Make ImplDecls evaluate to themselves. (#4352)

Change ImplDecls so they evaluate to themselves in general, rather than
having a special case in import handling that pretends that they do.

toolchain/check/eval.cpp

@@ -1278,6 +1278,7 @@ static auto TryEvalInstInContext(EvalContext& eval_context,
                            .specific_id = SemIR::SpecificId::Invalid},
           Phase::Template);
     }
+
     case CARBON_KIND(SemIR::InterfaceDecl interface_decl): {
       // If the interface has generic parameters, we don't produce an interface
       // type, but a callable whose return value is an interface type.
@@ -1311,10 +1312,12 @@ static auto TryEvalInstInContext(EvalContext& eval_context,
     // These cases are treated as being the unique canonical definition of the
     // corresponding constant value.
     // TODO: This doesn't properly handle redeclarations. Consider adding a
-    // corresponding `Value` inst for each of these cases.
+    // corresponding `Value` inst for each of these cases, or returning the
+    // first declaration.
     case SemIR::AssociatedConstantDecl::Kind:
     case SemIR::BaseDecl::Kind:
     case SemIR::FieldDecl::Kind:
+    case SemIR::ImplDecl::Kind:
     case SemIR::Namespace::Kind:
       return SemIR::ConstantId::ForTemplateConstant(inst_id);
 
@@ -1451,7 +1454,6 @@ static auto TryEvalInstInContext(EvalContext& eval_context,
     case SemIR::Branch::Kind:
     case SemIR::BranchIf::Kind:
     case SemIR::BranchWithArg::Kind:
-    case SemIR::ImplDecl::Kind:
     case SemIR::ImportDecl::Kind:
     case SemIR::Param::Kind:
     case SemIR::RequirementEquivalent::Kind:

toolchain/check/import_ref.cpp

@@ -1580,24 +1580,6 @@ class ImportRefResolver {
         context_.types().GetConstantId(interface_val.type_id()));
   }
 
-  // Forms a constant ID that represents the given instruction ID that denotes
-  // an impl declaration. Impl declarations don't have a constant value, but for
-  // the purposes of importing we pretend that they do.
-  //
-  // TODO: Consider alternative options here. We could make impl declarations
-  // actually evaluate to themselves to avoid this hack.
-  static auto ImplDeclIdAsConstantId(SemIR::InstId impl_decl_id)
-      -> SemIR::ConstantId {
-    return SemIR::ConstantId::ForTemplateConstant(impl_decl_id);
-  }
-
-  // Gets the instruction ID for an impl declaration represented by the
-  // specified constant ID.
-  auto ConstantIdAsImplDeclId(SemIR::ConstantId impl_const_id)
-      -> SemIR::InstId {
-    return context_.constant_values().GetInstId(impl_const_id);
-  }
-
   // Make a declaration of an impl. This is done as a separate step from
   // importing the impl definition in order to resolve cycles.
   auto MakeImplDeclaration(const SemIR::Impl& import_impl)
@@ -1615,7 +1597,7 @@ class ImportRefResolver {
 
     // Write the impl ID into the ImplDecl.
     context_.ReplaceInstBeforeConstantUse(impl_decl_id, impl_decl);
-    return {impl_decl.impl_id, ImplDeclIdAsConstantId(impl_decl_id)};
+    return {impl_decl.impl_id, context_.constant_values().Get(impl_decl_id)};
   }
 
   // Imports the definition of an impl.

toolchain/check/testdata/as/overloaded.carbon

@@ -94,7 +94,7 @@ let n: i32 = ((4 as i32) as X) as i32;
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %X.decl: type = class_decl @X [template = constants.%X] {} {}
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %int.make_type_32: init type = call constants.%Int32() [template = i32]
 // CHECK:STDOUT:     %.loc15_6.1: type = value_of_initializer %int.make_type_32 [template = i32]
 // CHECK:STDOUT:     %.loc15_6.2: type = converted %int.make_type_32, %.loc15_6.1 [template = i32]
@@ -103,7 +103,7 @@ let n: i32 = ((4 as i32) as X) as i32;
 // CHECK:STDOUT:     %X.ref: type = name_ref X, file.%X.decl [template = constants.%X]
 // CHECK:STDOUT:     %.loc15_20: type = interface_type @As, @As(constants.%X) [template = constants.%.8]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.2 {} {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
 // CHECK:STDOUT:     %X.ref: type = name_ref X, file.%X.decl [template = constants.%X]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %As.ref: %As.type = name_ref As, imports.%import_ref.2 [template = constants.%As]

toolchain/check/testdata/function/builtin/method.carbon

@@ -64,7 +64,7 @@ var arr: [i32; 1.(I.F)(2)];
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %I.decl: type = interface_decl @I [template = constants.%.1] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %int.make_type_32: init type = call constants.%Int32() [template = i32]
 // CHECK:STDOUT:     %.loc15_6.1: type = value_of_initializer %int.make_type_32 [template = i32]
 // CHECK:STDOUT:     %.loc15_6.2: type = converted %int.make_type_32, %.loc15_6.1 [template = i32]

toolchain/check/testdata/function/builtin/no_prelude/call_from_operator.carbon

@@ -145,7 +145,7 @@ var arr: [i32; 1 + 2] = (3, 4, 3 + 4);
 // CHECK:STDOUT:     .arr = %arr
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %int.make_type_32: init type = call constants.%Int32() [template = i32]
 // CHECK:STDOUT:     %.loc6_6.1: type = value_of_initializer %int.make_type_32 [template = i32]
 // CHECK:STDOUT:     %.loc6_6.2: type = converted %int.make_type_32, %.loc6_6.1 [template = i32]

toolchain/check/testdata/impl/compound.carbon

@@ -92,7 +92,7 @@ fn InstanceCallIndirect(p: i32*) {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %Simple.decl: type = interface_decl @Simple [template = constants.%.1] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %int.make_type_32: init type = call constants.%Int32() [template = i32]
 // CHECK:STDOUT:     %.loc16_6.1: type = value_of_initializer %int.make_type_32 [template = i32]
 // CHECK:STDOUT:     %.loc16_6.2: type = converted %int.make_type_32, %.loc16_6.1 [template = i32]

toolchain/check/testdata/impl/declaration.carbon

@@ -44,7 +44,7 @@ impl i32 as I;
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %I.decl: type = interface_decl @I [template = constants.%.1] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %int.make_type_32: init type = call constants.%Int32() [template = i32]
 // CHECK:STDOUT:     %.loc13_6.1: type = value_of_initializer %int.make_type_32 [template = i32]
 // CHECK:STDOUT:     %.loc13_6.2: type = converted %int.make_type_32, %.loc13_6.1 [template = i32]

toolchain/check/testdata/impl/empty.carbon

@@ -47,7 +47,7 @@ impl i32 as Empty {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %Empty.decl: type = interface_decl @Empty [template = constants.%.1] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %int.make_type_32: init type = call constants.%Int32() [template = i32]
 // CHECK:STDOUT:     %.loc14_6.1: type = value_of_initializer %int.make_type_32 [template = i32]
 // CHECK:STDOUT:     %.loc14_6.2: type = converted %int.make_type_32, %.loc14_6.1 [template = i32]

