disallow impl without base (#4583)

toolchain/check/handle_function.cpp

@@ -212,6 +212,11 @@ static auto BuildFunctionDecl(Context& context,
       parent_scope_inst) {
     if (auto class_decl = parent_scope_inst->TryAs<SemIR::ClassDecl>()) {
       auto& class_info = context.classes().Get(class_decl->class_id);
+      if (virtual_modifier == SemIR::Function::VirtualModifier::Impl &&
+          !class_info.base_id.is_valid()) {
+        CARBON_DIAGNOSTIC(ImplWithoutBase, Error, "impl without base class");
+        context.emitter().Build(node_id, ImplWithoutBase).Emit();
+      }
       // TODO: If this is an `impl` function, check there's a matching base
       // function that's impl or virtual.
       class_info.is_dynamic = true;

toolchain/check/testdata/class/virtual_modifiers.carbon

@@ -14,16 +14,12 @@ package Modifiers;
 
 base class Base {
   virtual fn H();
-
-  impl fn I();
 }
 
 abstract class Abstract {
   abstract fn J();
 
   virtual fn K();
-
-  impl fn L();
 }
 
 // --- todo_fail_later_base.carbon
@@ -47,6 +43,48 @@ fn F() {
   var v: Modifiers.Base = {};
 }
 
+// --- impl_abstract.carbon
+
+package ImplAbstract;
+
+abstract class A1 {
+  virtual fn F();
+}
+
+abstract class A2 {
+  extend base: A1;
+  impl fn F();
+}
+
+// --- impl_base.carbon
+
+package ImplBase;
+
+base class B1 {
+  virtual fn F();
+}
+
+base class B2 {
+  extend base: B1;
+  impl fn F();
+}
+
+class C {
+  extend base: B2;
+  impl fn F();
+}
+
+// --- fail_modifiers.carbon
+
+package FailModifiers;
+
+class C {
+  // CHECK:STDERR: fail_modifiers.carbon:[[@LINE+3]]:3: error: impl without base class [ImplWithoutBase]
+  // CHECK:STDERR:   impl fn F();
+  // CHECK:STDERR:   ^~~~~~~~~~~~
+  impl fn F();
+}
+
 // --- init_members.carbon
 
