1/*
2 * Copyright 2015-present Facebook, Inc.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17/**
18 * GCC compatible wrappers around clang attributes.
19 *
20 * @author Dominik Gabi
21 */
22
23#pragma once
24
25#ifndef __has_attribute
26#define FOLLY_HAS_ATTRIBUTE(x) 0
27#else
28#define FOLLY_HAS_ATTRIBUTE(x) __has_attribute(x)
29#endif
30
31#ifndef __has_cpp_attribute
32#define FOLLY_HAS_CPP_ATTRIBUTE(x) 0
33#else
34#define FOLLY_HAS_CPP_ATTRIBUTE(x) __has_cpp_attribute(x)
35#endif
36
37#ifndef __has_extension
38#define FOLLY_HAS_EXTENSION(x) 0
39#else
40#define FOLLY_HAS_EXTENSION(x) __has_extension(x)
41#endif
42
43/**
44 * Fallthrough to indicate that `break` was left out on purpose in a switch
45 * statement, e.g.
46 *
47 * switch (n) {
48 * case 22:
49 * case 33: // no warning: no statements between case labels
50 * f();
51 * case 44: // warning: unannotated fall-through
52 * g();
53 * FOLLY_FALLTHROUGH; // no warning: annotated fall-through
54 * }
55 */
56#if FOLLY_HAS_CPP_ATTRIBUTE(fallthrough)
57#define FOLLY_FALLTHROUGH [[fallthrough]]
58#elif FOLLY_HAS_CPP_ATTRIBUTE(clang::fallthrough)
59#define FOLLY_FALLTHROUGH [[clang::fallthrough]]
60#elif FOLLY_HAS_CPP_ATTRIBUTE(gnu::fallthrough)
61#define FOLLY_FALLTHROUGH [[gnu::fallthrough]]
62#else
63#define FOLLY_FALLTHROUGH
64#endif
65
66/**
67 * Maybe_unused indicates that a function, variable or parameter might or
68 * might not be used, e.g.
69 *
70 * int foo(FOLLY_MAYBE_UNUSED int x) {
71 * #ifdef USE_X
72 * return x;
73 * #else
74 * return 0;
75 * #endif
76 * }
77 */
78#if FOLLY_HAS_CPP_ATTRIBUTE(maybe_unused)
79#define FOLLY_MAYBE_UNUSED [[maybe_unused]]
80#elif FOLLY_HAS_ATTRIBUTE(__unused__) || __GNUC__
81#define FOLLY_MAYBE_UNUSED __attribute__((__unused__))
82#else
83#define FOLLY_MAYBE_UNUSED
84#endif
85
86/**
87 * Nullable indicates that a return value or a parameter may be a `nullptr`,
88 * e.g.
89 *
90 * int* FOLLY_NULLABLE foo(int* a, int* FOLLY_NULLABLE b) {
91 * if (*a > 0) { // safe dereference
92 * return nullptr;
93 * }
94 * if (*b < 0) { // unsafe dereference
95 * return *a;
96 * }
97 * if (b != nullptr && *b == 1) { // safe checked dereference
98 * return new int(1);
99 * }
100 * return nullptr;
101 * }
102 */
103#if FOLLY_HAS_EXTENSION(nullability)
104#define FOLLY_NULLABLE _Nullable
105#define FOLLY_NONNULL _Nonnull
106#else
107#define FOLLY_NULLABLE
108#define FOLLY_NONNULL
109#endif
110
111/**
112 * "Cold" indicates to the compiler that a function is only expected to be
113 * called from unlikely code paths. It can affect decisions made by the
114 * optimizer both when processing the function body and when analyzing
115 * call-sites.
116 */
117#if __GNUC__
118#define FOLLY_COLD __attribute__((__cold__))
119#else
120#define FOLLY_COLD
121#endif
122