do not force comments to be indented with a comment trailing a line of code (#3833)

src/missed_spans.rs

@@ -3,10 +3,11 @@ use syntax::source_map::{BytePos, Pos, Span};
 use crate::comment::{is_last_comment_block, rewrite_comment, CodeCharKind, CommentCodeSlices};
 use crate::config::file_lines::FileLines;
 use crate::config::FileName;
+use crate::config::Version;
 use crate::coverage::transform_missing_snippet;
 use crate::shape::{Indent, Shape};
 use crate::source_map::LineRangeUtils;
-use crate::utils::{count_lf_crlf, count_newlines, last_line_width, mk_sp};
+use crate::utils::{count_lf_crlf, count_newlines, last_line_indent, last_line_width, mk_sp};
 use crate::visitor::FmtVisitor;
 
 struct SnippetStatus {
@@ -238,6 +239,7 @@ impl<'a> FmtVisitor<'a> {
             .next();
 
         let fix_indent = last_char.map_or(true, |rev_c| ['{', '\n'].contains(&rev_c));
+        let mut on_same_line = false;
 
         let comment_indent = if fix_indent {
             if let Some('{') = last_char {
@@ -246,6 +248,13 @@ impl<'a> FmtVisitor<'a> {
             let indent_str = self.block_indent.to_string(self.config);
             self.push_str(&indent_str);
             self.block_indent
+        } else if self.config.version() == Version::Two && !snippet.starts_with('\n') {
+            // The comment appears on the same line as the previous formatted code.
+            // Assuming that comment is logically associated with that code, we want to keep it on
+            // the same level and avoid mixing it with possible other comment.
+            on_same_line = true;
+            self.push_str(" ");
+            Indent::from_width(self.config, last_line_indent(&self.buffer))
         } else {
             self.push_str(" ");
             Indent::from_width(self.config, last_line_width(&self.buffer))
@@ -256,9 +265,34 @@ impl<'a> FmtVisitor<'a> {
             self.config.max_width() - self.block_indent.width(),
         );
         let comment_shape = Shape::legacy(comment_width, comment_indent);
-        let comment_str = rewrite_comment(subslice, false, comment_shape, self.config)
-            .unwrap_or_else(|| String::from(subslice));
-        self.push_str(&comment_str);
+
+        if on_same_line {
+            match subslice.find("\n") {
+                None => {
+                    self.push_str(subslice);
+                }
+                Some(offset) if offset + 1 == subslice.len() => {
+                    self.push_str(&subslice[..offset]);
+                }
+                Some(offset) => {
+                    // keep first line as is: if it were too long and wrapped, it may get mixed
+                    // with the other lines.
+                    let first_line = &subslice[..offset];
+                    self.push_str(first_line);
+                    self.push_str(&comment_indent.to_string_with_newline(self.config));
+
+                    let other_lines = &subslice[offset + 1..];
+                    let comment_str =
+                        rewrite_comment(other_lines, false, comment_shape, self.config)
+                            .unwrap_or_else(|| String::from(other_lines));
+                    self.push_str(&comment_str);
+                }
+            }
+        } else {
+            let comment_str = rewrite_comment(subslice, false, comment_shape, self.config)
+                .unwrap_or_else(|| String::from(subslice));
+            self.push_str(&comment_str);
+        }
 
         status.last_wspace = None;
         status.line_start = offset + subslice.len();

src/utils.rs

@@ -193,19 +193,26 @@ pub(crate) fn is_attributes_extendable(attrs_str: &str) -> bool {
     !attrs_str.contains('\n') && !last_line_contains_single_line_comment(attrs_str)
 }
 
-// The width of the first line in s.
+/// The width of the first line in s.
 #[inline]
 pub(crate) fn first_line_width(s: &str) -> usize {
     unicode_str_width(s.splitn(2, '\n').next().unwrap_or(""))
 }
 
-// The width of the last line in s.
+/// The width of the last line in s.
 #[inline]
 pub(crate) fn last_line_width(s: &str) -> usize {
     unicode_str_width(s.rsplitn(2, '\n').next().unwrap_or(""))
 }
 
