1 //===- FormatVariadicDetails.h - Helpers for FormatVariadic.h ----*- C++-*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8
9 #ifndef LLVM_SUPPORT_FORMATVARIADICDETAILS_H
10 #define LLVM_SUPPORT_FORMATVARIADICDETAILS_H
11
12 #include "llvm/ADT/StringRef.h"
13 #include "llvm/Support/raw_ostream.h"
14
15 #include <type_traits>
16
17 namespace llvm {
18 template <typename T, typename Enable = void> struct format_provider {};
19 class Error;
20
21 namespace detail {
22 class format_adapter {
23 virtual void anchor();
24
25 protected:
~format_adapter()26 virtual ~format_adapter() {}
27
28 public:
29 virtual void format(raw_ostream &S, StringRef Options) = 0;
30 };
31
32 template <typename T> class provider_format_adapter : public format_adapter {
33 T Item;
34
35 public:
provider_format_adapter(T && Item)36 explicit provider_format_adapter(T &&Item) : Item(std::forward<T>(Item)) {}
37
format(llvm::raw_ostream & S,StringRef Options)38 void format(llvm::raw_ostream &S, StringRef Options) override {
39 format_provider<std::decay_t<T>>::format(Item, S, Options);
40 }
41 };
42
43 template <typename T>
44 class stream_operator_format_adapter : public format_adapter {
45 T Item;
46
47 public:
stream_operator_format_adapter(T && Item)48 explicit stream_operator_format_adapter(T &&Item)
49 : Item(std::forward<T>(Item)) {}
50
format(llvm::raw_ostream & S,StringRef)51 void format(llvm::raw_ostream &S, StringRef) override { S << Item; }
52 };
53
54 template <typename T> class missing_format_adapter;
55
56 // Test if format_provider<T> is defined on T and contains a member function
57 // with the signature:
58 // static void format(const T&, raw_stream &, StringRef);
59 //
60 template <class T> class has_FormatProvider {
61 public:
62 using Decayed = std::decay_t<T>;
63 typedef void (*Signature_format)(const Decayed &, llvm::raw_ostream &,
64 StringRef);
65
66 template <typename U>
67 static char test(SameType<Signature_format, &U::format> *);
68
69 template <typename U> static double test(...);
70
71 static bool const value =
72 (sizeof(test<llvm::format_provider<Decayed>>(nullptr)) == 1);
73 };
74
75 // Test if raw_ostream& << T -> raw_ostream& is findable via ADL.
76 template <class T> class has_StreamOperator {
77 public:
78 using ConstRefT = const std::decay_t<T> &;
79
80 template <typename U>
81 static char test(
82 std::enable_if_t<std::is_same<decltype(std::declval<llvm::raw_ostream &>()
83 << std::declval<U>()),
84 llvm::raw_ostream &>::value,
85 int *>);
86
87 template <typename U> static double test(...);
88
89 static bool const value = (sizeof(test<ConstRefT>(nullptr)) == 1);
90 };
91
92 // Simple template that decides whether a type T should use the member-function
93 // based format() invocation.
94 template <typename T>
95 struct uses_format_member
96 : public std::integral_constant<
97 bool,
98 std::is_base_of<format_adapter, std::remove_reference_t<T>>::value> {
99 };
100
101 // Simple template that decides whether a type T should use the format_provider
102 // based format() invocation. The member function takes priority, so this test
103 // will only be true if there is not ALSO a format member.
104 template <typename T>
105 struct uses_format_provider
106 : public std::integral_constant<
107 bool, !uses_format_member<T>::value && has_FormatProvider<T>::value> {
108 };
109
110 // Simple template that decides whether a type T should use the operator<<
111 // based format() invocation. This takes last priority.
112 template <typename T>
113 struct uses_stream_operator
114 : public std::integral_constant<bool, !uses_format_member<T>::value &&
115 !uses_format_provider<T>::value &&
116 has_StreamOperator<T>::value> {};
117
118 // Simple template that decides whether a type T has neither a member-function
119 // nor format_provider based implementation that it can use. Mostly used so
120 // that the compiler spits out a nice diagnostic when a type with no format
121 // implementation can be located.
122 template <typename T>
123 struct uses_missing_provider
124 : public std::integral_constant<bool, !uses_format_member<T>::value &&
125 !uses_format_provider<T>::value &&
126 !uses_stream_operator<T>::value> {
127 };
128
129 template <typename T>
130 std::enable_if_t<uses_format_member<T>::value, T>
build_format_adapter(T && Item)131 build_format_adapter(T &&Item) {
132 return std::forward<T>(Item);
133 }
134
135 template <typename T>
136 std::enable_if_t<uses_format_provider<T>::value, provider_format_adapter<T>>
build_format_adapter(T && Item)137 build_format_adapter(T &&Item) {
138 return provider_format_adapter<T>(std::forward<T>(Item));
139 }
140
141 template <typename T>
142 std::enable_if_t<uses_stream_operator<T>::value,
143 stream_operator_format_adapter<T>>
build_format_adapter(T && Item)144 build_format_adapter(T &&Item) {
145 // If the caller passed an Error by value, then stream_operator_format_adapter
146 // would be responsible for consuming it.
147 // Make the caller opt into this by calling fmt_consume().
148 static_assert(
149 !std::is_same<llvm::Error, std::remove_cv_t<T>>::value,
150 "llvm::Error-by-value must be wrapped in fmt_consume() for formatv");
151 return stream_operator_format_adapter<T>(std::forward<T>(Item));
152 }
153
154 template <typename T>
155 std::enable_if_t<uses_missing_provider<T>::value, missing_format_adapter<T>>
build_format_adapter(T &&)156 build_format_adapter(T &&) {
157 return missing_format_adapter<T>();
158 }
159 }
160 }
161
162 #endif
163