 package InitMembers;
@@ -86,8 +124,6 @@ class Derived {
 // CHECK:STDOUT:   %Base: type = class_type @Base [template]
 // CHECK:STDOUT:   %H.type: type = fn_type @H [template]
 // CHECK:STDOUT:   %H: %H.type = struct_value () [template]
-// CHECK:STDOUT:   %I.type: type = fn_type @I [template]
-// CHECK:STDOUT:   %I: %I.type = struct_value () [template]
 // CHECK:STDOUT:   %.1: type = ptr_type <vtable> [template]
 // CHECK:STDOUT:   %.2: type = struct_type {.<vptr>: %.1} [template]
 // CHECK:STDOUT:   %.3: <witness> = complete_type_witness %.2 [template]
@@ -96,8 +132,6 @@ class Derived {
 // CHECK:STDOUT:   %J: %J.type = struct_value () [template]
 // CHECK:STDOUT:   %K.type: type = fn_type @K [template]
 // CHECK:STDOUT:   %K: %K.type = struct_value () [template]
-// CHECK:STDOUT:   %L.type: type = fn_type @L [template]
-// CHECK:STDOUT:   %L: %L.type = struct_value () [template]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: imports {
@@ -120,38 +154,30 @@ class Derived {
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @Base {
 // CHECK:STDOUT:   %H.decl: %H.type = fn_decl @H [template = constants.%H] {} {}
-// CHECK:STDOUT:   %I.decl: %I.type = fn_decl @I [template = constants.%I] {} {}
-// CHECK:STDOUT:   %.loc8: <witness> = complete_type_witness %.2 [template = constants.%.3]
+// CHECK:STDOUT:   %.loc6: <witness> = complete_type_witness %.2 [template = constants.%.3]
 // CHECK:STDOUT:
 // CHECK:STDOUT: !members:
 // CHECK:STDOUT:   .Self = constants.%Base
 // CHECK:STDOUT:   .H = %H.decl
-// CHECK:STDOUT:   .I = %I.decl
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @Abstract {
 // CHECK:STDOUT:   %J.decl: %J.type = fn_decl @J [template = constants.%J] {} {}
 // CHECK:STDOUT:   %K.decl: %K.type = fn_decl @K [template = constants.%K] {} {}
-// CHECK:STDOUT:   %L.decl: %L.type = fn_decl @L [template = constants.%L] {} {}
-// CHECK:STDOUT:   %.loc16: <witness> = complete_type_witness %.2 [template = constants.%.3]
+// CHECK:STDOUT:   %.loc12: <witness> = complete_type_witness %.2 [template = constants.%.3]
 // CHECK:STDOUT:
 // CHECK:STDOUT: !members:
 // CHECK:STDOUT:   .Self = constants.%Abstract
 // CHECK:STDOUT:   .J = %J.decl
 // CHECK:STDOUT:   .K = %K.decl
-// CHECK:STDOUT:   .L = %L.decl
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: virtual fn @H();
 // CHECK:STDOUT:
-// CHECK:STDOUT: impl fn @I();
-// CHECK:STDOUT:
 // CHECK:STDOUT: abstract fn @J();
 // CHECK:STDOUT:
 // CHECK:STDOUT: virtual fn @K();
 // CHECK:STDOUT:
-// CHECK:STDOUT: impl fn @L();
-// CHECK:STDOUT:
 // CHECK:STDOUT: --- todo_fail_later_base.carbon
 // CHECK:STDOUT:
 // CHECK:STDOUT: constants {
@@ -176,7 +202,6 @@ class Derived {
 // CHECK:STDOUT:   %import_ref.1: type = import_ref Modifiers//default, inst+3, loaded [template = constants.%Base]
 // CHECK:STDOUT:   %import_ref.2 = import_ref Modifiers//default, inst+4, unloaded
 // CHECK:STDOUT:   %import_ref.3 = import_ref Modifiers//default, inst+5, unloaded
-// CHECK:STDOUT:   %import_ref.4 = import_ref Modifiers//default, inst+9, unloaded
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: file {
@@ -208,7 +233,6 @@ class Derived {
 // CHECK:STDOUT: !members:
 // CHECK:STDOUT:   .Self = imports.%import_ref.2
 // CHECK:STDOUT:   .H = imports.%import_ref.3
-// CHECK:STDOUT:   .I = imports.%import_ref.4
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: virtual fn @F();
@@ -234,7 +258,6 @@ class Derived {
 // CHECK:STDOUT:   %import_ref.1: type = import_ref Modifiers//default, inst+3, loaded [template = constants.%Base]
 // CHECK:STDOUT:   %import_ref.2 = import_ref Modifiers//default, inst+4, unloaded
 // CHECK:STDOUT:   %import_ref.3 = import_ref Modifiers//default, inst+5, unloaded
-// CHECK:STDOUT:   %import_ref.4 = import_ref Modifiers//default, inst+9, unloaded
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: file {
@@ -252,7 +275,6 @@ class Derived {
 // CHECK:STDOUT: !members:
 // CHECK:STDOUT:   .Self = imports.%import_ref.2
 // CHECK:STDOUT:   .H = imports.%import_ref.3
-// CHECK:STDOUT:   .I = imports.%import_ref.4
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @F() {