-// The total used width of the last line.
+/// The indent width of the last line in s.
+#[inline]
+pub(crate) fn last_line_indent(s: &str) -> usize {
+    let last_line = s.rsplitn(2, '\n').next().unwrap_or("");
+    last_line.chars().take_while(|c| c.is_whitespace()).count()
+}
+
+/// The total used width of the last line.
 #[inline]
 pub(crate) fn last_line_used_width(s: &str, offset: usize) -> usize {
     if s.contains('\n') {

src/visitor.rs

@@ -7,6 +7,7 @@ use syntax::{ast, visit};
 
 use crate::attr::*;
 use crate::comment::{rewrite_comment, CodeCharKind, CommentCodeSlices};
+use crate::config::Version;
 use crate::config::{BraceStyle, Config};
 use crate::coverage::transform_missing_snippet;
 use crate::items::{
@@ -252,32 +253,60 @@ impl<'b, 'a: 'b> FmtVisitor<'a> {
 
                     let mut comment_shape =
                         Shape::indented(self.block_indent, config).comment(config);
-                    if comment_on_same_line {
-                        // 1 = a space before `//`
-                        let offset_len = 1 + last_line_width(&self.buffer)
-                            .saturating_sub(self.block_indent.width());
-                        match comment_shape
-                            .visual_indent(offset_len)
-                            .sub_width(offset_len)
-                        {
-                            Some(shp) => comment_shape = shp,
-                            None => comment_on_same_line = false,
-                        }
-                    };
-
-                    if comment_on_same_line {
+                    if self.config.version() == Version::Two && comment_on_same_line {
                         self.push_str(" ");
-                    } else {
-                        if count_newlines(snippet_in_between) >= 2 || extra_newline {
-                            self.push_str("\n");
-                        }
-                        self.push_str(&self.block_indent.to_string_with_newline(config));
-                    }
+                        // put the first line of the comment on the same line as the
+                        // block's last line
+                        match sub_slice.find("\n") {
+                            None => {
+                                self.push_str(&sub_slice);
+                            }
+                            Some(offset) if offset + 1 == sub_slice.len() => {
+                                self.push_str(&sub_slice[..offset]);
+                            }
+                            Some(offset) => {
+                                let first_line = &sub_slice[..offset];
+                                self.push_str(first_line);
+                                self.push_str(&self.block_indent.to_string_with_newline(config));
 
-                    let comment_str = rewrite_comment(&sub_slice, false, comment_shape, config);
-                    match comment_str {
-                        Some(ref s) => self.push_str(s),
-                        None => self.push_str(&sub_slice),
+                                // put the other lines below it, shaping it as needed
+                                let other_lines = &sub_slice[offset + 1..];
+                                let comment_str =
+                                    rewrite_comment(other_lines, false, comment_shape, config);
+                                match comment_str {
+                                    Some(ref s) => self.push_str(s),
+                                    None => self.push_str(other_lines),
+                                }
+                            }
+                        }
+                    } else {
+                        if comment_on_same_line {
+                            // 1 = a space before `//`
+                            let offset_len = 1 + last_line_width(&self.buffer)
+                                .saturating_sub(self.block_indent.width());
+                            match comment_shape
+                                .visual_indent(offset_len)
+                                .sub_width(offset_len)
+                            {
+                                Some(shp) => comment_shape = shp,
+                                None => comment_on_same_line = false,
+                            }
+                        };
+
+                        if comment_on_same_line {
+                            self.push_str(" ");
+                        } else {
+                            if count_newlines(snippet_in_between) >= 2 || extra_newline {
+                                self.push_str("\n");
+                            }
+                            self.push_str(&self.block_indent.to_string_with_newline(config));
+                        }
+
+                        let comment_str = rewrite_comment(&sub_slice, false, comment_shape, config);
+                        match comment_str {
+                            Some(ref s) => self.push_str(s),
+                            None => self.push_str(&sub_slice),
+                        }
                     }
                 }
                 CodeCharKind::Normal if skip_normal(&sub_slice) => {

