[gcc r14-6590] libstdc++: Do not add padding for std::print to std::ostream

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:8a5cac92e7c20e13f01ca0cfa5dc00d014caf0d3

commit r14-6590-g8a5cac92e7c20e13f01ca0cfa5dc00d014caf0d3
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Dec 15 12:21:36 2023 +0000

    libstdc++: Do not add padding for std::print to std::ostream
    
    Tim Song pointed out that although std::print behaves as a formatted
    output function, it does "determine padding" using the stream's flags.
    
    libstdc++-v3/ChangeLog:
    
            * include/std/ostream (vprint_nonunicode, vprint_unicode): Do
            not insert padding.
            * testsuite/27_io/basic_ostream/print/1.cc: Adjust expected
            behaviour.

Diff:
---
 libstdc++-v3/include/std/ostream                   | 46 +---------------------
 .../testsuite/27_io/basic_ostream/print/1.cc       | 10 +++--
 2 files changed, 8 insertions(+), 48 deletions(-)

diff --git a/libstdc++-v3/include/std/ostream b/libstdc++-v3/include/std/ostream
index 4f1cdc281a3..0cac293e4d6 100644
--- a/libstdc++-v3/include/std/ostream
+++ b/libstdc++-v3/include/std/ostream
@@ -891,21 +891,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 	__try
 	  {
-	    const streamsize __w = __os.width();
-	    const streamsize __n = __out.size();
-	    if (__w > __n)
-	      {
-		const bool __left
-		  = (__os.flags() & ios_base::adjustfield) == ios_base::left;
-		if (!__left)
-		  std::__ostream_fill(__os, __w - __n);
-		if (__os.good())
-		  std::__ostream_write(__os, __out.data(), __n);
-		if (__left && __os.good())
-		  std::__ostream_fill(__os, __w - __n);
-	      }
-	    else
-	      std::__ostream_write(__os, __out.data(), __n);
+	    std::__ostream_write(__os, __out.data(), __out.size());
 	  }
 	__catch(const __cxxabiv1::__forced_unwind&)
 	  {
@@ -923,11 +909,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     ostream::sentry __cerb(__os);
     if (__cerb)
       {
-
-	const streamsize __w = __os.width();
-	const bool __left
-	  = (__os.flags() & ios_base::adjustfield) == ios_base::left;
-
 	__format::_Str_sink<char> __buf;
 	std::vformat_to(__buf.out(), __os.getloc(), __fmt, __args);
 	auto __out = __buf.view();
@@ -938,18 +919,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	// If stream refers to a terminal, write a Unicode string to it.
 	if (auto __term = __open_terminal(__os.rdbuf()))
 	  {
-	    __format::_Str_sink<char> __buf2;
-	    if (__w != 0)
-	      {
-		char __fmt[] = "{0:..{1}}";
-		__fmt[3] == __os.fill();
-		__fmt[4] == __left ? '<' : '>';
-		string_view __str(__out);
-		std::vformat_to(__buf2.out(), // N.B. no need to use getloc()
-				__fmt, std::make_format_args(__str, __w));
-		__out = __buf2.view();
-	      }
-
 	    ios_base::iostate __err = ios_base::goodbit;
 	    __try
 	      {
@@ -981,18 +950,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	// Otherwise just insert the string as normal.
 	__try
 	  {
-	    const streamsize __n = __out.size();
-	    if (__w > __n)
-	      {
-		if (!__left)
-		  std::__ostream_fill(__os, __w - __n);
-		if (__os.good())
-		  std::__ostream_write(__os, __out.data(), __n);
-		if (__left && __os.good())
-		  std::__ostream_fill(__os, __w - __n);
-	      }
-	    else
-	      std::__ostream_write(__os, __out.data(), __n);
+	    std::__ostream_write(__os, __out.data(), __out.size());
 	  }
 	__catch(const __cxxabiv1::__forced_unwind&)
 	  {
diff --git a/libstdc++-v3/testsuite/27_io/basic_ostream/print/1.cc b/libstdc++-v3/testsuite/27_io/basic_ostream/print/1.cc
index 28dc8af33e6..b3abc570d1e 100644
--- a/libstdc++-v3/testsuite/27_io/basic_ostream/print/1.cc
+++ b/libstdc++-v3/testsuite/27_io/basic_ostream/print/1.cc
@@ -42,14 +42,16 @@ test_print_raw()
 }
 
 void
-test_print_formatted()
+test_print_no_padding()
 {
+  // [ostream.formatted.print] does not say this function "determines padding",
+  // see https://gcc.gnu.org/pipermail/gcc-patches/2023-December/640680.html
   char buf[64];
   std::spanstream os(buf);
-  os << std::setw(20) << std::setfill('*') << std::right;
+  os << std::setw(60) << std::setfill('?') << std::right; // should be ignored
   std::print(os, "{} Luftballons", 99);
   std::string_view txt(os.span());
-  VERIFY( txt == "******99 Luftballons" );
+  VERIFY( txt == "99 Luftballons" );
 }
 
 void
@@ -106,7 +108,7 @@ int main()
   test_print_ostream();
   test_println_ostream();
   test_print_raw();
-  test_print_formatted();
+  test_print_no_padding();
   test_vprint_nonunicode();
   test_locale();
 }