Diagnose `partial` applied to final types. (#5744)

Is it worth having a distinct diagnostic or phrasing for non-class types
(like tuples, structs, pointers, etc), also for declared-but-not-defined
class types (where we can't tell if they're final or not)? Happy to add
it, but not sure how much detail to put in here at this stage at least.

I chose "non-final type" as somewhat vague wording so it sort of applies
even to pointers/tuples/structs.

toolchain/check/handle_operator.cpp

@@ -314,6 +314,17 @@ auto HandleParseNode(Context& context, Parse::PrefixOperatorPartialId node_id)
     -> bool {
   auto value_id = context.node_stack().PopExpr();
   auto inner_type = ExprAsType(context, node_id, value_id);
+  auto class_type =
+      context.types().TryGetAs<SemIR::ClassType>(inner_type.type_id);
+
+  if (!class_type ||
+      context.classes().Get(class_type->class_id).inheritance_kind ==
+          SemIR::Class::InheritanceKind::Final) {
+    CARBON_DIAGNOSTIC(PartialOnFinal, Error,
+                      "`partial` applied to final type {0}", SemIR::TypeId);
+    context.emitter().Emit(node_id, PartialOnFinal, inner_type.type_id);
+  }
+
   // TODO: Add diagnostics for partial applied to non-base/abstract types.
   AddInstAndPush<SemIR::PartialType>(
       context, node_id,

toolchain/check/testdata/class/partial.carbon

@@ -28,16 +28,20 @@ abstract class C { }
 fn A(p: partial C);
 //@dump-sem-ir-end
 
-// --- todo_fail_partial_nondynamic.carbon
+// --- fail_partial_nondynamic.carbon
 library "[[@TEST_NAME]]";
 
 class C { }
 
 //@dump-sem-ir-begin
+// CHECK:STDERR: fail_partial_nondynamic.carbon:[[@LINE+4]]:9: error: `partial` applied to final type `C` [PartialOnFinal]
+// CHECK:STDERR: fn G(p: partial C);
+// CHECK:STDERR:         ^~~~~~~~~
+// CHECK:STDERR:
 fn G(p: partial C);
 //@dump-sem-ir-end
 
-// --- todo_fail_partial_final.carbon
+// --- fail_partial_final.carbon
 library "[[@TEST_NAME]]";
 
 base class Base { }
@@ -46,42 +50,65 @@ class Derived {
 }
 
 //@dump-sem-ir-begin
+// CHECK:STDERR: fail_partial_final.carbon:[[@LINE+4]]:9: error: `partial` applied to final type `Derived` [PartialOnFinal]
+// CHECK:STDERR: fn G(p: partial Derived);
+// CHECK:STDERR:         ^~~~~~~~~~~~~~~
+// CHECK:STDERR:
 fn G(p: partial Derived);
 //@dump-sem-ir-end
 
-// --- todo_fail_partial_decl.carbon
+// --- fail_partial_decl.carbon
 library "[[@TEST_NAME]]";
 
 class C;
 
+// TODO: This diagnostic could be more specific - the type might be non-final,
+// but since we only have a declaration, we don't know.
 //@dump-sem-ir-begin
+// applied to final type `C` [PartialOnFinal] CHECK:STDERR: fn G(p: partial C);
+// CHECK:STDERR: fail_partial_decl.carbon:[[@LINE+4]]:9: error: `partial` applied to final type `C` [PartialOnFinal]
+// CHECK:STDERR: fn G(p: partial C);
+// CHECK:STDERR:         ^~~~~~~~~
+// CHECK:STDERR:
 fn G(p: partial C);
 //@dump-sem-ir-end
 
-// --- todo_fail_partial_tuple.carbon
+// --- fail_partial_tuple.carbon
 library "[[@TEST_NAME]]";
 
 class C;
 
