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/ADT/STLExtras.h"
14 #include "llvm/Support/raw_ostream.h"
15 
16 #include <type_traits>
17 
18 namespace llvm {
19 template <typename T, typename Enable = void> struct format_provider {};
20 class Error;
21 
22 namespace detail {
23 class format_adapter {
24   virtual void anchor();
25 
26 protected:
27   virtual ~format_adapter() = default;
28 
29 public:
30   virtual void format(raw_ostream &S, StringRef Options) = 0;
31 };
32 
33 template <typename T> class provider_format_adapter : public format_adapter {
34   T Item;
35 
36 public:
37   explicit provider_format_adapter(T &&Item) : Item(std::forward<T>(Item)) {}
38 
39   void format(llvm::raw_ostream &S, StringRef Options) override {
40     format_provider<std::decay_t<T>>::format(Item, S, Options);
41   }
42 };
43 
44 template <typename T>
45 class stream_operator_format_adapter : public format_adapter {
46   T Item;
47 
48 public:
49   explicit stream_operator_format_adapter(T &&Item)
50       : Item(std::forward<T>(Item)) {}
51 
52   void format(llvm::raw_ostream &S, StringRef) override { S << Item; }
53 };
54 
55 template <typename T> class missing_format_adapter;
56 
57 // Test if format_provider<T> is defined on T and contains a member function
58 // with the signature:
59 //   static void format(const T&, raw_stream &, StringRef);
60 //
61 template <class T> class has_FormatProvider {
62 public:
63   using Decayed = std::decay_t<T>;
64   typedef void (*Signature_format)(const Decayed &, llvm::raw_ostream &,
65                                    StringRef);
66 
67   template <typename U>
68   static char test(SameType<Signature_format, &U::format> *);
69 
70   template <typename U> static double test(...);
71 
72   static bool const value =
73       (sizeof(test<llvm::format_provider<Decayed>>(nullptr)) == 1);
74 };
75 
76 // Test if raw_ostream& << T -> raw_ostream& is findable via ADL.
77 template <class T> class has_StreamOperator {
78 public:
79   using ConstRefT = const std::decay_t<T> &;
80 
81   template <typename U>
82   static char test(
83       std::enable_if_t<std::is_same<decltype(std::declval<llvm::raw_ostream &>()
84                                              << std::declval<U>()),
85                                     llvm::raw_ostream &>::value,
86                        int *>);
87 
88   template <typename U> static double test(...);
89 
90   static bool const value = (sizeof(test<ConstRefT>(nullptr)) == 1);
91 };
92 
93 // Simple template that decides whether a type T should use the member-function
94 // based format() invocation.
95 template <typename T>
96 struct uses_format_member
97     : public std::integral_constant<
98           bool,
99           std::is_base_of<format_adapter, std::remove_reference_t<T>>::value> {
100 };
101 
102 // Simple template that decides whether a type T should use the format_provider
103 // based format() invocation.  The member function takes priority, so this test
104 // will only be true if there is not ALSO a format member.
105 template <typename T>
106 struct uses_format_provider
107     : public std::integral_constant<
108           bool, !uses_format_member<T>::value && has_FormatProvider<T>::value> {
109 };
110 
111 // Simple template that decides whether a type T should use the operator<<
112 // based format() invocation.  This takes last priority.
113 template <typename T>
114 struct uses_stream_operator
115     : public std::integral_constant<bool, !uses_format_member<T>::value &&
116                                               !uses_format_provider<T>::value &&
117                                               has_StreamOperator<T>::value> {};
118 
119 // Simple template that decides whether a type T has neither a member-function
120 // nor format_provider based implementation that it can use.  Mostly used so
121 // that the compiler spits out a nice diagnostic when a type with no format
122 // implementation can be located.
123 template <typename T>
124 struct uses_missing_provider
125     : public std::integral_constant<bool, !uses_format_member<T>::value &&
126                                               !uses_format_provider<T>::value &&
127                                               !uses_stream_operator<T>::value> {
128 };
129 
130 template <typename T>
131 std::enable_if_t<uses_format_member<T>::value, T>
132 build_format_adapter(T &&Item) {
133   return std::forward<T>(Item);
134 }
135 
136 template <typename T>
137 std::enable_if_t<uses_format_provider<T>::value, provider_format_adapter<T>>
138 build_format_adapter(T &&Item) {
139   return provider_format_adapter<T>(std::forward<T>(Item));
140 }
141 
142 template <typename T>
143 std::enable_if_t<uses_stream_operator<T>::value,
144                  stream_operator_format_adapter<T>>
145 build_format_adapter(T &&Item) {
146   // If the caller passed an Error by value, then stream_operator_format_adapter
147   // would be responsible for consuming it.
148   // Make the caller opt into this by calling fmt_consume().
149   static_assert(
150       !std::is_same<llvm::Error, std::remove_cv_t<T>>::value,
151       "llvm::Error-by-value must be wrapped in fmt_consume() for formatv");
152   return stream_operator_format_adapter<T>(std::forward<T>(Item));
153 }
154 
155 template <typename T>
156 std::enable_if_t<uses_missing_provider<T>::value, missing_format_adapter<T>>
157 build_format_adapter(T &&) {
158   return missing_format_adapter<T>();
159 }
160 }
161 }
162 
163 #endif
164