[libc++][format] P3142R0: Printing Blank Lines with `println` #87277

H-G-Hristov · 2024-04-01T19:22:59Z

Implements https://wg21.link/P3142R0

Applied retroactively as DR, same as stdlibc++ and MS STL:
STL C++26 Features

Implements https://wg21.link/P3142R0

llvmbot · 2024-04-01T20:25:44Z

@llvm/pr-subscribers-libcxx

Author: Hristo Hristov (H-G-Hristov)

Changes

Implements https://wg21.link/P3142R0

Full diff: https://github.com/llvm/llvm-project/pull/87277.diff

8 Files Affected:

(modified) libcxx/docs/ReleaseNotes/19.rst (+1)
(modified) libcxx/include/ostream (+4)
(modified) libcxx/include/print (+8)
(modified) libcxx/test/std/input.output/iostream.format/output.streams/ostream.formatted/ostream.formatted.print/locale-specific_form.pass.cpp (+3-1)
(modified) libcxx/test/std/input.output/iostream.format/output.streams/ostream.formatted/ostream.formatted.print/println.pass.cpp (+3-1)
(modified) libcxx/test/std/input.output/iostream.format/print.fun/no_file_description.pass.cpp (+4-1)
(modified) libcxx/test/std/input.output/iostream.format/print.fun/println.file.pass.cpp (+18)
(modified) libcxx/test/std/input.output/iostream.format/print.fun/println.sh.cpp (+2-1)

diff --git a/libcxx/docs/ReleaseNotes/19.rst b/libcxx/docs/ReleaseNotes/19.rst
index dd39c1bbbc78a3..7bf1da91e2abb9 100644
--- a/libcxx/docs/ReleaseNotes/19.rst
+++ b/libcxx/docs/ReleaseNotes/19.rst
@@ -42,6 +42,7 @@ Implemented Papers
 - P2652R2 - Disallow User Specialization of ``allocator_traits``
 - P2819R2 - Add ``tuple`` protocol to ``complex``
 - P2495R3 - Interfacing ``stringstream``\s with ``string_view``
+- P3142R0 - Printing Blank Lines with ``println`` (as DR against C++23)
 - P2302R4 - ``std::ranges::contains``
 - P1659R3 - ``std::ranges::starts_with`` and ``std::ranges::ends_with``
 
diff --git a/libcxx/include/ostream b/libcxx/include/ostream
index 42819ceb252c65..d4fc1c58b8a941 100644
--- a/libcxx/include/ostream
+++ b/libcxx/include/ostream
@@ -164,6 +164,7 @@ template<class... Args>
   void print(ostream& os, format_string<Args...> fmt, Args&&... args);
 template<class... Args>                                                                                // since C++23
   void println(ostream& os, format_string<Args...> fmt, Args&&... args);
+void println(ostream& os);                                                                             // since C++26
 
 void vprint_unicode(ostream& os, string_view fmt, format_args args);                                   // since C++23
 void vprint_nonunicode(ostream& os, string_view fmt, format_args args);                                // since C++23
@@ -1163,6 +1164,9 @@ _LIBCPP_HIDE_FROM_ABI void println(ostream& __os, format_string<_Args...> __fmt,
 #  endif // _LIBCPP_HAS_NO_UNICODE
 }
 
+template <class = void> // TODO PRINT template or availability markup fires too eagerly (http://llvm.org/PR61563).
+_LIBCPP_HIDE_FROM_ABI inline void println(ostream& __os) { std::print(__os, "\n"); }
+
 #endif // _LIBCPP_STD_VER >= 23
 
 _LIBCPP_END_NAMESPACE_STD
diff --git a/libcxx/include/print b/libcxx/include/print
index a9f10433a7dc61..e0bcf214ea239b 100644
--- a/libcxx/include/print
+++ b/libcxx/include/print
@@ -15,8 +15,10 @@ namespace std {
   // [print.fun], print functions
   template<class... Args>
     void print(format_string<Args...> fmt, Args&&... args);
+  void println();                                                          // Since C++26
   template<class... Args>
     void print(FILE* stream, format_string<Args...> fmt, Args&&... args);
+  void println(FILE* stream);                                              // Since C++26
 
   template<class... Args>
     void println(format_string<Args...> fmt, Args&&... args);
@@ -356,6 +358,12 @@ _LIBCPP_HIDE_FROM_ABI void println(FILE* __stream, format_string<_Args...> __fmt
 #  endif // _LIBCPP_HAS_NO_UNICODE
 }
 
