Use the .Self symbolic binding as 1st arg of WhereExpr

toolchain/check/eval.cpp

@@ -1404,7 +1404,8 @@ auto TryEvalInstInContext(EvalContext& eval_context, SemIR::InstId inst_id,
     case CARBON_KIND(SemIR::WhereExpr typed_inst): {
       // TODO: This currently ignores the requirements and just produces the
       // left-hand type argument to the `where`.
-      return eval_context.GetConstantValue(typed_inst.lhs_id);
+      return eval_context.GetConstantValue(
+          eval_context.insts().Get(typed_inst.period_self_id).type_id());
     }
 
     // `not true` -> `false`, `not false` -> `true`.

toolchain/check/handle_where.cpp

@@ -18,9 +18,6 @@ auto HandleParseNode(Context& context, Parse::WhereOperandId node_id) -> bool {
   // TODO: Validate that `self_type_id` represents a facet type. Only facet
   // types may have `where` restrictions.
 
-  // FIXME: Should we save the self_id here instead?
-  context.node_stack().Push(node_id, self_type_id);
-
   // Introduce a name scope so that we can remove the `.Self` entry we are
   // adding to name lookup at the end of the `where` expression.
   context.scope_stack().Push();
@@ -45,6 +42,10 @@ auto HandleParseNode(Context& context, Parse::WhereOperandId node_id) -> bool {
   // Shouldn't have any names in newly created scope.
   CARBON_CHECK(!existing.is_valid());
 
+  // Save the `.Self` symbolic binding on the node stack. It will become the
+  // first argument to the `WhereExpr` instruction.
+  context.node_stack().Push(node_id, inst_id);
+
   // Going to put each requirement on `args_type_info_stack`, so we can have an
   // inst block with the varying number of requirements but keeping other
   // instructions on the current inst block from the `inst_block_stack()`.
@@ -104,12 +105,12 @@ auto HandleParseNode(Context& context, Parse::WhereExprId node_id) -> bool {
   // Remove `PeriodSelf` from name lookup, undoing the `Push` done for the
   // `WhereOperand`.
   context.scope_stack().Pop();
-  SemIR::TypeId lhs_type_id =
+  SemIR::InstId period_self_id =
       context.node_stack().Pop<Parse::NodeKind::WhereOperand>();
   SemIR::InstBlockId requirements_id = context.args_type_info_stack().Pop();
   context.AddInstAndPush<SemIR::WhereExpr>(
       node_id, {.type_id = SemIR::TypeId::TypeType,
-                .lhs_id = lhs_type_id,
+                .period_self_id = period_self_id,
                 .requirements_id = requirements_id});
   return true;
 }

toolchain/check/node_stack.h

@@ -425,6 +425,7 @@ class NodeStack {
         case Parse::NodeKind::ShortCircuitOperandOr:
         case Parse::NodeKind::StructField:
         case Parse::NodeKind::StructTypeField:
+        case Parse::NodeKind::WhereOperand:
           return Id::KindFor<SemIR::InstId>();
         case Parse::NodeKind::IfCondition:
         case Parse::NodeKind::IfExprIf:
@@ -449,8 +450,6 @@ class NodeStack {
         case Parse::NodeKind::DefaultLibrary:
         case Parse::NodeKind::LibraryName:
           return Id::KindFor<SemIR::LibraryNameId>();
-        case Parse::NodeKind::WhereOperand:
-          return Id::KindFor<SemIR::TypeId>();
         case Parse::NodeKind::ArrayExprSemi:
         case Parse::NodeKind::BuiltinName:
         case Parse::NodeKind::ClassIntroducer:

