Parenthesize conditional expressions (#2278)

Co-authored-by: Jordan Ephron <JEphron@users.noreply.github.com>
Co-authored-by: Richard Si <63936253+ichard26@users.noreply.github.com>
Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

CHANGES.md

@@ -16,6 +16,7 @@
 
 <!-- Changes that affect Black's preview style -->
 
+- Add parentheses around `if`-`else` expressions (#2278)
 - Improve the performance on large expressions that contain many strings (#3467)
 - Fix a crash in preview style with assert + parenthesized string (#3415)
 - Fix crashes in preview style with walrus operators used in function return annotations

src/black/__init__.py

@@ -478,16 +478,20 @@ def main(  # noqa: C901
             )
 
             normalized = [
+                (
                     (source, source)
                     if source == "-"
                     else (normalize_path_maybe_ignore(Path(source), root), source)
+                )
                 for source in src
             ]
             srcs_string = ", ".join(
                 [
+                    (
                         f'"{_norm}"'
                         if _norm
                         else f'\033[31m"{source} (skipping - invalid)"\033[34m'
+                    )
                     for _norm, source in normalized
                 ]
             )

src/black/linegen.py

@@ -140,6 +140,22 @@ def visit_default(self, node: LN) -> Iterator[Line]:
                 self.current_line.append(node)
         yield from super().visit_default(node)
 
+    def visit_test(self, node: Node) -> Iterator[Line]:
+        """Visit an `x if y else z` test"""
+
+        if Preview.parenthesize_conditional_expressions in self.mode:
+            already_parenthesized = (
+                node.prev_sibling and node.prev_sibling.type == token.LPAR
+            )
+
+            if not already_parenthesized:
+                lpar = Leaf(token.LPAR, "")
+                rpar = Leaf(token.RPAR, "")
+                node.insert_child(0, lpar)
+                node.append_child(rpar)
+
+        yield from self.visit_default(node)
+
     def visit_INDENT(self, node: Leaf) -> Iterator[Line]:
         """Increase indentation level, maybe yield a line."""
         # In blib2to3 INDENT never holds comments.

src/black/mode.py

@@ -161,6 +161,7 @@ class Preview(Enum):
     # NOTE: string_processing requires wrap_long_dict_values_in_parens
     # for https://github.com/psf/black/issues/3117 to be fixed.
     string_processing = auto()
+    parenthesize_conditional_expressions = auto()
     skip_magic_trailing_comma_in_subscript = auto()
     wrap_long_dict_values_in_parens = auto()
 

tests/data/conditional_expression.py

@@ -0,0 +1,160 @@
+long_kwargs_single_line = my_function(
+    foo="test, this is a sample value",
+    bar=some_long_value_name_foo_bar_baz if some_boolean_variable else some_fallback_value_foo_bar_baz,
+    baz="hello, this is a another value",
+)
+
+multiline_kwargs_indented = my_function(
+    foo="test, this is a sample value",
+    bar=some_long_value_name_foo_bar_baz
+    if some_boolean_variable
+    else some_fallback_value_foo_bar_baz,
+    baz="hello, this is a another value",
+)
+
+imploding_kwargs = my_function(
+    foo="test, this is a sample value",
+    bar=a
+    if foo
+    else b,
+    baz="hello, this is a another value",
+)
+
+imploding_line = (
+    1
+    if 1 + 1 == 2
+    else 0
+)
+
+exploding_line = "hello this is a slightly long string" if some_long_value_name_foo_bar_baz else "this one is a little shorter"
+
+positional_argument_test(some_long_value_name_foo_bar_baz if some_boolean_variable else some_fallback_value_foo_bar_baz)
+
+def weird_default_argument(x=some_long_value_name_foo_bar_baz
+        if SOME_CONSTANT
+        else some_fallback_value_foo_bar_baz):
+    pass
+
+nested = "hello this is a slightly long string" if (some_long_value_name_foo_bar_baz if
+                                                    nesting_test_expressions else some_fallback_value_foo_bar_baz) \
+    else "this one is a little shorter"
+
+generator_expression = (
+    some_long_value_name_foo_bar_baz if some_boolean_variable else some_fallback_value_foo_bar_baz for some_boolean_variable in some_iterable
+)
+
+
+def limit_offset_sql(self, low_mark, high_mark):
+    """Return LIMIT/OFFSET SQL clause."""
+    limit, offset = self._get_limit_offset_params(low_mark, high_mark)
+    return " ".join(
+        sql
+        for sql in (
+            "LIMIT %d" % limit if limit else None,
+            ("OFFSET %d" % offset) if offset else None,
+        )
+        if sql
+    )
+
+
+def something():
+    clone._iterable_class = (
+        NamedValuesListIterable
+        if named
+        else FlatValuesListIterable
+        if flat
+        else ValuesListIterable
+    )
+
+# output
+
+long_kwargs_single_line = my_function(
+    foo="test, this is a sample value",
+    bar=(
+        some_long_value_name_foo_bar_baz
+        if some_boolean_variable
+        else some_fallback_value_foo_bar_baz
+    ),
+    baz="hello, this is a another value",
+)
+
+multiline_kwargs_indented = my_function(
+    foo="test, this is a sample value",
+    bar=(
+        some_long_value_name_foo_bar_baz
+        if some_boolean_variable
+        else some_fallback_value_foo_bar_baz
+    ),
+    baz="hello, this is a another value",
+)
+
+imploding_kwargs = my_function(
+    foo="test, this is a sample value",
+    bar=a if foo else b,
+    baz="hello, this is a another value",
+)
+
+imploding_line = 1 if 1 + 1 == 2 else 0
+
+exploding_line = (
+    "hello this is a slightly long string"
+    if some_long_value_name_foo_bar_baz
+    else "this one is a little shorter"
+)
+
+positional_argument_test(
+    some_long_value_name_foo_bar_baz
+    if some_boolean_variable
+    else some_fallback_value_foo_bar_baz
+)
+
+
+def weird_default_argument(
+    x=(
+        some_long_value_name_foo_bar_baz
+        if SOME_CONSTANT
+        else some_fallback_value_foo_bar_baz
+    ),
+):
+    pass
+
+
+nested = (
+    "hello this is a slightly long string"
+    if (
+        some_long_value_name_foo_bar_baz
+        if nesting_test_expressions
+        else some_fallback_value_foo_bar_baz
+    )
+    else "this one is a little shorter"
+)
+
+generator_expression = (
+    (
+        some_long_value_name_foo_bar_baz
+        if some_boolean_variable
+        else some_fallback_value_foo_bar_baz
+    )
+    for some_boolean_variable in some_iterable
+)
+
+
+def limit_offset_sql(self, low_mark, high_mark):
+    """Return LIMIT/OFFSET SQL clause."""
+    limit, offset = self._get_limit_offset_params(low_mark, high_mark)
+    return " ".join(
+        sql
+        for sql in (
+            "LIMIT %d" % limit if limit else None,
+            ("OFFSET %d" % offset) if offset else None,
+        )
+        if sql
+    )
+
+
+def something():
+    clone._iterable_class = (
+        NamedValuesListIterable
+        if named
+        else FlatValuesListIterable if flat else ValuesListIterable
+    )