tests/source/trailing_comments.rs

@@ -0,0 +1,21 @@
+// rustfmt-version: Two
+// rustfmt-wrap_comments: true
+
+pub const IFF_MULTICAST: ::c_int = 0x0000000800; // Supports multicast
+// Multicast using broadcst. add.
+
+pub const SQ_CRETAB: u16 = 0x000e; // CREATE TABLE
+pub const SQ_DRPTAB: u16 = 0x000f; // DROP TABLE
+pub const SQ_CREIDX: u16 = 0x0010; // CREATE INDEX
+//const SQ_DRPIDX: u16 = 0x0011;	// DROP INDEX
+//const SQ_GRANT: u16 = 0x0012;	// GRANT
+//const SQ_REVOKE: u16 = 0x0013;	// REVOKE
+
+fn foo() {
+    let f = bar(); // Donec consequat mi. Quisque vitae dolor. Integer lobortis. Maecenas id nulla. Lorem.
+    // Id turpis. Nam posuere lectus vitae nibh. Etiam tortor orci, sagittis malesuada, rhoncus quis, hendrerit eget, libero. Quisque commodo nulla at nunc. Mauris consequat, enim vitae venenatis sollicitudin, dolor orci bibendum enim, a sagittis nulla nunc quis elit. Phasellus augue. Nunc suscipit, magna tincidunt lacinia faucibus, lacus tellus ornare purus, a pulvinar lacus orci eget nibh.  Maecenas sed nibh non lacus tempor faucibus. In hac habitasse platea dictumst. Vivamus a orci at nulla tristique condimentum. Donec arcu quam, dictum accumsan, convallis accumsan, cursus sit amet, ipsum.  In pharetra sagittis nunc.
+    let b = baz();
+
+    let normalized = self.ctfont.all_traits().normalized_weight(); // [-1.0, 1.0]
+    // TODO(emilio): It may make sense to make this range [.01, 10.0], to align with css-fonts-4's range of [1, 1000].
+}

tests/target/trailing_comments.rs

@@ -0,0 +1,30 @@
+// rustfmt-version: Two
+// rustfmt-wrap_comments: true
+
+pub const IFF_MULTICAST: ::c_int = 0x0000000800; // Supports multicast
+// Multicast using broadcst. add.
+
+pub const SQ_CRETAB: u16 = 0x000e; // CREATE TABLE
+pub const SQ_DRPTAB: u16 = 0x000f; // DROP TABLE
+pub const SQ_CREIDX: u16 = 0x0010; // CREATE INDEX
+//const SQ_DRPIDX: u16 = 0x0011;	// DROP INDEX
+//const SQ_GRANT: u16 = 0x0012;	// GRANT
+//const SQ_REVOKE: u16 = 0x0013;	// REVOKE
+
+fn foo() {
+    let f = bar(); // Donec consequat mi. Quisque vitae dolor. Integer lobortis. Maecenas id nulla. Lorem.
+    // Id turpis. Nam posuere lectus vitae nibh. Etiam tortor orci, sagittis
+    // malesuada, rhoncus quis, hendrerit eget, libero. Quisque commodo nulla at
+    // nunc. Mauris consequat, enim vitae venenatis sollicitudin, dolor orci
+    // bibendum enim, a sagittis nulla nunc quis elit. Phasellus augue. Nunc
+    // suscipit, magna tincidunt lacinia faucibus, lacus tellus ornare purus, a
+    // pulvinar lacus orci eget nibh.  Maecenas sed nibh non lacus tempor faucibus.
+    // In hac habitasse platea dictumst. Vivamus a orci at nulla tristique
+    // condimentum. Donec arcu quam, dictum accumsan, convallis accumsan, cursus sit
+    // amet, ipsum.  In pharetra sagittis nunc.
+    let b = baz();
+
+    let normalized = self.ctfont.all_traits().normalized_weight(); // [-1.0, 1.0]
+    // TODO(emilio): It may make sense to make this range [.01, 10.0], to align
+    // with css-fonts-4's range of [1, 1000].
+}