 //@dump-sem-ir-begin
+// CHECK:STDERR: fail_partial_tuple.carbon:[[@LINE+4]]:9: error: `partial` applied to final type `(C, C)` [PartialOnFinal]
+// CHECK:STDERR: fn G(p: partial (C, C));
+// CHECK:STDERR:         ^~~~~~~~~~~~~~
+// CHECK:STDERR:
 fn G(p: partial (C, C));
 //@dump-sem-ir-end
 
-// --- todo_fail_partial_struct.carbon
+// --- fail_partial_struct.carbon
 library "[[@TEST_NAME]]";
 
 class C;
 
 //@dump-sem-ir-begin
+// CHECK:STDERR: fail_partial_struct.carbon:[[@LINE+4]]:9: error: `partial` applied to final type `{.x: C}` [PartialOnFinal]
+// CHECK:STDERR: fn G(p: partial {.x: C});
+// CHECK:STDERR:         ^~~~~~~~~~~~~~~
+// CHECK:STDERR:
 fn G(p: partial {.x: C});
 //@dump-sem-ir-end
 
-// --- todo_fail_duplicate.carbon
+// --- fail_duplicate.carbon
 library "[[@TEST_NAME]]";
 
 base class C { }
 
 //@dump-sem-ir-begin
+// CHECK:STDERR: fail_duplicate.carbon:[[@LINE+4]]:9: error: `partial` applied to final type `partial C` [PartialOnFinal]
+// CHECK:STDERR: fn F(p: partial (partial C));
+// CHECK:STDERR:         ^~~~~~~~~~~~~~~~~~~
+// CHECK:STDERR:
 fn F(p: partial (partial C));
 //@dump-sem-ir-end
 
