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carbon-lang/toolchain/check/testdata/where_expr/designator.carbon
T
Dana JansensandRichard Smith cc5a42691e Add where T impls X constraints into the FacetTypeInfo (#7038) 
This makes them part of the identified facet type, and we can see the
constraints as part of stringify and format output.

But this does not do enough to make them useful yet: Any `T impls X`
constraint must contain a reference to `.Self` somewhere. And `.Self`
references do not get substituted, so neither `T(.Self) impls X` and `T
impls X(.Self)` will match against an incoming facet value derived from
an `impl T(U) as X` or `impl T as X(U)`, since `U` and `.Self` are never
the same thing until `.Self` can be substituted.

Now that impl lookup runs into facet values containing `.Self` (a
symbolic binding), such as in `C(.Self)`, we were crashing assuming the
type of `.Self` is a FacetType, but it can be `type` in the case of
`type where C(.Self) impls...`. Instead, use an empty facet type for the
type of `.Self` so it is always a facet. This assists with substituting
other facets into it, without having to insert an extra FacetAccessType.
`MakePeriodSelfFacetValue()` now enforces this requirement.

---------

Co-authored-by: Richard Smith <richard@metafoo.co.uk>
2026-04-10 14:29:36 +00:00

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// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
// INCLUDE-FILE: toolchain/testing/testdata/min_prelude/convert.carbon
//
// AUTOUPDATE
// TIP: To test this file alone, run:
// TIP: bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/where_expr/designator.carbon
// TIP: To dump output, run:
// TIP: bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/where_expr/designator.carbon
// --- success.carbon
library "[[@TEST_NAME]]";
interface I {
let Member:! type;
}
//@dump-sem-ir-begin
fn PeriodSelf(T:! I where .Self == ());
fn PeriodMember(U:! I where .Member == ());
fn TypeSelfImpls(V:! type where .Self impls I);
//@dump-sem-ir-end
// --- fail_wrong_member.carbon
library "[[@TEST_NAME]]";
interface J {
let Member:! type;
}
// CHECK:STDERR: fail_wrong_member.carbon:[[@LINE+4]]:31: error: member name `Mismatch` not found in `J` [MemberNameNotFoundInSpecificScope]
// CHECK:STDERR: fn PeriodMismatch(W:! J where .Mismatch = {});
// CHECK:STDERR: ^~~~~~~~~
// CHECK:STDERR:
fn PeriodMismatch(W:! J where .Mismatch = {});
// --- fail_designator_matches_var.carbon
library "[[@TEST_NAME]]";
fn Foo() -> () {
var unused x: ();
// CHECK:STDERR: fail_designator_matches_var.carbon:[[@LINE+5]]:10: error: name `.Self` not found [NameNotFound]
// CHECK:STDERR: return .x;
// CHECK:STDERR: ^~
// CHECK:STDERR: fail_designator_matches_var.carbon: note: designator may only be used when `.Self` is in scope [NoPeriodSelfForDesignator]
// CHECK:STDERR:
return .x;
}
// --- fail_unknown_designator.carbon
library "[[@TEST_NAME]]";
fn Bar() -> () {
// CHECK:STDERR: fail_unknown_designator.carbon:[[@LINE+5]]:10: error: name `.Self` not found [NameNotFound]
// CHECK:STDERR: return .undef;
// CHECK:STDERR: ^~~~~~
// CHECK:STDERR: fail_unknown_designator.carbon: note: designator may only be used when `.Self` is in scope [NoPeriodSelfForDesignator]
// CHECK:STDERR:
return .undef;
}
// --- fail_dot_self_method_return_value.carbon
library "[[@TEST_NAME]]";
class C {
// CHECK:STDERR: fail_dot_self_method_return_value.carbon:[[@LINE+4]]:27: error: name `.Self` not found [NameNotFound]
// CHECK:STDERR: fn F() -> Self { return .Self; }
// CHECK:STDERR: ^~~~~
// CHECK:STDERR:
fn F() -> Self { return .Self; }
}
// --- fail_dot_self_method_return_type.carbon
library "[[@TEST_NAME]]";
class D {
// CHECK:STDERR: fail_dot_self_method_return_type.carbon:[[@LINE+4]]:13: error: name `.Self` not found [NameNotFound]
// CHECK:STDERR: fn G() -> .Self { return Self; }
// CHECK:STDERR: ^~~~~
// CHECK:STDERR:
fn G() -> .Self { return Self; }
}
// --- fail_impls_constraint_does_not_constrain_self.carbon
library "[[@TEST_NAME]]";
interface I {}
// CHECK:STDERR: fail_impls_constraint_does_not_constrain_self.carbon:[[@LINE+4]]:27: error: `where` clause without a designator; expected `.Self` to appear in a requirement, or a member of `.Self` [WhereWithoutDesignator]
// CHECK:STDERR: fn F(U:! type, unused T:! type where U impls I) {}
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
fn F(U:! type, unused T:! type where U impls I) {}
// --- fail_equality_constraint_does_not_constrain_self.carbon
library "[[@TEST_NAME]]";
interface I {
let X:! type;
}
// CHECK:STDERR: fail_equality_constraint_does_not_constrain_self.carbon:[[@LINE+4]]:24: error: `where` clause without a designator; expected `.Self` to appear in a requirement, or a member of `.Self` [WhereWithoutDesignator]
// CHECK:STDERR: fn F(U:! I, unused T:! type where U.X == ()) {}
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
fn F(U:! I, unused T:! type where U.X == ()) {}
// --- fail_combined_constraint_does_not_constrain_self.carbon
library "[[@TEST_NAME]]";
interface I {
let X:! type;
}
// CHECK:STDERR: fail_combined_constraint_does_not_constrain_self.carbon:[[@LINE+4]]:24: error: `where` clause without a designator; expected `.Self` to appear in a requirement, or a member of `.Self` [WhereWithoutDesignator]
// CHECK:STDERR: fn F(U:! I, unused T:! type where U impls I and U.X == ()) {}
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
fn F(U:! I, unused T:! type where U impls I and U.X == ()) {}
// --- impls_constraint_does_constrain_self.carbon
library "[[@TEST_NAME]]";
interface I(T:! type) {}
class C(T:! type);
fn F(unused T:! type where C(.Self) impls I(())) {}
fn G(unused T:! type where C(()) impls I(.Self)) {}
// CHECK:STDOUT: --- success.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
// CHECK:STDOUT: %I.type: type = facet_type <@I> [concrete]
// CHECK:STDOUT: %I.assoc_type: type = assoc_entity_type @I [concrete]
// CHECK:STDOUT: %assoc0: %I.assoc_type = assoc_entity element0, @I.WithSelf.%Member [concrete]
// CHECK:STDOUT: %type: type = facet_type <type> [concrete]
// CHECK:STDOUT: %.Self.c39: %type = symbolic_binding .Self [symbolic_self]
// CHECK:STDOUT: %.Self.1dc: %I.type = symbolic_binding .Self [symbolic_self]
// CHECK:STDOUT: %empty_tuple.type: type = tuple_type () [concrete]
// CHECK:STDOUT: %empty_tuple: %empty_tuple.type = tuple_value () [concrete]
// CHECK:STDOUT: %I_where.type: type = facet_type <@I where TODO> [concrete]
// CHECK:STDOUT: %pattern_type.092: type = pattern_type %I_where.type [concrete]