toolchain/check/testdata/impl/fail_todo_impl_assoc_const.carbon

@@ -59,7 +59,7 @@ impl bool as I where .T = bool {}
 // CHECK:STDOUT:     %.Self.ref: %.1 = name_ref .Self, %.Self [symbolic = constants.%.Self]
 // CHECK:STDOUT:     %T.ref: %.2 = name_ref T, @I.%.loc11 [template = constants.%.3]
 // CHECK:STDOUT:     %bool.make_type.loc16_27: init type = call constants.%Bool() [template = bool]
-// CHECK:STDOUT:     %.loc16_16: type = where_expr %.1 [template = constants.%.1] {
+// CHECK:STDOUT:     %.loc16_16: type = where_expr %.Self [template = constants.%.1] {
 // CHECK:STDOUT:       requirement_rewrite %T.ref, %bool.make_type.loc16_27
 // CHECK:STDOUT:     }
 // CHECK:STDOUT:   }

toolchain/check/testdata/where_expr/constraints.carbon

@@ -142,7 +142,7 @@ fn NotEmptyStruct() {
 // CHECK:STDOUT:     %.Self.ref: %.2 = name_ref .Self, %.Self [symbolic = constants.%.Self.1]
 // CHECK:STDOUT:     %Member.ref: %.3 = name_ref Member, @I.%.loc7 [template = constants.%.4]
 // CHECK:STDOUT:     %.loc11_33: %.8 = struct_literal ()
-// CHECK:STDOUT:     %.loc11_16: type = where_expr %.2 [template = constants.%.2] {
+// CHECK:STDOUT:     %.loc11_16: type = where_expr %.Self [template = constants.%.2] {
 // CHECK:STDOUT:       requirement_rewrite %Member.ref, %.loc11_33
 // CHECK:STDOUT:     }
 // CHECK:STDOUT:     %T.param: %.2 = param T, runtime_param<invalid>
@@ -155,7 +155,7 @@ fn NotEmptyStruct() {
 // CHECK:STDOUT:     %.Self: %.2 = bind_symbolic_name .Self 0 [symbolic = constants.%.Self.1]
 // CHECK:STDOUT:     %.Self.ref: %.2 = name_ref .Self, %.Self [symbolic = constants.%.Self.1]
 // CHECK:STDOUT:     %.loc13_37: %.5 = tuple_literal ()
-// CHECK:STDOUT:     %.loc13_21: type = where_expr %.2 [template = constants.%.2] {
+// CHECK:STDOUT:     %.loc13_21: type = where_expr %.Self [template = constants.%.2] {
 // CHECK:STDOUT:       requirement_equivalent %.Self.ref, %.loc13_37
 // CHECK:STDOUT:     }
 // CHECK:STDOUT:     %U.param: %.2 = param U, runtime_param<invalid>
@@ -168,7 +168,7 @@ fn NotEmptyStruct() {
 // CHECK:STDOUT:     %.Self: %.1 = bind_symbolic_name .Self 0 [symbolic = constants.%.Self.2]
 // CHECK:STDOUT:     %.Self.ref: %.1 = name_ref .Self, %.Self [symbolic = constants.%.Self.2]
 // CHECK:STDOUT:     %I.ref: type = name_ref I, file.%I.decl [template = constants.%.2]
-// CHECK:STDOUT:     %.loc15: type = where_expr %.1 [template = constants.%.1] {
+// CHECK:STDOUT:     %.loc15: type = where_expr %.Self [template = constants.%.1] {
 // CHECK:STDOUT:       requirement_impls %.Self.ref, %I.ref
 // CHECK:STDOUT:     }
 // CHECK:STDOUT:     %V.param: %.1 = param V, runtime_param<invalid>
@@ -186,7 +186,7 @@ fn NotEmptyStruct() {
 // CHECK:STDOUT:     %Member.ref: %.3 = name_ref Member, @I.%.loc7 [template = constants.%.4]
 // CHECK:STDOUT:     %.Self.ref.loc17_50: %.2 = name_ref .Self, %.Self [symbolic = constants.%.Self.1]
 // CHECK:STDOUT:     %Second.ref.loc17_50: %.6 = name_ref Second, @I.%.loc8 [template = constants.%.7]
-// CHECK:STDOUT:     %.loc17: type = where_expr %.2 [template = constants.%.2] {
+// CHECK:STDOUT:     %.loc17: type = where_expr %.Self [template = constants.%.2] {
 // CHECK:STDOUT:       requirement_impls %Second.ref.loc17_20, %I.ref.loc17_34
 // CHECK:STDOUT:       requirement_rewrite %Member.ref, %Second.ref.loc17_50
 // CHECK:STDOUT:     }
@@ -319,7 +319,7 @@ fn NotEmptyStruct() {
 // CHECK:STDOUT:     %.Self.ref: %.1 = name_ref .Self, %.Self [symbolic = constants.%.Self]
 // CHECK:STDOUT:     %Member.ref: %.3 = name_ref Member, imports.%import_ref.8 [template = constants.%.4]
 // CHECK:STDOUT:     %.loc8_39: i32 = int_literal 2 [template = constants.%.5]
-// CHECK:STDOUT:     %.loc8_23: type = where_expr %.1 [template = constants.%.1] {
+// CHECK:STDOUT:     %.loc8_23: type = where_expr %.Self [template = constants.%.1] {
 // CHECK:STDOUT:       requirement_rewrite %Member.ref, %.loc8_39
 // CHECK:STDOUT:     }
 // CHECK:STDOUT:     %X.param: %.1 = param X, runtime_param<invalid>
@@ -440,7 +440,7 @@ fn NotEmptyStruct() {
 // CHECK:STDOUT:     %.Self: %.3 = bind_symbolic_name .Self 0 [symbolic = constants.%.Self]
 // CHECK:STDOUT:     %.Self.ref: %.3 = name_ref .Self, %.Self [symbolic = constants.%.Self]
 // CHECK:STDOUT:     %.loc26_38: %.1 = struct_literal ()
-// CHECK:STDOUT:     %.loc26_22: type = where_expr %.3 [template = constants.%.3] {
+// CHECK:STDOUT:     %.loc26_22: type = where_expr %.Self [template = constants.%.3] {
 // CHECK:STDOUT:       requirement_equivalent %.Self.ref, %.loc26_38
 // CHECK:STDOUT:     }
 // CHECK:STDOUT:     %Y.param: %.3 = param Y, runtime_param<invalid>

