1//===- FormatVariadic.h - Efficient type-safe string formatting --*- 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// This file implements the formatv() function which can be used with other LLVM
10// subsystems to provide printf-like formatting, but with improved safety and
11// flexibility. The result of `formatv` is an object which can be streamed to
12// a raw_ostream or converted to a std::string or llvm::SmallString.
13//
14// // Convert to std::string.
15// std::string S = formatv("{0} {1}", 1234.412, "test").str();
16//
17// // Convert to llvm::SmallString
18// SmallString<8> S = formatv("{0} {1}", 1234.412, "test").sstr<8>();
19//
20// // Stream to an existing raw_ostream.
21// OS << formatv("{0} {1}", 1234.412, "test");
22//
23//===----------------------------------------------------------------------===//
24
25#ifndef LLVM_SUPPORT_FORMATVARIADIC_H
26#define LLVM_SUPPORT_FORMATVARIADIC_H
27
28#include "llvm/ADT/ArrayRef.h"
29#include "llvm/ADT/Optional.h"
30#include "llvm/ADT/STLExtras.h"
31#include "llvm/ADT/SmallString.h"
32#include "llvm/ADT/StringRef.h"
33#include "llvm/Support/FormatCommon.h"
34#include "llvm/Support/FormatProviders.h"
35#include "llvm/Support/FormatVariadicDetails.h"
36#include "llvm/Support/raw_ostream.h"
37#include <cstddef>
38#include <string>
39#include <tuple>
40#include <utility>
41#include <vector>
42
43namespace llvm {
44
45enum class ReplacementType { Empty, Format, Literal };
46
47struct ReplacementItem {
48 ReplacementItem() = default;
49 explicit ReplacementItem(StringRef Literal)
50 : Type(ReplacementType::Literal), Spec(Literal) {}
51 ReplacementItem(StringRef Spec, size_t Index, size_t Align, AlignStyle Where,
52 char Pad, StringRef Options)
53 : Type(ReplacementType::Format), Spec(Spec), Index(Index), Align(Align),
54 Where(Where), Pad(Pad), Options(Options) {}
55
56 ReplacementType Type = ReplacementType::Empty;
57 StringRef Spec;
58 size_t Index = 0;
59 size_t Align = 0;
60 AlignStyle Where = AlignStyle::Right;
61 char Pad = 0;
62 StringRef Options;
63};
64
65class formatv_object_base {
66protected:
67 StringRef Fmt;
68 ArrayRef<detail::format_adapter *> Adapters;
69
70 static bool consumeFieldLayout(StringRef &Spec, AlignStyle &Where,
71 size_t &Align, char &Pad);
72
73 static std::pair<ReplacementItem, StringRef>
74 splitLiteralAndReplacement(StringRef Fmt);
75
76 formatv_object_base(StringRef Fmt,
77 ArrayRef<detail::format_adapter *> Adapters)
78 : Fmt(Fmt), Adapters(Adapters) {}
79
80 formatv_object_base(formatv_object_base const &rhs) = delete;
81 formatv_object_base(formatv_object_base &&rhs) = default;
82
83public:
84 void format(raw_ostream &S) const {
85 for (auto &R : parseFormatString(Fmt)) {
86 if (R.Type == ReplacementType::Empty)
87 continue;
88 if (R.Type == ReplacementType::Literal) {
89 S << R.Spec;
90 continue;
91 }
92 if (R.Index >= Adapters.size()) {
93 S << R.Spec;
94 continue;
95 }
96
97 auto W = Adapters[R.Index];
98
99 FmtAlign Align(*W, R.Where, R.Align, R.Pad);
100 Align.format(S, R.Options);
101 }
102 }
103 static SmallVector<ReplacementItem, 2> parseFormatString(StringRef Fmt);
104
105 static Optional<ReplacementItem> parseReplacementItem(StringRef Spec);
106
107 std::string str() const {
108 std::string Result;
109 raw_string_ostream Stream(Result);
110 Stream << *this;
111 Stream.flush();
112 return Result;
113 }
114
115 template <unsigned N> SmallString<N> sstr() const {
116 SmallString<N> Result;
117 raw_svector_ostream Stream(Result);
118 Stream << *this;
119 return Result;
120 }
121
122 template <unsigned N> operator SmallString<N>() const { return sstr<N>(); }
123
124 operator std::string() const { return str(); }
125};
126
127template <typename Tuple> class formatv_object : public formatv_object_base {
128 // Storage for the parameter adapters. Since the base class erases the type
129 // of the parameters, we have to own the storage for the parameters here, and
130 // have the base class store type-erased pointers into this tuple.
131 Tuple Parameters;
132 std::array<detail::format_adapter *, std::tuple_size<Tuple>::value>
133 ParameterPointers;
134
135 // The parameters are stored in a std::tuple, which does not provide runtime
136 // indexing capabilities. In order to enable runtime indexing, we use this
137 // structure to put the parameters into a std::array. Since the parameters
138 // are not all the same type, we use some type-erasure by wrapping the
139 // parameters in a template class that derives from a non-template superclass.
