[PATCH] Fix path::iterator post-increment and post-decrement

[Jonathan Wakely]

I made a dumb mistake in the post-inc and post-dec operators for
the path::iterator type, forgetting that _M_cur is sometimes null (for
a single-element path).

        * include/experimental/bits/fs_path.h (path::iterator++(int))
        (path::iterator--(int)): Fix for paths with only one component.
        * testsuite/experimental/filesystem/path/itr/traversal.cc: Test
        post-increment and post-decrement.

Tested powerpc64le-linux, committed to trunk.

It's too late to fix this on the gcc-5 branch but I'll backport it to
gcc-6 and gcc-7 soon.


commit 1c773ea81a8781dfbb4381a496aa5bab5bd623de
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Wed Oct 18 02:47:24 2017 +0100

    Fix path::iterator post-increment and post-decrement
    
            * include/experimental/bits/fs_path.h (path::iterator++(int))
            (path::iterator--(int)): Fix for paths with only one component.
            * testsuite/experimental/filesystem/path/itr/traversal.cc: Test
            post-increment and post-decrement.

diff --git a/libstdc++-v3/include/experimental/bits/fs_path.h 
b/libstdc++-v3/include/experimental/bits/fs_path.h
index cde3897b8e5..9121439b7f2 100644
--- a/libstdc++-v3/include/experimental/bits/fs_path.h
+++ b/libstdc++-v3/include/experimental/bits/fs_path.h
@@ -725,10 +725,10 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     pointer   operator->() const { return std::__addressof(**this); }
 
     iterator& operator++();
-    iterator  operator++(int) { auto __tmp = *this; ++_M_cur; return __tmp; }
+    iterator  operator++(int) { auto __tmp = *this; ++*this; return __tmp; }
 
     iterator& operator--();
-    iterator  operator--(int) { auto __tmp = *this; --_M_cur; return __tmp; }
+    iterator  operator--(int) { auto __tmp = *this; --*this; return __tmp; }
 
     friend bool operator==(const iterator& __lhs, const iterator& __rhs)
     { return __lhs._M_equals(__rhs); }
diff --git 
a/libstdc++-v3/testsuite/experimental/filesystem/path/itr/traversal.cc 
b/libstdc++-v3/testsuite/experimental/filesystem/path/itr/traversal.cc
index bc1091476b5..dbb4d46796d 100644
--- a/libstdc++-v3/testsuite/experimental/filesystem/path/itr/traversal.cc
+++ b/libstdc++-v3/testsuite/experimental/filesystem/path/itr/traversal.cc
@@ -79,9 +79,28 @@ test02()
   }
 }
 
+void
+test03()
+{
+  path paths[] = { "single", "multiple/elements" };
+  for (const path& p : paths)
+    for (auto iter = p.begin(); iter != p.end(); ++iter)
+    {
+      auto iter2 = iter;
+      ++iter;
+      iter2++;
+      VERIFY( iter2 == iter );
+      auto iter3 = iter;
+      --iter3;
+      iter2--;
+      VERIFY( iter2 == iter3 );
+    }
+}
+
 int
 main()
 {
   test01();
   test02();
+  test03();
 }