// CHECK:STDOUT: %T: %I_where.type = symbolic_binding T, 0 [symbolic]
// CHECK:STDOUT: %PeriodSelf.type: type = fn_type @PeriodSelf [concrete]
// CHECK:STDOUT: %PeriodSelf: %PeriodSelf.type = struct_value () [concrete]
// CHECK:STDOUT: %.Self.binding.as_type.15d: type = symbolic_binding_type .Self, %.Self.1dc [symbolic_self]
// CHECK:STDOUT: %I.lookup_impl_witness: <witness> = lookup_impl_witness %.Self.1dc, @I [symbolic_self]
// CHECK:STDOUT: %impl.elem0: type = impl_witness_access %I.lookup_impl_witness, element0 [symbolic_self]
// CHECK:STDOUT: %U: %I_where.type = symbolic_binding U, 0 [symbolic]
// CHECK:STDOUT: %PeriodMember.type: type = fn_type @PeriodMember [concrete]
// CHECK:STDOUT: %PeriodMember: %PeriodMember.type = struct_value () [concrete]
// CHECK:STDOUT: %.Self.binding.as_type.8db: type = symbolic_binding_type .Self, %.Self.c39 [symbolic_self]
// CHECK:STDOUT: %type_where: type = facet_type <type where .Self impls @I> [concrete]
// CHECK:STDOUT: %pattern_type.17f: type = pattern_type %type_where [concrete]
// CHECK:STDOUT: %V: %type_where = symbolic_binding V, 0 [symbolic]
// CHECK:STDOUT: %TypeSelfImpls.type: type = fn_type @TypeSelfImpls [concrete]
// CHECK:STDOUT: %TypeSelfImpls: %TypeSelfImpls.type = struct_value () [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: file {
// CHECK:STDOUT: %PeriodSelf.decl: %PeriodSelf.type = fn_decl @PeriodSelf [concrete = constants.%PeriodSelf] {
// CHECK:STDOUT: %T.patt: %pattern_type.092 = symbolic_binding_pattern T, 0 [concrete]
// CHECK:STDOUT: } {
// CHECK:STDOUT: %.loc9_21.1: type = splice_block %.loc9_21.2 [concrete = constants.%I_where.type] {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: %I.ref: type = name_ref I, file.%I.decl [concrete = constants.%I.type]
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: %.Self.ref: %I.type = name_ref .Self, %.Self.2 [symbolic_self = constants.%.Self.1dc]
// CHECK:STDOUT: %.loc9_37: %empty_tuple.type = tuple_literal () [concrete = constants.%empty_tuple]
// CHECK:STDOUT: %.loc9_21.2: type = where_expr %.Self.2 [concrete = constants.%I_where.type] {
// CHECK:STDOUT: requirement_base_facet_type constants.%I.type
// CHECK:STDOUT: requirement_equivalent %.Self.ref, %.loc9_37
// CHECK:STDOUT: }
// CHECK:STDOUT: }
// CHECK:STDOUT: %T.loc9_16.2: %I_where.type = symbolic_binding T, 0 [symbolic = %T.loc9_16.1 (constants.%T)]
// CHECK:STDOUT: }
// CHECK:STDOUT: %PeriodMember.decl: %PeriodMember.type = fn_decl @PeriodMember [concrete = constants.%PeriodMember] {
// CHECK:STDOUT: %U.patt: %pattern_type.092 = symbolic_binding_pattern U, 0 [concrete]
// CHECK:STDOUT: } {
// CHECK:STDOUT: %.loc11_23.1: type = splice_block %.loc11_23.2 [concrete = constants.%I_where.type] {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: %I.ref: type = name_ref I, file.%I.decl [concrete = constants.%I.type]
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: %.Self.ref: %I.type = name_ref .Self, %.Self.2 [symbolic_self = constants.%.Self.1dc]
// CHECK:STDOUT: %.Self.as_type: type = facet_access_type %.Self.ref [symbolic_self = constants.%.Self.binding.as_type.15d]
// CHECK:STDOUT: %.loc11_29: type = converted %.Self.ref, %.Self.as_type [symbolic_self = constants.%.Self.binding.as_type.15d]
