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[clang][DR2621] using enum NAME lookup fix
Although using-enum's grammar is 'using elaborated-enum-specifier', the lookup for the enum is ordinary lookup (and not the tagged-type lookup that normally occurs wth an tagged-type specifier). Thus (a) we can find typedefs and (b) do not find enum tags hidden by a non-tag name (the struct stat thing). This reimplements that part of using-enum handling, to address DR2621, where clang's behaviour does not match std intent (and other compilers). Reviewed By: aaron.ballman Differential Revision: https://reviews.llvm.org/D134283
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‎clang/docs/ReleaseNotes.rst

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@@ -356,6 +356,8 @@ C++20 Feature Support
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the time of checking, which should now allow the libstdc++ ranges implementation
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to work for at least trivial examples. This fixes
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`Issue 44178 <https://github.com/llvm/llvm-project/issues/44178>`_.
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- Clang implements DR2621, correcting a defect in ``using enum`` handling. The
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name is found via ordinary lookup so typedefs are found.
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C++2b Feature Support
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^^^^^^^^^^^^^^^^^^^^^

‎clang/include/clang/Basic/DiagnosticParseKinds.td

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@@ -607,6 +607,9 @@ def warn_cxx17_compat_using_enum_declaration : Warning<
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def ext_using_enum_declaration : ExtWarn<
608608
"using enum declaration is a C++20 extension">,
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InGroup<CXX20>;
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def err_using_enum_expect_identifier : Error<
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"using enum %select{requires an enum or typedef name|"
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"does not permit an elaborated enum specifier}0">;
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def err_constructor_bad_name : Error<
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"missing return type for function %0; did you mean the constructor name %1?">;
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def err_destructor_tilde_identifier : Error<

‎clang/include/clang/Basic/DiagnosticSemaKinds.td

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@@ -562,6 +562,8 @@ def warn_cxx17_compat_using_decl_class_member_enumerator : Warning<
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"with C++ standards before C++20">, InGroup<CXXPre20Compat>, DefaultIgnore;
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def err_using_enum_is_dependent : Error<
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"using-enum cannot name a dependent type">;
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def err_using_enum_not_enum : Error<
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"%0 is not an enumerated type">;
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def err_ambiguous_inherited_constructor : Error<
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"constructor of %0 inherited from multiple base class subobjects">;
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def note_ambiguous_inherited_constructor_using : Note<

‎clang/include/clang/Sema/Sema.h

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@@ -6125,7 +6125,9 @@ class Sema final {
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const ParsedAttributesView &AttrList);
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Decl *ActOnUsingEnumDeclaration(Scope *CurScope, AccessSpecifier AS,
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SourceLocation UsingLoc,
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SourceLocation EnumLoc, const DeclSpec &);
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SourceLocation EnumLoc,
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SourceLocation IdentLoc, IdentifierInfo &II,
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CXXScopeSpec *SS = nullptr);
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Decl *ActOnAliasDeclaration(Scope *CurScope, AccessSpecifier AS,
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MultiTemplateParamsArg TemplateParams,
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SourceLocation UsingLoc, UnqualifiedId &Name,