toolchain/check/testdata/impl/extend_impl.carbon

@@ -97,7 +97,7 @@ fn G(c: C) {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @C {
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %HasF.ref: type = name_ref HasF, file.%HasF.decl [template = constants.%.1]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %.loc19: <witness> = complete_type_witness %.6 [template = constants.%.7]

toolchain/check/testdata/impl/fail_call_invalid.carbon

@@ -64,7 +64,7 @@ fn InstanceCall(n: i32) {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %Simple.decl: type = interface_decl @Simple [template = constants.%.1] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %int.make_type_32: init type = call constants.%Int32() [template = i32]
 // CHECK:STDOUT:     %.loc15_6.1: type = value_of_initializer %int.make_type_32 [template = i32]
 // CHECK:STDOUT:     %.loc15_6.2: type = converted %int.make_type_32, %.loc15_6.1 [template = i32]

toolchain/check/testdata/impl/fail_extend_impl_forall.carbon

@@ -121,7 +121,7 @@ class C {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @C {
-// CHECK:STDOUT:   impl_decl @impl {
+// CHECK:STDOUT:   impl_decl @impl [template] {
 // CHECK:STDOUT:     %T.patt: type = symbolic_binding_pattern T 0
 // CHECK:STDOUT:   } {
 // CHECK:STDOUT:     %T.param: type = param T, runtime_param<invalid>

toolchain/check/testdata/impl/fail_extend_impl_scope.carbon

@@ -48,7 +48,7 @@ extend impl i32 as I {}
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %I.decl: type = interface_decl @I [template = constants.%.1] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %int.make_type_32: init type = call constants.%Int32() [template = i32]
 // CHECK:STDOUT:     %.loc16_13.1: type = value_of_initializer %int.make_type_32 [template = i32]
 // CHECK:STDOUT:     %.loc16_13.2: type = converted %int.make_type_32, %.loc16_13.1 [template = i32]

toolchain/check/testdata/impl/fail_extend_impl_type_as.carbon

@@ -110,7 +110,7 @@ class E {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @C {
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %int.make_type_32: init type = call constants.%Int32() [template = i32]
 // CHECK:STDOUT:     %.loc18_15.1: type = value_of_initializer %int.make_type_32 [template = i32]
 // CHECK:STDOUT:     %.loc18_15.2: type = converted %int.make_type_32, %.loc18_15.1 [template = i32]
@@ -124,7 +124,7 @@ class E {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @D {
-// CHECK:STDOUT:   impl_decl @impl.2 {} {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
 // CHECK:STDOUT:     %D.ref: type = name_ref D, file.%D.decl [template = constants.%D]
 // CHECK:STDOUT:     %I.ref: type = name_ref I, file.%I.decl [template = constants.%.1]
 // CHECK:STDOUT:   }
@@ -136,7 +136,7 @@ class E {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @E {
-// CHECK:STDOUT:   impl_decl @impl.3 {} {
+// CHECK:STDOUT:   impl_decl @impl.3 [template] {} {
 // CHECK:STDOUT:     %Self.ref: type = name_ref Self, constants.%E [template = constants.%E]
 // CHECK:STDOUT:     %I.ref: type = name_ref I, file.%I.decl [template = constants.%.1]
 // CHECK:STDOUT:   }

toolchain/check/testdata/impl/fail_extend_non_interface.carbon

@@ -55,7 +55,7 @@ class C {
 // CHECK:STDOUT: class @C {
 // CHECK:STDOUT:   %.loc15_18.1: type = value_of_initializer @impl.%int.make_type_32 [template = i32]
 // CHECK:STDOUT:   %.loc15_18.2: type = converted @impl.%int.make_type_32, %.loc15_18.1 [template = i32]
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %int.make_type_32: init type = call constants.%Int32() [template = i32]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %.loc16: <witness> = complete_type_witness %.2 [template = constants.%.3]

toolchain/check/testdata/impl/fail_extend_partially_defined_interface.carbon

@@ -72,7 +72,7 @@ interface I {
 // CHECK:STDOUT: !definition:
 // CHECK:STDOUT:
 // CHECK:STDOUT:   class {
-// CHECK:STDOUT:     impl_decl @impl {} {
+// CHECK:STDOUT:     impl_decl @impl [template] {} {
 // CHECK:STDOUT:       %I.ref: type = name_ref I, file.%I.decl [template = constants.%.1]
 // CHECK:STDOUT:     }
 // CHECK:STDOUT:     %.loc20: <witness> = complete_type_witness %.2 [template = constants.%.3]

toolchain/check/testdata/impl/fail_extend_undefined_interface.carbon

@@ -58,7 +58,7 @@ class C {
 // CHECK:STDOUT: impl @impl: %C as %.1;
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @C {
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %I.ref: type = name_ref I, file.%I.decl [template = constants.%.1]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %.loc21: <witness> = complete_type_witness %.2 [template = constants.%.3]

toolchain/check/testdata/impl/fail_impl_as_scope.carbon

@@ -54,7 +54,7 @@ impl as Simple {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %Simple.decl: type = interface_decl @Simple [template = constants.%.1] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %Simple.ref: type = name_ref Simple, file.%Simple.decl [template = constants.%.1]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT: }

toolchain/check/testdata/impl/fail_impl_bad_assoc_const.carbon

@@ -49,7 +49,7 @@ impl bool as I {}
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %I.decl: type = interface_decl @I [template = constants.%.1] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %bool.make_type: init type = call constants.%Bool() [template = bool]
 // CHECK:STDOUT:     %.loc16_6.1: type = value_of_initializer %bool.make_type [template = bool]
 // CHECK:STDOUT:     %.loc16_6.2: type = converted %bool.make_type, %.loc16_6.1 [template = bool]

