id.has_value() &&
-                             context.insts().Is<SemIR::InterfaceDecl>(inst_id);
-  }
+  auto is_template =
+      context.node_stack()
+          .PopAndDiscardSoloNodeIdIf<Parse::NodeKind::TemplateBindingName>();
+  // A non-generic template binding is diagnosed by the parser.
+  is_template &= is_generic;
 
-  bool needs_compile_time_binding = is_generic && !is_associated_constant;
+  // Every other kind of pattern binding has a name.
+  auto [name_node, name_id] = context.node_stack().PopNameWithNodeId();
 
   const DeclIntroducerState& introducer =
       context.decl_introducer_state_stack().innermost();
@@ -53,16 +47,12 @@ static auto HandleAnyBindingPattern(Context& context, Parse::NodeId node_id,
     auto binding_pattern_id = SemIR::InstId::None;
     // TODO: Eventually the name will need to support associations with other
     // scopes, but right now we don't support qualified names here.
-    auto entity_name_id = context.entity_names().Add(
-        {.name_id = name_id,
-         .parent_scope_id = context.scope_stack().PeekNameScopeId(),
-         // TODO: Don't allocate a compile-time binding index for an associated
-         // constant declaration.
-         .bind_index = needs_compile_time_binding
-                           ? context.scope_stack().AddCompileTimeBinding()
-                           : SemIR::CompileTimeBindIndex::None});
+    auto entity_name_id = context.entity_names().AddSymbolicBindingName(
+        name_id, context.scope_stack().PeekNameScopeId(),
+        is_generic ? context.scope_stack().AddCompileTimeBinding()
+                   : SemIR::CompileTimeBindIndex::None,
+        is_template);
     if (is_generic) {
-      // TODO: Create a `BindTemplateName` instead inside a `template` pattern.
       bind_id = context.AddInstInNoBlock(SemIR::LocIdAndInst(
           name_node, SemIR::BindSymbolicName{.type_id = cast_type_id,
                                              .entity_name_id = entity_name_id,
@@ -83,7 +73,7 @@ static auto HandleAnyBindingPattern(Context& context, Parse::NodeId node_id,
 
     // Add name to lookup immediately, so it can be used in the rest of the
     // enclosing pattern.
-    if (needs_compile_time_binding) {
+    if (is_generic) {
       context.scope_stack().PushCompileTimeBinding(bind_id);
     }
     auto name_context =
@@ -114,7 +104,7 @@ static auto HandleAnyBindingPattern(Context& context, Parse::NodeId node_id,
   // so we handle it separately.
   if (auto parent_class_decl =
           context.scope_stack().GetCurrentScopeAs<SemIR::ClassDecl>();
-      parent_class_decl.has_value() &&
+      parent_class_decl.has_value() && !is_generic &&
       node_kind == Parse::NodeKind::VarBindingPattern) {
     cast_type_id = AsConcreteType(
         context, cast_type_id, type_node,
@@ -131,9 +121,7 @@ static auto HandleAnyBindingPattern(Context& context, Parse::NodeId node_id,
                                          cast_type_id);
         });
     auto binding_id =
-        is_generic
-            ? Parse::NodeId::None
-            : context.parse_tree().As<Parse::VarBindingPatternId>(node_id);
+        context.parse_tree().As<Parse::VarBindingPatternId>(node_id);
     auto& class_info = context.classes().Get(parent_class_decl->class_id);
     auto field_type_id =
         context.GetUnboundElementType(class_info.self_type_id, cast_type_id);
@@ -157,12 +145,18 @@ static auto HandleAnyBindingPattern(Context& context, Parse::NodeId node_id,
           context.scope_stack().GetCurrentScopeAs<SemIR::InterfaceDecl>();
       parent_interface_decl.has_value() && is_generic) {
     cast_type_id = AsCompleteType(context, cast_type_id, type_node, [&] {
-      CARBON_DIAGNOSTIC(IncompleteTypeInAssociatedDecl, Error,
+      CARBON_DIAGNOSTIC(IncompleteTypeInAssociatedConstantDecl, Error,
                         "associated constant has incomplete type {0}",
                         SemIR::TypeId);
-      return context.emitter().Build(type_node, IncompleteTypeInAssociatedDecl,
-                                     cast_type_id);
+      return context.emitter().Build(
+          type_node, IncompleteTypeInAssociatedConstantDecl, cast_type_id);
     });
+    if (is_template) {
+      CARBON_DIAGNOSTIC(TemplateBindingInAssociatedConstantDecl, Error,
+                        "associated constant has `template` binding");
+      context.emitter().Emit(type_node,
+                             TemplateBindingInAssociatedConstantDecl);
+    }
 