‎clang/lib/Parse/ParseDeclCXX.cpp

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@@ -678,6 +678,8 @@ bool Parser::ParseUsingDeclarator(DeclaratorContext Context,
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///
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/// using-enum-declaration: [C++20, dcl.enum]
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/// 'using' elaborated-enum-specifier ;
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/// The terminal name of the elaborated-enum-specifier undergoes
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/// ordinary lookup
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///
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/// elaborated-enum-specifier:
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/// 'enum' nested-name-specifier[opt] identifier
@@ -697,21 +699,47 @@ Parser::DeclGroupPtrTy Parser::ParseUsingDeclaration(
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DiagnoseCXX11AttributeExtension(PrefixAttrs);
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700-
DeclSpec DS(AttrFactory);
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ParseEnumSpecifier(UELoc, DS, TemplateInfo, AS,
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// DSC_trailing has the semantics we desire
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DeclSpecContext::DSC_trailing);
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if (TemplateInfo.Kind) {
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SourceRange R = TemplateInfo.getSourceRange();
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Diag(UsingLoc, diag::err_templated_using_directive_declaration)
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<< 1 /* declaration */ << R << FixItHint::CreateRemoval(R);
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SkipUntil(tok::semi);
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return nullptr;
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}
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CXXScopeSpec SS;
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if (ParseOptionalCXXScopeSpecifier(SS, /*ParsedType=*/nullptr,
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/*ObectHasErrors=*/false,
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/*EnteringConttext=*/false,
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/*MayBePseudoDestructor=*/nullptr,
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/*IsTypename=*/false,
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/*IdentifierInfo=*/nullptr,
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/*OnlyNamespace=*/false,
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/*InUsingDeclaration=*/true)) {
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SkipUntil(tok::semi);
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return nullptr;
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}
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if (Tok.is(tok::code_completion)) {
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cutOffParsing();
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Actions.CodeCompleteUsing(getCurScope());
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return nullptr;
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}
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if (!Tok.is(tok::identifier)) {
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Diag(Tok.getLocation(), diag::err_using_enum_expect_identifier)
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<< Tok.is(tok::kw_enum);
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SkipUntil(tok::semi);
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return nullptr;
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}
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IdentifierInfo *IdentInfo = Tok.getIdentifierInfo();
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SourceLocation IdentLoc = ConsumeToken();
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Decl *UED = Actions.ActOnUsingEnumDeclaration(
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getCurScope(), AS, UsingLoc, UELoc, IdentLoc, *IdentInfo, &SS);
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if (!UED) {
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SkipUntil(tok::semi);
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return nullptr;
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}
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713-
Decl *UED = Actions.ActOnUsingEnumDeclaration(getCurScope(), AS, UsingLoc,
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UELoc, DS);
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DeclEnd = Tok.getLocation();
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if (ExpectAndConsume(tok::semi, diag::err_expected_after,
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"using-enum declaration"))

‎clang/lib/Sema/SemaDeclCXX.cpp

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@@ -11851,30 +11851,30 @@ Decl *Sema::ActOnUsingDeclaration(Scope *S, AccessSpecifier AS,
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Decl *Sema::ActOnUsingEnumDeclaration(Scope *S, AccessSpecifier AS,
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SourceLocation UsingLoc,
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SourceLocation EnumLoc,
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const DeclSpec &DS) {
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switch (DS.getTypeSpecType()) {
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case DeclSpec::TST_error:
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// This will already have been diagnosed
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SourceLocation IdentLoc,
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IdentifierInfo &II, CXXScopeSpec *SS) {
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assert(!SS->isInvalid() && "ScopeSpec is invalid");
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ParsedType TypeRep = getTypeName(II, IdentLoc, S, SS);
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if (!TypeRep) {
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Diag(IdentLoc, SS && isDependentScopeSpecifier(*SS)
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? diag::err_using_enum_is_dependent
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: diag::err_unknown_typename)
11862+
<< II.getName()
11863+
<< SourceRange(SS ? SS->getBeginLoc() : IdentLoc, IdentLoc);
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return nullptr;
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}
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case DeclSpec::TST_enum:
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break;
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case DeclSpec::TST_typename:
11864-
Diag(DS.getTypeSpecTypeLoc(), diag::err_using_enum_is_dependent);
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auto *Enum = dyn_cast_if_present<EnumDecl>(TypeRep.get()->getAsTagDecl());
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if (!Enum) {
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Diag(IdentLoc, diag::err_using_enum_not_enum) << TypeRep.get();
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return nullptr;
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default:
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llvm_unreachable("unexpected DeclSpec type");
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}
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11871-
// As with enum-decls, we ignore attributes for now.
11872-
auto *Enum = cast<EnumDecl>(DS.getRepAsDecl());
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if (auto *Def = Enum->getDefinition())
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Enum = Def;
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11876-
auto *UD = BuildUsingEnumDeclaration(S, AS, UsingLoc, EnumLoc,
11877-
DS.getTypeSpecTypeNameLoc(), Enum);
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auto *UD =
11877+
BuildUsingEnumDeclaration(S, AS, UsingLoc, EnumLoc, IdentLoc, Enum);
1187811878
if (UD)
1187911879
PushOnScopeChains(UD, S, /*AddToContext*/ false);
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‎clang/test/CXX/drs/dr26xx.cpp

