Fixed #1542: Bug in VERTICAL_PREFIX_FROM_MODULE_IMPORT wrap mode.

CHANGELOG.md

@@ -6,6 +6,7 @@ Find out more about isort's release policy [here](https://pycqa.github.io/isort/
 
 ### 5.6.2 TBD
   - Fixed #1548: On rare occasions an unecessary empty line can be added when an import is marked as skipped.
+  - Fixed #1542: Bug in VERTICAL_PREFIX_FROM_MODULE_IMPORT wrap mode.
 
 ### 5.6.1 [Hotfix] October 8, 2020
   - Fixed #1546: Unstable (non-idempotent) behavior with certain src trees.

isort/wrap_modes.py

@@ -273,33 +273,41 @@ def vertical_hanging_indent_bracket(**interface):
 def vertical_prefix_from_module_import(**interface):
     if not interface["imports"]:
         return ""
+
     prefix_statement = interface["statement"]
-    interface["statement"] += interface["imports"].pop(0)
-    while interface["imports"]:
-        next_import = interface["imports"].pop(0)
-        next_statement = isort.comments.add_to_line(
-            interface["comments"],
-            interface["statement"] + ", " + next_import,
+    output_statement = prefix_statement + interface["imports"].pop(0)
+    comments = interface["comments"]
+
+    statement = output_statement
+    statement_with_comments = ""
+    for next_import in interface["imports"]:
+        statement = statement + ", " + next_import
+        statement_with_comments = isort.comments.add_to_line(
+            comments,
+            statement,
             removed=interface["remove_comments"],
             comment_prefix=interface["comment_prefix"],
         )
         if (
-            len(next_statement.split(interface["line_separator"])[-1]) + 1
+            len(statement_with_comments.split(interface["line_separator"])[-1]) + 1
             > interface["line_length"]
         ):
-            next_statement = (
+            statement = (
                 isort.comments.add_to_line(
                     interface["comments"],
-                    f"{interface['statement']}",
+                    output_statement,
                     removed=interface["remove_comments"],
                     comment_prefix=interface["comment_prefix"],
                 )
                 + f"{interface['line_separator']}{prefix_statement}{next_import}"
             )
-            interface["comments"] = []
-        interface["statement"] = next_statement
-    return interface["statement"]
-
+            comments = []
+        output_statement = statement
+
+    if comments and statement_with_comments:
+        output_statement = statement_with_comments
+    return output_statement
+
 
 @_wrap_mode
 def hanging_indent_with_parentheses(**interface):

tests/unit/test_regressions.py

@@ -1422,3 +1422,36 @@ def test_isort_shouldnt_split_skip_issue_1548():
 import os
 """
     )
+
+
+def test_isort_losing_imports_vertical_prefix_from_module_import_wrap_mode_issue_1542():
+    """Ensure isort doesnt lose imports when a comment is combined with an import and
+    wrap mode VERTICAL_PREFIX_FROM_MODULE_IMPORT is used.
+    See: https://github.com/PyCQA/isort/issues/1542.
+    """
+    assert isort.code(
+        """
+from xxxxxxxxxxxxxxxx import AAAAAAAAAA, BBBBBBBBBB
+from xxxxxxxxxxxxxxxx import CCCCCCCCC, DDDDDDDDD  # xxxxxxxxxxxxxxxxxx
+
+print(CCCCCCCCC)
+""",
+        multi_line_output=9,
+    ) == """
+from xxxxxxxxxxxxxxxx import AAAAAAAAAA, BBBBBBBBBB  # xxxxxxxxxxxxxxxxxx
+from xxxxxxxxxxxxxxxx import CCCCCCCCC, DDDDDDDDD
+
+print(CCCCCCCCC)
+"""
+
+    assert isort.check_code(
+        """
+from xxxxxxxxxxxxxxxx import AAAAAAAAAA, BBBBBBBBBB
+
+from xxxxxxxxxxxxxxxx import CCCCCCCCC, DDDDDDDDD  # xxxxxxxxxxxxxxxxxx isort: skip
+
+print(CCCCCCCCC)
+""",
+        show_diff = True,
+        multi_line_output=9,
+    )