toolchain/check/testdata/where_expr/no_prelude/designator.carbon

@@ -123,7 +123,7 @@ class D {
 // CHECK:STDOUT:     %.Self: %.1 = bind_symbolic_name .Self 0 [symbolic = constants.%.Self.1]
 // CHECK:STDOUT:     %.Self.ref: %.1 = name_ref .Self, %.Self [symbolic = constants.%.Self.1]
 // CHECK:STDOUT:     %.loc8_37: %.4 = tuple_literal ()
-// CHECK:STDOUT:     %.loc8_21: type = where_expr %.1 [template = constants.%.1] {
+// CHECK:STDOUT:     %.loc8_21: type = where_expr %.Self [template = constants.%.1] {
 // CHECK:STDOUT:       requirement_equivalent %.Self.ref, %.loc8_37
 // CHECK:STDOUT:     }
 // CHECK:STDOUT:     %T.param: %.1 = param T, runtime_param<invalid>
@@ -137,7 +137,7 @@ class D {
 // CHECK:STDOUT:     %.Self.ref: %.1 = name_ref .Self, %.Self [symbolic = constants.%.Self.1]
 // CHECK:STDOUT:     %Member.ref: %.2 = name_ref Member, @I.%.loc5 [template = constants.%.3]
 // CHECK:STDOUT:     %.loc10_40: %.5 = struct_literal ()
-// CHECK:STDOUT:     %.loc10_23: type = where_expr %.1 [template = constants.%.1] {
+// CHECK:STDOUT:     %.loc10_23: type = where_expr %.Self [template = constants.%.1] {
 // CHECK:STDOUT:       requirement_rewrite %Member.ref, %.loc10_40
 // CHECK:STDOUT:     }
 // CHECK:STDOUT:     %U.param: %.1 = param U, runtime_param<invalid>
@@ -149,7 +149,7 @@ class D {
 // CHECK:STDOUT:     %.Self: type = bind_symbolic_name .Self 0 [symbolic = constants.%.Self.2]
 // CHECK:STDOUT:     %.Self.ref: type = name_ref .Self, %.Self [symbolic = constants.%.Self.2]
 // CHECK:STDOUT:     %I.ref: type = name_ref I, file.%I.decl [template = constants.%.1]
-// CHECK:STDOUT:     %.loc12: type = where_expr type [template = type] {
+// CHECK:STDOUT:     %.loc12: type = where_expr %.Self [template = type] {
 // CHECK:STDOUT:       requirement_impls %.Self.ref, %I.ref
 // CHECK:STDOUT:     }
 // CHECK:STDOUT:     %V.param: type = param V, runtime_param<invalid>
@@ -227,7 +227,7 @@ class D {
 // CHECK:STDOUT:     %.Self.ref: %.1 = name_ref .Self, %.Self [symbolic = constants.%.Self]
 // CHECK:STDOUT:     %Mismatch.ref: <error> = name_ref Mismatch, <error> [template = <error>]
 // CHECK:STDOUT:     %.loc12_44: %.5 = struct_literal ()
-// CHECK:STDOUT:     %.loc12_25: type = where_expr %.1 [template = constants.%.1] {
+// CHECK:STDOUT:     %.loc12_25: type = where_expr %.Self [template = constants.%.1] {
 // CHECK:STDOUT:       requirement_rewrite %Mismatch.ref, %.loc12_44
 // CHECK:STDOUT:     }
 // CHECK:STDOUT:     %W.param: %.1 = param W, runtime_param<invalid>

