libstdc++: Add nodiscard attribute to filesystem operations

Some of these are not truly "pure" because they access the file system,
e.g. exists and file_size, but they do not modify anything and are only
useful for the return value.

If you really want to use one of those functions just to check whether
an error is reported (either via an exception or an error_code&
argument) you can still do so, but you need to cast the discarded result
to void.  Several tests need such a change, because they were indeed
only calling the functions to check for expected errors.

libstdc++-v3/ChangeLog:

	* include/bits/fs_ops.h: Add nodiscard to all pure functions.
	* include/experimental/bits/fs_ops.h: Likewise.
	* testsuite/27_io/filesystem/operations/all.cc: Do not discard
	results of absolute and canonical.
	* testsuite/27_io/filesystem/operations/absolute.cc: Cast
	discarded result to void.
	* testsuite/27_io/filesystem/operations/canonical.cc: Likewise.
	* testsuite/27_io/filesystem/operations/exists.cc: Likewise.
	* testsuite/27_io/filesystem/operations/is_empty.cc: Likewise.
	* testsuite/27_io/filesystem/operations/read_symlink.cc:
	Likewise.
	* testsuite/27_io/filesystem/operations/status.cc: Likewise.
	* testsuite/27_io/filesystem/operations/symlink_status.cc:
	Likewise.
	* testsuite/27_io/filesystem/operations/temp_directory_path.cc:
	Likewise.
	* testsuite/experimental/filesystem/operations/canonical.cc:
	Likewise.
	* testsuite/experimental/filesystem/operations/exists.cc:
	Likewise.
	* testsuite/experimental/filesystem/operations/is_empty.cc:
	Likewise.
	* testsuite/experimental/filesystem/operations/read_symlink.cc:
	Likewise.
	* testsuite/experimental/filesystem/operations/temp_directory_path.cc:
	Likewise.

(cherry picked from commit f7a148304a71f3d3ad6845b7966fdc3af88c9e45)

9 files changed, 15 insertions, 15 deletions

diff --git a/libstdc++-v3/testsuite/27_io/filesystem/operations/absolute.cc b/libstdc++-v3/testsuite/27_io/filesystem/operations/absolute.cc
index 236e1b2fad7..295b755ada7 100644
--- a/libstdc++-v3/testsuite/27_io/filesystem/operations/absolute.cc
+++ b/libstdc++-v3/testsuite/27_io/filesystem/operations/absolute.cc
@@ -84,7 +84,7 @@ test03()
   VERIFY( eabs.empty() );
 
   try {
-    absolute(path{});
+    (void) absolute(path{});
     VERIFY( false );
   } catch (const std::filesystem::filesystem_error& e) {
     VERIFY( e.code() == std::errc::invalid_argument );
diff --git a/libstdc++-v3/testsuite/27_io/filesystem/operations/all.cc b/libstdc++-v3/testsuite/27_io/filesystem/operations/all.cc
index d5d6c8731c3..3c8ab78b78a 100644
--- a/libstdc++-v3/testsuite/27_io/filesystem/operations/all.cc
+++ b/libstdc++-v3/testsuite/27_io/filesystem/operations/all.cc
@@ -42,11 +42,11 @@ main()
   bool b [[maybe_unused]];
   std::uintmax_t size;
 
-  std::filesystem::absolute(p);
-  std::filesystem::absolute(p, ec);
+  p2 = std::filesystem::absolute(p);
+  p2 = std::filesystem::absolute(p, ec);
 
-  std::filesystem::canonical(p);
-  std::filesystem::canonical(p, ec);
+  p2 = std::filesystem::canonical(p);
+  p2 = std::filesystem::canonical(p, ec);
 
   std::filesystem::copy(p, p);
   std::filesystem::copy(p, p, ec);
diff --git a/libstdc++-v3/testsuite/27_io/filesystem/operations/canonical.cc b/libstdc++-v3/testsuite/27_io/filesystem/operations/canonical.cc
index bc7ef0de2b7..5e618b25025 100644
--- a/libstdc++-v3/testsuite/27_io/filesystem/operations/canonical.cc
+++ b/libstdc++-v3/testsuite/27_io/filesystem/operations/canonical.cc
@@ -31,7 +31,7 @@ test01()
   const std::error_code bad_ec = make_error_code(std::errc::invalid_argument);
   std::error_code ec;
   auto p = __gnu_test::nonexistent_path();
-  canonical( p, ec );
+  (void) canonical( p, ec );
   VERIFY( ec );
 
