rust-lang/style-team#189: rhs-should-use-indent-of-last-line-of-lhs

Author: johnhuichen

src/expr.rs

@@ -2101,6 +2101,25 @@ pub(crate) fn rewrite_assign_rhs_expr<R: Rewrite>(
  rhs_kind: &RhsAssignKind<'_>,
  rhs_tactics: RhsTactics,
 ) -> Option<String> {
+ let get_lhs_last_line_shape = || {
+ let last_line = lhs.rsplitn(2, "\n").next().unwrap_or_default();
+ let tab_spaces = context.config.tab_spaces();
+ let new_shape = shape
+ .block_indent(tab_spaces)
+ .saturating_sub_width(tab_spaces);
+ let extra_indent_string = new_shape.to_string(&context.config).to_string();
+ if last_line.starts_with(&extra_indent_string) {
+ new_shape
+ } else {
+ shape
+ }
+ };
+ let shape = if context.config.style_edition() >= StyleEdition::Edition2024 {
+ get_lhs_last_line_shape()
+ } else {
+ shape
+ };
+
  let last_line_width = last_line_width(lhs).saturating_sub(if lhs.contains('\n') {
  shape.indent.width()
  } else {

src/shape.rs

@@ -278,6 +278,12 @@ impl Shape {
  offset_indent.to_string_inner(config, 0)
  }
 
+ pub(crate) fn to_string(&self, config: &Config) -> Cow<'static, str> {
+ let mut offset_indent = self.indent;
+ offset_indent.alignment = self.offset;
+ offset_indent.to_string_inner(config, 1)
+ }
+
  /// Creates a `Shape` with a virtually infinite width.
  pub(crate) fn infinite_width(&self) -> Shape {
  Shape {

tests/source/rust-lang/style-team#189.rs

@@ -0,0 +1,24 @@
+// rustfmt-style_edition: 2024
+
+impl SomeType {
+ fn method(&mut self) {
+ self.array[array_index as usize]
+ .as_mut()
+ .expect("thing must exist")
+ .extra_info = Some(ExtraInfo {
+ parent,
+ count: count as u16,
+ children: children.into_boxed_slice(),
+ });
+ }
+}
+
+impl SomeType {
+ fn method(&mut self) {
+ self.array[array_index as usize]
+ .as_mut()
+ .expect("thing must exist")
+ .extra_info =
+ long_long_long_long_long_long_long_long_long_long_long_long_long_long_long;
+ }
+}

tests/target/rust-lang/style-team#189.rs

@@ -0,0 +1,24 @@
+// rustfmt-style_edition: 2024
+
+impl SomeType {
+ fn method(&mut self) {
+ self.array[array_index as usize]
+ .as_mut()
+ .expect("thing must exist")
+ .extra_info = Some(ExtraInfo {
+ parent,
+ count: count as u16,
+ children: children.into_boxed_slice(),
+ });
+ }
+}
+
+impl SomeType {
+ fn method(&mut self) {
+ self.array[array_index as usize]
+ .as_mut()
+ .expect("thing must exist")
+ .extra_info =
+ long_long_long_long_long_long_long_long_long_long_long_long_long_long_long;
+ }
+}