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@@ -1,5 +1,19 @@
11
// RUN: %clang_cc1 -std=c++20 -triple x86_64-unknown-unknown %s -verify
22

3+
namespace dr2621 { // dr2621: yes
4+
enum class E { a };
5+
namespace One {
6+
using E_t = E;
7+
using enum E_t; // typedef ok
8+
auto v = a;
9+
}
10+
namespace Two {
11+
using dr2621::E;
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int E; // we see this
13+
using enum E; // expected-error {{unknown type name E}}
14+
}
15+
}
16+
317
namespace dr2628 { // dr2628: yes
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519
template <bool A = false, bool B = false>

‎clang/test/CodeCompletion/using-enum.cpp

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@@ -2,6 +2,6 @@ enum class AAA { X, Y, Z };
22

33
namespace N2 {
44
using enum AAA;
5-
// RUN: %clang_cc1 -fsyntax-only -code-completion-at=%s:4:14 %s | FileCheck -check-prefix=CHECK-CC1 %s
5+
// RUN: %clang_cc1 -std=c++20 -fsyntax-only -code-completion-at=%s:4:14 %s | FileCheck -check-prefix=CHECK-CC1 %s
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// CHECK-CC1: COMPLETION: AAA
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};

‎clang/test/Parser/cxx20-using-enum.cpp

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@@ -4,9 +4,9 @@ namespace GH57347 {
44
namespace A {}
55

66
void f() {
7-
using enum A::+; // expected-error {{expected identifier}}
8-
using enum; // expected-error {{expected identifier or '{'}}
9-
using enum class; // expected-error {{expected identifier or '{'}}
10-
using enum : blah; // expected-error {{unknown type name 'blah'}} expected-error {{unnamed enumeration must be a definition}}
7+
using enum A::+; // expected-error {{using enum requires an enum or typedef name}}
8+
using enum; // expected-error {{using enum requires an enum or typedef name}}
9+
using enum class; // expected-error {{using enum requires an enum or typedef name}}
10+
using enum enum q; // expected-error {{using enum does not permit an elaborated enum specifier}}
1111
}
1212
}

‎clang/test/SemaCXX/cxx20-using-enum.cpp

Lines changed: 13 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@ namespace Bob {
88
enum A { a, // expected-note{{declared here}}
99
b,
1010
c };
11-
class C; // expected-note{{previous use}}
11+
class C;
1212
enum class D : int;
1313
enum class D { d,
1414
e,
@@ -20,11 +20,11 @@ using enum Bob::A;
2020
#if __cplusplus < 202002
2121
// expected-warning@-2{{is a C++20 extension}}
2222
#endif
23-
using enum Bob::B; // expected-error{{no enum named 'B'}}
23+
using enum Bob::B; // expected-error{{unknown type name B}}
2424
#if __cplusplus < 202002
2525
// expected-warning@-2{{is a C++20 extension}}
2626
#endif
27-
using enum Bob::C; // expected-error{{tag type that does not match}}
27+
using enum Bob::C; // expected-error{{'Bob::C' is not an enumerated type}}
2828
#if __cplusplus < 202002
2929
// expected-warning@-2{{is a C++20 extension}}
3030
#endif
@@ -38,6 +38,16 @@ using enum Bob::D;
3838
#if __cplusplus < 202002
3939
// expected-warning@-2{{is a C++20 extension}}
4040
#endif
41+
42+
void DR2621() {
43+
using A_t = Bob::A;
44+
using enum A_t;
45+
#if __cplusplus < 202002
46+
// expected-warning@-2{{is a C++20 extension}}
47+
#endif
48+
A_t x = a;
49+
}
50+
4151
} // namespace One
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4353
namespace Two {

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