@@ -101,6 +128,44 @@ fn G(p: partial C*) -> C* {
   return p;
 }
 
+// --- fail_derive_from_partial.carbon
+library "[[@TEST_NAME]]";
+
+base class C { }
+
+class Derived {
+  // CHECK:STDERR: fail_derive_from_partial.carbon:[[@LINE+4]]:16: error: deriving from final type `partial C`; base type must be an `abstract` or `base` class [BaseIsFinal]
+  // CHECK:STDERR:   extend base: partial C;
+  // CHECK:STDERR:                ^~~~~~~~~
+  // CHECK:STDERR:
+  extend base: partial C;
+}
+
+// --- fail_todo_partial_template_dependent.carbon
+library "[[@TEST_NAME]]";
+
+// TODO: This should be accepted because `T` might be final once we know what it
+// is.
+
+// CHECK:STDERR: fail_todo_partial_template_dependent.carbon:[[@LINE+4]]:28: error: `partial` applied to final type `T` [PartialOnFinal]
+// CHECK:STDERR: fn G[template T:! type](p: partial T*);
+// CHECK:STDERR:                            ^~~~~~~~~
+// CHECK:STDERR:
+fn G[template T:! type](p: partial T*);
+
+// --- fail_partial_generic.carbon
+library "[[@TEST_NAME]]";
+
+// TODO: Maybe rephrase this to use some common/generic phrasing to refer to the
+// generic type and its requirements, as distinct from the concrete type that
+// might be used here in any specific.
+
+// CHECK:STDERR: fail_partial_generic.carbon:[[@LINE+4]]:19: error: `partial` applied to final type `T` [PartialOnFinal]
+// CHECK:STDERR: fn F[T:! type](p: partial T*);
+// CHECK:STDERR:                   ^~~~~~~~~
+// CHECK:STDERR:
+fn F[T:! type](p: partial T*);
+
 // CHECK:STDOUT: --- base.carbon
 // CHECK:STDOUT:
 // CHECK:STDOUT: constants {
@@ -159,7 +224,7 @@ fn G(p: partial C*) -> C* {
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @A(%p.param: %.43f);
 // CHECK:STDOUT:
-// CHECK:STDOUT: --- todo_fail_partial_nondynamic.carbon
+// CHECK:STDOUT: --- fail_partial_nondynamic.carbon
 // CHECK:STDOUT:
 // CHECK:STDOUT: constants {
 // CHECK:STDOUT:   %C: type = class_type @C [concrete]
@@ -178,9 +243,9 @@ fn G(p: partial C*) -> C* {
 // CHECK:STDOUT:     %p.param_patt: %pattern_type = value_param_pattern %p.patt, call_param0 [concrete]
 // CHECK:STDOUT:   } {
 // CHECK:STDOUT:     %p.param: %.43f = value_param call_param0
-// CHECK:STDOUT:     %.loc6_9.1: type = splice_block %.loc6_9.2 [concrete = constants.%.43f] {
+// CHECK:STDOUT:     %.loc10_9.1: type = splice_block %.loc10_9.2 [concrete = constants.%.43f] {
 // CHECK:STDOUT:       %C.ref: type = name_ref C, file.%C.decl [concrete = constants.%C]
-// CHECK:STDOUT:       %.loc6_9.2: type = partial_type %C.ref [concrete = constants.%.43f]
+// CHECK:STDOUT:       %.loc10_9.2: type = partial_type %C.ref [concrete = constants.%.43f]
 // CHECK:STDOUT:     }
 // CHECK:STDOUT:     %p: %.43f = bind_name p, %p.param
 // CHECK:STDOUT:   }
@@ -188,7 +253,7 @@ fn G(p: partial C*) -> C* {
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @G(%p.param: %.43f);
 // CHECK:STDOUT:
-// CHECK:STDOUT: --- todo_fail_partial_final.carbon
+// CHECK:STDOUT: --- fail_partial_final.carbon
 // CHECK:STDOUT:
 // CHECK:STDOUT: constants {
 // CHECK:STDOUT:   %Derived: type = class_type @Derived [concrete]
@@ -207,9 +272,9 @@ fn G(p: partial C*) -> C* {
 // CHECK:STDOUT:     %p.param_patt: %pattern_type = value_param_pattern %p.patt, call_param0 [concrete]
 // CHECK:STDOUT:   } {
 // CHECK:STDOUT:     %p.param: %.604 = value_param call_param0