     SemIR::AssociatedConstantDecl assoc_const_decl = {
         .type_id = cast_type_id,
@@ -357,8 +351,10 @@ auto HandleParseNode(Context& context, Parse::AddrId node_id) -> bool {
   return true;
 }
 
-auto HandleParseNode(Context& context, Parse::TemplateId node_id) -> bool {
-  return context.TODO(node_id, "HandleTemplate");
+auto HandleParseNode(Context& context, Parse::TemplateBindingNameId node_id)
+    -> bool {
+  context.node_stack().Push(node_id);
+  return true;
 }
 
 }  // namespace Carbon::Check

toolchain/check/handle_interface.cpp

@@ -169,10 +169,10 @@ auto HandleParseNode(Context& context,
   // We model `Self` as a symbolic binding whose type is the interface.
   // Because there is no equivalent non-symbolic value, we use `None` as
   // the `value_id` on the `BindSymbolicName`.
-  auto entity_name_id = context.entity_names().Add(
-      {.name_id = SemIR::NameId::SelfType,
-       .parent_scope_id = interface_info.scope_id,
-       .bind_index = context.scope_stack().AddCompileTimeBinding()});
+  auto entity_name_id = context.entity_names().AddSymbolicBindingName(
+      SemIR::NameId::SelfType, interface_info.scope_id,
+      context.scope_stack().AddCompileTimeBinding(),
+      /*is_template=*/false);
   interface_info.self_param_id =
       context.AddInst(SemIR::LocIdAndInst::NoLoc<SemIR::BindSymbolicName>(
           {.type_id = self_type_id,

toolchain/check/handle_where.cpp

@@ -31,9 +31,7 @@ auto HandleParseNode(Context& context, Parse::WhereOperandId node_id) -> bool {
   // expression to the left of `where`, so `MyInterface` in the example above.
   auto entity_name_id = context.entity_names().Add(
       {.name_id = SemIR::NameId::PeriodSelf,
-       .parent_scope_id = context.scope_stack().PeekNameScopeId(),
-       // `None` because this is not the parameter of a generic.
-       .bind_index = SemIR::CompileTimeBindIndex::None});
+       .parent_scope_id = context.scope_stack().PeekNameScopeId()});
   auto inst_id =
       context.AddInst(SemIR::LocIdAndInst::NoLoc<SemIR::BindSymbolicName>(
           {.type_id = self_type_id,

toolchain/check/import.cpp

@@ -179,9 +179,7 @@ static auto CopySingleNameScopeFromImportIR(
   // Produce the namespace for the entry.
   auto make_import_id = [&]() {
     auto entity_name_id = context.entity_names().Add(
-        {.name_id = name_id,
-         .parent_scope_id = parent_scope_id,
-         .bind_index = SemIR::CompileTimeBindIndex::None});
+        {.name_id = name_id, .parent_scope_id = parent_scope_id});
     auto import_ir_inst_id = context.import_ir_insts().Add(
         {.ir_id = ir_id, .inst_id = import_inst_id});
     auto inst_id = context.AddInstInNoBlock(
@@ -273,9 +271,7 @@ static auto AddImportRefOrMerge(Context& context, SemIR::ImportIRId ir_id,
   auto& entry = parent_scope.GetEntry(entry_id);
   if (inserted) {
     auto entity_name_id = context.entity_names().Add(
-        {.name_id = name_id,
-         .parent_scope_id = parent_scope_id,
-         .bind_index = SemIR::CompileTimeBindIndex::None});
+        {.name_id = name_id, .parent_scope_id = parent_scope_id});
     entry.result = SemIR::ScopeLookupResult::MakeFound(
         AddImportRef(context, {.ir_id = ir_id, .inst_id = import_inst_id},
                      entity_name_id),
@@ -313,9 +309,7 @@ static auto AddScopedImportRef(Context& context,
                                SemIR::AccessKind access_kind) -> SemIR::InstId {
   // Add an ImportRef for other instructions.
   auto impl_entity_name_id = context.entity_names().Add(
-      {.name_id = name_id,
-       .parent_scope_id = parent_scope_id,
-       .bind_index = SemIR::CompileTimeBindIndex::None});
+      {.name_id = name_id, .parent_scope_id = parent_scope_id});
   auto import_ref_id = AddImportRef(context, import_inst, impl_entity_name_id);
   parent_scope.AddRequired({.name_id = name_id,
                             .result = SemIR::ScopeLookupResult::MakeFound(

