fix: empty fn comments (FuelLabs#4093)

## Description

closes FuelLabs#4092

Note that this PR also moves the block indentation logic up one level
into the `ItemFn` level instead of at the `CurlyBrace` impl.

## Checklist

- [x] I have linked to any relevant issues.
- [ ] I have commented my code, particularly in hard-to-understand
areas.
- [ ] I have updated the documentation where relevant (API docs, the
reference, and the Sway book).
- [x] I have added tests that prove my fix is effective or that my
feature works.
- [ ] I have added (or requested a maintainer to add) the necessary
`Breaking*` or `New Feature` labels where relevant.
- [ ] I have done my best to ensure that my PR adheres to [the Fuel Labs
Code Review
Standards](https://github.com/FuelLabs/rfcs/blob/master/text/code-standards/external-contributors.md).
- [ ] I have requested a review from the relevant team or maintainers.

---------

Co-authored-by: Joshua Batty <[email protected]>

swayfmt/src/items/item_fn/mod.rs

@@ -1,4 +1,5 @@
 use crate::{
+    comments::{has_comments, maybe_write_comments_from_map},
     config::items::ItemBraceStyle,
     formatter::{
         shape::{ExprKind, LineStyle},
@@ -9,7 +10,7 @@ use crate::{
         {CurlyBrace, Parenthesis},
     },
 };
-use std::fmt::Write;
+use std::{fmt::Write, ops::Range};
 use sway_ast::{
     keywords::{MutToken, RefToken, SelfToken, Token},
     token::Delimiter,
@@ -35,10 +36,18 @@ impl Format for ItemFn {
                 let body = self.body.get();
                 if !body.statements.is_empty() || body.final_expr_opt.is_some() {
                     Self::open_curly_brace(formatted_code, formatter)?;
+                    formatter.shape.block_indent(&formatter.config);
                     body.format(formatted_code, formatter)?;
                     Self::close_curly_brace(formatted_code, formatter)?;
                 } else {
-                    write!(formatted_code, " {{}}")?;
+                    Self::open_curly_brace(formatted_code, formatter)?;
+                    let range: Range<usize> = self.span().into();
+                    let comments = formatter.comment_map.comments_between(&range);
+                    if has_comments(comments) {
+                        formatter.shape.block_indent(&formatter.config);
+                        maybe_write_comments_from_map(formatted_code, range, formatter)?;
+                    }
+                    Self::close_curly_brace(formatted_code, formatter)?;
                 }
 
                 Ok(())
@@ -60,23 +69,19 @@ impl CurlyBrace for ItemFn {
             ItemBraceStyle::AlwaysNextLine => {
                 // Add openning brace to the next line.
                 writeln!(line, "\n{open_brace}")?;
-                formatter.shape.block_indent(&formatter.config);
             }
             ItemBraceStyle::SameLineWhere => match formatter.shape.code_line.has_where_clause {
                 true => {
                     write!(line, "{open_brace}")?;
                     formatter.shape.code_line.update_where_clause(false);
-                    formatter.shape.block_indent(&formatter.config);
                 }
                 false => {
                     write!(line, " {open_brace}")?;
-                    formatter.shape.block_indent(&formatter.config);
                 }
             },
             _ => {
                 // TODO: implement PreferSameLine
                 writeln!(line, " {open_brace}")?;
-                formatter.shape.block_indent(&formatter.config);
             }
         }
 

swayfmt/tests/mod.rs

@@ -570,6 +570,41 @@ trait AlignMyComments {
     );
 }
 
+#[test]
+fn comments_empty_fns() {
+    check(
+        r#"contract;
+
+fn single_comment_same_line() { /* a comment */ }
+
+fn single_comment() -> bool {
+    // TODO: This is a TODO
+}
+
+fn multiline_comments() {
+    // Multi
+        // line
+// comment
+}"#,
+        r#"contract;
+
+fn single_comment_same_line() {
+    /* a comment */
+}
+
+fn single_comment() -> bool {
+    // TODO: This is a TODO
+}
+
+fn multiline_comments() {
+    // Multi
+    // line
+    // comment
+}
+"#,
+    );
+}
+
 #[test]
 fn enum_comments() {
     check(