Formatter collapses parenthesized if-expression

[cnpryer]

Somewhat related: #6588

Line-length: 88

IMO Ruff's output is better. Reporting anyway.

# Input
class A:
    def b():
        before = (
            # comment
            0
            if self.thing is None
            else before - after
        )

# Black (23.7.0)
class A:
    def b():
        before = (
            # comment
            0
            if self.thing is None
            else before - after
        )

# Ruff (0.0.287)
class A:
    def b():
        before = (
            # comment
            0 if self.thing is None else before - after
        )

Black Playground

Ruff Playground

[cnpryer]

Oh wow I called it a comprehension 🙈 lol. Thanks!

[charliermarsh]

Oh no prob :) It might also apply to comprehensions, I’m not sure, but I renamed to reflect the example.

[charliermarsh]

I don't fully understand Black's rules here (some examples -- e.g., the first vs. second case is odd and likely a bug given that they drop the comment entirely). The preview style is also quite different.

It might be sufficient to expand the parent if the IfExp has leading or trailing own-line comments:

diff --git a/crates/ruff_python_formatter/src/expression/expr_if_exp.rs b/crates/ruff_python_formatter/src/expression/expr_if_exp.rs
index 1b22fb568..dec9b7d5f 100644
--- a/crates/ruff_python_formatter/src/expression/expr_if_exp.rs
+++ b/crates/ruff_python_formatter/src/expression/expr_if_exp.rs
@@ -53,9 +53,13 @@ impl FormatNodeRule<ExprIfExp> for FormatExprIfExp {
         let comments = f.context().comments().clone();

         let inner = format_with(|f: &mut PyFormatter| {
-            // We place `if test` and `else orelse` on a single line, so the `test` and `orelse` leading
-            // comments go on the line before the `if` or `else` instead of directly ahead `test` or
-            // `orelse`
+            if comments.has_leading(item) || comments.has_trailing(item) {
+                expand_parent().fmt(f)?;
+            }

[charliermarsh]

It would be nice to map this behavior to code in Black to better understand the rules.

[charliermarsh]

We decided to accept this as a deviation: #7082