toolchain/check/testdata/impl/fail_impl_bad_assoc_fn.carbon

@@ -734,7 +734,7 @@ class SelfNestedBadReturnType {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @NoF {
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %I.ref: type = name_ref I, file.%I.decl [template = constants.%.1]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %.loc22: <witness> = complete_type_witness %.5 [template = constants.%.6]
@@ -744,7 +744,7 @@ class SelfNestedBadReturnType {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @FNotFunction {
-// CHECK:STDOUT:   impl_decl @impl.2 {} {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
 // CHECK:STDOUT:     %I.ref: type = name_ref I, file.%I.decl [template = constants.%.1]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %.loc35: <witness> = complete_type_witness %.5 [template = constants.%.6]
@@ -756,7 +756,7 @@ class SelfNestedBadReturnType {
 // CHECK:STDOUT: class @F.16;
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @FAlias {
-// CHECK:STDOUT:   impl_decl @impl.3 {} {
+// CHECK:STDOUT:   impl_decl @impl.3 [template] {} {
 // CHECK:STDOUT:     %I.ref: type = name_ref I, file.%I.decl [template = constants.%.1]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %.loc51: <witness> = complete_type_witness %.5 [template = constants.%.6]
@@ -766,7 +766,7 @@ class SelfNestedBadReturnType {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @FExtraParam {
-// CHECK:STDOUT:   impl_decl @impl.4 {} {
+// CHECK:STDOUT:   impl_decl @impl.4 [template] {} {
 // CHECK:STDOUT:     %I.ref: type = name_ref I, file.%I.decl [template = constants.%.1]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %.loc64: <witness> = complete_type_witness %.5 [template = constants.%.6]
@@ -776,7 +776,7 @@ class SelfNestedBadReturnType {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @FExtraImplicitParam {
-// CHECK:STDOUT:   impl_decl @impl.5 {} {
+// CHECK:STDOUT:   impl_decl @impl.5 [template] {} {
 // CHECK:STDOUT:     %I.ref: type = name_ref I, file.%I.decl [template = constants.%.1]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %.loc77: <witness> = complete_type_witness %.5 [template = constants.%.6]
@@ -786,7 +786,7 @@ class SelfNestedBadReturnType {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @FExtraReturnType {
-// CHECK:STDOUT:   impl_decl @impl.6 {} {
+// CHECK:STDOUT:   impl_decl @impl.6 [template] {} {
 // CHECK:STDOUT:     %I.ref: type = name_ref I, file.%I.decl [template = constants.%.1]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %.loc91: <witness> = complete_type_witness %.5 [template = constants.%.6]
@@ -796,7 +796,7 @@ class SelfNestedBadReturnType {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @FMissingParam {
-// CHECK:STDOUT:   impl_decl @impl.7 {} {
+// CHECK:STDOUT:   impl_decl @impl.7 [template] {} {
 // CHECK:STDOUT:     %J.ref: type = name_ref J, file.%J.decl [template = constants.%.7]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %.loc106: <witness> = complete_type_witness %.5 [template = constants.%.6]
@@ -806,7 +806,7 @@ class SelfNestedBadReturnType {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @FMissingImplicitParam {
-// CHECK:STDOUT:   impl_decl @impl.8 {} {
+// CHECK:STDOUT:   impl_decl @impl.8 [template] {} {
 // CHECK:STDOUT:     %J.ref: type = name_ref J, file.%J.decl [template = constants.%.7]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %.loc119: <witness> = complete_type_witness %.5 [template = constants.%.6]
@@ -816,7 +816,7 @@ class SelfNestedBadReturnType {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @FMissingReturnType {
-// CHECK:STDOUT:   impl_decl @impl.9 {} {
+// CHECK:STDOUT:   impl_decl @impl.9 [template] {} {
 // CHECK:STDOUT:     %J.ref: type = name_ref J, file.%J.decl [template = constants.%.7]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %.loc132: <witness> = complete_type_witness %.5 [template = constants.%.6]
@@ -826,7 +826,7 @@ class SelfNestedBadReturnType {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @FDifferentParamType {
-// CHECK:STDOUT:   impl_decl @impl.10 {} {
+// CHECK:STDOUT:   impl_decl @impl.10 [template] {} {
 // CHECK:STDOUT:     %J.ref: type = name_ref J, file.%J.decl [template = constants.%.7]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %.loc145: <witness> = complete_type_witness %.5 [template = constants.%.6]
@@ -836,7 +836,7 @@ class SelfNestedBadReturnType {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @FDifferentImplicitParamType {
-// CHECK:STDOUT:   impl_decl @impl.11 {} {
+// CHECK:STDOUT:   impl_decl @impl.11 [template] {} {
 // CHECK:STDOUT:     %J.ref: type = name_ref J, file.%J.decl [template = constants.%.7]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %.loc158: <witness> = complete_type_witness %.5 [template = constants.%.6]
@@ -846,7 +846,7 @@ class SelfNestedBadReturnType {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @FDifferentReturnType {
-// CHECK:STDOUT:   impl_decl @impl.12 {} {
+// CHECK:STDOUT:   impl_decl @impl.12 [template] {} {
 // CHECK:STDOUT:     %J.ref: type = name_ref J, file.%J.decl [template = constants.%.7]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %.loc171: <witness> = complete_type_witness %.5 [template = constants.%.6]
@@ -856,7 +856,7 @@ class SelfNestedBadReturnType {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @FDifferentParamName {
-// CHECK:STDOUT:   impl_decl @impl.13 {} {
+// CHECK:STDOUT:   impl_decl @impl.13 [template] {} {
 // CHECK:STDOUT:     %J.ref: type = name_ref J, file.%J.decl [template = constants.%.7]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %.loc185: <witness> = complete_type_witness %.5 [template = constants.%.6]
@@ -866,7 +866,7 @@ class SelfNestedBadReturnType {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @SelfNestedBadParam {
-// CHECK:STDOUT:   impl_decl @impl.14 {} {
+// CHECK:STDOUT:   impl_decl @impl.14 [template] {} {
 // CHECK:STDOUT:     %SelfNested.ref: type = name_ref SelfNested, file.%SelfNested.decl [template = constants.%.10]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %.loc202: <witness> = complete_type_witness %.5 [template = constants.%.6]
@@ -876,7 +876,7 @@ class SelfNestedBadReturnType {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @SelfNestedBadReturnType {
-// CHECK:STDOUT:   impl_decl @impl.15 {} {
+// CHECK:STDOUT:   impl_decl @impl.15 [template] {} {
 // CHECK:STDOUT:     %SelfNested.ref: type = name_ref SelfNested, file.%SelfNested.decl [template = constants.%.10]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %.loc214: <witness> = complete_type_witness %.5 [template = constants.%.6]

toolchain/check/testdata/impl/fail_impl_bad_interface.carbon

@@ -76,7 +76,7 @@ impl i32 as false {}
 // CHECK:STDOUT:   %.loc21_13.2: %.7 = specific_constant imports.%import_ref.4, @ImplicitAs(type) [template = constants.%.8]
 // CHECK:STDOUT:   %Convert.ref: %.7 = name_ref Convert, %.loc21_13.2 [template = constants.%.8]
 // CHECK:STDOUT:   %.loc21_13.3: type = converted @impl.%.loc21_13, <error> [template = <error>]
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %int.make_type_32: init type = call constants.%Int32() [template = i32]
 // CHECK:STDOUT:     %.loc21_6.1: type = value_of_initializer %int.make_type_32 [template = i32]
 // CHECK:STDOUT:     %.loc21_6.2: type = converted %int.make_type_32, %.loc21_6.1 [template = i32]

toolchain/check/testdata/impl/fail_redefinition.carbon

@@ -53,13 +53,13 @@ impl i32 as I {}
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %I.decl: type = interface_decl @I [template = constants.%.1] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %int.make_type_32.loc13: init type = call constants.%Int32() [template = i32]
 // CHECK:STDOUT:     %.loc13_6.1: type = value_of_initializer %int.make_type_32.loc13 [template = i32]
 // CHECK:STDOUT:     %.loc13_6.2: type = converted %int.make_type_32.loc13, %.loc13_6.1 [template = i32]
 // CHECK:STDOUT:     %I.ref.loc13: type = name_ref I, file.%I.decl [template = constants.%.1]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %int.make_type_32.loc21: init type = call constants.%Int32() [template = i32]
 // CHECK:STDOUT:     %.loc21_6.1: type = value_of_initializer %int.make_type_32.loc21 [template = i32]
 // CHECK:STDOUT:     %.loc21_6.2: type = converted %int.make_type_32.loc21, %.loc21_6.1 [template = i32]

