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db93ef14ae
This is a rebase of #95112 with my own feedback apply as @MitalAshok has been inactive for a while. It's fairly important this makes clang 20 as it is a blocker for #107451 --- [CWG2813](https://cplusplus.github.io/CWG/issues/2813.html) prvalue.member_fn(expression-list) now will not materialize a temporary for prvalue if member_fn is an explicit object member function, and prvalue will bind directly to the object parameter. The E1 in E1.static_member is now a discarded-value expression, so if E1 was a call to a [[nodiscard]] function, there will now be a warning. This also affects C++98 with [[gnu::warn_unused_result]] functions. This should not affect C where TemporaryMaterializationConversion is a no-op. Closes #100314 Fixes #100341 --------- Co-authored-by: Mital Ashok <mital@mitalashok.co.uk>
185 lines
7.9 KiB
C++
185 lines
7.9 KiB
C++
// RUN: %clang_cc1 -fsyntax-only -std=c++11 -verify=expected,cxx11,cxx11-17 -pedantic %s
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// RUN: %clang_cc1 -fsyntax-only -std=c++17 -verify=expected,cxx11-17,since-cxx17 -pedantic %s
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// RUN: %clang_cc1 -fsyntax-only -std=c++20 -verify=expected,since-cxx17 -pedantic %s
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// RUN: %clang_cc1 -fsyntax-only -std=c++23 -verify=expected,since-cxx17 -pedantic %s
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struct [[nodiscard]] S {};
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// cxx11-warning@-1 {{use of the 'nodiscard' attribute is a C++17 extension}}
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S get_s();
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S& get_s_ref();
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enum [[nodiscard]] E {};
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// cxx11-warning@-1 {{use of the 'nodiscard' attribute is a C++17 extension}}
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E get_e();
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[[nodiscard]] int get_i();
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// cxx11-warning@-1 {{use of the 'nodiscard' attribute is a C++17 extension}}
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[[nodiscard]] volatile int &get_vi();
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// cxx11-warning@-1 {{use of the 'nodiscard' attribute is a C++17 extension}}
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void f() {
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get_s(); // expected-warning {{ignoring return value of type 'S' declared with 'nodiscard' attribute}}
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get_i(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
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get_vi(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
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get_e(); // expected-warning {{ignoring return value of type 'E' declared with 'nodiscard' attribute}}
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// Okay, warnings are not encouraged
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get_s_ref();
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(void)get_s();
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(void)get_i();
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(void)get_vi();
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(void)get_e();
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}
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[[nodiscard]] volatile char &(*fp)(); // expected-warning {{'nodiscard' attribute only applies to functions, classes, or enumerations}}
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// cxx11-warning@-1 {{use of the 'nodiscard' attribute is a C++17 extension}}
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void g() {
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fp(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
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// OK, warning suppressed.
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(void)fp();
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}
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namespace PR31526 {
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typedef E (*fp1)();
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typedef S (*fp2)();
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typedef S S_alias;
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typedef S_alias (*fp3)();
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typedef fp2 fp2_alias;
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void f() {
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fp1 one;
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fp2 two;
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fp3 three;
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fp2_alias four;
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one(); // expected-warning {{ignoring return value of type 'E' declared with 'nodiscard' attribute}}
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two(); // expected-warning {{ignoring return value of type 'S' declared with 'nodiscard' attribute}}
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three(); // expected-warning {{ignoring return value of type 'S' declared with 'nodiscard' attribute}}
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four(); // expected-warning {{ignoring return value of type 'S' declared with 'nodiscard' attribute}}
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// These are all okay because of the explicit cast to void.
