Add magic trailing comma option

10 files changed, 71 insertions, 8 deletions

diff --git a/docs/configuration/options.md b/docs/configuration/options.md
index 527798a6..56239d6f 100644
--- a/docs/configuration/options.md
+++ b/docs/configuration/options.md
@@ -889,6 +889,17 @@ Includes a trailing comma on multi line imports that include parentheses.
 
 - --tc
 - --trailing-comma
+## Split on Trailing Comma
+
+Split imports list followed by a trailing comma into VERTICAL_HANGING_INDENT mode. This follows Black style magic comma.
+
+**Type:** Bool  
+**Default:** `False`  
+**Config default:** `false`  
+**Python & Config File Name:** split_on_trailing_comma
+**CLI Flags:**
+
+- --split-on-trailing-comma
 
 ## From First
 
diff --git a/docs/configuration/profiles.md b/docs/configuration/profiles.md
index a8e09dd2..56b10757 100644
--- a/docs/configuration/profiles.md
+++ b/docs/configuration/profiles.md
@@ -16,6 +16,7 @@ To use any of the listed profiles, use `isort --profile PROFILE_NAME` from the c
  - **use_parentheses**: `True`
  - **ensure_newline_before_comments**: `True`
  - **line_length**: `88`
+ - **split_on_trailing_comma**: `True`
 
 #django
 
diff --git a/isort/main.py b/isort/main.py
index 40725a6a..de3cb1c0 100644
--- a/isort/main.py
+++ b/isort/main.py
@@ -714,6 +714,12 @@ def _build_arg_parser() -> argparse.ArgumentParser:
         dest="star_first",
         action="store_true",
     )
+    output_group.add_argument(
+        "--split-on-trailing-comma",
+        help="Split imports list followed by a trailing comma into VERTICAL_HANGING_INDENT mode",
+        dest="split_on_trailing_comma",
+        action="store_true",
+    )
 
     section_group.add_argument(
         "--sd",
diff --git a/isort/output.py b/isort/output.py
index d049daf6..c59be936 100644
--- a/isort/output.py
+++ b/isort/output.py
@@ -505,7 +505,17 @@ def _with_from_imports(
                 ):
                     do_multiline_reformat = True
 
-                if do_multiline_reformat:
+                if config.split_on_trailing_comma and module in parsed.trailing_commas:
+                    import_statement = wrap.import_statement(
+                        import_start=import_start,
+                        from_imports=from_import_section,
+                        comments=comments,
+                        line_separator=parsed.line_separator,
+                        config=config,
+                        explode=True,
+                    )
+
+                elif do_multiline_reformat:
                     import_statement = wrap.import_statement(
                         import_start=import_start,
                         from_imports=from_import_section,
@@ -530,7 +540,7 @@ def _with_from_imports(
                             > config.line_length
                         ):
                             import_statement = other_import_statement
-                if not do_multiline_reformat and len(import_statement) > config.line_length:
+                elif len(import_statement) > config.line_length:
                     import_statement = wrap.line(import_statement, parsed.line_separator, config)
 
             if import_statement:
diff --git a/isort/parse.py b/isort/parse.py
index 7fc6c8e6..c60938d8 100644
--- a/isort/parse.py
+++ b/isort/parse.py
@@ -2,7 +2,7 @@
 from collections import OrderedDict, defaultdict
 from functools import partial
 from itertools import chain
-from typing import TYPE_CHECKING, Any, Dict, List, NamedTuple, Optional, Tuple
+from typing import TYPE_CHECKING, Any, Dict, List, NamedTuple, Optional, Set, Tuple
 from warnings import warn
 
 from . import place
@@ -138,6 +138,7 @@ class ParsedContent(NamedTuple):
     line_separator: str
     sections: Any
     verbose_output: List[str]
+    trailing_commas: Set[str]
 
 
 def file_contents(contents: str, config: Config = DEFAULT_CONFIG) -> ParsedContent:
@@ -176,6 +177,8 @@ def file_contents(contents: str, config: Config = DEFAULT_CONFIG) -> ParsedConte
         "above": {"straight": {}, "from": {}},
     }
 