toolchain/check/testdata/impl/fail_todo_impl_assoc_const.carbon

@@ -50,7 +50,7 @@ impl bool as I where .T = bool {}
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %I.decl: type = interface_decl @I [template = constants.%.1] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %bool.make_type.loc16_6: init type = call constants.%Bool() [template = bool]
 // CHECK:STDOUT:     %.loc16_6.1: type = value_of_initializer %bool.make_type.loc16_6 [template = bool]
 // CHECK:STDOUT:     %.loc16_6.2: type = converted %bool.make_type.loc16_6, %.loc16_6.1 [template = bool]

toolchain/check/testdata/impl/impl_as.carbon

@@ -86,7 +86,7 @@ class C {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @C {
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %Simple.ref: type = name_ref Simple, file.%Simple.decl [template = constants.%.1]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %.loc22: <witness> = complete_type_witness %.6 [template = constants.%.7]

toolchain/check/testdata/impl/impl_forall.carbon

@@ -52,7 +52,7 @@ impl forall [T:! type] T as Simple {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %Simple.decl: type = interface_decl @Simple [template = constants.%.1] {} {}
-// CHECK:STDOUT:   impl_decl @impl {
+// CHECK:STDOUT:   impl_decl @impl [template] {
 // CHECK:STDOUT:     %T.patt: type = symbolic_binding_pattern T 0
 // CHECK:STDOUT:   } {
 // CHECK:STDOUT:     %T.param: type = param T, runtime_param<invalid>

toolchain/check/testdata/impl/lookup/alias.carbon

@@ -69,7 +69,7 @@ fn G(c: C) {
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %HasF.decl: type = interface_decl @HasF [template = constants.%.1] {} {}
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %HasF.ref: type = name_ref HasF, file.%HasF.decl [template = constants.%.1]
 // CHECK:STDOUT:   }

toolchain/check/testdata/impl/lookup/fail_todo_undefined_impl.carbon

@@ -82,7 +82,7 @@ impl C as I {
 // CHECK:STDOUT:     %.loc19_11.2: type = converted %int.make_type_32, %.loc19_11.1 [template = i32]
 // CHECK:STDOUT:     %return: ref i32 = var <return slot>
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.2 {} {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %I.ref: type = name_ref I, file.%I.decl [template = constants.%.1]
 // CHECK:STDOUT:   }
@@ -111,7 +111,7 @@ impl C as I {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @C {
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %I.ref: type = name_ref I, file.%I.decl [template = constants.%.1]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %.loc17: <witness> = complete_type_witness %.5 [template = constants.%.6]

toolchain/check/testdata/impl/lookup/import.carbon

@@ -70,7 +70,7 @@ fn G(c: Impl.C) {
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %HasF.decl: type = interface_decl @HasF [template = constants.%.1] {} {}
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %HasF.ref: type = name_ref HasF, file.%HasF.decl [template = constants.%.1]
 // CHECK:STDOUT:   }

toolchain/check/testdata/impl/lookup/instance_method.carbon

@@ -129,7 +129,7 @@ fn F(c: C) -> i32 {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @C {
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %I.ref: type = name_ref I, file.%I.decl [template = constants.%.1]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %.loc21: <witness> = complete_type_witness %.6 [template = constants.%.7]

toolchain/check/testdata/impl/lookup/no_prelude/impl_forall.carbon

@@ -121,7 +121,7 @@ fn TestSpecific(a: A({})) -> {} {
 // CHECK:STDOUT:     %U.param: type = param U, runtime_param<invalid>
 // CHECK:STDOUT:     %U.loc6: type = bind_symbolic_name U 0, %U.param [symbolic = %U.1 (constants.%U)]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl {
+// CHECK:STDOUT:   impl_decl @impl [template] {
 // CHECK:STDOUT:     %V.patt: type = symbolic_binding_pattern V 0
 // CHECK:STDOUT:   } {
 // CHECK:STDOUT:     %V.param: type = param V, runtime_param<invalid>

toolchain/check/testdata/impl/lookup/no_prelude/import.carbon

@@ -55,7 +55,7 @@ fn G(c: Impl.C) {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %HasF.decl: type = interface_decl @HasF [template = constants.%.1] {} {}
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %HasF.ref: type = name_ref HasF, file.%HasF.decl [template = constants.%.1]
 // CHECK:STDOUT:   }

toolchain/check/testdata/impl/no_prelude/basic.carbon

@@ -43,7 +43,7 @@ impl C as Simple {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Simple.decl: type = interface_decl @Simple [template = constants.%.1] {} {}
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Simple.ref: type = name_ref Simple, file.%Simple.decl [template = constants.%.1]
 // CHECK:STDOUT:   }

toolchain/check/testdata/impl/no_prelude/fail_impl_bad_type.carbon

@@ -30,7 +30,7 @@ impl true as I {}
 // CHECK:STDOUT:     .I = %I.decl
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %I.decl: type = interface_decl @I [template = constants.%.1] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %.loc16_6.1: bool = bool_literal true [template = constants.%.2]
 // CHECK:STDOUT:     %.loc16_6.2: type = converted %.loc16_6.1, <error> [template = <error>]
 // CHECK:STDOUT:     %I.ref: type = name_ref I, file.%I.decl [template = constants.%.1]

