[Support] Add raw_ostream_iterator: ostream_iterator for raw_ostream.

[nlguillemot]

Summary

Adds a class raw_ostream_iterator that behaves like
std::ostream_iterator, but can be used with raw_ostream.
This is useful for using raw_ostream with std algorithms.

For example, it can be used to output std containers as follows:

std::vector<int> V = { 1, 2, 3 };
std::copy(V.begin(), V.end(), raw_ostream_iterator<int>(outs(), ", "));
// Output: "1, 2, 3, "

The API tries to follow std::ostream_iterator as closely as is
practically possible.

[nlguillemot]

This is patch is mainly useful for enabling some of the refactors that happen in the next patch here: https://reviews.llvm.org/D78796

[nlguillemot]

Some example code and the commit message were showing an example of printing a vector<double>. It turns out that doubles don't print so beautifully by default, so switch the example to use int instead to avoid being misleading.

[dblaikie]

Maybe some more test coverage (empty range at least) but otherwise looks good.

Maybe hold of on committing this until some of the rest of the patch sequence has been reviewed/approved, in case it doesn't end up being needed.

llvm/include/llvm/Support/raw_ostream.h

637

Could use a non-static data member initializer for Delim = nullptr, and not bother initializing it here, perhaps? (I don't feel super strongly about this)

llvm/unittests/Support/raw_ostream_test.cpp

358–360

FWIW (again, don't feel strongly) I'd probably use an explicit scope rather than an explicit call to flush here. *shrug*

[dblaikie]

llvm/unittests/Support/raw_ostream_test.cpp

355–371

If you could simplify the testing to not use another whole container type and standard algorithm, that'd probably be good, in my opinion.

It'd make the tests more explicit/obvious about the surface area they're testing. You could test the empty case, and writing a few elements to the output iterator.

(this I feel a bit more strongly about than the other two comments)

[nlguillemot]

• Added some basic tests that use raw_ostream_iterator manually instead of through std::copy.
• Replaced manual calls to flush() in the test with an artificial scope (takes advantage of the fact that ~raw_string_ostream() calls flush())
• Added a test for std::copy with an empty range.

[nlguillemot]

In D78795#2007027, @dblaikie wrote:

Maybe hold of on committing this until some of the rest of the patch sequence has been reviewed/approved, in case it doesn't end up being needed.

I agree.

[nlguillemot]

Thanks for the review @dblaikie !

[mkitzan]

Looks like a good helper class. Just some minor nits. (haven't looked into the tests just yet)

llvm/include/llvm/Support/raw_ostream.h

629–637

Alternatively, could collapse into one ctor with a default argument for Delim.
raw_ostream_iterator(raw_ostream &Stream, const CharT * Delim = nullptr) : OutStream(Stream), Delim(Delim) {}.

637

Yeah, changing L637 to : OutStream(Stream) {} and L612 to const CharT *Delim = nullptr would comply better with CppCoreGuidelines C.48, but it's still a nit.

645

Also a nit, could just be if (Delim) or if you really want to explicitly show the comparison if (Delim != nullptr) (CppCoreGuideline ES.87).

[nlguillemot]

llvm/include/llvm/Support/raw_ostream.h

629–637

I agree that would be cleaner, but I kept it as two constructors to match the specification here: https://en.cppreference.com/w/cpp/iterator/ostream_iterator/ostream_iterator

645

it's kind of silly, but I wrote it this way to match the code here as closely as possible: https://en.cppreference.com/w/cpp/iterator/ostream_iterator/operator%3D

[nlguillemot]

Rebased the patch onto main.

