1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
|
// RUN: %clang_cc1 -fsyntax-only -std=c++20 -verify -Wc++20-extensions %s
// RUN: %clang_cc1 -fsyntax-only -std=c++17 -verify -Wc++17-extensions %s
// RUN: %clang_cc1 -fsyntax-only -std=c++11 -verify -DEXT -Wc++17-extensions -Wc++20-extensions %s
struct [[nodiscard]] S {};
S get_s();
S& get_s_ref();
enum [[nodiscard]] E {};
E get_e();
[[nodiscard]] int get_i();
[[nodiscard]] volatile int &get_vi();
void f() {
get_s(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
get_i(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
get_vi(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
get_e(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
// Okay, warnings are not encouraged
get_s_ref();
(void)get_s();
(void)get_i();
(void)get_vi();
(void)get_e();
}
[[nodiscard]] volatile char &(*fp)(); // expected-warning {{'nodiscard' attribute only applies to functions, classes, or enumerations}}
void g() {
fp(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
// OK, warning suppressed.
(void)fp();
}
namespace PR31526 {
typedef E (*fp1)();
typedef S (*fp2)();
typedef S S_alias;
typedef S_alias (*fp3)();
typedef fp2 fp2_alias;
void f() {
fp1 one;
fp2 two;
fp3 three;
fp2_alias four;
one(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
two(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
three(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
four(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
// These are all okay because of the explicit cast to void.
(void)one();
(void)two();
(void)three();
(void)four();
}
} // namespace PR31526
struct [[nodiscard("reason")]] ReasonStruct {};
struct LaterReason;
struct [[nodiscard("later reason")]] LaterReason {};
ReasonStruct get_reason();
LaterReason get_later_reason();
[[nodiscard("another reason")]] int another_reason();
[[nodiscard("conflicting reason")]] int conflicting_reason();
[[nodiscard("special reason")]] int conflicting_reason();
void cxx20_use() {
get_reason(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute: reason}}
get_later_reason(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute: later reason}}
another_reason(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute: another reason}}
conflicting_reason(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute: special reason}}
}
namespace p1771 {
struct[[nodiscard("Don't throw me away!")]] ConvertTo{};
struct S {
[[nodiscard]] S();
[[nodiscard("Don't let that S-Char go!")]] S(char);
S(int);
[[gnu::warn_unused_result]] S(double);
operator ConvertTo();
[[nodiscard]] operator int();
[[nodiscard("Don't throw away as a double")]] operator double();
};
struct[[nodiscard("Don't throw me away either!")]] Y{};
void usage() {
S(); // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
S('A'); // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute: Don't let that S-Char go!}}
S(1);
S(2.2);
Y(); // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute: Don't throw me away either!}}
S s;
ConvertTo{}; // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute: Don't throw me away!}}
// AST is different in C++20 mode, pre-2017 a move ctor for ConvertTo is there
// as well, hense the constructor warning.
#if __cplusplus >= 201703L
// expected-warning@+4 {{ignoring return value of function declared with 'nodiscard' attribute: Don't throw me away!}}
#else
// expected-warning@+2 {{ignoring temporary created by a constructor declared with 'nodiscard' attribute: Don't throw me away!}}
#endif
(ConvertTo) s;
(int)s; // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
(S)'c'; // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute: Don't let that S-Char go!}}
#if __cplusplus >= 201703L
// expected-warning@+4 {{ignoring return value of function declared with 'nodiscard' attribute: Don't throw me away!}}
#else
// expected-warning@+2 {{ignoring temporary created by a constructor declared with 'nodiscard' attribute: Don't throw me away!}}
#endif
static_cast<ConvertTo>(s);
static_cast<int>(s); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
static_cast<double>(s); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute: Don't throw away as a double}}
}
}; // namespace p1771
#ifdef EXT
// expected-warning@5 {{use of the 'nodiscard' attribute is a C++17 extension}}
// expected-warning@9 {{use of the 'nodiscard' attribute is a C++17 extension}}
// expected-warning@12 {{use of the 'nodiscard' attribute is a C++17 extension}}
// expected-warning@13 {{use of the 'nodiscard' attribute is a C++17 extension}}
// expected-warning@29 {{use of the 'nodiscard' attribute is a C++17 extension}}
// expected-warning@65 {{use of the 'nodiscard' attribute is a C++20 extension}}
// expected-warning@67 {{use of the 'nodiscard' attribute is a C++20 extension}}
// expected-warning@71 {{use of the 'nodiscard' attribute is a C++20 extension}}
// expected-warning@73 {{use of the 'nodiscard' attribute is a C++20 extension}}
// expected-warning@74 {{use of the 'nodiscard' attribute is a C++20 extension}}
// expected-warning@84 {{use of the 'nodiscard' attribute is a C++20 extension}}
// expected-warning@86 {{use of the 'nodiscard' attribute is a C++17 extension}}
// expected-warning@87 {{use of the 'nodiscard' attribute is a C++20 extension}}
// expected-warning@91 {{use of the 'nodiscard' attribute is a C++17 extension}}
// expected-warning@92 {{use of the 'nodiscard' attribute is a C++20 extension}}
// expected-warning@95 {{use of the 'nodiscard' attribute is a C++20 extension}}
#endif
|
