Improve call chain

CHANGES.md

@@ -23,6 +23,8 @@
   blocks, except immediately before a docstring (#4130)
 - For stubs, fix logic to enforce empty line after nested classes with bodies (#4141)
 - Fix crash when using a walrus in a dictionary (#4155)
+- When a line contains more than one method call, it is treated as a call chain, and the
+  fluent style is prioritized for formatting this line (#4153)
 
 ### Configuration
 

src/black/brackets.py

@@ -245,8 +245,9 @@ def is_split_before_delimiter(leaf: Leaf, previous: Optional[Leaf] = None) -> Pr
     if (
         leaf.type == token.DOT
         and leaf.parent
-        and leaf.parent.type not in {syms.import_from, syms.dotted_name}
-        and (previous is None or previous.type in CLOSING_BRACKETS)
+        and leaf.parent.type == syms.trailer
+        and previous
+        and previous.type in CLOSING_BRACKETS
     ):
         return DOT_PRIORITY
 

src/black/linegen.py

@@ -915,6 +915,9 @@ def _maybe_split_omitting_optional_parens(
         and not line.is_import
         # and we can actually remove the parens
         and can_omit_invisible_parens(rhs, mode.line_length)
+        and not (
+            Preview.improve_call_chain in mode and rhs.body.should_use_fluent_style
+        )
     ):
         omit = {id(rhs.closing_bracket), *omit}
         try:
@@ -1184,9 +1187,12 @@ def delimiter_split(
     except ValueError:
         raise CannotSplit("No delimiters found") from None
 
-    if delimiter_priority == DOT_PRIORITY:
-        if bt.delimiter_count_with_priority(delimiter_priority) == 1:
-            raise CannotSplit("Splitting a single attribute from its owner looks wrong")
+    if (
+        not (Preview.improve_call_chain in mode and line.should_use_fluent_style)
+        and delimiter_priority == DOT_PRIORITY
+        and bt.delimiter_count_with_priority(delimiter_priority) == 1
+    ):
+        raise CannotSplit("Splitting a single attribute from its owner looks wrong")
 
     current_line = Line(
         mode=line.mode, depth=line.depth, inside_brackets=line.inside_brackets

src/black/lines.py

@@ -220,6 +220,31 @@ def is_chained_assignment(self) -> bool:
         """Is the line a chained assignment"""
         return [leaf.type for leaf in self.leaves].count(token.EQUAL) > 1
 
+    @property
+    def should_use_fluent_style(self) -> bool:
+        """Should the line use fluent style?"""
+        if self.comments:
+            return False
+        line_node = self.leaves[0].parent
+        if not line_node:
+            return False
+        is_dot_trailer_open = False
+        significant_method_call_count = 0
+        for child in line_node.children:
+            if isinstance(child, Node) and child.type == syms.trailer:
+                if child.children[0].type == token.DOT:
+                    is_dot_trailer_open = True
+                elif (
+                    child.children[0].type in OPENING_BRACKETS
+                    and len(str(child)) > 10
+                    and is_dot_trailer_open
+                ):
+                    is_dot_trailer_open = False
+                    significant_method_call_count += 1
+                    if significant_method_call_count > 1:
+                        return True
+        return False
+
     @property
     def opens_block(self) -> bool:
         """Does this line open a new level of indentation."""

src/black/mode.py

@@ -197,6 +197,7 @@ class Preview(Enum):
     allow_form_feeds = auto()
     unify_docstring_detection = auto()
     respect_east_asian_width = auto()
+    improve_call_chain = auto()
 
 
 class Deprecated(UserWarning):

tests/data/cases/preview_call_chain.py

@@ -0,0 +1,27 @@
+# flags: --preview
+a = str(my_very_very_very_long_url_name.with_user(and_very_long_username).with_password(and_very_long_password))
+a = my_very_very_very_long_url_name.with_user(and_very_long_username).with_password(and_very_long_password)
+
+
+def foo():
+    completion_time = (a.read_namespaced_job(job.metadata.name, namespace="default").status().completion_time())
+
+
+# output
+
+a = str(
+    my_very_very_very_long_url_name.with_user(and_very_long_username)
+    .with_password(and_very_long_password)
+)
+a = (
+    my_very_very_very_long_url_name.with_user(and_very_long_username)
+    .with_password(and_very_long_password)
+)
+
+
+def foo():
+    completion_time = (
+        a.read_namespaced_job(job.metadata.name, namespace="default")
+        .status()
+        .completion_time()
+    )