+template <class = void> // TODO PRINT template or availability markup fires too eagerly (http://llvm.org/PR61563).
+_LIBCPP_HIDE_FROM_ABI inline void println(FILE* __stream) { std::print(__stream, "\n"); }
+
+template <class = void> // TODO PRINT template or availability markup fires too eagerly (http://llvm.org/PR61563).
+_LIBCPP_HIDE_FROM_ABI inline void println() { println(stdout); }
+
 template <class... _Args>
 _LIBCPP_HIDE_FROM_ABI void println(format_string<_Args...> __fmt, _Args&&... __args) {
   std::println(stdout, __fmt, std::forward<_Args>(__args)...);
diff --git a/libcxx/test/std/input.output/iostream.format/output.streams/ostream.formatted/ostream.formatted.print/locale-specific_form.pass.cpp b/libcxx/test/std/input.output/iostream.format/output.streams/ostream.formatted/ostream.formatted.print/locale-specific_form.pass.cpp
index 6b62e2f1754de5..8edfb90b15b86d 100644
--- a/libcxx/test/std/input.output/iostream.format/output.streams/ostream.formatted/ostream.formatted.print/locale-specific_form.pass.cpp
+++ b/libcxx/test/std/input.output/iostream.format/output.streams/ostream.formatted/ostream.formatted.print/locale-specific_form.pass.cpp
@@ -26,6 +26,7 @@
 //   void print(ostream& os, format_string<Args...> fmt, Args&&... args);
 // template<class... Args>
 //   void println(ostream& os, format_string<Args...> fmt, Args&&... args);
+// void println(ostream& os);                                                // since C++26
 //
 // void vprint_unicode(ostream& os, string_view fmt, format_args args);
 // void vprint_nonunicode(ostream& os, string_view fmt, format_args args);
@@ -86,10 +87,11 @@ test(std::stringstream& stream, std::string expected, test_format_string<char, A
   }
   // *** println ***
   {
-    expected += '\n'; // Tested last since it changes the expected value.
+    expected += "\n\n"; // Tested last since it changes the expected value.
     stream.str("");
     ;
     std::println(stream, fmt, std::forward<Args>(args)...);
+    std::println(stream);
     std::string out = stream.str();
     TEST_REQUIRE(out == expected,
                  TEST_WRITE_CONCATENATED(
diff --git a/libcxx/test/std/input.output/iostream.format/output.streams/ostream.formatted/ostream.formatted.print/println.pass.cpp b/libcxx/test/std/input.output/iostream.format/output.streams/ostream.formatted/ostream.formatted.print/println.pass.cpp
index 479a3de0a93c8d..b61fcf174422af 100644
--- a/libcxx/test/std/input.output/iostream.format/output.streams/ostream.formatted/ostream.formatted.print/println.pass.cpp
+++ b/libcxx/test/std/input.output/iostream.format/output.streams/ostream.formatted/ostream.formatted.print/println.pass.cpp
@@ -17,6 +17,7 @@
 
 // template<class... Args>
 //   void println(ostream& os, format_string<Args...> fmt, Args&&... args);
+// void println(ostream& os);                                                // since C++26
 