140 // Essentially, we are converting a std::tuple<Derived<Ts...>> to a
141 // std::array<Base*>.
142 struct create_adapters {
143 template <typename... Ts>
144 std::array<detail::format_adapter *, std::tuple_size<Tuple>::value>
145 operator()(Ts &... Items) {
146 return {{&Items...}};
147 }
148 };
149
150public:
151 formatv_object(StringRef Fmt, Tuple &&Params)
152 : formatv_object_base(Fmt, ParameterPointers),
153 Parameters(std::move(Params)) {
154 ParameterPointers = apply_tuple(create_adapters(), Parameters);
155 }
156
157 formatv_object(formatv_object const &rhs) = delete;
158
159 formatv_object(formatv_object &&rhs)
160 : formatv_object_base(std::move(rhs)),
161 Parameters(std::move(rhs.Parameters)) {
162 ParameterPointers = apply_tuple(create_adapters(), Parameters);
163 Adapters = ParameterPointers;
164 }
165};
166
167// Format text given a format string and replacement parameters.
168//
169// ===General Description===
170//
171// Formats textual output. `Fmt` is a string consisting of one or more
172// replacement sequences with the following grammar:
173//
174// rep_field ::= "{" [index] ["," layout] [":" format] "}"
175// index ::= <non-negative integer>
176// layout ::= [[[char]loc]width]
177// format ::= <any string not containing "{" or "}">
178// char ::= <any character except "{" or "}">
179// loc ::= "-" | "=" | "+"
180// width ::= <positive integer>
181//
182// index - A non-negative integer specifying the index of the item in the
183// parameter pack to print. Any other value is invalid.
184// layout - A string controlling how the field is laid out within the available
185// space.
186// format - A type-dependent string used to provide additional options to
187// the formatting operation. Refer to the documentation of the
188// various individual format providers for per-type options.
189// char - The padding character. Defaults to ' ' (space). Only valid if
190// `loc` is also specified.
191// loc - Where to print the formatted text within the field. Only valid if
192// `width` is also specified.
193// '-' : The field is left aligned within the available space.
194// '=' : The field is centered within the available space.
195// '+' : The field is right aligned within the available space (this
196// is the default).
197// width - The width of the field within which to print the formatted text.
198// If this is less than the required length then the `char` and `loc`
199// fields are ignored, and the field is printed with no leading or
200// trailing padding. If this is greater than the required length,
201// then the text is output according to the value of `loc`, and padded
202// as appropriate on the left and/or right by `char`.
203//
204// ===Special Characters===
205//
206// The characters '{' and '}' are reserved and cannot appear anywhere within a
207// replacement sequence. Outside of a replacement sequence, in order to print
208// a literal '{' it must be doubled as "{{".
209//
210// ===Parameter Indexing===
211//
212// `index` specifies the index of the parameter in the parameter pack to format
213// into the output. Note that it is possible to refer to the same parameter
214// index multiple times in a given format string. This makes it possible to
215// output the same value multiple times without passing it multiple times to the
216// function. For example:
217//
218// formatv("{0} {1} {0}", "a", "bb")
219//
220// would yield the string "abba". This can be convenient when it is expensive
221// to compute the value of the parameter, and you would otherwise have had to
222// save it to a temporary.
223//
224// ===Formatter Search===
225//
226// For a given parameter of type T, the following steps are executed in order
227// until a match is found:
228//
229// 1. If the parameter is of class type, and inherits from format_adapter,
230// Then format() is invoked on it to produce the formatted output. The
231// implementation should write the formatted text into `Stream`.
232// 2. If there is a suitable template specialization of format_provider<>
233// for type T containing a method whose signature is:
234// void format(const T &Obj, raw_ostream &Stream, StringRef Options)
235// Then this method is invoked as described in Step 1.
236// 3. If an appropriate operator<< for raw_ostream exists, it will be used.
237// For this to work, (raw_ostream& << const T&) must return raw_ostream&.
238//
239// If a match cannot be found through either of the above methods, a compiler
240// error is generated.
241//
242// ===Invalid Format String Handling===
243//
244// In the case of a format string which does not match the grammar described
245// above, the output is undefined. With asserts enabled, LLVM will trigger an
246// assertion. Otherwise, it will try to do something reasonable, but in general
247// the details of what that is are undefined.
248//
249template <typename... Ts>
250inline auto formatv(const char *Fmt, Ts &&... Vals) -> formatv_object<decltype(
251 std::make_tuple(detail::build_format_adapter(std::forward<Ts>(Vals))...))> {
252 using ParamTuple = decltype(
253 std::make_tuple(detail::build_format_adapter(std::forward<Ts>(Vals))...));
254 return formatv_object<ParamTuple>(
255 Fmt,
256 std::make_tuple(detail::build_format_adapter(std::forward<Ts>(Vals))...));
257}
258
259} // end namespace llvm
260
261#endif // LLVM_SUPPORT_FORMATVARIADIC_H
262