+    trailing_commas: Set[str] = set()
+
     index = 0
     import_index = -1
     in_quote = ""
@@ -515,6 +518,9 @@ def file_contents(contents: str, config: Config = DEFAULT_CONFIG) -> ParsedConte
 
                 if comments and attach_comments_to is not None:
                     attach_comments_to.extend(comments)
+
+                if "," in import_string.split(just_imports[-1])[-1]:
+                    trailing_commas.add(import_from)
             else:
                 if comments and attach_comments_to is not None:
                     attach_comments_to.extend(comments)
@@ -587,4 +593,5 @@ def file_contents(contents: str, config: Config = DEFAULT_CONFIG) -> ParsedConte
         line_separator=line_separator,
         sections=config.sections,
         verbose_output=verbose_output,
+        trailing_commas=trailing_commas,
     )
diff --git a/isort/settings.py b/isort/settings.py
index f13afade..f6fd6f51 100644
--- a/isort/settings.py
+++ b/isort/settings.py
@@ -243,6 +243,7 @@ class _Config:
     format_success: str = "{success}: {message}"
     sort_order: str = "natural"
     sort_reexports: bool = False
+    split_on_trailing_comma: bool = False
 
     def __post_init__(self) -> None:
         py_version = self.py_version
diff --git a/isort/wrap.py b/isort/wrap.py
index 5fb4631f..eb4c2483 100644
--- a/isort/wrap.py
+++ b/isort/wrap.py
@@ -4,7 +4,7 @@ from typing import List, Optional, Sequence
 
 from .settings import DEFAULT_CONFIG, Config
 from .wrap_modes import WrapModes as Modes
-from .wrap_modes import formatter_from_string
+from .wrap_modes import formatter_from_string, vertical_hanging_indent
 
 
 def import_statement(
@@ -14,12 +14,19 @@ def import_statement(
     line_separator: str = "\n",
     config: Config = DEFAULT_CONFIG,
     multi_line_output: Optional[Modes] = None,
+    explode: bool = False,
 ) -> str:
     """Returns a multi-line wrapped form of the provided from import statement."""
-    formatter = formatter_from_string((multi_line_output or config.multi_line_output).name)
+    if explode:
+        formatter = vertical_hanging_indent
+        line_length = 1
+        include_trailing_comma = True
+    else:
+        formatter = formatter_from_string((multi_line_output or config.multi_line_output).name)
+        line_length = config.wrap_length or config.line_length
+        include_trailing_comma = config.include_trailing_comma
     dynamic_indent = " " * (len(import_start) + 1)
     indent = config.indent
-    line_length = config.wrap_length or config.line_length
     statement = formatter(
         statement=import_start,
         imports=copy.copy(from_imports),
@@ -29,7 +36,7 @@ def import_statement(
         comments=comments,
         line_separator=line_separator,
         comment_prefix=config.comment_prefix,
-        include_trailing_comma=config.include_trailing_comma,
+        include_trailing_comma=include_trailing_comma,
         remove_comments=config.ignore_comments,
     )
     if config.balanced_wrapping:
@@ -52,7 +59,7 @@ def import_statement(
                 comments=comments,
                 line_separator=line_separator,
                 comment_prefix=config.comment_prefix,
-                include_trailing_comma=config.include_trailing_comma,
+                include_trailing_comma=include_trailing_comma,
                 remove_comments=config.ignore_comments,
             )
             lines = new_import_statement.split(line_separator)
diff --git a/tests/unit/test_isort.py b/tests/unit/test_isort.py
index 293b99be..4b86f7ec 100644
--- a/tests/unit/test_isort.py
+++ b/tests/unit/test_isort.py
@@ -5562,3 +5562,19 @@ def test_find_imports_in_stream() -> None:
     test_input = NonSeekableTestStream("import m2\n" "import m1\n" "not_import = 7")
     identified_imports = list(map(str, api.find_imports_in_stream(test_input)))
     assert identified_imports == [":1 import m2", ":2 import m1"]
+
+
+def test_split_on_trailing_comma() -> None:
+    test_input = "from lib import (a, b, c,)"
+    expected_output = """from lib import (
+    a,
+    b,
+    c,
+)
+"""
+
+    output = isort.code(test_input, split_on_trailing_comma=True)
+    assert output == expected_output
+
+    output = isort.code(expected_output, split_on_trailing_comma=True)
+    assert output == expected_output
diff --git a/tests/unit/test_parse.py b/tests/unit/test_parse.py
index 0becac90..1a66a5cd 100644
--- a/tests/unit/test_parse.py
+++ b/tests/unit/test_parse.py
@@ -38,6 +38,7 @@ def test_file_contents():
         _,
         _,
         _,
+        _,
     ) = parse.file_contents(TEST_CONTENTS, config=Config(default_section=""))
     assert "\n".join(in_lines) == TEST_CONTENTS
     assert "import" not in "\n".join(out_lines)
diff --git a/tests/unit/test_wrap.py b/tests/unit/test_wrap.py
index 2b8ec6fa..2e35951f 100644
--- a/tests/unit/test_wrap.py
+++ b/tests/unit/test_wrap.py
@@ -13,3 +13,6 @@ def test_import_statement():
         == """from long_import (verylong, verylong, verylong, verylong, verylong, verylong,
                   verylong, verylong, verylong, verylong)"""
     )
+    assert wrap.import_statement("from x import ", ["y", "z"], [], explode=True) == (
+        "from x import (\n    y,\n    z,\n)"
+    )