 // [ostream.formatted.print]/3
 //   If the function is vprint_unicode and os is a stream that refers to
@@ -37,10 +38,11 @@
 #include "test_macros.h"
 
 auto test_file = []<class... Args>(std::string_view e, test_format_string<char, Args...> fmt, Args&&... args) {
-  std::string expected = std::string{e} + '\n';
+  std::string expected = std::string{e} + "\n\n";
 
   std::stringstream sstr;
   std::println(sstr, fmt, std::forward<Args>(args)...);
+  std::println(sstr);
 
   std::string out = sstr.str();
   TEST_REQUIRE(out == expected,
diff --git a/libcxx/test/std/input.output/iostream.format/print.fun/no_file_description.pass.cpp b/libcxx/test/std/input.output/iostream.format/print.fun/no_file_description.pass.cpp
index f502616b677b77..450ca45a6d4b7e 100644
--- a/libcxx/test/std/input.output/iostream.format/print.fun/no_file_description.pass.cpp
+++ b/libcxx/test/std/input.output/iostream.format/print.fun/no_file_description.pass.cpp
@@ -25,8 +25,10 @@
 
 // template<class... Args>
 //   void print(FILE* stream, format_string<Args...> fmt, Args&&... args);
+// void println();                                                          // Since C++26
 // template<class... Args>
 //   void println(FILE* stream, format_string<Args...> fmt, Args&&... args);
+// void println(FILE* stream);                                              // Since C++26
 // void vprint_unicode(FILE* stream, string_view fmt, format_args args);
 // void vprint_nonunicode(FILE* stream, string_view fmt, format_args args);
 
@@ -56,11 +58,12 @@ static void test_println() {
   assert(file);
 
   std::println(file, "hello world{}", '!');
+  std::println(file);
   long pos = std::ftell(file);
   std::fclose(file);
 
   assert(pos > 0);
-  assert(std::string_view(buffer.data(), pos) == "hello world!\n");
+  assert(std::string_view(buffer.data(), pos) == "hello world!\n\n");
 }
 
 static void test_vprint_unicode() {
diff --git a/libcxx/test/std/input.output/iostream.format/print.fun/println.file.pass.cpp b/libcxx/test/std/input.output/iostream.format/print.fun/println.file.pass.cpp
index 07272ebb57e5fc..9e96864aa822dd 100644
--- a/libcxx/test/std/input.output/iostream.format/print.fun/println.file.pass.cpp
+++ b/libcxx/test/std/input.output/iostream.format/print.fun/println.file.pass.cpp
@@ -112,6 +112,17 @@ static void test_new_line() {
     FILE* file = fopen(filename.c_str(), "w");
     assert(file);
 
+    std::println(file);
+#ifndef _WIN32
+    assert(std::ftell(file) == 1);
+#else
+    assert(std::ftell(file) == 2);
+#endif
+  }
+  {
+    FILE* file = fopen(filename.c_str(), "w");
+    assert(file);
+
     std::println(file, "");
 #ifndef _WIN32
     assert(std::ftell(file) == 1);
@@ -124,6 +135,13 @@ static void test_new_line() {
     FILE* file = fopen(filename.c_str(), "wb");
     assert(file);
 
+    std::println(file);
+    assert(std::ftell(file) == 1);
+  }
+  {
+    FILE* file = fopen(filename.c_str(), "wb");
+    assert(file);
+
     std::println(file, "");
     assert(std::ftell(file) == 1);
   }
diff --git a/libcxx/test/std/input.output/iostream.format/print.fun/println.sh.cpp b/libcxx/test/std/input.output/iostream.format/print.fun/println.sh.cpp
index b811b4f2a24933..67343b3a730c54 100644
--- a/libcxx/test/std/input.output/iostream.format/print.fun/println.sh.cpp
+++ b/libcxx/test/std/input.output/iostream.format/print.fun/println.sh.cpp
@@ -36,7 +36,7 @@
 
 // FILE_DEPENDENCIES: echo.sh
 // RUN: %{build}
-// RUN: %{exec} bash echo.sh -ne "1234 一二三四\ntrue 0x0\n" > %t.expected
+// RUN: %{exec} bash echo.sh -ne "1234 一二三四\ntrue 0x0\n\n" > %t.expected
 // RUN: %{exec} "%t.exe" > %t.actual
 // RUN: diff -u %t.actual %t.expected
 
@@ -46,6 +46,7 @@ int main(int, char**) {
   // The data is passed as-is so it does not depend on the encoding of the input.
   std::println("{} {}", 1234, "一二三四");
   std::println("{} {}", true, nullptr);
+  std::println();
 
   return 0;
 }

mordante

This looks quite good. A few minor comments. Can you rebase so you can update the status page.