toolchain/check/testdata/impl/no_prelude/generic_redeclaration.carbon

@@ -80,7 +80,7 @@ impl (C, C).0 as I {}
 // CHECK:STDOUT:   %I.decl: type = interface_decl @I [template = constants.%.1] {} {}
 // CHECK:STDOUT:   %J.decl: type = interface_decl @J [template = constants.%.2] {} {}
 // CHECK:STDOUT:   %K.decl: type = interface_decl @K [template = constants.%.3] {} {}
-// CHECK:STDOUT:   impl_decl @impl.1 {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {
 // CHECK:STDOUT:     %T.patt: %.1 = symbolic_binding_pattern T 0
 // CHECK:STDOUT:   } {
 // CHECK:STDOUT:     %I.ref: type = name_ref I, file.%I.decl [template = constants.%.1]
@@ -91,7 +91,7 @@ impl (C, C).0 as I {}
 // CHECK:STDOUT:     %.loc8_21.2: type = converted %T.ref, %.loc8_21.1 [symbolic = %T.1 (constants.%T.1)]
 // CHECK:STDOUT:     %K.ref: type = name_ref K, file.%K.decl [template = constants.%.3]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.2 {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {
 // CHECK:STDOUT:     %T.patt: %.2 = symbolic_binding_pattern T 0
 // CHECK:STDOUT:   } {
 // CHECK:STDOUT:     %J.ref: type = name_ref J, file.%J.decl [template = constants.%.2]
@@ -102,7 +102,7 @@ impl (C, C).0 as I {}
 // CHECK:STDOUT:     %.loc9_21.2: type = converted %T.ref, %.loc9_21.1 [symbolic = %T.1 (constants.%T.2)]
 // CHECK:STDOUT:     %K.ref: type = name_ref K, file.%K.decl [template = constants.%.3]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.3 {
+// CHECK:STDOUT:   impl_decl @impl.3 [template] {
 // CHECK:STDOUT:     %T.patt: %.1 = symbolic_binding_pattern T 0
 // CHECK:STDOUT:   } {
 // CHECK:STDOUT:     %I.ref: type = name_ref I, file.%I.decl [template = constants.%.1]
@@ -113,7 +113,7 @@ impl (C, C).0 as I {}
 // CHECK:STDOUT:     %.loc13_21.2: type = converted %T.ref, %.loc13_21.1 [symbolic = %T.1 (constants.%T.1)]
 // CHECK:STDOUT:     %K.ref: type = name_ref K, file.%K.decl [template = constants.%.3]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.4 {
+// CHECK:STDOUT:   impl_decl @impl.4 [template] {
 // CHECK:STDOUT:     %T.patt: %.2 = symbolic_binding_pattern T 0
 // CHECK:STDOUT:   } {
 // CHECK:STDOUT:     %J.ref: type = name_ref J, file.%J.decl [template = constants.%.2]
@@ -219,7 +219,7 @@ impl (C, C).0 as I {}
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %I.decl: type = interface_decl @I [template = constants.%.1] {} {}
 // CHECK:STDOUT:   %J.decl: type = interface_decl @J [template = constants.%.2] {} {}
-// CHECK:STDOUT:   impl_decl @impl {
+// CHECK:STDOUT:   impl_decl @impl [template] {
 // CHECK:STDOUT:     %T.patt: %.1 = symbolic_binding_pattern T 0
 // CHECK:STDOUT:   } {
 // CHECK:STDOUT:     %I.ref.loc7: type = name_ref I, file.%I.decl [template = constants.%.1]
@@ -230,7 +230,7 @@ impl (C, C).0 as I {}
 // CHECK:STDOUT:     %.loc7_21.2: type = converted %T.ref.loc7, %.loc7_21.1 [symbolic = %T.1 (constants.%T)]
 // CHECK:STDOUT:     %J.ref.loc7: type = name_ref J, file.%J.decl [template = constants.%.2]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl {
+// CHECK:STDOUT:   impl_decl @impl [template] {
 // CHECK:STDOUT:     %T.patt: %.1 = symbolic_binding_pattern T 0
 // CHECK:STDOUT:   } {
 // CHECK:STDOUT:     %I.ref.loc14: type = name_ref I, file.%I.decl [template = constants.%.1]
@@ -293,11 +293,11 @@ impl (C, C).0 as I {}
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
 // CHECK:STDOUT:   %I.decl: type = interface_decl @I [template = constants.%.1] {} {}
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %I.ref: type = name_ref I, file.%I.decl [template = constants.%.1]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.2 {} {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
 // CHECK:STDOUT:     %C.ref.loc14_7: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %C.ref.loc14_10: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %.loc14_11.1: %.4 = tuple_literal (%C.ref.loc14_7, %C.ref.loc14_10)

toolchain/check/testdata/impl/no_prelude/import_generic.carbon

@@ -66,7 +66,7 @@ impl forall [T:! type] C as I(T*) {}
 // CHECK:STDOUT:     %T.param: type = param T, runtime_param<invalid>
 // CHECK:STDOUT:     %T.loc5: type = bind_symbolic_name T 0, %T.param [symbolic = %T.1 (constants.%T)]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.1 {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {
 // CHECK:STDOUT:     %T.patt: type = symbolic_binding_pattern T 0
 // CHECK:STDOUT:   } {
 // CHECK:STDOUT:     %T.param: type = param T, runtime_param<invalid>
@@ -76,7 +76,7 @@ impl forall [T:! type] C as I(T*) {}
 // CHECK:STDOUT:     %T.ref: type = name_ref T, %T.loc7 [symbolic = %T.1 (constants.%T)]
 // CHECK:STDOUT:     %.loc7: type = interface_type @I, @I(constants.%T) [symbolic = %.1 (constants.%.4)]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.2 {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {
 // CHECK:STDOUT:     %T.patt: type = symbolic_binding_pattern T 0
 // CHECK:STDOUT:   } {
 // CHECK:STDOUT:     %T.param: type = param T, runtime_param<invalid>
@@ -200,7 +200,7 @@ impl forall [T:! type] C as I(T*) {}
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %default.import.loc2_6.1 = import <invalid>
 // CHECK:STDOUT:   %default.import.loc2_6.2 = import <invalid>
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %T.param: type = param T, runtime_param<invalid>
 // CHECK:STDOUT:     %T.loc4: type = bind_symbolic_name T 0, %T.param [symbolic = constants.%T]
 // CHECK:STDOUT:     %C.ref: type = name_ref C, imports.%import_ref.1 [template = constants.%C]
@@ -323,7 +323,7 @@ impl forall [T:! type] C as I(T*) {}
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %default.import.loc2_6.1 = import <invalid>
 // CHECK:STDOUT:   %default.import.loc2_6.2 = import <invalid>
-// CHECK:STDOUT:   impl_decl @impl.2 {} {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
 // CHECK:STDOUT:     %T.param: type = param T, runtime_param<invalid>
 // CHECK:STDOUT:     %T.loc11: type = bind_symbolic_name T 0, %T.param [symbolic = constants.%T]
 // CHECK:STDOUT:     %C.ref: type = name_ref C, imports.%import_ref.1 [template = constants.%C]

toolchain/check/testdata/impl/no_prelude/import_self.carbon

@@ -120,7 +120,7 @@ fn F(x: (), y: ()) -> () {
 // CHECK:STDOUT:     .F = %F.decl
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %default.import = import <invalid>
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %.loc6_7.1: %.1 = tuple_literal ()
 // CHECK:STDOUT:     %.loc6_7.2: type = converted %.loc6_7.1, constants.%.1 [template = constants.%.1]
 // CHECK:STDOUT:     %Add.ref: type = name_ref Add, imports.%import_ref.1 [template = constants.%.2]

toolchain/check/testdata/impl/no_prelude/interface_args.carbon

@@ -126,7 +126,7 @@ fn MakeC(a: A) -> C {
 // CHECK:STDOUT:   %A.decl: type = class_decl @A [template = constants.%A] {} {}
 // CHECK:STDOUT:   %B.decl: type = class_decl @B [template = constants.%B] {} {}
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %A.ref: type = name_ref A, file.%A.decl [template = constants.%A]
 // CHECK:STDOUT:     %Action.ref: %Action.type = name_ref Action, file.%Action.decl [template = constants.%Action]
 // CHECK:STDOUT:     %B.ref: type = name_ref B, file.%B.decl [template = constants.%B]
@@ -593,7 +593,7 @@ fn MakeC(a: A) -> C {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %A.decl: type = class_decl @A [template = constants.%A] {} {}
 // CHECK:STDOUT:   %B.decl: type = class_decl @B [template = constants.%B] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %A.ref: type = name_ref A, file.%A.decl [template = constants.%A]
 // CHECK:STDOUT:     %Factory.ref: %Factory.type = name_ref Factory, file.%Factory.decl [template = constants.%Factory]
 // CHECK:STDOUT:     %B.ref: type = name_ref B, file.%B.decl [template = constants.%B]

