From cdc0d5fb0c12408eaa057fc6e2b9bbd1ee31622e Mon Sep 17 00:00:00 2001
From: Ayaz Hafiz <ayaz.hafiz.1@gmail.com>
Date: Thu, 2 Jul 2020 09:52:25 -0700
Subject: [PATCH] Do not add trailing space to empty lines in comment code
 blocks

Currently, the first line pushed in a code block is a comment line
delimiter that includes a trailing space, even if the content of that
line is empty. Later lines are handled correctly because their content
is checked before adding the comment line delimiter. So, just apply the
same logic as is done for later lines to the first line.

Closes #4251
---
 src/formatting/comment.rs  | 32 ++++++++++++++++++++++----------
 tests/source/issue-4251.rs |  6 ++++++
 tests/target/issue-4251.rs |  6 ++++++
 3 files changed, 34 insertions(+), 10 deletions(-)
 create mode 100644 tests/source/issue-4251.rs
 create mode 100644 tests/target/issue-4251.rs

diff --git a/src/formatting/comment.rs b/src/formatting/comment.rs
index 4ca31878f32..907a0335306 100644
--- a/src/formatting/comment.rs
+++ b/src/formatting/comment.rs
@@ -576,16 +576,22 @@ impl<'a> CommentRewrite<'a> {
         cr
     }
 
-    fn join_block(s: &str, sep: &str) -> String {
+    fn join_block(s: &str, sep: &str, add_sep_prefix: bool) -> String {
         let mut result = String::with_capacity(s.len() + 128);
         let mut iter = s.lines().peekable();
+        let get_sep = |line: Option<&&str>| -> &str {
+            match line {
+                Some(&"") => sep.trim_end(),
+                Some(..) => sep,
+                None => "",
+            }
+        };
+        if add_sep_prefix {
+            result.push_str(get_sep(iter.peek()));
+        }
         while let Some(line) = iter.next() {
             result.push_str(line);
-            result.push_str(match iter.peek() {
-                Some(next_line) if next_line.is_empty() => sep.trim_end(),
-                Some(..) => &sep,
-                None => "",
-            });
+            result.push_str(get_sep(iter.peek()));
         }
         result
     }
@@ -594,10 +600,10 @@ impl<'a> CommentRewrite<'a> {
         if !self.code_block_buffer.is_empty() {
             // There is a code block that is not properly enclosed by backticks.
             // We will leave them untouched.
-            self.result.push_str(&self.comment_line_separator);
             self.result.push_str(&Self::join_block(
                 &trim_custom_comment_prefix(&self.code_block_buffer),
                 &self.comment_line_separator,
+                true, /* add_sep_prefix */
             ));
         }
 
@@ -615,10 +621,12 @@ impl<'a> CommentRewrite<'a> {
                 Some(s) => self.result.push_str(&Self::join_block(
                     &s,
                     &format!("{}{}", self.comment_line_separator, ib.line_start),
+                    false, /* add_sep_prefix */
                 )),
                 None => self.result.push_str(&Self::join_block(
                     &ib.original_block_as_string(),
                     &self.comment_line_separator,
+                    false, /* add_sep_prefix */
                 )),
             };
         }
@@ -658,10 +666,12 @@ impl<'a> CommentRewrite<'a> {
                 Some(s) => self.result.push_str(&Self::join_block(
                     &s,
                     &format!("{}{}", self.comment_line_separator, ib.line_start),
+                    false, /* add_sep_prefix */
                 )),
                 None => self.result.push_str(&Self::join_block(
                     &ib.original_block_as_string(),
                     &self.comment_line_separator,
+                    false, /* add_sep_prefix */
                 )),
             };
         } else if self.code_block_attr.is_some() {
@@ -689,9 +699,11 @@ impl<'a> CommentRewrite<'a> {
                     }
                 };
                 if !code_block.is_empty() {
-                    self.result.push_str(&self.comment_line_separator);
-                    self.result
-                        .push_str(&Self::join_block(&code_block, &self.comment_line_separator));
+                    self.result.push_str(&Self::join_block(
+                        &code_block,
+                        &self.comment_line_separator,
+                        true, /* add_sep_prefix */
+                    ));
                 }
                 self.code_block_buffer.clear();
                 self.result.push_str(&self.comment_line_separator);
diff --git a/tests/source/issue-4251.rs b/tests/source/issue-4251.rs
new file mode 100644
index 00000000000..af54bc6d4c4
--- /dev/null
+++ b/tests/source/issue-4251.rs
@@ -0,0 +1,6 @@
+// rustfmt-wrap_comments: true
+
+//! ```
+//! 
+//! use something;
+//! ```
diff --git a/tests/target/issue-4251.rs b/tests/target/issue-4251.rs
new file mode 100644
index 00000000000..852cf5cbae8
--- /dev/null
+++ b/tests/target/issue-4251.rs
@@ -0,0 +1,6 @@
+// rustfmt-wrap_comments: true
+
+//! ```
+//!
+//! use something;
+//! ```