Fix PyCQA#1275 in the case where the --add-imports option was given

isort/api.py

@@ -456,6 +456,11 @@ def _sort_imports(
                         import_section += line_separator.join(add_imports) + line_separator
                         contains_imports = True
                         add_imports = []
+
+                        # HACK: This will occur on the blank line after a
+                        # module docstring. We want to preserve this blank
+                        # line.
+                        output_stream.write(line_separator)
                     else:
                         not_imports = True
                 elif (

tests/test_isort.py

@@ -810,7 +810,7 @@ def test_add_imports() -> None:
     test_input = '"""Module docstring"""\n' "\nclass MyClass(object):\n    pass\n"
     test_output = isort.code(code=test_input, add_imports=["from __future__ import print_function"])
     assert test_output == (
-        '"""Module docstring"""\n'
+        '"""Module docstring"""\n\n'
         "from __future__ import print_function\n"
         "\n"
         "\n"

tests/test_regressions.py

@@ -42,23 +42,25 @@ def test_blank_lined_removed_issue_1275():
     """Ensure isort doesn't accidentally remove blank lines after doc strings and before imports.
     See: https://github.com/timothycrosley/isort/issues/1275
     """
-    assert (
-        isort.code(
-            '''"""
+    input_code = '''"""
 My docstring
 """
 
 from b import thing
 from a import other_thing
 '''
-        )
-        == '''"""
+    output_code = '''"""
 My docstring
 """
 
 from a import other_thing
 from b import thing
 '''
+
+    assert isort.code(input_code) == output_code
+    assert (
+        isort.code(input_code, add_imports=["from c import cthing"])
+        == output_code + "from c import cthing\n"
     )