toolchain/check/testdata/impl/no_prelude/no_definition_in_impl_file.carbon

@@ -92,7 +92,7 @@ impl () as D;
 // CHECK:STDOUT:     .A = %A.decl
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %A.decl: type = interface_decl @A [template = constants.%.1] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %.loc6_7.1: %.2 = tuple_literal ()
 // CHECK:STDOUT:     %.loc6_7.2: type = converted %.loc6_7.1, constants.%.2 [template = constants.%.2]
 // CHECK:STDOUT:     %A.ref: type = name_ref A, file.%A.decl [template = constants.%.1]
@@ -129,12 +129,12 @@ impl () as D;
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %default.import.loc2_6.1 = import <invalid>
 // CHECK:STDOUT:   %default.import.loc2_6.2 = import <invalid>
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %.loc4_7.1: %.2 = tuple_literal ()
 // CHECK:STDOUT:     %.loc4_7.2: type = converted %.loc4_7.1, constants.%.2 [template = constants.%.2]
 // CHECK:STDOUT:     %A.ref.loc4: type = name_ref A, imports.%import_ref.1 [template = constants.%.1]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %.loc6_7.1: %.2 = tuple_literal ()
 // CHECK:STDOUT:     %.loc6_7.2: type = converted %.loc6_7.1, constants.%.2 [template = constants.%.2]
 // CHECK:STDOUT:     %A.ref.loc6: type = name_ref A, imports.%import_ref.1 [template = constants.%.1]
@@ -202,7 +202,7 @@ impl () as D;
 // CHECK:STDOUT:     .B = %B.decl
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %B.decl: type = interface_decl @B [template = constants.%.1] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %.loc6_7.1: %.2 = tuple_literal ()
 // CHECK:STDOUT:     %.loc6_7.2: type = converted %.loc6_7.1, constants.%.2 [template = constants.%.2]
 // CHECK:STDOUT:     %B.ref: type = name_ref B, file.%B.decl [template = constants.%.1]
@@ -261,7 +261,7 @@ impl () as D;
 // CHECK:STDOUT:     .C = %C.decl
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %C.decl: type = interface_decl @C [template = constants.%.1] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %.loc6_7.1: %.2 = tuple_literal ()
 // CHECK:STDOUT:     %.loc6_7.2: type = converted %.loc6_7.1, constants.%.2 [template = constants.%.2]
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%.1]
@@ -297,7 +297,7 @@ impl () as D;
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %default.import.loc2_6.1 = import <invalid>
 // CHECK:STDOUT:   %default.import.loc2_6.2 = import <invalid>
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %.loc8_7.1: %.2 = tuple_literal ()
 // CHECK:STDOUT:     %.loc8_7.2: type = converted %.loc8_7.1, constants.%.2 [template = constants.%.2]
 // CHECK:STDOUT:     %C.ref: type = name_ref C, imports.%import_ref.1 [template = constants.%.1]
@@ -333,7 +333,7 @@ impl () as D;
 // CHECK:STDOUT:   %default.import.loc2_6.1 = import <invalid>
 // CHECK:STDOUT:   %default.import.loc2_6.2 = import <invalid>
 // CHECK:STDOUT:   %D.decl: type = interface_decl @D [template = constants.%.1] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %.loc9_7.1: %.2 = tuple_literal ()
 // CHECK:STDOUT:     %.loc9_7.2: type = converted %.loc9_7.1, constants.%.2 [template = constants.%.2]
 // CHECK:STDOUT:     %D.ref: type = name_ref D, file.%D.decl [template = constants.%.1]

toolchain/check/testdata/impl/no_prelude/self_in_class.carbon

@@ -90,7 +90,7 @@ class A {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @A {
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %DefaultConstructible.ref: type = name_ref DefaultConstructible, file.%DefaultConstructible.decl [template = constants.%.1]
 // CHECK:STDOUT:   }

toolchain/check/testdata/impl/no_prelude/self_in_signature.carbon

@@ -93,20 +93,20 @@ impl D as SelfNested {
 // CHECK:STDOUT:   %UseSelf.decl: type = interface_decl @UseSelf [template = constants.%.1] {} {}
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
 // CHECK:STDOUT:   %D.decl: type = class_decl @D [template = constants.%D] {} {}
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %UseSelf.ref: type = name_ref UseSelf, file.%UseSelf.decl [template = constants.%.1]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.2 {} {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
 // CHECK:STDOUT:     %D.ref: type = name_ref D, file.%D.decl [template = constants.%D]
 // CHECK:STDOUT:     %UseSelf.ref: type = name_ref UseSelf, file.%UseSelf.decl [template = constants.%.1]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %SelfNested.decl: type = interface_decl @SelfNested [template = constants.%.10] {} {}
-// CHECK:STDOUT:   impl_decl @impl.3 {} {
+// CHECK:STDOUT:   impl_decl @impl.3 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %SelfNested.ref: type = name_ref SelfNested, file.%SelfNested.decl [template = constants.%.10]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.4 {} {
+// CHECK:STDOUT:   impl_decl @impl.4 [template] {} {
 // CHECK:STDOUT:     %D.ref: type = name_ref D, file.%D.decl [template = constants.%D]
 // CHECK:STDOUT:     %SelfNested.ref: type = name_ref SelfNested, file.%SelfNested.decl [template = constants.%.10]
 // CHECK:STDOUT:   }

toolchain/check/testdata/impl/redeclaration.carbon

@@ -55,14 +55,14 @@ impl i32 as I {}
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %I.decl: type = interface_decl @I [template = constants.%.1] {} {}
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %int.make_type_32.loc13: init type = call constants.%Int32() [template = i32]
 // CHECK:STDOUT:     %.loc13_6.1: type = value_of_initializer %int.make_type_32.loc13 [template = i32]
 // CHECK:STDOUT:     %.loc13_6.2: type = converted %int.make_type_32.loc13, %.loc13_6.1 [template = i32]
 // CHECK:STDOUT:     %I.ref.loc13: type = name_ref I, file.%I.decl [template = constants.%.1]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %X.decl: type = class_decl @X [template = constants.%X] {} {}
-// CHECK:STDOUT:   impl_decl @impl.2 {} {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
 // CHECK:STDOUT:     %int.make_type_32: init type = call constants.%Int32() [template = i32]
 // CHECK:STDOUT:     %.loc19_6.1: type = value_of_initializer %int.make_type_32 [template = i32]
 // CHECK:STDOUT:     %.loc19_6.2: type = converted %int.make_type_32, %.loc19_6.1 [template = i32]
@@ -88,7 +88,7 @@ impl i32 as I {}
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @X {
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %int.make_type_32.loc16: init type = call constants.%Int32() [template = i32]
 // CHECK:STDOUT:     %.loc16_8.1: type = value_of_initializer %int.make_type_32.loc16 [template = i32]
 // CHECK:STDOUT:     %.loc16_8.2: type = converted %int.make_type_32.loc16, %.loc16_8.1 [template = i32]

toolchain/check/testdata/interface/no_prelude/default_fn.carbon

@@ -72,7 +72,7 @@ class C {
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @C {
 // CHECK:STDOUT:   %I.decl: type = interface_decl @I [template = constants.%.1] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %I.ref: type = name_ref I, @C.%I.decl [template = constants.%.1]
 // CHECK:STDOUT:   }

toolchain/check/testdata/interface/no_prelude/generic.carbon

@@ -231,12 +231,12 @@ fn G(T:! Generic(B)) {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @C {
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %Simple.ref: %Simple.type = name_ref Simple, file.%Simple.decl [template = constants.%Simple]
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %.loc14_17: type = interface_type @Simple, @Simple(constants.%C) [template = constants.%.8]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.2 {} {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
 // CHECK:STDOUT:     %WithAssocFn.ref: %WithAssocFn.type = name_ref WithAssocFn, file.%WithAssocFn.decl [template = constants.%WithAssocFn]
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %.loc15_22: type = interface_type @WithAssocFn, @WithAssocFn(constants.%C) [template = constants.%.10]