...ormat/output.streams/ostream.formatted/ostream.formatted.print/locale-specific_form.pass.cpp

…-std_println

...ormat/output.streams/ostream.formatted/ostream.formatted.print/locale-specific_form.pass.cpp

…-std_println

mordante

Thanks! LGTM!

Zingam · 2024-04-06T18:52:39Z

@mordante Thank you!

vvereschaka · 2024-04-08T04:59:20Z

@H-G-Hristov ,

the llvm-libc++-static.cfg.in::println.blank_line.sh.cpp test gets failed on the windows to linux cross builders with the following messages

diff -u C:\buildbot\as-builder-1\x-armv7l\build\runtimes\runtimes-armv7-unknown-linux-gnueabihf-bins\test\std\input.output\iostream.format\print.fun\Output\println.blank_line.sh.cpp.dir\t.tmp.actual C:\buildbot\as-builder-1\x-armv7l\build\runtimes\runtimes-armv7-unknown-linux-gnueabihf-bins\test\std\input.output\iostream.format\print.fun\Output\println.blank_line.sh.cpp.dir\t.tmp.expected
# executed command: diff -u 'C:\buildbot\as-builder-1\x-armv7l\build\runtimes\runtimes-armv7-unknown-linux-gnueabihf-bins\test\std\input.output\iostream.format\print.fun\Output\println.blank_line.sh.cpp.dir\t.tmp.actual' 'C:\buildbot\as-builder-1\x-armv7l\build\runtimes\runtimes-armv7-unknown-linux-gnueabihf-bins\test\std\input.output\iostream.format\print.fun\Output\println.blank_line.sh.cpp.dir\t.tmp.expected'
# .---command stdout------------
# | --- C:\buildbot\as-builder-1\x-armv7l\build\runtimes\runtimes-armv7-unknown-linux-gnueabihf-bins\test\std\input.output\iostream.format\print.fun\Output\println.blank_line.sh.cpp.dir\t.tmp.actual
# | +++ C:\buildbot\as-builder-1\x-armv7l\build\runtimes\runtimes-armv7-unknown-linux-gnueabihf-bins\test\std\input.output\iostream.format\print.fun\Output\println.blank_line.sh.cpp.dir\t.tmp.expected
# | @@ -1 +1 @@
# | -
# | +n
# `-----------------------------
# error: command failed with exit status: 1

would you take care of it?

mordante · 2024-04-08T15:51:23Z

I had a look and a similar test std/input.output/iostream.format/print.fun/println.sh.cpp passes on this platform. Maybe the issue is that the output only contains \n. Maybe changing the test to

print("hello world");
println();

might solve the issue. @Zingam can you provide a followup patch to make this change?
@vvereschaka would you be able to test that followup patch? Do you feel this is so urgent it warrants a temporary revert?

If the suggested solution works we should add comment why we output we do that.

…-win-x-* configurations Fix for issue: llvm#87277 (comment)

H-G-Hristov · 2024-04-08T16:33:05Z

@vvereschaka @mordante I created a PR with the proposed resolution with a slight twist here: #88011 Thank you for the heads-up!

I wonder if double println() will resolve the issue too but I don't know how to test it.

…-win-x-* configurations (#88011) Fix for issue: #87277 (comment) The test fails on the windows to linux cross builders. The proposed resolution is to print some text. The issue is possibly due to the original test outputting a single `\n` character.

