From 1689db493f10262555196f658c52e370aacb4a33 Mon Sep 17 00:00:00 2001
From: Tom Nicholas <35968931+TomNicholas@users.noreply.github.com>
Date: Sun, 12 Jan 2020 13:04:01 +0000
Subject: [PATCH] ds.merge(da) bugfix (#3677)

* Added mwe as test

* Cast to Dataset

* Updated what's new

* black formatted

* Use assert_identical
---
 doc/whats-new.rst          | 2 ++
 xarray/core/dataset.py     | 1 +
 xarray/tests/test_merge.py | 7 +++++++
 3 files changed, 10 insertions(+)

diff --git a/doc/whats-new.rst b/doc/whats-new.rst
index eacf8433c0a..6eeb55c23cb 100644
--- a/doc/whats-new.rst
+++ b/doc/whats-new.rst
@@ -74,6 +74,8 @@ Bug fixes
   By `Justus Magin <https://github.com/keewis>`_.
 - :py:meth:`Dataset.rename`, :py:meth:`DataArray.rename` now check for conflicts with
   MultiIndex level names.
+- :py:meth:`Dataset.merge` no longer fails when passed a `DataArray` instead of a `Dataset` object.
+  By `Tom Nicholas <https://github.com/TomNicholas>`_.
 
 Documentation
 ~~~~~~~~~~~~~
diff --git a/xarray/core/dataset.py b/xarray/core/dataset.py
index c314eb41458..6ecd9b59f8e 100644
--- a/xarray/core/dataset.py
+++ b/xarray/core/dataset.py
@@ -3607,6 +3607,7 @@ def merge(
             If any variables conflict (see ``compat``).
         """
         _check_inplace(inplace)
+        other = other.to_dataset() if isinstance(other, xr.DataArray) else other
         merge_result = dataset_merge_method(
             self,
             other,
diff --git a/xarray/tests/test_merge.py b/xarray/tests/test_merge.py
index c1e6c7a5ce8..6c8f3f65657 100644
--- a/xarray/tests/test_merge.py
+++ b/xarray/tests/test_merge.py
@@ -3,6 +3,7 @@
 
 import xarray as xr
 from xarray.core import dtypes, merge
+from xarray.testing import assert_identical
 
 from . import raises_regex
 from .test_dataset import create_test_data
@@ -253,3 +254,9 @@ def test_merge_no_conflicts(self):
         with pytest.raises(xr.MergeError):
             ds3 = xr.Dataset({"a": ("y", [2, 3]), "y": [1, 2]})
             ds1.merge(ds3, compat="no_conflicts")
+
+    def test_merge_dataarray(self):
+        ds = xr.Dataset({"a": 0})
+        da = xr.DataArray(data=1, name="b")
+
+        assert_identical(ds.merge(da), xr.merge([ds, da]))