// CHECK:STDOUT: %Member.ref: %I.assoc_type = name_ref Member, @Member.%assoc0 [concrete = constants.%assoc0]
// CHECK:STDOUT: %impl.elem0: type = impl_witness_access constants.%I.lookup_impl_witness, element0 [symbolic_self = constants.%impl.elem0]
// CHECK:STDOUT: %.loc11_41: %empty_tuple.type = tuple_literal () [concrete = constants.%empty_tuple]
// CHECK:STDOUT: %.loc11_23.2: type = where_expr %.Self.2 [concrete = constants.%I_where.type] {
// CHECK:STDOUT: requirement_base_facet_type constants.%I.type
// CHECK:STDOUT: requirement_equivalent %impl.elem0, %.loc11_41
// CHECK:STDOUT: }
// CHECK:STDOUT: }
// CHECK:STDOUT: %U.loc11_18.2: %I_where.type = symbolic_binding U, 0 [symbolic = %U.loc11_18.1 (constants.%U)]
// CHECK:STDOUT: }
// CHECK:STDOUT: %TypeSelfImpls.decl: %TypeSelfImpls.type = fn_decl @TypeSelfImpls [concrete = constants.%TypeSelfImpls] {
// CHECK:STDOUT: %V.patt: %pattern_type.17f = symbolic_binding_pattern V, 0 [concrete]
// CHECK:STDOUT: } {
// CHECK:STDOUT: %.loc13_27.1: type = splice_block %.loc13_27.2 [concrete = constants.%type_where] {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: %.loc13_22: type = type_literal type [concrete = type]
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: %.Self.ref: %type = name_ref .Self, %.Self.2 [symbolic_self = constants.%.Self.c39]
// CHECK:STDOUT: %I.ref: type = name_ref I, file.%I.decl [concrete = constants.%I.type]
// CHECK:STDOUT: %.Self.as_type: type = facet_access_type %.Self.ref [symbolic_self = constants.%.Self.binding.as_type.8db]
// CHECK:STDOUT: %.loc13_33: type = converted %.Self.ref, %.Self.as_type [symbolic_self = constants.%.Self.binding.as_type.8db]
// CHECK:STDOUT: %.loc13_27.2: type = where_expr %.Self.2 [concrete = constants.%type_where] {
// CHECK:STDOUT: requirement_base_facet_type type
// CHECK:STDOUT: requirement_impls %.loc13_33, %I.ref
// CHECK:STDOUT: }
// CHECK:STDOUT: }
// CHECK:STDOUT: %V.loc13_19.2: %type_where = symbolic_binding V, 0 [symbolic = %V.loc13_19.1 (constants.%V)]
// CHECK:STDOUT: }
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: generic fn @PeriodSelf(%T.loc9_16.2: %I_where.type) {
// CHECK:STDOUT: %T.loc9_16.1: %I_where.type = symbolic_binding T, 0 [symbolic = %T.loc9_16.1 (constants.%T)]
// CHECK:STDOUT:
// CHECK:STDOUT: fn();
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: generic fn @PeriodMember(%U.loc11_18.2: %I_where.type) {
// CHECK:STDOUT: %U.loc11_18.1: %I_where.type = symbolic_binding U, 0 [symbolic = %U.loc11_18.1 (constants.%U)]
// CHECK:STDOUT:
// CHECK:STDOUT: fn();
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: generic fn @TypeSelfImpls(%V.loc13_19.2: %type_where) {
// CHECK:STDOUT: %V.loc13_19.1: %type_where = symbolic_binding V, 0 [symbolic = %V.loc13_19.1 (constants.%V)]
// CHECK:STDOUT:
// CHECK:STDOUT: fn();
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: specific @PeriodSelf(constants.%T) {
// CHECK:STDOUT: %T.loc9_16.1 => constants.%T
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: specific @PeriodMember(constants.%U) {
// CHECK:STDOUT: %U.loc11_18.1 => constants.%U
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: specific @TypeSelfImpls(constants.%V) {
// CHECK:STDOUT: %V.loc13_19.1 => constants.%V
// CHECK:STDOUT: }
// CHECK:STDOUT:
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