third-party/unittest/googletest/include/gtest/internal/custom/raw-ostream.h

   1 //===-- raw-ostream.h - Support for printing using raw_ostream --*- 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 // This file is not part of gtest, but extends it to support LLVM libraries.
   9 // This is not a public API for testing - it's a detail of LLVM's gtest.
  10 //
  11 // gtest allows providing printers for custom types by defining operator<<.
  12 // In LLVM, operator<< usually takes llvm:raw_ostream& instead of std::ostream&.
  13 //
  14 // This file defines a template printable(V), which returns a version of V that
  15 // can be streamed into a std::ostream.
  16 //
  17 // This interface is chosen so that in the default case (printable(V) is V),
  18 // the main gtest code calls operator<<(OS, V) itself. gtest-printers carefully
  19 // controls the lookup to enable fallback printing (see testing::internal2).
  20 //===----------------------------------------------------------------------===//
  21
  22 #ifndef GTEST_INCLUDE_GTEST_INTERNAL_CUSTOM_RAW_OSTREAM_H_
  23 #define GTEST_INCLUDE_GTEST_INTERNAL_CUSTOM_RAW_OSTREAM_H_
  24
  25 namespace llvm_gtest {
  26 // StreamSwitch is a trait that tells us how to stream a T into a std::ostream.
  27 // By default, we just stream the T directly. We'll specialize this later.
  28 template <typename T, typename Enable = void> struct StreamSwitch {
  29   static const T& printable(const T& V) { return V; }
  30 };
  31
  32 // printable() returns a version of its argument that can be streamed into a
  33 // std::ostream. This may be the argument itself, or some other representation.
  34 template <typename T> decltype(auto) printable(const T &V) {
  35   // We delegate to the trait, to allow partial specialization.
  36   return StreamSwitch<T>::printable(V);
  37 }
  38 } // namespace llvm_gtest
  39
  40 // If raw_ostream support is enabled, we specialize for types with operator<<
  41 // that takes a raw_ostream.
  42 #if !GTEST_NO_LLVM_SUPPORT
  43 #include "llvm/Support/raw_os_ostream.h"
  44 #include "llvm/Support/raw_ostream.h"
  45 #include <optional>
  46 #include <ostream>
  47 namespace llvm_gtest {
  48
  49 // The printable() of a raw_ostream-enabled type T is a RawStreamProxy<T>.
  50 // It uses raw_os_ostream to write the wrapped value to a std::ostream.
  51 template <typename T>
  52 struct RawStreamProxy {
  53   const T& V;
  54   friend std::ostream &operator<<(std::ostream &S, const RawStreamProxy<T> &V) {
  55     llvm::raw_os_ostream OS(S);
  56     OS << V.V;
  57     return S;
  58   }
  59 };
  60
  61 // We enable raw_ostream treatment if `(raw_ostream&) << (const T&)` is valid.
  62 // We don't want implicit conversions on the RHS (e.g. to bool!), so "consume"
  63 // the possible conversion by passing something convertible to const T& instead.
  64 template <typename T> struct ConvertibleTo { operator T(); };
  65 template <typename T>
  66 struct StreamSwitch<T, decltype((void)(std::declval<llvm::raw_ostream &>()
  67                                        << ConvertibleTo<const T &>()))> {
  68   static const RawStreamProxy<T> printable(const T &V) { return {V}; }
  69 };
  70
  71 // std::optional has a template operator<<, which means it will not accept any
  72 // implicit conversions, so we need to special-case it here.
  73 template <typename T>
  74 struct StreamSwitch<std::optional<T>,
  75                     decltype((void)(std::declval<llvm::raw_ostream &>()
  76                                     << std::declval<std::optional<T>>()))> {
  77   static const RawStreamProxy<std::optional<T>>
  78   printable(const std::optional<T> &V) {
  79     return {V};
  80   }
  81 };
  82 } // namespace llvm_gtest
  83 #endif  // !GTEST_NO_LLVM_SUPPORT
  84
  85 #endif // GTEST_INCLUDE_GTEST_INTERNAL_CUSTOM_RAW_OSTREAM_H_