toolchain/check/testdata/where_expr/no_prelude/non_generic.carbon

@@ -41,7 +41,7 @@ fn NotGenericF(U: I where .T = {}) {}
 // CHECK:STDOUT:     %.Self.ref: %.1 = name_ref .Self, %.Self [symbolic = constants.%.Self]
 // CHECK:STDOUT:     %T.ref: %.2 = name_ref T, @I.%.loc11 [template = constants.%.3]
 // CHECK:STDOUT:     %.loc14_33: %.5 = struct_literal ()
-// CHECK:STDOUT:     %.loc14_21: type = where_expr %.1 [template = constants.%.1] {
+// CHECK:STDOUT:     %.loc14_21: type = where_expr %.Self [template = constants.%.1] {
 // CHECK:STDOUT:       requirement_rewrite %T.ref, %.loc14_33
 // CHECK:STDOUT:     }
 // CHECK:STDOUT:     %U.param: %.1 = param U, runtime_param0

toolchain/sem_ir/file.cpp

@@ -415,7 +415,8 @@ static auto StringifyTypeExprImpl(const SemIR::File& outer_sem_ir,
         if (step.index == 0) {
           out << "<where restriction on ";
           steps.push_back(step.Next());
-          push_inst_id(sem_ir.types().GetInstId(inst.lhs_id));
+          TypeId type_id = sem_ir.insts().Get(inst.period_self_id).type_id();
+          push_inst_id(sem_ir.types().GetInstId(type_id));
           // TODO: also output restrictions from the inst block
           // inst.requirements_id
         } else {

toolchain/sem_ir/formatter.cpp

@@ -858,7 +858,7 @@ class FormatterImpl {
   }
 
   auto FormatInstRHS(WhereExpr inst) -> void {
-    FormatArgs(inst.lhs_id);
+    FormatArgs(inst.period_self_id);
     FormatTrailingBlock(inst.requirements_id);
   }
 

toolchain/sem_ir/typed_insts.h

@@ -1144,7 +1144,9 @@ struct WhereExpr {
        .constant_kind = InstConstantKind::Conditional});
 
   TypeId type_id;
-  TypeId lhs_id;
+  // This is the `.Self` symbolic binding. Its type matches the left type
+  // argument of the `where`.
+  InstId period_self_id;
   InstBlockId requirements_id;
 };