-// CHECK:STDOUT:     %.loc9_9.1: type = splice_block %.loc9_9.2 [concrete = constants.%.604] {
+// CHECK:STDOUT:     %.loc13_9.1: type = splice_block %.loc13_9.2 [concrete = constants.%.604] {
 // CHECK:STDOUT:       %Derived.ref: type = name_ref Derived, file.%Derived.decl [concrete = constants.%Derived]
-// CHECK:STDOUT:       %.loc9_9.2: type = partial_type %Derived.ref [concrete = constants.%.604]
+// CHECK:STDOUT:       %.loc13_9.2: type = partial_type %Derived.ref [concrete = constants.%.604]
 // CHECK:STDOUT:     }
 // CHECK:STDOUT:     %p: %.604 = bind_name p, %p.param
 // CHECK:STDOUT:   }
@@ -217,7 +282,7 @@ fn G(p: partial C*) -> C* {
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @G(%p.param: %.604);
 // CHECK:STDOUT:
-// CHECK:STDOUT: --- todo_fail_partial_decl.carbon
+// CHECK:STDOUT: --- fail_partial_decl.carbon
 // CHECK:STDOUT:
 // CHECK:STDOUT: constants {
 // CHECK:STDOUT:   %C: type = class_type @C [concrete]
@@ -236,9 +301,9 @@ fn G(p: partial C*) -> C* {
 // CHECK:STDOUT:     %p.param_patt: %pattern_type = value_param_pattern %p.patt, call_param0 [concrete]
 // CHECK:STDOUT:   } {
 // CHECK:STDOUT:     %p.param: %.43f = value_param call_param0
-// CHECK:STDOUT:     %.loc6_9.1: type = splice_block %.loc6_9.2 [concrete = constants.%.43f] {
+// CHECK:STDOUT:     %.loc13_9.1: type = splice_block %.loc13_9.2 [concrete = constants.%.43f] {
 // CHECK:STDOUT:       %C.ref: type = name_ref C, file.%C.decl [concrete = constants.%C]
-// CHECK:STDOUT:       %.loc6_9.2: type = partial_type %C.ref [concrete = constants.%.43f]
+// CHECK:STDOUT:       %.loc13_9.2: type = partial_type %C.ref [concrete = constants.%.43f]
 // CHECK:STDOUT:     }
 // CHECK:STDOUT:     %p: %.43f = bind_name p, %p.param
 // CHECK:STDOUT:   }
@@ -246,7 +311,7 @@ fn G(p: partial C*) -> C* {
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @G(%p.param: %.43f);
 // CHECK:STDOUT:
-// CHECK:STDOUT: --- todo_fail_partial_tuple.carbon
+// CHECK:STDOUT: --- fail_partial_tuple.carbon
 // CHECK:STDOUT:
 // CHECK:STDOUT: constants {
 // CHECK:STDOUT:   %C: type = class_type @C [concrete]
@@ -267,12 +332,12 @@ fn G(p: partial C*) -> C* {
 // CHECK:STDOUT:     %p.param_patt: %pattern_type = value_param_pattern %p.patt, call_param0 [concrete]
 // CHECK:STDOUT:   } {
 // CHECK:STDOUT:     %p.param: %.62c = value_param call_param0
-// CHECK:STDOUT:     %.loc6_9.1: type = splice_block %.loc6_9.3 [concrete = constants.%.62c] {
-// CHECK:STDOUT:       %C.ref.loc6_18: type = name_ref C, file.%C.decl [concrete = constants.%C]
-// CHECK:STDOUT:       %C.ref.loc6_21: type = name_ref C, file.%C.decl [concrete = constants.%C]
-// CHECK:STDOUT:       %.loc6_22: %tuple.type.24b = tuple_literal (%C.ref.loc6_18, %C.ref.loc6_21)
-// CHECK:STDOUT:       %.loc6_9.2: type = converted %.loc6_22, constants.%tuple.type.56b [concrete = constants.%tuple.type.56b]
-// CHECK:STDOUT:       %.loc6_9.3: type = partial_type %.loc6_9.2 [concrete = constants.%.62c]
+// CHECK:STDOUT:     %.loc10_9.1: type = splice_block %.loc10_9.3 [concrete = constants.%.62c] {
+// CHECK:STDOUT:       %C.ref.loc10_18: type = name_ref C, file.%C.decl [concrete = constants.%C]
+// CHECK:STDOUT:       %C.ref.loc10_21: type = name_ref C, file.%C.decl [concrete = constants.%C]
+// CHECK:STDOUT:       %.loc10_22: %tuple.type.24b = tuple_literal (%C.ref.loc10_18, %C.ref.loc10_21)