[nlguillemot]

Reverted since there are some build errors on Windows bots. Here's the error log:

[739/841] Building CXX object unittests\Support\CMakeFiles\SupportTests.dir\raw_ostream_test.cpp.obj
FAILED: unittests/Support/CMakeFiles/SupportTests.dir/raw_ostream_test.cpp.obj 
C:\PROGRA~2\MICROS~3\2019\PROFES~1\VC\Tools\MSVC\1428~1.293\bin\Hostx64\x64\cl.exe  /nologo /TP -DGTEST_HAS_RTTI=0 -DGTEST_HAS_TR1_TUPLE=0 -DUNICODE -D_CRT_NONSTDC_NO_DEPRECATE -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_SECURE_NO_DEPRECATE -D_CRT_SECURE_NO_WARNINGS -D_HAS_EXCEPTIONS=0 -D_SCL_SECURE_NO_DEPRECATE -D_SCL_SECURE_NO_WARNINGS -D_UNICODE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -Iunittests\Support -IC:\b\slave\clang-x64-windows-msvc\llvm-project\llvm\unittests\Support -Iinclude -IC:\b\slave\clang-x64-windows-msvc\llvm-project\llvm\include -IC:\b\slave\clang-x64-windows-msvc\llvm-project\llvm\utils\unittest\googletest\include -IC:\b\slave\clang-x64-windows-msvc\llvm-project\llvm\utils\unittest\googlemock\include /DWIN32 /D_WINDOWS   /Zc:inline /Zc:__cplusplus /Zi /Zc:strictStrings /Oi /Zc:rvalueCast /bigobj /W4 -wd4141 -wd4146 -wd4244 -wd4267 -wd4291 -wd4351 -wd4456 -wd4457 -wd4458 -wd4459 -wd4503 -wd4624 -wd4722 -wd4100 -wd4127 -wd4512 -wd4505 -wd4610 -w
d4510 -wd4702 -wd4245 -wd4706 -wd4310 -wd4701 -wd4703 -wd4389 -wd4611 -wd4805 -wd4204 -wd4577 -wd4091 -wd4592 -wd4319 -wd4709 -wd4324 -w14062 -we4238 /Gw /MD /O2 /Ob2  /EHs-c- /GR- -UNDEBUG -std:c++14 /showIncludes /Founittests\Support\CMakeFiles\SupportTests.dir\raw_ostream_test.cpp.obj /Fdunittests\Support\CMakeFiles\SupportTests.dir\ /FS -c C:\b\slave\clang-x64-windows-msvc\llvm-project\llvm\unittests\Support\raw_ostream_test.cpp
C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\VC\Tools\MSVC\14.28.29333\include\xutility(1492): error C2280: 'llvm::raw_ostream_iterator<char,char> &llvm::raw_ostream_iterator<char,char>::operator =(const llvm::raw_ostream_iterator<char,char> &)': attempting to reference a deleted function
C:\b\slave\clang-x64-windows-msvc\llvm-project\llvm\include\llvm/Support/raw_ostream.h(776): note: compiler has generated 'llvm::raw_ostream_iterator<char,char>::operator =' here
C:\b\slave\clang-x64-windows-msvc\llvm-project\llvm\include\llvm/Support/raw_ostream.h(776): note: 'llvm::raw_ostream_iterator<char,char> &llvm::raw_ostream_iterator<char,char>::operator =(const llvm::raw_ostream_iterator<char,char> &)': function was implicitly deleted because 'llvm::raw_ostream_iterator<char,char>' has a data member 'llvm::raw_ostream_iterator<char,char>::OutStream' of reference type
C:\b\slave\clang-x64-windows-msvc\llvm-project\llvm\include\llvm/Support/raw_ostream.h(731): note: see declaration of 'llvm::raw_ostream_iterator<char,char>::OutStream'
C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\VC\Tools\MSVC\14.28.29333\include\xutility(4429): note: see reference to function template instantiation 'void std::_Seek_wrapped<_OutIt,_OutIt>(_Iter &,_UIter &&)' being compiled
