Repository: databricks/koalas

Issue:
Fail CI if doc generation contains WARNINGs
Right now we have a bunch of errors:

```
WARNING: failed to import DataFrame.unique
/Users/rxin/workspace/koalas/docs/source/reference/api/databricks.koalas.DataFrame.rst:52:<autosummary>:1: WARNING: Inline emphasis start-string without end-string.
/Users/rxin/workspace/koalas/docs/source/reference/api/databricks.koalas.DataFrame.rst:52:<autosummary>:1: WARNING: Inline strong start-string without end-string.
/Users/rxin/workspace/koalas/databricks/koalas/frame.py:docstring of databricks.koalas.DataFrame.dropna:11: WARNING: Unexpected indentation.
/Users/rxin/workspace/koalas/databricks/koalas/frame.py:docstring of databricks.koalas.DataFrame.iteritems:8: WARNING: Title underline too short.

Returns
------
/Users/rxin/workspace/koalas/databricks/koalas/frame.py:docstring of databricks.koalas.DataFrame.iteritems:8: WARNING: Unexpected section title.

Returns
------
/Users/rxin/workspace/koalas/databricks/koalas/frame.py:docstring of databricks.koalas.DataFrame.pipe:2: WARNING: Inline emphasis start-string without end-string.
/Users/rxin/workspace/koalas/databricks/koalas/frame.py:docstring of databricks.koalas.DataFrame.pipe:2: WARNING: Inline strong start-string without end-string.
/Users/rxin/workspace/koalas/docs/source/reference/frame.rst:59:<autosummary>:1: WARNING: Inline emphasis start-string without end-string.
/Users/rxin/workspace/koalas/docs/source/reference/frame.rst:59:<autosummary>:1: WARNING: Inline strong start-string without end-string.
looking for now-outdated files... none found
pickling environment... done
checking consistency... done
preparing documents... done
writing output... [100%] reference/series                                                                                                       
/Users/rxin/workspace/koalas/databricks/koalas/series.py:docstring of databricks.koalas.Series.dropna:4: WARNING: undefined label: missing_data (if the link has no caption the label must precede a section header)
generating indices...
highlighting module code... [100%] databricks.koalas.series                                                                                     
writing additional pages... search
copying static files... WARNING: html_static_path entry '/Users/rxin/workspace/koalas/docs/source/_static' does not exist
done
```

We should fail CI if there are errors.



Discussion:

Resolving patch:
diff --git a/databricks/koalas/frame.py b/databricks/koalas/frame.py
--- a/databricks/koalas/frame.py
+++ b/databricks/koalas/frame.py
@@ -173,7 +173,7 @@ def iteritems(self):
         the column name and the content as a Series.
 
         Returns
-        ------
+        -------
         label : object
             The column names for the DataFrame being iterated over.
         content : Series
@@ -841,7 +841,7 @@ def dropna(self, axis=0, how='any', thresh=None, subset=None, inplace=False):
             Determine rows which contain missing values are removed.
             * 0, or 'index' : Drop rows which contain missing values.
             .. dropna currently only works for axis=0 or axis='index'
-               axis=1 is yet to be implemented.
+            axis=1 is yet to be implemented.
         how : {'any', 'all'}, default 'any'
             Determine if row or column is removed from DataFrame, when we have
             at least one NA or all NA.
@@ -1446,13 +1446,13 @@ def isin(self, values):
         return DataFrame(self._sdf.select(_select_columns), self._metadata.copy())
 
     def pipe(self, func, *args, **kwargs):
-        """
-        Apply func(self, *args, **kwargs).
+        r"""
+        Apply func(self, \*args, \*\*kwargs).
 
         Parameters
         ----------
         func : function
-            function to apply to the Dataframe.
+            function to apply to the DataFrame.
             ``args``, and ``kwargs`` are passed into ``func``.
             Alternatively a ``(callable, data_keyword)`` tuple where
             ``data_keyword`` is a string indicating the keyword of
@@ -1466,7 +1466,6 @@ def pipe(self, func, *args, **kwargs):
         -------
         object : the return type of ``func``.
 
-
         Notes
         -----
         Use ``.pipe`` when chaining together functions that expect
diff --git a/databricks/koalas/series.py b/databricks/koalas/series.py
--- a/databricks/koalas/series.py
+++ b/databricks/koalas/series.py
@@ -484,7 +484,7 @@ def notnull(self):
 
     notna = notnull
 
-    @derived_from(pd.Series)
+    # TODO: inline documentation with Pandas'
     def dropna(self, axis=0, inplace=False, **kwargs):
         ks = _col(self.to_dataframe().dropna(axis=axis, inplace=False))
         if inplace:
diff --git a/docs/source/conf.py b/docs/source/conf.py
--- a/docs/source/conf.py
+++ b/docs/source/conf.py
@@ -73,7 +73,7 @@
 # Add any paths that contain custom static files (such as style sheets) here,
 # relative to this directory. They are copied after the builtin static files,
 # so a file named "default.css" will overwrite the builtin "default.css".
-html_static_path = ['_static']
+html_static_path = []
 
 # Add any paths that contain custom themes here, relative to this directory.
 html_theme_path = ['themes']


Test patch: