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Diagnose using named constraint's name inside its definition (#6906)

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Using a named constraint inside itself is problematic:
- If there were not require decls written above, it identifies as an
empty set. This makes `Z(Self)` essentially disappear in the identified
facet type, which produces "no use of Self" diagnostics while the user
can see a use of Self in the code.
- It won't include require decls that are written after, and so `require
T impls Z` won't actually enforce that `T` impls all of `Z`.

Previously this was an error because using the named constraint would
require it to be identified, and it's not identified until it is
complete. But this will change in proposal #6902. So that proposal also
includes changes to preserve diagnostics for incorrect use of a named
constraint before it's complete, which is implemented here.

Discussed in open discussion [on
2026-03-12](https://docs.google.com/document/d/1mjllGO3ZCL4qGt9uJHUtcxKoHAGEY7Y999ie4EtBWB8/edit?tab=t.0#heading=h.1dvbbrp5a6t3).

The new tests exposed a bug where we're not copying named constraints in
a facet type on the RHS of `where .Self impls` into the facet type on
the left, which is now fixed. The
`fail_require_impls_incomplete_self_in_period_self_impls.carbon` test
would not diagnose its error without this fix.
This commit is contained in:
Dana Jansens
2026-03-13 16:54:58 +00:00
committed by GitHub
parent 6706162582
commit bad9beddc7
4 changed files with 96 additions and 93 deletions
Download Patch File Download Diff File Expand all files Collapse all files
toolchain/check/eval.cpp
+4
View File
@@ -2494,6 +2494,10 @@ auto TryEvalTypedInst<SemIR::WhereExpr>(EvalContext& eval_context,
more_info.extend_constraints);
llvm::append_range(info.self_impls_constraints,
more_info.self_impls_constraints);
llvm::append_range(info.self_impls_named_constraints,
more_info.extend_named_constraints);
llvm::append_range(info.self_impls_named_constraints,
more_info.self_impls_named_constraints);
// Other requirements are copied in.
llvm::append_range(info.rewrite_constraints,
more_info.rewrite_constraints);
toolchain/check/handle_require.cpp
+31
View File
@@ -17,6 +17,7 @@
#include "toolchain/parse/node_ids.h"
#include "toolchain/sem_ir/ids.h"
#include "toolchain/sem_ir/named_constraint.h"
#include "toolchain/sem_ir/specific_named_constraint.h"
#include "toolchain/sem_ir/type_iterator.h"
#include "toolchain/sem_ir/typed_insts.h"
@@ -209,6 +210,36 @@ static auto ValidateRequire(Context& context, SemIR::LocId loc_id,
return std::nullopt;
}
if (auto named_constraint =
context.insts().TryGetAs<SemIR::NamedConstraintWithSelfDecl>(
scope_inst_id)) {
const auto& constraint_facet_type_info =
context.facet_types().Get(constraint_facet_type->facet_type_id);
// TODO: Handle other impls named constraints for the
// RequireImplsReferenceCycle diagnostic.
if (constraint_facet_type_info.other_requirements) {
context.TODO(constraint_inst_id,
"facet type has constraints that we don't handle yet");
return std::nullopt;
}
auto named_constraints = llvm::concat<const SemIR::SpecificNamedConstraint>(
constraint_facet_type_info.extend_named_constraints,
constraint_facet_type_info.self_impls_named_constraints);
for (auto c : named_constraints) {
if (c.named_constraint_id == named_constraint->named_constraint_id) {
const auto& named_constraint =
context.named_constraints().Get(c.named_constraint_id);
CARBON_DIAGNOSTIC(RequireImplsReferenceCycle, Error,
"facet type in `require` declaration refers to the "
"named constraint `{0}` from within its definition",
SemIR::NameId);
context.emitter().Emit(constraint_inst_id, RequireImplsReferenceCycle,
named_constraint.name_id);
return std::nullopt;
}
}
}
auto identified_facet_type_id = RequireIdentifiedFacetType(
context, SemIR::LocId(constraint_inst_id), self_constant_value_id,
*constraint_facet_type, [&](auto& builder) {
toolchain/check/testdata/named_constraint/require.carbon
Vendored
+60 -93
View File
@@ -175,34 +175,82 @@ constraint Z {
// --- fail_require_impls_incomplete_self.carbon
library "[[@TEST_NAME]]";
//@dump-sem-ir-begin
constraint Z {
// CHECK:STDERR: fail_require_impls_incomplete_self.carbon:[[@LINE+7]]:17: error: facet type `Z` cannot be identified in `require` declaration [RequireImplsUnidentifiedFacetType]
// CHECK:STDERR: fail_require_impls_incomplete_self.carbon:[[@LINE+4]]:17: error: facet type in `require` declaration refers to the named constraint `Z` from within its definition [RequireImplsReferenceCycle]
// CHECK:STDERR: require impls Z;
// CHECK:STDERR: ^
// CHECK:STDERR: fail_require_impls_incomplete_self.carbon:[[@LINE-4]]:1: note: constraint is currently being defined [NamedConstraintIncompleteWithinDefinition]
// CHECK:STDERR: constraint Z {
// CHECK:STDERR: ^~~~~~~~~~~~~~
// CHECK:STDERR:
require impls Z;
}
//@dump-sem-ir-end
// --- fail_require_impls_incomplete_self_forward_declared.carbon
library "[[@TEST_NAME]]";
constraint Z;
constraint Z {
// CHECK:STDERR: fail_require_impls_incomplete_self_forward_declared.carbon:[[@LINE+4]]:17: error: facet type in `require` declaration refers to the named constraint `Z` from within its definition [RequireImplsReferenceCycle]
// CHECK:STDERR: require impls Z;
// CHECK:STDERR: ^
// CHECK:STDERR:
require impls Z;
}
// --- fail_require_impls_incomplete_self_in_period_self_impls.carbon
library "[[@TEST_NAME]]";
constraint Z {
// CHECK:STDERR: fail_require_impls_incomplete_self_in_period_self_impls.carbon:[[@LINE+4]]:17: error: facet type in `require` declaration refers to the named constraint `Z` from within its definition [RequireImplsReferenceCycle]
// CHECK:STDERR: require impls type where .Self impls Z;
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
require impls type where .Self impls Z;
}
// --- fail_require_impls_incomplete_self_in_class_impls.carbon
library "[[@TEST_NAME]]";
class C;
constraint Z {
// TODO: This should be a RequireImplsReferenceCycle error since `Z` is being
// used inside `Z`.
// CHECK:STDERR: fail_require_impls_incomplete_self_in_class_impls.carbon:[[@LINE+4]]:17: error: semantics TODO: `facet type has constraints that we don't handle yet` [SemanticsTodo]
// CHECK:STDERR: require impls type where C impls Z;
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
require impls type where C impls Z;
}
// --- fail_require_impls_incomplete_indirect.carbon
library "[[@TEST_NAME]]";
constraint Z;
constraint Y {
// CHECK:STDERR: fail_require_impls_incomplete_indirect.carbon:[[@LINE+7]]:17: error: facet type `Z` cannot be identified in `require` declaration [RequireImplsUnidentifiedFacetType]
// CHECK:STDERR: require impls Z;
// CHECK:STDERR: ^
// CHECK:STDERR: fail_require_impls_incomplete_indirect.carbon:[[@LINE-6]]:1: note: constraint was forward declared here [NamedConstraintForwardDeclaredHere]
// CHECK:STDERR: constraint Z;
// CHECK:STDERR: ^~~~~~~~~~~~~
// CHECK:STDERR:
require impls Z;
}
constraint Z {
require impls Y;
}
// --- fail_require_impls_incomplete_self_specific.carbon
library "[[@TEST_NAME]]";
//@dump-sem-ir-begin
constraint Z(T:! type) {
// CHECK:STDERR: fail_require_impls_incomplete_self_specific.carbon:[[@LINE+7]]:19: error: facet type `Z(Self)` cannot be identified in `require` declaration [RequireImplsUnidentifiedFacetType]
// CHECK:STDERR: fail_require_impls_incomplete_self_specific.carbon:[[@LINE+4]]:19: error: facet type in `require` declaration refers to the named constraint `Z` from within its definition [RequireImplsReferenceCycle]
// CHECK:STDERR: require T impls Z(Self);
// CHECK:STDERR: ^~~~~~~
// CHECK:STDERR: fail_require_impls_incomplete_self_specific.carbon:[[@LINE-4]]:1: note: constraint is currently being defined [NamedConstraintIncompleteWithinDefinition]
// CHECK:STDERR: constraint Z(T:! type) {
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
require T impls Z(Self);
}
//@dump-sem-ir-end
// --- fail_require_impls_without_self.carbon
library "[[@TEST_NAME]]";
@@ -1064,87 +1112,6 @@ fn F() {
// CHECK:STDOUT:
// CHECK:STDOUT: specific @Z.WithSelf(constants.%Self) {}
// CHECK:STDOUT:
// CHECK:STDOUT: --- fail_require_impls_incomplete_self.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
// CHECK:STDOUT: %Z.type: type = facet_type <@Z> [concrete]
// CHECK:STDOUT: %Self: %Z.type = symbolic_binding Self, 0 [symbolic]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: file {
// CHECK:STDOUT: %Z.decl: type = constraint_decl @Z [concrete = constants.%Z.type] {} {}
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: constraint @Z {
// CHECK:STDOUT: %Self: %Z.type = symbolic_binding Self, 0 [symbolic = constants.%Self]
// CHECK:STDOUT: %Z.WithSelf.decl = constraint_with_self_decl @Z [concrete]
// CHECK:STDOUT:
// CHECK:STDOUT: !members:
// CHECK:STDOUT: .Self = %Self
// CHECK:STDOUT: .Z = <poisoned>
// CHECK:STDOUT: .Z = <poisoned>
// CHECK:STDOUT:
// CHECK:STDOUT: !requires:
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: specific @Z.WithSelf(constants.%Self) {}
// CHECK:STDOUT:
// CHECK:STDOUT: --- fail_require_impls_incomplete_self_specific.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
// CHECK:STDOUT: %T: type = symbolic_binding T, 0 [symbolic]
// CHECK:STDOUT: %pattern_type: type = pattern_type type [concrete]
// CHECK:STDOUT: %Z.type.7a8: type = generic_named_constaint_type @Z [concrete]
// CHECK:STDOUT: %empty_struct: %Z.type.7a8 = struct_value () [concrete]
// CHECK:STDOUT: %Z.type.d682d6.1: type = facet_type <@Z, @Z(%T)> [symbolic]
// CHECK:STDOUT: %Self: %Z.type.d682d6.1 = symbolic_binding Self, 1 [symbolic]
// CHECK:STDOUT: %Self.binding.as_type: type = symbolic_binding_type Self, 1, %Self [symbolic]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: file {
// CHECK:STDOUT: %Z.decl: %Z.type.7a8 = constraint_decl @Z [concrete = constants.%empty_struct] {
// CHECK:STDOUT: %T.patt: %pattern_type = symbolic_binding_pattern T, 0 [concrete]
// CHECK:STDOUT: } {
// CHECK:STDOUT: %.loc4_18.1: type = splice_block %.loc4_18.2 [concrete = type] {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: %.loc4_18.2: type = type_literal type [concrete = type]
// CHECK:STDOUT: }
// CHECK:STDOUT: %T.loc4_14.2: type = symbolic_binding T, 0 [symbolic = %T.loc4_14.1 (constants.%T)]
// CHECK:STDOUT: }
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: generic constraint @Z(%T.loc4_14.2: type) {
// CHECK:STDOUT: %T.loc4_14.1: type = symbolic_binding T, 0 [symbolic = %T.loc4_14.1 (constants.%T)]
// CHECK:STDOUT:
// CHECK:STDOUT: !definition:
// CHECK:STDOUT: %Z.type: type = facet_type <@Z, @Z(%T.loc4_14.1)> [symbolic = %Z.type (constants.%Z.type.d682d6.1)]
// CHECK:STDOUT: %Self.loc4_24.2: @Z.%Z.type (%Z.type.d682d6.1) = symbolic_binding Self, 1 [symbolic = %Self.loc4_24.2 (constants.%Self)]
// CHECK:STDOUT:
// CHECK:STDOUT: constraint {
// CHECK:STDOUT: %Self.loc4_24.1: @Z.%Z.type (%Z.type.d682d6.1) = symbolic_binding Self, 1 [symbolic = %Self.loc4_24.2 (constants.%Self)]
// CHECK:STDOUT: %Z.WithSelf.decl = constraint_with_self_decl @Z [concrete]
// CHECK:STDOUT:
// CHECK:STDOUT: !members:
// CHECK:STDOUT: .Self = %Self.loc4_24.1
// CHECK:STDOUT: .T = <poisoned>
// CHECK:STDOUT: .Z = <poisoned>
// CHECK:STDOUT: .T = <poisoned>
// CHECK:STDOUT: .Z = <poisoned>
// CHECK:STDOUT:
// CHECK:STDOUT: !requires:
// CHECK:STDOUT: }
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: specific @Z(constants.%T) {
// CHECK:STDOUT: %T.loc4_14.1 => constants.%T
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: specific @Z.WithSelf(constants.%T, constants.%Self) {}
// CHECK:STDOUT:
// CHECK:STDOUT: specific @Z(constants.%Self.binding.as_type) {
// CHECK:STDOUT: %T.loc4_14.1 => constants.%Self.binding.as_type
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: --- fail_require_impls_without_self.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
toolchain/diagnostics/kind.def
+1
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@@ -381,6 +381,7 @@ CARBON_DIAGNOSTIC_KIND(RequireImplsMissingFacetType)
CARBON_DIAGNOSTIC_KIND(RequireImplsMissingSelf)
CARBON_DIAGNOSTIC_KIND(RequireImplsMissingSelfEmptyFacetType)
CARBON_DIAGNOSTIC_KIND(RequireImplsIncompleteFacetType)
CARBON_DIAGNOSTIC_KIND(RequireImplsReferenceCycle)
CARBON_DIAGNOSTIC_KIND(RequireImplsUnidentifiedFacetType)
CARBON_DIAGNOSTIC_KIND(RequireImplsNotImplemented)
CARBON_DIAGNOSTIC_KIND(RequireInWrongScope)