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.

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 2eac997..4f3715b 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 bf26c06..e999e11 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 b0a0f15..cc7117b 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();