+// CHECK:STDOUT:       %.loc10_9.2: type = converted %.loc10_22, constants.%tuple.type.56b [concrete = constants.%tuple.type.56b]
+// CHECK:STDOUT:       %.loc10_9.3: type = partial_type %.loc10_9.2 [concrete = constants.%.62c]
 // CHECK:STDOUT:     }
 // CHECK:STDOUT:     %p: %.62c = bind_name p, %p.param
 // CHECK:STDOUT:   }
@@ -280,7 +345,7 @@ fn G(p: partial C*) -> C* {
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @G(%p.param: %.62c);
 // CHECK:STDOUT:
-// CHECK:STDOUT: --- todo_fail_partial_struct.carbon
+// CHECK:STDOUT: --- fail_partial_struct.carbon
 // CHECK:STDOUT:
 // CHECK:STDOUT: constants {
 // CHECK:STDOUT:   %C: type = class_type @C [concrete]
@@ -300,10 +365,10 @@ fn G(p: partial C*) -> C* {
 // CHECK:STDOUT:     %p.param_patt: %pattern_type = value_param_pattern %p.patt, call_param0 [concrete]
 // CHECK:STDOUT:   } {
 // CHECK:STDOUT:     %p.param: %.1ed = value_param call_param0
-// CHECK:STDOUT:     %.loc6_9.1: type = splice_block %.loc6_9.2 [concrete = constants.%.1ed] {
+// CHECK:STDOUT:     %.loc10_9.1: type = splice_block %.loc10_9.2 [concrete = constants.%.1ed] {
 // CHECK:STDOUT:       %C.ref: type = name_ref C, file.%C.decl [concrete = constants.%C]
 // CHECK:STDOUT:       %struct_type.x: type = struct_type {.x: %C} [concrete = constants.%struct_type.x]
-// CHECK:STDOUT:       %.loc6_9.2: type = partial_type %struct_type.x [concrete = constants.%.1ed]
+// CHECK:STDOUT:       %.loc10_9.2: type = partial_type %struct_type.x [concrete = constants.%.1ed]
 // CHECK:STDOUT:     }
 // CHECK:STDOUT:     %p: %.1ed = bind_name p, %p.param
 // CHECK:STDOUT:   }
@@ -311,7 +376,7 @@ fn G(p: partial C*) -> C* {
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @G(%p.param: %.1ed);
 // CHECK:STDOUT:
-// CHECK:STDOUT: --- todo_fail_duplicate.carbon
+// CHECK:STDOUT: --- fail_duplicate.carbon
 // CHECK:STDOUT:
 // CHECK:STDOUT: constants {
 // CHECK:STDOUT:   %C: type = class_type @C [concrete]
@@ -331,10 +396,10 @@ fn G(p: partial C*) -> C* {
 // CHECK:STDOUT:     %p.param_patt: %pattern_type = value_param_pattern %p.patt, call_param0 [concrete]
 // CHECK:STDOUT:   } {
 // CHECK:STDOUT:     %p.param: %.a34 = value_param call_param0
-// CHECK:STDOUT:     %.loc6_9.1: type = splice_block %.loc6_9.2 [concrete = constants.%.a34] {
+// CHECK:STDOUT:     %.loc10_9.1: type = splice_block %.loc10_9.2 [concrete = constants.%.a34] {
 // CHECK:STDOUT:       %C.ref: type = name_ref C, file.%C.decl [concrete = constants.%C]
-// CHECK:STDOUT:       %.loc6_18: type = partial_type %C.ref [concrete = constants.%.43f]
-// CHECK:STDOUT:       %.loc6_9.2: type = partial_type %.loc6_18 [concrete = constants.%.a34]
+// CHECK:STDOUT:       %.loc10_18: type = partial_type %C.ref [concrete = constants.%.43f]
+// CHECK:STDOUT:       %.loc10_9.2: type = partial_type %.loc10_18 [concrete = constants.%.a34]
 // CHECK:STDOUT:     }
 // CHECK:STDOUT:     %p: %.a34 = bind_name p, %p.param
 // CHECK:STDOUT:   }

toolchain/diagnostics/diagnostic_kind.def

@@ -425,6 +425,7 @@ CARBON_DIAGNOSTIC_KIND(TupleIndexNotConstant)
 CARBON_DIAGNOSTIC_KIND(TupleIndexOnANonTupleType)
 CARBON_DIAGNOSTIC_KIND(TupleIndexOutOfBounds)
 CARBON_DIAGNOSTIC_KIND(TupleInitElementCountMismatch)
+CARBON_DIAGNOSTIC_KIND(PartialOnFinal)
 CARBON_DIAGNOSTIC_KIND(ReturnedVarHere)
 CARBON_DIAGNOSTIC_KIND(ReturnedVarShadowed)
 CARBON_DIAGNOSTIC_KIND(ReturnedVarWithNoReturnType)