Only use trailing commas in function signatures when it's safe

[etc/vim.git] / black.py

diff --git a/black.py b/black.py
index 774d91dc2a7f64ec2dbc252a55e0fe051d5c429c..0a9d3eae46fa1a548f1eb3c9674fc7be3ba6812b 100644 (file)
--- a/black.py
+++ b/black.py
@@ -7,6 +7,7 @@ import keyword
 import os
 from pathlib import Path
 import tokenize
+import sys
 from typing import (
     Dict, Generic, Iterable, Iterator, List, Optional, Set, Tuple, TypeVar, Union
 )
@@ -192,6 +193,7 @@ def format_str(src_contents: str, line_length: int) -> FileContent:
     comments: List[Line] = []
     lines = LineGenerator()
     elt = EmptyLineTracker()
+    py36 = is_python36(src_node)
     empty_line = Line()
     after = 0
     for current_line in lines.visit(src_node):
@@ -204,7 +206,7 @@ def format_str(src_contents: str, line_length: int) -> FileContent:
             for comment in comments:
                 dst_contents += str(comment)
             comments = []
-            for line in split_line(current_line, line_length=line_length):
+            for line in split_line(current_line, line_length=line_length, py36=py36):
                 dst_contents += str(line)
         else:
             comments.append(current_line)
@@ -1108,13 +1110,18 @@ def generate_comments(leaf: Leaf) -> Iterator[Leaf]:
         yield Leaf(STANDALONE_COMMENT, line)
 
 
-def split_line(line: Line, line_length: int, inner: bool = False) -> Iterator[Line]:
+def split_line(
+    line: Line, line_length: int, inner: bool = False, py36: bool = False
+) -> Iterator[Line]:
     """Splits a `line` into potentially many lines.
 
     They should fit in the allotted `line_length` but might not be able to.
     `inner` signifies that there were a pair of brackets somewhere around the
     current `line`, possibly transitively. This means we can fallback to splitting
     by delimiters if the LHS/RHS don't yield any results.
+
+    If `py36` is True, splitting may generate syntax that is only compatible
+    with Python 3.6 and later.
     """
     line_str = str(line).strip('\n')
     if len(line_str) <= line_length and '\n' not in line_str:
@@ -1137,11 +1144,13 @@ def split_line(line: Line, line_length: int, inner: bool = False) -> Iterator[Li
         # split altogether.
         result: List[Line] = []
         try:
-            for l in split_func(line):
+            for l in split_func(line, py36=py36):
                 if str(l).strip('\n') == line_str:
                     raise CannotSplit("Split function returned an unchanged result")
 
-                result.extend(split_line(l, line_length=line_length, inner=True))
+                result.extend(
+                    split_line(l, line_length=line_length, inner=True, py36=py36)
+                )
         except CannotSplit as cs:
             continue
 
@@ -1153,7 +1162,7 @@ def split_line(line: Line, line_length: int, inner: bool = False) -> Iterator[Li
         yield line
 
 
-def left_hand_split(line: Line) -> Iterator[Line]:
+def left_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
     """Split line into many lines, starting with the first matching bracket pair.
 
     Note: this usually looks weird, only use this for function definitions.
@@ -1208,7 +1217,7 @@ def left_hand_split(line: Line) -> Iterator[Line]:
             yield result
 
 
-def right_hand_split(line: Line) -> Iterator[Line]:
+def right_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
     """Split line into many lines, starting with the last matching bracket pair."""
     head = Line(depth=line.depth)
     body = Line(depth=line.depth + 1, inside_brackets=True)
@@ -1259,10 +1268,12 @@ def right_hand_split(line: Line) -> Iterator[Line]:
             yield result
 
 
-def delimiter_split(line: Line) -> Iterator[Line]:
+def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:
     """Split according to delimiters of the highest priority.
 
     This kind of split doesn't increase indentation.
+    If `py36` is True, the split will add trailing commas also in function
+    signatures that contain * and **.
     """
     try:
         last_leaf = line.leaves[-1]
@@ -1276,11 +1287,20 @@ def delimiter_split(line: Line) -> Iterator[Line]:
         raise CannotSplit("No delimiters found")
 
     current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)
+    lowest_depth = sys.maxsize
+    trailing_comma_safe = True
     for leaf in line.leaves:
         current_line.append(leaf, preformatted=True)
         comment_after = line.comments.get(id(leaf))
         if comment_after:
             current_line.append(comment_after, preformatted=True)
+        lowest_depth = min(lowest_depth, leaf.bracket_depth)
+        if (
+            leaf.bracket_depth == lowest_depth and  # type: ignore
+            leaf.type == token.STAR or
+            leaf.type == token.DOUBLESTAR
+        ):
+            trailing_comma_safe = trailing_comma_safe and py36
         leaf_priority = delimiters.get(id(leaf))
         if leaf_priority == delimiter_priority:
             normalize_prefix(current_line.leaves[0])
@@ -1290,7 +1310,8 @@ def delimiter_split(line: Line) -> Iterator[Line]:
     if current_line:
         if (
             delimiter_priority == COMMA_PRIORITY and
-            current_line.leaves[-1].type != token.COMMA
+            current_line.leaves[-1].type != token.COMMA and
+            trailing_comma_safe
         ):
             current_line.append(Leaf(token.COMMA, ','))
         normalize_prefix(current_line.leaves[0])
@@ -1325,6 +1346,31 @@ def normalize_prefix(leaf: Leaf) -> None:
     leaf.prefix = ''
 
 
+def is_python36(node: Node) -> bool:
+    """Returns True if the current file is using Python 3.6+ features.
+
+    Currently looking for:
+    - f-strings; and
+    - trailing commas after * or ** in function signatures.
+    """
+    for n in node.pre_order():
+        if n.type == token.STRING:
+            assert isinstance(n, Leaf)
+            if n.value[:2] in {'f"', 'F"', "f'", "F'", 'rf', 'fr', 'RF', 'FR'}:
+                return True
+
+        elif (
+            n.type == syms.typedargslist and
+            n.children and
+            n.children[-1].type == token.COMMA
+        ):
+            for ch in n.children:
+                if ch.type == token.STAR or ch.type == token.DOUBLESTAR:
+                    return True
+
+    return False
+
+
 PYTHON_EXTENSIONS = {'.py'}
 BLACKLISTED_DIRECTORIES = {
     'build', 'buck-out', 'dist', '_build', '.git', '.hg', '.mypy_cache', '.tox', '.venv'