respect magic trailing commas in return types (#3916)

[etc/vim.git] / src / black / linegen.py

diff --git a/src/black/linegen.py b/src/black/linegen.py
index 9ddd4619f691275a8a1ce9b70d4bce7348596281..bdc4ee54ab285351588659f458f804aa212573c2 100644 (file)
--- a/src/black/linegen.py
+++ b/src/black/linegen.py
@@ -573,7 +573,7 @@ def transform_line(
             transformers = [string_merge, string_paren_strip]
         else:
             transformers = []
-    elif line.is_def:
+    elif line.is_def and not should_split_funcdef_with_rhs(line, mode):
         transformers = [left_hand_split]
     else:
 
@@ -652,6 +652,40 @@ def transform_line(
         yield line
 
 
+def should_split_funcdef_with_rhs(line: Line, mode: Mode) -> bool:
+    """If a funcdef has a magic trailing comma in the return type, then we should first
+    split the line with rhs to respect the comma.
+    """
+    if Preview.respect_magic_trailing_comma_in_return_type not in mode:
+        return False
+
+    return_type_leaves: List[Leaf] = []
+    in_return_type = False
+
+    for leaf in line.leaves:
+        if leaf.type == token.COLON:
+            in_return_type = False
+        if in_return_type:
+            return_type_leaves.append(leaf)
+        if leaf.type == token.RARROW:
+            in_return_type = True
+
+    # using `bracket_split_build_line` will mess with whitespace, so we duplicate a
+    # couple lines from it.
+    result = Line(mode=line.mode, depth=line.depth)
+    leaves_to_track = get_leaves_inside_matching_brackets(return_type_leaves)
+    for leaf in return_type_leaves:
+        result.append(
+            leaf,
+            preformatted=True,
+            track_bracket=id(leaf) in leaves_to_track,
+        )
+
+    # we could also return true if the line is too long, and the return type is longer
+    # than the param list. Or if `should_split_rhs` returns True.
+    return result.magic_trailing_comma is not None
+
+
 class _BracketSplitComponent(Enum):
     head = auto()
     body = auto()