Optionally remove leading newlines in recover_missing_comment_in_span

A new parameter was added to recover_missing_comment_in_span to control
whether leading newline characters should always be removed from its
output.

Author: ytmimi

src/attr.rs

@@ -419,6 +419,7 @@ impl Rewrite for [ast::Attribute] {
                         shape.with_max_width(context.config),
                         context,
                         0,
+                        false,
                     )?;
                     let comment = if comment.is_empty() {
                         format!("\n{}", mlb)
@@ -449,6 +450,7 @@ impl Rewrite for [ast::Attribute] {
                         shape.with_max_width(context.config),
                         context,
                         0,
+                        false,
                     )?;
                     result.push_str(&comment);
                     if let Some(next) = attrs.get(derives.len()) {
@@ -482,6 +484,7 @@ impl Rewrite for [ast::Attribute] {
                     shape.with_max_width(context.config),
                     context,
                     0,
+                    false,
                 )?;
                 result.push_str(&comment);
                 if let Some(next) = attrs.get(1) {

src/comment.rs

@@ -965,6 +965,7 @@ pub(crate) fn recover_missing_comment_in_span(
     shape: Shape,
     context: &RewriteContext<'_>,
     used_width: usize,
+    remove_leading_newlines: bool,
 ) -> Option<String> {
     let missing_comment = rewrite_missing_comment(span, shape, context)?;
     if missing_comment.is_empty() {
@@ -976,7 +977,9 @@ pub(crate) fn recover_missing_comment_in_span(
         let total_width = missing_comment.len() + used_width + 1;
         let force_new_line_before_comment =
             missing_snippet[..pos].contains('\n') || total_width > context.config.max_width();
-        let sep = if force_new_line_before_comment {
+        let sep = if remove_leading_newlines && force_new_line_before_comment {
+            shape.indent.to_string(context.config)
+        } else if force_new_line_before_comment {
             shape.indent.to_string_with_newline(context.config)
         } else {
             Cow::from(" ")

src/items.rs

@@ -713,6 +713,7 @@ pub(crate) fn format_impl(
                 Shape::indented(offset, context.config),
                 context,
                 last_line_width(&result),
+                false,
             ) {
                 Some(ref missing_comment) if !missing_comment.is_empty() => {
                     result.push_str(missing_comment);
@@ -1092,6 +1093,7 @@ pub(crate) fn format_trait(
                         Shape::indented(offset, context.config),
                         context,
                         last_line_width(&result),
+                        false,
                     ) {
                         Some(ref missing_comment) if !missing_comment.is_empty() => {
                             result.push_str(missing_comment);
@@ -2482,6 +2484,7 @@ fn rewrite_fn_base(
                 shape,
                 context,
                 last_line_width(&result),
+                false,
             ) {
                 Some(ref missing_comment) if !missing_comment.is_empty() => {
                     result.push_str(missing_comment);