@@ -268,6 +290,189 @@ class Derived {
 // CHECK:STDOUT:   return
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
+// CHECK:STDOUT: --- impl_abstract.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: constants {
+// CHECK:STDOUT:   %A1: type = class_type @A1 [template]
+// CHECK:STDOUT:   %F.type.1: type = fn_type @F.1 [template]
+// CHECK:STDOUT:   %F.1: %F.type.1 = struct_value () [template]
+// CHECK:STDOUT:   %.1: type = ptr_type <vtable> [template]
+// CHECK:STDOUT:   %.2: type = struct_type {.<vptr>: %.1} [template]
+// CHECK:STDOUT:   %.3: <witness> = complete_type_witness %.2 [template]
+// CHECK:STDOUT:   %A2: type = class_type @A2 [template]
+// CHECK:STDOUT:   %.5: type = unbound_element_type %A2, %A1 [template]
+// CHECK:STDOUT:   %F.type.2: type = fn_type @F.2 [template]
+// CHECK:STDOUT:   %F.2: %F.type.2 = struct_value () [template]
+// CHECK:STDOUT:   %.6: type = struct_type {.base: %A1} [template]
+// CHECK:STDOUT:   %.7: <witness> = complete_type_witness %.6 [template]
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: imports {
+// CHECK:STDOUT:   %Core: <namespace> = namespace file.%Core.import, [template] {
+// CHECK:STDOUT:     import Core//prelude
+// CHECK:STDOUT:     import Core//prelude/...
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .Core = imports.%Core
+// CHECK:STDOUT:     .A1 = %A1.decl
+// CHECK:STDOUT:     .A2 = %A2.decl
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Core.import = import Core
+// CHECK:STDOUT:   %A1.decl: type = class_decl @A1 [template = constants.%A1] {} {}
+// CHECK:STDOUT:   %A2.decl: type = class_decl @A2 [template = constants.%A2] {} {}
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: class @A1 {
+// CHECK:STDOUT:   %F.decl: %F.type.1 = fn_decl @F.1 [template = constants.%F.1] {} {}
+// CHECK:STDOUT:   %.loc6: <witness> = complete_type_witness %.2 [template = constants.%.3]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = constants.%A1
+// CHECK:STDOUT:   .F = %F.decl
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: class @A2 {
+// CHECK:STDOUT:   %A1.ref: type = name_ref A1, file.%A1.decl [template = constants.%A1]
+// CHECK:STDOUT:   %.loc9: %.5 = base_decl %A1, element0 [template]
+// CHECK:STDOUT:   %F.decl: %F.type.2 = fn_decl @F.2 [template = constants.%F.2] {} {}
+// CHECK:STDOUT:   %.loc11: <witness> = complete_type_witness %.6 [template = constants.%.7]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = constants.%A2
+// CHECK:STDOUT:   .base = %.loc9
+// CHECK:STDOUT:   .F = %F.decl
+// CHECK:STDOUT:   extend %A1.ref
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: virtual fn @F.1();
+// CHECK:STDOUT:
+// CHECK:STDOUT: impl fn @F.2();
+// CHECK:STDOUT:
+// CHECK:STDOUT: --- impl_base.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: constants {
+// CHECK:STDOUT:   %B1: type = class_type @B1 [template]
+// CHECK:STDOUT:   %F.type.1: type = fn_type @F.1 [template]
+// CHECK:STDOUT:   %F.1: %F.type.1 = struct_value () [template]
+// CHECK:STDOUT:   %.1: type = ptr_type <vtable> [template]
+// CHECK:STDOUT:   %.2: type = struct_type {.<vptr>: %.1} [template]
+// CHECK:STDOUT:   %.3: <witness> = complete_type_witness %.2 [template]
+// CHECK:STDOUT:   %B2: type = class_type @B2 [template]
+// CHECK:STDOUT:   %.5: type = unbound_element_type %B2, %B1 [template]
+// CHECK:STDOUT:   %F.type.2: type = fn_type @F.2 [template]
+// CHECK:STDOUT:   %F.2: %F.type.2 = struct_value () [template]
+// CHECK:STDOUT:   %.6: type = struct_type {.base: %B1} [template]
+// CHECK:STDOUT:   %.7: <witness> = complete_type_witness %.6 [template]
+// CHECK:STDOUT:   %C: type = class_type @C [template]
+// CHECK:STDOUT:   %.10: type = unbound_element_type %C, %B2 [template]
+// CHECK:STDOUT:   %F.type.3: type = fn_type @F.3 [template]
+// CHECK:STDOUT:   %F.3: %F.type.3 = struct_value () [template]
+// CHECK:STDOUT:   %.11: type = struct_type {.base: %B2} [template]
+// CHECK:STDOUT:   %.12: <witness> = complete_type_witness %.11 [template]
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: imports {
