Also remove trailing bare lines in comments

Block comments with bare lines are handled differently than those
without bare lines (unless `normalize_comments` is configured). If
`normalize_comments` is false but `wrap_comments` is true, trailing
blank lines should be removed from block comments, including those with
bare lines.

Signed-off-by: Ross Williams <ross@ross-williams.net>

Author: overhacked

src/comment.rs

@@ -10,8 +10,8 @@ use crate::rewrite::RewriteContext;
 use crate::shape::{Indent, Shape};
 use crate::string::{rewrite_string, StringFormat};
 use crate::utils::{
-    count_newlines, first_line_width, last_line_width, trim_left_preserve_layout,
-    trimmed_last_line_width, unicode_str_width,
+    count_newlines, first_line_width, is_horizontal_space, last_line_width,
+    trim_left_preserve_layout, trimmed_last_line_width, unicode_str_width,
 };
 use crate::{ErrorKind, FormattingError};
 
@@ -346,7 +346,14 @@ fn identify_comment(
     let (first_group, rest) = orig.split_at(first_group_ending);
     let rewritten_first_group =
         if !config.normalize_comments() && has_bare_lines && style.is_block_comment() {
-            trim_left_preserve_layout(first_group, shape.indent, config)?
+            let reindented = trim_left_preserve_layout(first_group, shape.indent, config)?;
+
+            // If wrap_comments is enabled, then remove any trailing blank lines
+            if config.wrap_comments() {
+                strip_comment_trailing_lines(reindented, style)
+            } else {
+                reindented
+            }
         } else if !config.normalize_comments()
             && !config.wrap_comments()
             && !(
@@ -1053,6 +1060,46 @@ fn trim_end_unless_two_whitespaces(s: &str, is_doc_comment: bool) -> &str {
     }
 }
 
+/// Removes blank lines at the end of block comments
+fn strip_comment_trailing_lines(comment: String, style: CommentStyle<'_>) -> String {
+    debug_assert!(
+        style.is_block_comment(),
+        "strip_suffix(style.closer()) ensures this function is a no-op on non-block comments"
+    );
+
+    // If final line is a normal closing line, look for trailing blank lines
+    if let Some(without_closer) = comment
+        .strip_suffix(style.closer())
+        .map(|s| s.trim_end_matches(is_horizontal_space))
+        .and_then(|s| s.strip_suffix('\n'))
+    {
+        let mut trimmed = without_closer.trim_end();
+        let closer_line = &comment[without_closer.len()..];
+        let line_start = style.line_start().trim_end();
+        // Start trimming trailing blank lines
+        loop {
+            // Remove any asterisk-prefixed or bare block comment lines
+            let t = trimmed.trim_end_matches(line_start).trim_end();
+            if t.len() == trimmed.len() {
+                // If no trimming occurred
+                break;
+            } else {
+                // ... otherwise, keep trying to trim
+                trimmed = t;
+            }
+        }
+
+        if without_closer.len() == trimmed.len() {
+            // No blank lines were removed
+            comment
+        } else {
+            trimmed.to_string() + closer_line
+        }
+    } else {
+        // Final line either didn't have a closer or had non-whitespace along with the closer
+        comment
+    }
+}
 /// Trims whitespace and aligns to indent, but otherwise does not change comments.
 fn light_rewrite_comment(
     orig: &str,

src/utils.rs

@@ -675,6 +675,10 @@ pub(crate) fn is_empty_line(s: &str) -> bool {
     s.is_empty() || s.chars().all(char::is_whitespace)
 }
 
+pub(crate) fn is_horizontal_space(c: char) -> bool {
+    c == ' ' || c == '\t'
+}
+
 fn get_prefix_space_width(config: &Config, s: &str) -> usize {
     let mut width = 0;
     for c in s.chars() {

tests/source/comment_trailing_lines.rs

@@ -19,3 +19,10 @@ pub mod bar {}
  *
  */
 pub mod block {}
+
+/**
+Outer Block doc comment with multiple trailing lines
+
+
+ */
+pub mod outer_block_doc_comment {}

tests/target/comment_trailing_lines.rs

@@ -12,3 +12,8 @@ pub mod bar {}
  * Block comment with multiple trailing lines
  */
 pub mod block {}
+
+/**
+Outer Block doc comment with multiple trailing lines
+ */
+pub mod outer_block_doc_comment {}