[gcc r12-4070] libstdc++: Add utility for creating std::error_code from OS errors

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

https://gcc.gnu.org/g:d71476c9df931f3ca674941f1942b03eabea010d

commit r12-4070-gd71476c9df931f3ca674941f1942b03eabea010d
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Feb 10 18:00:00 2021 +0000

    libstdc++: Add utility for creating std::error_code from OS errors
    
    This adds a helper function to encapsulate obtaining an error code for
    errors from OS calls. For Windows we want to use GetLastError() and the
    system error category, but otherwise just use errno and the generic
    error category.
    
    This should not be used to replace existing uses of
    ec.assign(errno, generic_category()) because in those cases we really do
    want to get the value of errno, not a system-specific error. Only the
    cases that currently use GetLastError() are replace by this new
    function.
    
    Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
    
    libstdc++-v3/ChangeLog:
    
            * src/filesystem/ops-common.h (last_error): New helper function.
            (filesystem::do_space): Use last_error().
            * src/c++17/fs_ops.cc (fs::absolute, fs::create_hard_link)
            (fs::equivalent, fs::remove, fs::temp_directory_path): Use
            last_error().
            * src/filesystem/ops.cc (fs::create_hard_link)
            (fs::remove, fs::temp_directory_path): Likewise.

Diff:
---
 libstdc++-v3/src/c++17/fs_ops.cc         | 10 +++++-----
 libstdc++-v3/src/filesystem/ops-common.h | 16 ++++++++++++++--
 libstdc++-v3/src/filesystem/ops.cc       |  4 ++--
 3 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/libstdc++-v3/src/c++17/fs_ops.cc b/libstdc++-v3/src/c++17/fs_ops.cc
index 2eac9977785..4f3715bbbec 100644
--- a/libstdc++-v3/src/c++17/fs_ops.cc
+++ b/libstdc++-v3/src/c++17/fs_ops.cc
@@ -113,7 +113,7 @@ fs::absolute(const path& p, error_code& ec)
   while (len > buf.size());
 
   if (len == 0)
-    ec.assign((int)GetLastError(), std::system_category());
+    ec = __last_system_error();
   else
     {
       buf.resize(len);
@@ -682,7 +682,7 @@ fs::create_hard_link(const path& to, const path& new_hard_link,
   if (CreateHardLinkW(new_hard_link.c_str(), to.c_str(), NULL))
     ec.clear();
   else
-    ec.assign((int)GetLastError(), system_category());
+    ec = __last_system_error();
 #else
   ec = std::make_error_code(std::errc::not_supported);
 #endif
@@ -874,12 +874,12 @@ fs::equivalent(const path& p1, const path& p2, error_code& ec) noexcept
       if (!h1 || !h2)
 	{
 	  if (!h1 && !h2)
-	    ec.assign((int)GetLastError(), system_category());
+	    ec = __last_system_error();
 	  return false;
 	}
       if (!h1.get_info() || !h2.get_info())
 	{
-	  ec.assign((int)GetLastError(), system_category());
+	  ec = __last_system_error();
 	  return false;
 	}
       return h1.info.dwVolumeSerialNumber == h2.info.dwVolumeSerialNumber
@@ -1255,7 +1255,7 @@ fs::remove(const path& p, error_code& ec) noexcept
 	  return true;
 	}
       else if (!ec)
-	ec.assign((int)GetLastError(), system_category());
+	ec = __last_system_error();
     }
   else if (status_known(st))
     ec.clear();
diff --git a/libstdc++-v3/src/filesystem/ops-common.h b/libstdc++-v3/src/filesystem/ops-common.h
index bf26c06b7b5..e999e11b422 100644
--- a/libstdc++-v3/src/filesystem/ops-common.h
+++ b/libstdc++-v3/src/filesystem/ops-common.h
@@ -57,6 +57,18 @@
 namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+  // Get the last OS error (for POSIX this is just errno).
+  inline error_code
+  __last_system_error() noexcept
+  {
+#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+    return {::GetLastError(), std::system_category()};
+#else
+    return {errno, std::generic_category()};
+#endif
+  }
+
 namespace filesystem
 {
 namespace __gnu_posix
@@ -558,7 +570,7 @@ _GLIBCXX_BEGIN_NAMESPACE_FILESYSTEM
 	ec.clear();
       }
     else
-      ec.assign((int)GetLastError(), std::system_category());
+      ec = std::last_system_error();
 #else
     ec = std::make_error_code(std::errc::not_supported);
 #endif
@@ -583,7 +595,7 @@ _GLIBCXX_BEGIN_NAMESPACE_FILESYSTEM
       } while (len > buf.size());
 
     if (len == 0)
-      ec.assign((int)GetLastError(), std::system_category());
+      ec = __last_system_error();
     else
       ec.clear();
 
diff --git a/libstdc++-v3/src/filesystem/ops.cc b/libstdc++-v3/src/filesystem/ops.cc
index b0a0f15e98f..cc7117b0cd1 100644
--- a/libstdc++-v3/src/filesystem/ops.cc
+++ b/libstdc++-v3/src/filesystem/ops.cc
@@ -590,7 +590,7 @@ fs::create_hard_link(const path& to, const path& new_hard_link,
   if (CreateHardLinkW(new_hard_link.c_str(), to.c_str(), NULL))
     ec.clear();
   else
-    ec.assign((int)GetLastError(), system_category());
+    ec = __last_system_error();
 #else
   ec = std::make_error_code(std::errc::not_supported);
 #endif
@@ -1062,7 +1062,7 @@ fs::remove(const path& p, error_code& ec) noexcept
 	  return true;
 	}
       else if (!ec)
-	ec.assign((int)GetLastError(), system_category());
+	ec = __last_system_error();
     }
   else if (status_known(st))
     ec.clear();