toolchain/check/import_ref.cpp

@@ -1024,9 +1024,7 @@ static auto GetLocalParamPatternsId(ImportContext& context,
     switch (binding.kind) {
       case SemIR::BindingPattern::Kind: {
         auto entity_name_id = context.local_entity_names().Add(
-            {.name_id = name_id,
-             .parent_scope_id = SemIR::NameScopeId::None,
-             .bind_index = SemIR::CompileTimeBindIndex::None});
+            {.name_id = name_id, .parent_scope_id = SemIR::NameScopeId::None});
         new_param_id =
             context.local_context().AddInstInNoBlock<SemIR::BindingPattern>(
                 AddImportIRInst(context, binding_id),
@@ -1279,9 +1277,7 @@ static auto AddAssociatedEntities(ImportContext& context,
     }
     auto name_id = GetLocalNameId(context, import_name_id);
     auto entity_name_id = context.local_entity_names().Add(
-        {.name_id = name_id,
-         .parent_scope_id = local_name_scope_id,
-         .bind_index = SemIR::CompileTimeBindIndex::None});
+        {.name_id = name_id, .parent_scope_id = local_name_scope_id});
     new_associated_entities.push_back(
         AddImportRef(context, inst_id, entity_name_id));
   }
@@ -1531,10 +1527,11 @@ static auto TryResolveTypedInst(ImportRefResolver& resolver,
   const auto& import_entity_name =
       resolver.import_entity_names().Get(inst.entity_name_id);
   auto name_id = GetLocalNameId(resolver, import_entity_name.name_id);
-  auto entity_name_id = resolver.local_entity_names().Add(
-      {.name_id = name_id,
-       .parent_scope_id = SemIR::NameScopeId::None,
-       .bind_index = import_entity_name.bind_index});
+  // TODO: Use the same `EntityName` for the `SymbolicBindingPattern` and the
+  // `BindSymbolicName`.
+  auto entity_name_id = resolver.local_entity_names().AddSymbolicBindingName(
+      name_id, SemIR::NameScopeId::None, import_entity_name.bind_index(),
+      import_entity_name.is_template);
   return ResolveAs<SemIR::BindSymbolicName>(
       resolver,
       {.type_id = resolver.local_context().GetTypeIdForTypeConstant(type_id),
@@ -1553,10 +1550,11 @@ static auto TryResolveTypedInst(ImportRefResolver& resolver,
   const auto& import_entity_name =
       resolver.import_entity_names().Get(inst.entity_name_id);
   auto name_id = GetLocalNameId(resolver, import_entity_name.name_id);
-  auto entity_name_id = resolver.local_entity_names().Add(
-      {.name_id = name_id,
-       .parent_scope_id = SemIR::NameScopeId::None,
-       .bind_index = import_entity_name.bind_index});
+  // TODO: Use the same `EntityName` for the `SymbolicBindingPattern` and the
+  // `BindSymbolicName`.
+  auto entity_name_id = resolver.local_entity_names().AddSymbolicBindingName(
+      name_id, SemIR::NameScopeId::None, import_entity_name.bind_index(),
+      import_entity_name.is_template);
   return ResolveAs<SemIR::SymbolicBindingPattern>(
       resolver,
       {.type_id = resolver.local_context().GetTypeIdForTypeConstant(type_id),

toolchain/check/node_stack.h

@@ -445,6 +445,7 @@ class NodeStack {
       case Parse::NodeKind::StructLiteralStart:
       case Parse::NodeKind::StructTypeLiteralField:
       case Parse::NodeKind::StructTypeLiteralStart:
+      case Parse::NodeKind::TemplateBindingName:
       case Parse::NodeKind::TupleLiteralStart:
       case Parse::NodeKind::TuplePatternStart:
       case Parse::NodeKind::VariableInitializer:
@@ -508,7 +509,6 @@ class NodeStack {
       case Parse::NodeKind::StructLiteralComma:
       case Parse::NodeKind::StructFieldDesignator:
       case Parse::NodeKind::StructTypeLiteralComma:
-      case Parse::NodeKind::Template:
       case Parse::NodeKind::TupleLiteralComma:
         return Id::Kind::Invalid;
       default:

toolchain/check/subst.cpp

@@ -342,7 +342,7 @@ class SubstConstantCallbacks final : public SubstInstCallbacks {
     // TODO: Consider building a hash map for substitutions. We might have a
     // lot of them.
     for (auto [bind_index, replacement_id] : substitutions_) {
-      if (context_.entity_names().Get(entity_name_id).bind_index ==
+      if (context_.entity_names().Get(entity_name_id).bind_index() ==
           bind_index) {
         // This is the binding we're replacing. Perform substitution.
         inst_id = context_.constant_values().GetInstId(replacement_id);