…-win-x-* configurations (#88011) Fix for issue: llvm/llvm-project#87277 (comment) The test fails on the windows to linux cross builders. The proposed resolution is to print some text. The issue is possibly due to the original test outputting a single `\n` character. NOKEYCHECK=True GitOrigin-RevId: ea2392ed33f765018002f833da9a04cd0571ab83

[libc++][format] P3142R0 - Printing Blank Lines with println

327f8fe

Implements https://wg21.link/P3142R0

H-G-Hristov changed the title ~~[libc++][format] P3142R0 - Printing Blank Lines with println~~ [libc++][format] P3142R0: Printing Blank Lines with println Apr 1, 2024

H-G-Hristov added 2 commits April 1, 2024 23:20

Try to fix Apple CI

d39dbbe

Updated tests for consistency

36c65f2

H-G-Hristov marked this pull request as ready for review April 1, 2024 20:25

H-G-Hristov requested a review from a team as a code owner April 1, 2024 20:25

llvmbot added the libc++ libc++ C++ Standard Library. Not GNU libstdc++. Not libc++abi. label Apr 1, 2024

mordante requested changes Apr 3, 2024

View reviewed changes

...ormat/output.streams/ostream.formatted/ostream.formatted.print/locale-specific_form.pass.cpp Outdated Show resolved Hide resolved

H-G-Hristov added 4 commits April 4, 2024 23:19

Merge branch 'main' into hgh/libcxx/P3142R0-Printing-Blank-Lines-with…

1b00673

…-std_println

Addressed review comments

8c93e19

Split tests 1

02fbb0b

Split tests 2

6de4539

mordante reviewed Apr 5, 2024

View reviewed changes

...ormat/output.streams/ostream.formatted/ostream.formatted.print/locale-specific_form.pass.cpp Outdated Show resolved Hide resolved

H-G-Hristov added 5 commits April 5, 2024 21:15

Addressed review comments

853bae6

Addressed review comments

32cfe09

Addressed review comments

689a46e

Merge branch 'main' into hgh/libcxx/P3142R0-Printing-Blank-Lines-with…

cf2226a

…-std_println

Cleanup

bfd052b

Zingam requested a review from mordante April 6, 2024 07:13

mordante approved these changes Apr 6, 2024

View reviewed changes

Zingam merged commit 7f9f82e into llvm:main Apr 6, 2024

H-G-Hristov added a commit to H-G-Hristov/llvm-project that referenced this pull request Apr 8, 2024

[libc++][format] Fixed println.blank_line.sh.cpp test on llvm-clang…

863475f

…-win-x-* configurations Fix for issue: llvm#87277 (comment)

H-G-Hristov mentioned this pull request Apr 8, 2024

[libc++][format] Fixed println.blank_line.sh.cpp test on llvm-clang-win-x-* configurations #88011

Merged

H-G-Hristov deleted the hgh/libcxx/P3142R0-Printing-Blank-Lines-with-std_println branch April 13, 2024 21:08

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

[libc++][format] P3142R0: Printing Blank Lines with `println` #87277

[libc++][format] P3142R0: Printing Blank Lines with `println` #87277

Uh oh!

H-G-Hristov commented Apr 1, 2024 •

edited by Zingam

Loading

Uh oh!

llvmbot commented Apr 1, 2024

Uh oh!

mordante left a comment

Uh oh!

Uh oh!

Uh oh!

mordante left a comment

Uh oh!

Zingam commented Apr 6, 2024

Uh oh!

vvereschaka commented Apr 8, 2024

Uh oh!

mordante commented Apr 8, 2024

Uh oh!

H-G-Hristov commented Apr 8, 2024 •

edited

Loading

Uh oh!

Uh oh!

[libc++][format] P3142R0: Printing Blank Lines with println #87277

[libc++][format] P3142R0: Printing Blank Lines with println #87277

Uh oh!

Conversation

H-G-Hristov commented Apr 1, 2024 • edited by Zingam Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

llvmbot commented Apr 1, 2024

Uh oh!

mordante left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

mordante left a comment

Choose a reason for hiding this comment

Uh oh!

Zingam commented Apr 6, 2024

Uh oh!

vvereschaka commented Apr 8, 2024

Uh oh!

mordante commented Apr 8, 2024

Uh oh!

H-G-Hristov commented Apr 8, 2024 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Uh oh!

[libc++][format] P3142R0: Printing Blank Lines with `println` #87277

[libc++][format] P3142R0: Printing Blank Lines with `println` #87277

H-G-Hristov commented Apr 1, 2024 •

edited by Zingam

Loading

H-G-Hristov commented Apr 8, 2024 •

edited

Loading