toolchain/check/testdata/interface/no_prelude/generic_import.carbon

@@ -134,7 +134,7 @@ impl C as AddWith(C) {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %default.import = import <invalid>
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %C.ref.loc7_6: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %AddWith.ref: %AddWith.type = name_ref AddWith, imports.%import_ref.1 [template = constants.%AddWith]
 // CHECK:STDOUT:     %C.ref.loc7_19: type = name_ref C, file.%C.decl [template = constants.%C]

toolchain/check/testdata/interface/no_prelude/generic_vs_params.carbon

@@ -108,29 +108,29 @@ interface A(T: type) {}
 // CHECK:STDOUT:     %T.loc8: type = bind_symbolic_name T 0, %T.param [symbolic = %T.1 (constants.%T)]
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %X.decl: type = class_decl @X [template = constants.%X] {} {}
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %X.ref: type = name_ref X, file.%X.decl [template = constants.%X]
 // CHECK:STDOUT:     %NotGenericNoParams.ref: type = name_ref NotGenericNoParams, file.%NotGenericNoParams.decl [template = constants.%.1]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.2 {} {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
 // CHECK:STDOUT:     %X.ref: type = name_ref X, file.%X.decl [template = constants.%X]
 // CHECK:STDOUT:     %NotGenericButParams.ref: %NotGenericButParams.type = name_ref NotGenericButParams, file.%NotGenericButParams.decl [template = constants.%NotGenericButParams]
 // CHECK:STDOUT:     %.loc15_30: type = interface_type @NotGenericButParams [template = constants.%.3]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.3 {} {
+// CHECK:STDOUT:   impl_decl @impl.3 [template] {} {
 // CHECK:STDOUT:     %X.ref.loc16_6: type = name_ref X, file.%X.decl [template = constants.%X]
 // CHECK:STDOUT:     %GenericAndParams.ref: %GenericAndParams.type.1 = name_ref GenericAndParams, file.%GenericAndParams.decl [template = constants.%GenericAndParams.1]
 // CHECK:STDOUT:     %X.ref.loc16_28: type = name_ref X, file.%X.decl [template = constants.%X]
 // CHECK:STDOUT:     %.loc16_27: type = interface_type @GenericAndParams.1, @GenericAndParams.1(constants.%X) [template = constants.%.11]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.4 {} {
+// CHECK:STDOUT:   impl_decl @impl.4 [template] {} {
 // CHECK:STDOUT:     %X.ref.loc17_6: type = name_ref X, file.%X.decl [template = constants.%X]
 // CHECK:STDOUT:     %C.ref: %C.type = name_ref C, file.%C.decl [template = constants.%C.1]
 // CHECK:STDOUT:     %X.ref.loc17_13: type = name_ref X, file.%X.decl [template = constants.%X]
 // CHECK:STDOUT:     %C: type = class_type @C, @C(constants.%X) [template = constants.%C.3]
 // CHECK:STDOUT:     %GenericNoParams.ref: type = name_ref GenericNoParams, @C.%GenericNoParams.decl [template = constants.%.5]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.5 {} {
+// CHECK:STDOUT:   impl_decl @impl.5 [template] {} {
 // CHECK:STDOUT:     %X.ref.loc18_6: type = name_ref X, file.%X.decl [template = constants.%X]
 // CHECK:STDOUT:     %C.ref: %C.type = name_ref C, file.%C.decl [template = constants.%C.1]
 // CHECK:STDOUT:     %X.ref.loc18_13: type = name_ref X, file.%X.decl [template = constants.%X]

toolchain/check/testdata/interface/no_prelude/import_interface_decl.carbon

@@ -29,7 +29,7 @@ impl library "[[@TEST_NAME]]";
 // CHECK:STDOUT:     .A = %A.decl
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %A.decl: type = interface_decl @A [template = constants.%.1] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %.loc3_7.1: %.2 = tuple_literal ()
 // CHECK:STDOUT:     %.loc3_7.2: type = converted %.loc3_7.1, constants.%.2 [template = constants.%.2]
 // CHECK:STDOUT:     %A.ref: type = name_ref A, file.%A.decl [template = constants.%.1]

toolchain/check/testdata/operators/overloaded/add.carbon

@@ -100,12 +100,12 @@ fn TestAssign(a: C*, b: C) {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %Add.ref: type = name_ref Add, imports.%import_ref.1 [template = constants.%.3]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.2 {} {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %AddAssign.ref: type = name_ref AddAssign, imports.%import_ref.5 [template = constants.%.7]

toolchain/check/testdata/operators/overloaded/bit_and.carbon

@@ -100,12 +100,12 @@ fn TestAssign(a: C*, b: C) {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %BitAnd.ref: type = name_ref BitAnd, imports.%import_ref.1 [template = constants.%.3]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.2 {} {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %BitAndAssign.ref: type = name_ref BitAndAssign, imports.%import_ref.5 [template = constants.%.7]

toolchain/check/testdata/operators/overloaded/bit_complement.carbon

@@ -73,7 +73,7 @@ fn TestOp(a: C) -> C {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %BitComplement.ref: type = name_ref BitComplement, imports.%import_ref.1 [template = constants.%.3]

toolchain/check/testdata/operators/overloaded/bit_or.carbon

@@ -100,12 +100,12 @@ fn TestAssign(a: C*, b: C) {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %BitOr.ref: type = name_ref BitOr, imports.%import_ref.1 [template = constants.%.3]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.2 {} {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %BitOrAssign.ref: type = name_ref BitOrAssign, imports.%import_ref.5 [template = constants.%.7]

toolchain/check/testdata/operators/overloaded/bit_xor.carbon

@@ -100,12 +100,12 @@ fn TestAssign(a: C*, b: C) {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %BitXor.ref: type = name_ref BitXor, imports.%import_ref.1 [template = constants.%.3]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.2 {} {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %BitXorAssign.ref: type = name_ref BitXorAssign, imports.%import_ref.5 [template = constants.%.7]

toolchain/check/testdata/operators/overloaded/dec.carbon

@@ -74,7 +74,7 @@ fn TestOp() {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %Dec.ref: type = name_ref Dec, imports.%import_ref.1 [template = constants.%.3]

toolchain/check/testdata/operators/overloaded/div.carbon

@@ -100,12 +100,12 @@ fn TestAssign(a: C*, b: C) {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %Div.ref: type = name_ref Div, imports.%import_ref.1 [template = constants.%.3]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.2 {} {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %DivAssign.ref: type = name_ref DivAssign, imports.%import_ref.5 [template = constants.%.7]

toolchain/check/testdata/operators/overloaded/eq.carbon

@@ -146,7 +146,7 @@ fn TestLhsBad(a: D, b: C) -> bool {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %Eq.ref: type = name_ref Eq, imports.%import_ref.1 [template = constants.%.3]
@@ -531,7 +531,7 @@ fn TestLhsBad(a: D, b: C) -> bool {
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
 // CHECK:STDOUT:   %D.decl: type = class_decl @D [template = constants.%D] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %Eq.ref: type = name_ref Eq, imports.%import_ref.1 [template = constants.%.3]