       with
       [
           _OutIt=llvm::raw_ostream_iterator<char,char>,
           _Iter=llvm::raw_ostream_iterator<char,char>,
           _UIter=llvm::raw_ostream_iterator<char,char>
       ]
C:\b\slave\clang-x64-windows-msvc\llvm-project\llvm\unittests\Support\raw_ostream_test.cpp(456): note: see reference to function template instantiation '_OutIt std::copy<InputIt,llvm::raw_ostream_iterator<char,char>>(_InIt,_InIt,_OutIt)' being compiled
       with
       [
           _OutIt=llvm::raw_ostream_iterator<char,char>,
           InputIt=std::_Vector_iterator<std::_Vector_val<std::_Simple_types<char>>>,
           _InIt=std::_Vector_iterator<std::_Vector_val<std::_Simple_types<char>>>
       ]
C:\b\slave\clang-x64-windows-msvc\llvm-project\llvm\unittests\Support\raw_ostream_test.cpp(475): note: see reference to function template instantiation 'std::string `anonymous-namespace'::iterator_str<char,std::_Vector_iterator<std::_Vector_val<std::_Simple_types<_Elem>>>>(InputIt,InputIt)' being compiled
       with
       [
           _Elem=char,
           InputIt=std::_Vector_iterator<std::_Vector_val<std::_Simple_types<char>>>
       ]
C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\VC\Tools\MSVC\14.28.29333\include\xutility(1492): error C2280: 'llvm::raw_ostream_iterator<int,char> &llvm::raw_ostream_iterator<int,char>::operator =(const llvm::raw_ostream_iterator<int,char> &)': attempting to reference a deleted function
C:\b\slave\clang-x64-windows-msvc\llvm-project\llvm\include\llvm/Support/raw_ostream.h(776): note: compiler has generated 'llvm::raw_ostream_iterator<int,char>::operator =' here
C:\b\slave\clang-x64-windows-msvc\llvm-project\llvm\include\llvm/Support/raw_ostream.h(776): note: 'llvm::raw_ostream_iterator<int,char> &llvm::raw_ostream_iterator<int,char>::operator =(const llvm::raw_ostream_iterator<int,char> &)': function was implicitly deleted because 'llvm::raw_ostream_iterator<int,char>' has a data member 'llvm::raw_ostream_iterator<int,char>::OutStream' of reference type
C:\b\slave\clang-x64-windows-msvc\llvm-project\llvm\include\llvm/Support/raw_ostream.h(731): note: see declaration of 'llvm::raw_ostream_iterator<int,char>::OutStream'
C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\VC\Tools\MSVC\14.28.29333\include\xutility(4429): note: see reference to function template instantiation 'void std::_Seek_wrapped<_OutIt,_OutIt>(_Iter &,_UIter &&)' being compiled
       with
       [
           _OutIt=llvm::raw_ostream_iterator<int,char>,
           _Iter=llvm::raw_ostream_iterator<int,char>,
           _UIter=llvm::raw_ostream_iterator<int,char>
       ]
C:\b\slave\clang-x64-windows-msvc\llvm-project\llvm\unittests\Support\raw_ostream_test.cpp(466): note: see reference to function template instantiation '_OutIt std::copy<InputIt,llvm::raw_ostream_iterator<int,char>>(_InIt,_InIt,_OutIt)' being compiled
       with

