1 //===- FormatVariadicDetails.h - Helpers for FormatVariadic.h ----*- C++-*-===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #ifndef LLVM_SUPPORT_FORMATVARIADIC_DETAILS_H
11 #define LLVM_SUPPORT_FORMATVARIADIC_DETAILS_H
12 
13 #include "llvm/ADT/StringRef.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() {}
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<typename std::decay<T>::type>::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 Options) 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 = typename std::decay<T>::type;
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 typename std::decay<T>::type &;
80 
81   template <typename U>
82   static char test(typename std::enable_if<
83                    std::is_same<decltype(std::declval<llvm::raw_ostream &>()
84                                          << std::declval<U>()),
85                                 llvm::raw_ostream &>::value,
86                    int *>::type);
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,
100                           typename std::remove_reference<T>::type>::value> {};
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 typename std::enable_if<uses_format_member<T>::value, T>::type
132 build_format_adapter(T &&Item) {
133   return std::forward<T>(Item);
134 }
135 
136 template <typename T>
137 typename std::enable_if<uses_format_provider<T>::value,
138                         provider_format_adapter<T>>::type
139 build_format_adapter(T &&Item) {
140   return provider_format_adapter<T>(std::forward<T>(Item));
141 }
142 
143 template <typename T>
144 typename std::enable_if<uses_stream_operator<T>::value,
145                         stream_operator_format_adapter<T>>::type
146 build_format_adapter(T &&Item) {
147   // If the caller passed an Error by value, then stream_operator_format_adapter
148   // would be responsible for consuming it.
149   // Make the caller opt into this by calling fmt_consume().
150   static_assert(
151       !std::is_same<llvm::Error, typename std::remove_cv<T>::type>::value,
152       "llvm::Error-by-value must be wrapped in fmt_consume() for formatv");
153   return stream_operator_format_adapter<T>(std::forward<T>(Item));
154 }
155 
156 template <typename T>
157 typename std::enable_if<uses_missing_provider<T>::value,
158                         missing_format_adapter<T>>::type
159 build_format_adapter(T &&Item) {
160   return missing_format_adapter<T>();
161 }
162 }
163 }
164 
165 #endif
166