Maybe parenthesize long constants and names (#6816)

crates/ruff_python_formatter/src/expression/parentheses.rs

@@ -1,5 +1,5 @@
 use ruff_formatter::prelude::tag::Condition;
-use ruff_formatter::{format_args, write, Argument, Arguments};
+use ruff_formatter::{format_args, write, Argument, Arguments, FormatContext, FormatOptions};
 use ruff_python_ast::node::AnyNodeRef;
 use ruff_python_ast::{ExpressionRef, Ranged};
 use ruff_python_trivia::{first_non_trivia_token, SimpleToken, SimpleTokenKind, SimpleTokenizer};
@@ -15,14 +15,37 @@ pub(crate) enum OptionalParentheses {
     /// Add parentheses if the expression expands over multiple lines
     Multiline,
 
-    /// Always set parentheses regardless if the expression breaks or if they were
+    /// Always set parentheses regardless if the expression breaks or if they are
     /// present in the source.
     Always,
 
-    /// Never add parentheses
+    /// Add parentheses if it helps to make this expression fit. Otherwise never add parentheses.
+    /// This mode should only be used for expressions that don't have their own split points, e.g. identifiers,
+    /// or constants.
+    BestFit,
+
+    /// Never add parentheses. Use it for expressions that have their own parentheses or if the expression body always spans multiple lines (multiline strings).
     Never,
 }
 
+pub(super) fn should_use_best_fit<T>(value: T, context: &PyFormatContext) -> bool
+where
+    T: Ranged,
+{
+    let text_len = context.source()[value.range()].len();
+
+    // Only use best fits if:
+    // * The text is longer than 5 characters:
+    //   This is to align the behavior with `True` and `False`, that don't use best fits and are 5 characters long.
+    //   It allows to avoid [`OptionalParentheses::BestFit`] for most numbers and common identifiers like `self`.
+    //   The downside is that it can result in short values not being parenthesized if they exceed the line width.
+    //   This is considered an edge case not worth the performance penalty and IMO, breaking an identifier
+    //   of 5 characters to avoid it exceeding the line width by 1 reduces the readability.
+    // * The text is know to never fit: The text can never fit even when parenthesizing if it is longer
+    //   than the configured line width (minus indent).
+    text_len > 5 && text_len < context.options().line_width().value() as usize
+}
+
 pub(crate) trait NeedsParentheses {
     /// Determines if this object needs optional parentheses or if it is safe to omit the parentheses.
     fn needs_parentheses(