+// CHECK:STDOUT:   %Core: <namespace> = namespace file.%Core.import, [template] {
+// CHECK:STDOUT:     import Core//prelude
+// CHECK:STDOUT:     import Core//prelude/...
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .Core = imports.%Core
+// CHECK:STDOUT:     .B1 = %B1.decl
+// CHECK:STDOUT:     .B2 = %B2.decl
+// CHECK:STDOUT:     .C = %C.decl
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Core.import = import Core
+// CHECK:STDOUT:   %B1.decl: type = class_decl @B1 [template = constants.%B1] {} {}
+// CHECK:STDOUT:   %B2.decl: type = class_decl @B2 [template = constants.%B2] {} {}
+// CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: class @B1 {
+// CHECK:STDOUT:   %F.decl: %F.type.1 = fn_decl @F.1 [template = constants.%F.1] {} {}
+// CHECK:STDOUT:   %.loc6: <witness> = complete_type_witness %.2 [template = constants.%.3]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = constants.%B1
+// CHECK:STDOUT:   .F = %F.decl
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: class @B2 {
+// CHECK:STDOUT:   %B1.ref: type = name_ref B1, file.%B1.decl [template = constants.%B1]
+// CHECK:STDOUT:   %.loc9: %.5 = base_decl %B1, element0 [template]
+// CHECK:STDOUT:   %F.decl: %F.type.2 = fn_decl @F.2 [template = constants.%F.2] {} {}
+// CHECK:STDOUT:   %.loc11: <witness> = complete_type_witness %.6 [template = constants.%.7]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = constants.%B2
+// CHECK:STDOUT:   .base = %.loc9
+// CHECK:STDOUT:   .F = %F.decl
+// CHECK:STDOUT:   extend %B1.ref
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: class @C {
+// CHECK:STDOUT:   %B2.ref: type = name_ref B2, file.%B2.decl [template = constants.%B2]
+// CHECK:STDOUT:   %.loc14: %.10 = base_decl %B2, element0 [template]
+// CHECK:STDOUT:   %F.decl: %F.type.3 = fn_decl @F.3 [template = constants.%F.3] {} {}
+// CHECK:STDOUT:   %.loc16: <witness> = complete_type_witness %.11 [template = constants.%.12]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = constants.%C
+// CHECK:STDOUT:   .base = %.loc14
+// CHECK:STDOUT:   .F = %F.decl
+// CHECK:STDOUT:   extend %B2.ref
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: virtual fn @F.1();
+// CHECK:STDOUT:
+// CHECK:STDOUT: impl fn @F.2();
+// CHECK:STDOUT:
+// CHECK:STDOUT: impl fn @F.3();
+// CHECK:STDOUT:
+// CHECK:STDOUT: --- fail_modifiers.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: constants {
+// CHECK:STDOUT:   %C: type = class_type @C [template]
+// CHECK:STDOUT:   %F.type: type = fn_type @F [template]
+// CHECK:STDOUT:   %F: %F.type = struct_value () [template]
+// CHECK:STDOUT:   %.1: type = ptr_type <vtable> [template]
+// CHECK:STDOUT:   %.2: type = struct_type {.<vptr>: %.1} [template]
+// CHECK:STDOUT:   %.3: <witness> = complete_type_witness %.2 [template]
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: imports {
+// CHECK:STDOUT:   %Core: <namespace> = namespace file.%Core.import, [template] {
+// CHECK:STDOUT:     import Core//prelude
+// CHECK:STDOUT:     import Core//prelude/...
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .Core = imports.%Core
+// CHECK:STDOUT:     .C = %C.decl
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Core.import = import Core
+// CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: class @C {
+// CHECK:STDOUT:   %F.decl: %F.type = fn_decl @F [template = constants.%F] {} {}
+// CHECK:STDOUT:   %.loc9: <witness> = complete_type_witness %.2 [template = constants.%.3]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = constants.%C
+// CHECK:STDOUT:   .F = %F.decl
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: impl fn @F();
+// CHECK:STDOUT:
 // CHECK:STDOUT: --- init_members.carbon
 // CHECK:STDOUT:
 // CHECK:STDOUT: constants {

toolchain/diagnostics/diagnostic_kind.def

@@ -225,6 +225,7 @@ CARBON_DIAGNOSTIC_KIND(ClassForwardDeclaredHere)
 CARBON_DIAGNOSTIC_KIND(ClassSpecificDeclOutsideClass)
 CARBON_DIAGNOSTIC_KIND(ClassSpecificDeclPrevious)
 CARBON_DIAGNOSTIC_KIND(ClassIncompleteWithinDefinition)
+CARBON_DIAGNOSTIC_KIND(ImplWithoutBase)
 
 // Deduction.
 CARBON_DIAGNOSTIC_KIND(DeductionIncomplete)