   create_directory(p);
@@ -90,7 +90,7 @@ test02()
 #if __cpp_exceptions
   fs::path e1, e2;
   try {
-    canonical(p);
+    (void) canonical(p);
   } catch (const fs::filesystem_error& e) {
     e1 = e.path1();
     e2 = e.path2();
diff --git a/libstdc++-v3/testsuite/27_io/filesystem/operations/exists.cc b/libstdc++-v3/testsuite/27_io/filesystem/operations/exists.cc
index b3063564ab4..f9956970b25 100644
--- a/libstdc++-v3/testsuite/27_io/filesystem/operations/exists.cc
+++ b/libstdc++-v3/testsuite/27_io/filesystem/operations/exists.cc
@@ -95,7 +95,7 @@ test04()
   ec.clear();
   try
   {
-    exists(unr);
+    (void) exists(unr);
   }
   catch(const std::filesystem::filesystem_error& ex)
   {
diff --git a/libstdc++-v3/testsuite/27_io/filesystem/operations/is_empty.cc b/libstdc++-v3/testsuite/27_io/filesystem/operations/is_empty.cc
index 23246a4228c..d1dfd9f6dda 100644
--- a/libstdc++-v3/testsuite/27_io/filesystem/operations/is_empty.cc
+++ b/libstdc++-v3/testsuite/27_io/filesystem/operations/is_empty.cc
@@ -40,7 +40,7 @@ test01()
   VERIFY( !result );
 
   try {
-    fs::is_empty(p);
+    (void) fs::is_empty(p);
   } catch (const fs::filesystem_error& e) {
     ec2 = e.code();
   }
@@ -51,7 +51,7 @@ test01()
   VERIFY( !result );
 
   try {
-    fs::is_empty(p/"f");
+    (void) fs::is_empty(p/"f");
   } catch (const fs::filesystem_error& e) {
     ec2 = e.code();
   }
diff --git a/libstdc++-v3/testsuite/27_io/filesystem/operations/read_symlink.cc b/libstdc++-v3/testsuite/27_io/filesystem/operations/read_symlink.cc
index 68bbab33bc9..ccfc4cb7312 100644
--- a/libstdc++-v3/testsuite/27_io/filesystem/operations/read_symlink.cc
+++ b/libstdc++-v3/testsuite/27_io/filesystem/operations/read_symlink.cc
@@ -31,7 +31,7 @@ test01()
   auto p = __gnu_test::nonexistent_path();
   std::error_code ec;
 
-  read_symlink(p, ec);
+  (void) read_symlink(p, ec);
   VERIFY( ec );
 
   fs::path tgt = ".";
diff --git a/libstdc++-v3/testsuite/27_io/filesystem/operations/status.cc b/libstdc++-v3/testsuite/27_io/filesystem/operations/status.cc
index f2d2582ce41..c43ba29fd7f 100644
--- a/libstdc++-v3/testsuite/27_io/filesystem/operations/status.cc
+++ b/libstdc++-v3/testsuite/27_io/filesystem/operations/status.cc
@@ -74,7 +74,7 @@ test03()
   std::error_code ec2;
   fs::path p, p2;
   try {
-    fs::symlink_status(f.path);
+    (void) fs::symlink_status(f.path);
   } catch (const fs::filesystem_error& e) {
     caught = true;
     p = e.path1();
diff --git a/libstdc++-v3/testsuite/27_io/filesystem/operations/symlink_status.cc b/libstdc++-v3/testsuite/27_io/filesystem/operations/symlink_status.cc
index ef973b7807b..faa1db540d1 100644
--- a/libstdc++-v3/testsuite/27_io/filesystem/operations/symlink_status.cc
+++ b/libstdc++-v3/testsuite/27_io/filesystem/operations/symlink_status.cc
@@ -94,7 +94,7 @@ test03()
   std::error_code ec2;
   fs::path p, p2;
   try {
-    fs::symlink_status(f.path);
+    (void) fs::symlink_status(f.path);
   } catch (const fs::filesystem_error& e) {
     caught = true;
     p = e.path1();
diff --git a/libstdc++-v3/testsuite/27_io/filesystem/operations/temp_directory_path.cc b/libstdc++-v3/testsuite/27_io/filesystem/operations/temp_directory_path.cc
index b4ef77f05e4..9dd52112330 100644
--- a/libstdc++-v3/testsuite/27_io/filesystem/operations/temp_directory_path.cc
+++ b/libstdc++-v3/testsuite/27_io/filesystem/operations/temp_directory_path.cc
@@ -117,7 +117,7 @@ test03()
 
   std::error_code ec2;
   try {
-    fs::temp_directory_path();
+    (void) fs::temp_directory_path();
   } catch (const fs::filesystem_error& e) {
     ec2 = e.code();
   }
@@ -141,7 +141,7 @@ test04()
 
   std::error_code ec2;
   try {
-    fs::temp_directory_path();
+    (void) fs::temp_directory_path();
   } catch (const fs::filesystem_error& e) {
     ec2 = e.code();
   }