[nlguillemot]

Here's a repro for the compile error on Windows: https://godbolt.org/z/5EdWKn

llvm/include/llvm/Support/raw_ostream.h

 #define LLVM_SUPPORT_RAW_OSTREAM_H
 
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include <cassert>
 #include <cstddef>
 #include <cstdint>
 #include <cstring>
+#include <iterator>
 #include <string>
 #include <system_error>
 #include <type_traits>
 
 namespace llvm {
 
 class formatv_object_base;
 class format_object_base;
class buffer_ostream : public raw_svector_ostream {
 
   virtual void anchor() override;
 
 public:
   buffer_ostream(raw_ostream &OS) : raw_svector_ostream(Buffer), OS(OS) {}
   ~buffer_ostream() override { OS << str(); }
 };
 
+/// Wrapper to make a raw_ostream look like an output iterator.
+/// Designed to match the API of std::ostream_iterator.
+/// Enables reusing STL algorithms with raw_ostream. For example:
+///
+/// \code{.cpp}
+///
+/// std::vector<double> V = { 0.1, 0.2, 0.3 };
+/// std::copy(V.begin(), V.end(), raw_ostream_iterator<double>(outs(), ", "));
+///
+/// \endcode
+///
+/// The code above outputs: "0.1, 0.2, 0.3, "
+template <class T, class CharT = char> class raw_ostream_iterator {
+  raw_ostream &OutStream;
+  const CharT *Delim;
+
+public:
+  using iterator_category = std::output_iterator_tag;
+  using value_type = void;
+  using difference_type = void;
+  using pointer = void;
+  using reference = void;
+  using char_type = CharT;
+
+  /// Constructs the iterator with \p Stream as the associated stream and \p
+  /// Delim as the delimiter.
+  ///
+  /// \param Stream The output stream to be accessed by this iterator.
+  ///
+  /// \param Delim The null-terminated character string to be inserted into the
+  /// stream after each output.
+  raw_ostream_iterator(raw_ostream &Stream, const CharT *Delim)
+      : OutStream(Stream), Delim(Delim) {}
+
+  /// Constructs the iterator with \p Stream as the associated stream and a null
+  /// pointer as the delimiter.
+  ///
+  /// \param Stream The output stream to be accessed by this iterator.
+  raw_ostream_iterator(raw_ostream &Stream)
+      : OutStream(Stream), Delim(nullptr) {}
+
+  /// Inserts \p Value into the associated stream, then inserts the delimiter,
+  /// if one was specified at construction time.
+  ///
+  /// \param value The object to insert.
+  raw_ostream_iterator &operator=(const T &Value) {
+    OutStream << Value;
+    if (Delim != 0)
+      OutStream << Delim;
+    return *this;
+  }
+
+  /// No-op. Provided to satisfy the requirements of LegacyOutputIterator.
+  ///@{
+  raw_ostream_iterator &operator*() { return *this; }
+  raw_ostream_iterator &operator++() { return *this; }
+  raw_ostream_iterator &operator++(int) { return *this; }
+  ///@}
+};
+
 } // end namespace llvm
 
 #endif // LLVM_SUPPORT_RAW_OSTREAM_H

llvm/unittests/Support/raw_ostream_test.cpp

 }
 
 TEST(raw_fd_ostreamTest, multiple_raw_fd_ostream_to_stdout) {
   std::error_code EC;
 
   { raw_fd_ostream("-", EC, sys::fs::OpenFlags::OF_None); }
   { raw_fd_ostream("-", EC, sys::fs::OpenFlags::OF_None); }
 }
+
+template <class T, class InputIt>
+std::string iterator_str(InputIt First, InputIt Last) {
+  std::string S;
+  raw_string_ostream Str(S);
+  std::copy(First, Last, raw_ostream_iterator<T>(Str));
+  Str.flush();
+  return S;
+}
+
+template <class T, class InputIt>
+std::string iterator_str(InputIt First, InputIt Last, const char *Delim) {
+  std::string S;
+  raw_string_ostream Str(S);
+  std::copy(First, Last, raw_ostream_iterator<T>(Str, Delim));
+  Str.flush();
+  return S;
+}
+
+TEST(raw_ostream_iteratorTest, raw_ostream_iterator_std_copy) {
+  // Test without a delimiter.
+  std::vector<char> V1 = {'a', 'b', 'c'};
+  EXPECT_EQ("abc", iterator_str<char>(V1.begin(), V1.end()));
+
+  // Test with a delimiter.
+  std::vector<int> V2 = {1, 2, 3};
+  EXPECT_EQ("1, 2, 3, ", iterator_str<int>(V2.begin(), V2.end(), ", "));
+}
+
 }