[PATCH] PR libstdc++/90557 fix path assignment that alters source

[Jonathan Wakely]

        PR libstdc++/90557
        * src/c++17/fs_path.cc (path::_List::operator=(const _List&)): Fix
        reversed arguments to uninitialized_copy_n.
        * testsuite/27_io/filesystem/path/assign/copy.cc: Check that source
        is unchanged by copy assignment.
        * testsuite/util/testsuite_fs.h (compare_paths): Use std::equal to
        compare path components.

Tested x86_64-linux, committed to trunk. I'll backport it to
gcc-9-branch too.



commit edcb23ee78d194cbb518a151c7edfbb2895c48d3
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Wed May 22 22:07:50 2019 +0100

    PR libstdc++/90557 fix path assignment that alters source
    
            PR libstdc++/90557
            * src/c++17/fs_path.cc (path::_List::operator=(const _List&)): Fix
            reversed arguments to uninitialized_copy_n.
            * testsuite/27_io/filesystem/path/assign/copy.cc: Check that source
            is unchanged by copy assignment.
            * testsuite/util/testsuite_fs.h (compare_paths): Use std::equal to
            compare path components.

diff --git a/libstdc++-v3/src/c++17/fs_path.cc 
b/libstdc++-v3/src/c++17/fs_path.cc
index 605f62cbf81..8e01bf510d3 100644
--- a/libstdc++-v3/src/c++17/fs_path.cc
+++ b/libstdc++-v3/src/c++17/fs_path.cc
@@ -278,8 +278,8 @@ path::_List::operator=(const _List& other)
            to[i]._M_pathname.reserve(from[i]._M_pathname.length());
          if (newsize > oldsize)
            {
-             std::uninitialized_copy_n(to + oldsize, newsize - oldsize,
-                                       from + oldsize);
+             std::uninitialized_copy_n(from + oldsize, newsize - oldsize,
+                                       to + oldsize);
              impl->_M_size = newsize;
            }
          else if (newsize < oldsize)
diff --git a/libstdc++-v3/testsuite/27_io/filesystem/path/assign/copy.cc 
b/libstdc++-v3/testsuite/27_io/filesystem/path/assign/copy.cc
index 775dbffad36..6aa25ae12ef 100644
--- a/libstdc++-v3/testsuite/27_io/filesystem/path/assign/copy.cc
+++ b/libstdc++-v3/testsuite/27_io/filesystem/path/assign/copy.cc
@@ -64,10 +64,25 @@ test03()
   VERIFY( ptr2 == p.begin()->c_str() );
 }
 
+void
+test04()
+{
+  // PR libstdc++/90557
+  path p1 = "a/b/c";
+  const path p2 = "d/e";
+  const path p3 = p2;
+  p1.clear();
+  p1 = p2;
+  __gnu_test::compare_paths(p1, p2);
+  __gnu_test::compare_paths(p1, p3);
+  __gnu_test::compare_paths(p2, p3);
+}
+
 int
 main()
 {
   test01();
   test02();
   test03();
+  test04();
 }
diff --git a/libstdc++-v3/testsuite/util/testsuite_fs.h 
b/libstdc++-v3/testsuite/util/testsuite_fs.h
index baba90eaa0c..b2a5ee6e655 100644
--- a/libstdc++-v3/testsuite/util/testsuite_fs.h
+++ b/libstdc++-v3/testsuite/util/testsuite_fs.h
@@ -30,6 +30,7 @@ namespace test_fs = std::filesystem;
 #include <experimental/filesystem>
 namespace test_fs = std::experimental::filesystem;
 #endif
+#include <algorithm>
 #include <fstream>
 #include <string>
 #include <cstdio>
@@ -62,10 +63,15 @@ namespace __gnu_test
     PATH_CHK( p1, p2, is_relative );
     auto d1 = std::distance(p1.begin(), p1.end());
     auto d2 = std::distance(p2.begin(), p2.end());
-    if( d1 != d2 )
+    if (d1 != d2)
       throw test_fs::filesystem_error(
-         "distance(begin, end)", p1, p2,
+         "distance(begin1, end1) != distance(begin2, end2)", p1, p2,
          std::make_error_code(std::errc::invalid_argument) );
+    if (!std::equal(p1.begin(), p1.end(), p2.begin(), p2.end()))
+      throw test_fs::filesystem_error(
+         "!equal(begin1, end1, begin2, end2)", p1, p2,
+         std::make_error_code(std::errc::invalid_argument) );
+
   }
 
   const std::string test_paths[] = {