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(void)one();
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(void)two();
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(void)three();
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(void)four();
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}
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} // namespace PR31526
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struct [[nodiscard("reason")]] ReasonStruct {};
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// cxx11-17-warning@-1 {{use of the 'nodiscard' attribute is a C++20 extension}}
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struct LaterReason;
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struct [[nodiscard("later reason")]] LaterReason {};
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// cxx11-17-warning@-1 {{use of the 'nodiscard' attribute is a C++20 extension}}
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ReasonStruct get_reason();
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LaterReason get_later_reason();
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[[nodiscard("another reason")]] int another_reason();
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// cxx11-17-warning@-1 {{use of the 'nodiscard' attribute is a C++20 extension}}
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[[nodiscard("conflicting reason")]] int conflicting_reason();
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// cxx11-17-warning@-1 {{use of the 'nodiscard' attribute is a C++20 extension}}
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[[nodiscard("special reason")]] int conflicting_reason();
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// cxx11-17-warning@-1 {{use of the 'nodiscard' attribute is a C++20 extension}}
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void cxx20_use() {
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get_reason(); // expected-warning {{ignoring return value of type 'ReasonStruct' declared with 'nodiscard' attribute: reason}}
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get_later_reason(); // expected-warning {{ignoring return value of type 'LaterReason' declared with 'nodiscard' attribute: later reason}}
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another_reason(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute: another reason}}
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conflicting_reason(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute: special reason}}
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}
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namespace p1771 {
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struct[[nodiscard("Don't throw me away!")]] ConvertTo{};
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// cxx11-17-warning@-1 {{use of the 'nodiscard' attribute is a C++20 extension}}
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struct S {
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[[nodiscard]] S();
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// cxx11-warning@-1 {{use of the 'nodiscard' attribute is a C++17 extension}}
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[[nodiscard("Don't let that S-Char go!")]] S(char);
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// cxx11-17-warning@-1 {{use of the 'nodiscard' attribute is a C++20 extension}}
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S(int);
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[[gnu::warn_unused_result]] S(double);
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operator ConvertTo();
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[[nodiscard]] operator int();
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// cxx11-warning@-1 {{use of the 'nodiscard' attribute is a C++17 extension}}
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[[nodiscard("Don't throw away as a double")]] operator double();
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// cxx11-17-warning@-1 {{use of the 'nodiscard' attribute is a C++20 extension}}
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};
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struct[[nodiscard("Don't throw me away either!")]] Y{};
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// cxx11-17-warning@-1 {{use of the 'nodiscard' attribute is a C++20 extension}}
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void usage() {
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S(); // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
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S('A'); // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute: Don't let that S-Char go!}}
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S(1);
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S(2.2);
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Y(); // expected-warning {{ignoring temporary of type 'Y' declared with 'nodiscard' attribute: Don't throw me away either!}}
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S s;
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ConvertTo{}; // expected-warning {{ignoring return value of type 'ConvertTo' declared with 'nodiscard' attribute: Don't throw me away!}}
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// AST is different in C++17 mode. Before, a move ctor for ConvertTo is there
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// as well, hence the constructor warning.
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// since-cxx17-warning@+2 {{ignoring return value of type 'ConvertTo' declared with 'nodiscard' attribute: Don't throw me away!}}
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// cxx11-warning@+1 {{ignoring temporary of type 'ConvertTo' declared with 'nodiscard' attribute: Don't throw me away!}}
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(ConvertTo) s;
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(int)s; // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
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(S)'c'; // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute: Don't let that S-Char go!}}
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// since-cxx17-warning@+2 {{ignoring return value of type 'ConvertTo' declared with 'nodiscard' attribute: Don't throw me away!}}
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// cxx11-warning@+1 {{ignoring temporary of type 'ConvertTo' declared with 'nodiscard' attribute: Don't throw me away!}}
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static_cast<ConvertTo>(s);
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static_cast<int>(s); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
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static_cast<double>(s); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute: Don't throw away as a double}}
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}
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} // namespace p1771
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namespace discarded_member_access {
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struct X {
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union {
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int variant_member;
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};
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struct { // expected-warning {{anonymous structs are a GNU extension}}
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int anonymous_struct_member;
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};
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int data_member;
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static int static_data_member;
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enum {
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unscoped_enum
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};
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enum class scoped_enum_t {
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scoped_enum
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};
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using enum scoped_enum_t;
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// cxx11-17-warning@-1 {{using enum declaration is a C++20 extension}}
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void implicit_object_member_function();
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static void static_member_function();
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#if __cplusplus >= 202302L
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void explicit_object_member_function(this X self);
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#endif
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};
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[[nodiscard]] X get_X();
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// cxx11-warning@-1 {{use of the 'nodiscard' attribute is a C++17 extension}}
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void f() {
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(void) get_X().variant_member;
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(void) get_X().anonymous_struct_member;
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(void) get_X().data_member;
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(void) get_X().static_data_member;
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// expected-warning@-1 {{ignoring return value of function declared with 'nodiscard' attribute}}
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(void) get_X().unscoped_enum;
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// expected-warning@-1 {{ignoring return value of function declared with 'nodiscard' attribute}}
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(void) get_X().scoped_enum;
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// expected-warning@-1 {{ignoring return value of function declared with 'nodiscard' attribute}}
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(void) get_X().implicit_object_member_function();
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(void) get_X().static_member_function();
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// expected-warning@-1 {{ignoring return value of function declared with 'nodiscard' attribute}}
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#if __cplusplus >= 202302L
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(void) get_X().explicit_object_member_function();
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#endif
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}
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} // namespace discarded_member_access
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