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46bb0fecd4fecfd5e3b7d1b8de903f0586e0b5ac
carbon-lang/toolchain/check/testdata/where_expr/designator.carbon
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Dana Jansens 46bb0fecd4 Properly diagnose ambiguous .Self in T impls X where... (#7132) 
A `where` expression nested inside a `T impls X` constraint makes
`.Self` ambiguous on the right-hand side of the `where` if `T` is
anything other than `.Self`. After the `where`, the value of a `.Self`
could be `T` or could be the value of `.Self` before the `impls`
constraint: the so-called top-level value of `.Self`.

Implicit use of `.Self` in designators is always allowed, and they are
bound (and replaced by a reference) to the inner-most possible value of
`.Self`. On the right-hand side of the nested `where` above, they have
the value `T as X`.

`.Self impls ...` is also always allowed, since it acts more as a
keyword here, and it always refers to the inner-most possible value of
`.Self`.

Any other explicit use of `.Self` is diagnosed when ambiguous, in any
kind of constraint. This is done in the handling of `WhereExpr` since it
has enough context to allow `.Self impls` (which is an explicit use)
while disallowing other explicit uses. And because it has non-canonical
instructions to work with, so it is able to diagnose errors with precise
locations.

Since `.Self` is no longer going to be marked with depth modifiers, the
eval of `WhereExpr` does not need an input facet value instruction
representing `.Self` to compare with, as they are now going to all be
equivalent. So revert it back to just looking for the `PeriodSelf` name
id, through a shared helper being introduced as `IsPeriodSelf`. And drop
the period self InstId from the `WhereExpr` instruction. This causes
most of the formatted SemIR changes.

Move helpers for working with and replacing `.Self` to their own file,
out of the `facet_type.h` header/cpp files. These are working with
`.Self` facet values more than facet types, though `.Self` is a name
that only exists inside the scope of a facet type.
2026-05-01 21:22:32 +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.as_type.e58: type = facet_access_type %.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.as_type.246: type = facet_access_type %.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 [concrete = constants.%I_where.type] {
// CHECK:STDOUT: requirement_base_facet_type %I.ref
// 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.as_type.e58]
// CHECK:STDOUT: %.loc11_29: type = converted %.Self.ref, %.Self.as_type [symbolic_self = constants.%.Self.as_type.e58]
// 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 [concrete = constants.%I_where.type] {
// CHECK:STDOUT: requirement_base_facet_type %I.ref
// 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.as_type.246]
// CHECK:STDOUT: %.loc13_33: type = converted %.Self.ref, %.Self.as_type [symbolic_self = constants.%.Self.as_type.246]
// CHECK:STDOUT: %.loc13_27.2: type = where_expr [concrete = constants.%type_where] {
// CHECK:STDOUT: requirement_base_facet_type %.loc13_22
// 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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