toolchain/check/testdata/operators/overloaded/fail_assign_non_ref.carbon

@@ -109,12 +109,12 @@ fn TestAddAssignNonRef(a: C, b: C) {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %Inc.ref: type = name_ref Inc, imports.%import_ref.1 [template = constants.%.3]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.2 {} {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %AddAssign.ref: type = name_ref AddAssign, imports.%import_ref.5 [template = constants.%.8]

toolchain/check/testdata/operators/overloaded/fail_no_impl_for_arg.carbon

@@ -143,12 +143,12 @@ fn TestAssign(b: D) {
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
 // CHECK:STDOUT:   %D.decl: type = class_decl @D [template = constants.%D] {} {}
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %Add.ref: type = name_ref Add, imports.%import_ref.1 [template = constants.%.3]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.2 {} {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %AddAssign.ref: type = name_ref AddAssign, imports.%import_ref.5 [template = constants.%.6]

toolchain/check/testdata/operators/overloaded/implicit_as.carbon

@@ -113,7 +113,7 @@ fn Test() {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %X.decl: type = class_decl @X [template = constants.%X] {} {}
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %int.make_type_32: init type = call constants.%Int32() [template = i32]
 // CHECK:STDOUT:     %.loc15_6.1: type = value_of_initializer %int.make_type_32 [template = i32]
 // CHECK:STDOUT:     %.loc15_6.2: type = converted %int.make_type_32, %.loc15_6.1 [template = i32]
@@ -122,7 +122,7 @@ fn Test() {
 // CHECK:STDOUT:     %X.ref: type = name_ref X, file.%X.decl [template = constants.%X]
 // CHECK:STDOUT:     %.loc15_28: type = interface_type @ImplicitAs, @ImplicitAs(constants.%X) [template = constants.%.8]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.2 {} {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
 // CHECK:STDOUT:     %X.ref: type = name_ref X, file.%X.decl [template = constants.%X]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %ImplicitAs.ref: %ImplicitAs.type = name_ref ImplicitAs, imports.%import_ref.2 [template = constants.%ImplicitAs]

toolchain/check/testdata/operators/overloaded/inc.carbon

@@ -74,7 +74,7 @@ fn TestOp() {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %Inc.ref: type = name_ref Inc, imports.%import_ref.1 [template = constants.%.3]

toolchain/check/testdata/operators/overloaded/left_shift.carbon

@@ -100,12 +100,12 @@ fn TestAssign(a: C*, b: C) {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %LeftShift.ref: type = name_ref LeftShift, imports.%import_ref.1 [template = constants.%.3]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.2 {} {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %LeftShiftAssign.ref: type = name_ref LeftShiftAssign, imports.%import_ref.5 [template = constants.%.7]

toolchain/check/testdata/operators/overloaded/mod.carbon

@@ -100,12 +100,12 @@ fn TestAssign(a: C*, b: C) {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %Mod.ref: type = name_ref Mod, imports.%import_ref.1 [template = constants.%.3]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.2 {} {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %ModAssign.ref: type = name_ref ModAssign, imports.%import_ref.5 [template = constants.%.7]

toolchain/check/testdata/operators/overloaded/mul.carbon

@@ -100,12 +100,12 @@ fn TestAssign(a: C*, b: C) {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %Mul.ref: type = name_ref Mul, imports.%import_ref.1 [template = constants.%.3]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.2 {} {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %MulAssign.ref: type = name_ref MulAssign, imports.%import_ref.5 [template = constants.%.7]

toolchain/check/testdata/operators/overloaded/negate.carbon

@@ -73,7 +73,7 @@ fn TestOp(a: C) -> C {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %Negate.ref: type = name_ref Negate, imports.%import_ref.1 [template = constants.%.3]

toolchain/check/testdata/operators/overloaded/ordered.carbon

@@ -162,7 +162,7 @@ fn TestGreaterEqual(a: D, b: D) -> bool {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %Ordered.ref: type = name_ref Ordered, imports.%import_ref.1 [template = constants.%.3]

toolchain/check/testdata/operators/overloaded/right_shift.carbon

@@ -100,12 +100,12 @@ fn TestAssign(a: C*, b: C) {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %RightShift.ref: type = name_ref RightShift, imports.%import_ref.1 [template = constants.%.3]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.2 {} {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %RightShiftAssign.ref: type = name_ref RightShiftAssign, imports.%import_ref.5 [template = constants.%.7]

toolchain/check/testdata/operators/overloaded/sub.carbon

@@ -100,12 +100,12 @@ fn TestAssign(a: C*, b: C) {
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl.1 {} {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %Sub.ref: type = name_ref Sub, imports.%import_ref.1 [template = constants.%.3]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   impl_decl @impl.2 {} {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %Core.ref: <namespace> = name_ref Core, imports.%Core [template = imports.%Core]
 // CHECK:STDOUT:     %SubAssign.ref: type = name_ref SubAssign, imports.%import_ref.5 [template = constants.%.7]

toolchain/check/testdata/where_expr/constraints.carbon

@@ -428,7 +428,7 @@ fn NotEmptyStruct() {
 // CHECK:STDOUT:   %Core.import = import Core
 // CHECK:STDOUT:   %default.import = import <invalid>
 // CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
-// CHECK:STDOUT:   impl_decl @impl {} {
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [template = constants.%C]
 // CHECK:STDOUT:     %J.ref: type = name_ref J, imports.%import_ref.1 [template = constants.%.3]
 // CHECK:STDOUT:   }

toolchain/lower/constant.cpp

@@ -9,7 +9,6 @@
 #include "llvm/IR/Value.h"
 #include "toolchain/base/kind_switch.h"
 #include "toolchain/lower/file_context.h"
-#include "toolchain/sem_ir/generic.h"
 #include "toolchain/sem_ir/inst.h"
 #include "toolchain/sem_ir/typed_insts.h"
 
@@ -198,6 +197,13 @@ static auto EmitAsConstant(ConstantContext& context,
   return context.GetUnusedConstant(inst.type_id);
 }
 
+static auto EmitAsConstant(ConstantContext& /*context*/,
+                           SemIR::ImplDecl /*inst*/) -> llvm::Constant* {
+  // An ImplDecl isn't a value, so this constant value won't ever be used.
+  // It also doesn't even have a type, so we can't use GetUnusedConstant.
+  return nullptr;
+}
+
 static auto EmitAsConstant(ConstantContext& context, SemIR::IntLiteral inst)
     -> llvm::Constant* {
   return llvm::ConstantInt::get(context.GetType(inst.type_id),

toolchain/sem_ir/typed_insts.h

@@ -646,7 +646,9 @@ struct GenericInterfaceType {
 // An `impl` declaration.
 struct ImplDecl {
   static constexpr auto Kind = InstKind::ImplDecl.Define<Parse::AnyImplDeclId>(
-      {.ir_name = "impl_decl", .is_lowered = false});
+      {.ir_name = "impl_decl",
+       .constant_kind = InstConstantKind::Always,
+       .is_lowered = false});
 
   // No type: an impl declaration is not a value.
   ImplId impl_id;