[PATCH] libstdc++: Fix vector(from_range_t, R&&) for exceptions [PR120367]

[Jonathan Wakely]

Because this constructor delegates to vector(a) the object has been
fully constructed and the destructor will run if an exception happens.
That means we need to set _M_finish == _M_start so that the destructor
doesn't try to destroy any elements.

libstdc++-v3/ChangeLog:

        PR libstdc++/120367
        * include/bits/stl_vector.h (_M_range_initialize): Initialize
        _M_impl._M_finish.
        * testsuite/23_containers/vector/cons/from_range.cc: Check with
        a type that throws on construction.
        exceptions during construction.
---

Tested x86_64-linux.

 libstdc++-v3/include/bits/stl_vector.h        |  1 +
 .../23_containers/vector/cons/from_range.cc   | 22 +++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/libstdc++-v3/include/bits/stl_vector.h 
b/libstdc++-v3/include/bits/stl_vector.h
index 57680b7bbcf3..43b913da778d 100644
--- a/libstdc++-v3/include/bits/stl_vector.h
+++ b/libstdc++-v3/include/bits/stl_vector.h
@@ -1971,6 +1971,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        {
          pointer __start = this->_M_impl._M_start =
            this->_M_allocate(_S_check_init_len(__n, _M_get_Tp_allocator()));
+         this->_M_impl._M_finish = __start;
          this->_M_impl._M_end_of_storage = __start + __n;
          this->_M_impl._M_finish
              = std::__uninitialized_copy_a(_GLIBCXX_MOVE(__first), __last,
diff --git a/libstdc++-v3/testsuite/23_containers/vector/cons/from_range.cc 
b/libstdc++-v3/testsuite/23_containers/vector/cons/from_range.cc
index 7a62645283d2..3784b9cd66ad 100644
--- a/libstdc++-v3/testsuite/23_containers/vector/cons/from_range.cc
+++ b/libstdc++-v3/testsuite/23_containers/vector/cons/from_range.cc
@@ -106,8 +106,30 @@ test_constexpr()
   return true;
 }
 
+void
+test_pr120367()
+{
+#ifdef __cpp_exceptions
+  struct X
+  {
+    X(int) { throw 1; }     // Cannot successfully construct an X.
+    ~X() { VERIFY(false); } // So should never need to destroy one.
+  };
+
+  try
+  {
+    int i[1]{};
+    std::vector<X> v(std::from_range, i);
+  }
+  catch (int)
+  {
+  }
+#endif
+}
+
 int main()
 {
   test_ranges();
   static_assert( test_constexpr() );
+  test_pr120367();
 }
-- 
2.49.0