Fix struct comment_width off-by-one error

src/lists.rs

@@ -21,7 +21,11 @@ pub(crate) struct ListFormatting<'a> {
     separator: &'a str,
     trailing_separator: SeparatorTactic,
     separator_place: SeparatorPlace,
+    // The shape available to a list item, including any width reserved for its separator.
     shape: Shape,
+    // Overrides the item shape for pre-comments. The item shape may reserve space for a separator,
+    // which is not part of a preceding comment.
+    pre_comment_shape: Option<Shape>,
     // Non-expressions, e.g., items, will have a new line at the end of the list.
     // Important for comment styles.
     ends_with_newline: bool,
@@ -42,6 +46,7 @@ impl<'a> ListFormatting<'a> {
             trailing_separator: SeparatorTactic::Never,
             separator_place: SeparatorPlace::Back,
             shape,
+            pre_comment_shape: None,
             ends_with_newline: true,
             preserve_newline: false,
             nested: false,
@@ -70,6 +75,11 @@ impl<'a> ListFormatting<'a> {
         self
     }
 
+    pub(crate) fn pre_comment_shape(mut self, pre_comment_shape: Shape) -> Self {
+        self.pre_comment_shape = Some(pre_comment_shape);
+        self
+    }
+
     pub(crate) fn ends_with_newline(mut self, ends_with_newline: bool) -> Self {
         self.ends_with_newline = ends_with_newline;
         self
@@ -366,8 +376,8 @@ where
             // Block style in non-vertical mode.
             let block_mode = tactic == DefinitiveListTactic::Horizontal;
             // Width restriction is only relevant in vertical mode.
-            let comment =
-                rewrite_comment(comment, block_mode, formatting.shape, formatting.config)?;
+            let comment_shape = formatting.pre_comment_shape.unwrap_or(formatting.shape);
+            let comment = rewrite_comment(comment, block_mode, comment_shape, formatting.config)?;
             result.push_str(&comment);
 
             if !inner_item.is_empty() {
@@ -941,6 +951,7 @@ pub(crate) fn struct_lit_formatting<'a>(
         },
         separator_place: SeparatorPlace::Back,
         shape,
+        pre_comment_shape: None,
         ends_with_newline,
         preserve_newline: true,
         nested: false,

src/vertical.rs

@@ -214,6 +214,7 @@ fn rewrite_aligned_items_inner<T: AlignedItem>(
 ) -> Option<String> {
     // 1 = ","
     let item_shape = Shape::indented(offset, context.config).sub_width_opt(1)?;
+    let pre_comment_shape = Shape::indented(offset, context.config);
     let (mut field_prefix_max_width, field_prefix_min_width) =
         struct_field_prefix_max_min_width(context, fields, item_shape);
     let max_diff = field_prefix_max_width.saturating_sub(field_prefix_min_width);
@@ -265,6 +266,7 @@ fn rewrite_aligned_items_inner<T: AlignedItem>(
     let fmt = ListFormatting::new(item_shape, context.config)
         .tactic(tactic)
         .trailing_separator(separator_tactic)
+        .pre_comment_shape(pre_comment_shape)
         .preserve_newline(true);
     write_list(&items, &fmt).ok()
 }

tests/source/issue_6180.rs

@@ -0,0 +1,18 @@
+// rustfmt-wrap_comments: true
+// rustfmt-comment_width: 100
+
+pub struct Foo {
+    // This line has 99 characters ...............................................................9
+    pub foo: u8,
+
+    // This line has 100 characters ...............................................................9
+    pub bar: u8,
+
+    // This line has 101 characters ................................................................9
+    pub baz: u8,
+}
+
+pub mod foo {
+    // This line has 100 characters ...............................................................9
+    pub fn foo() {}
+}

tests/target/configs/struct_field_align_threshold/20.rs

@@ -321,8 +321,8 @@ fn main() {
 
     A {
         // Lorem ipsum dolor sit amet, consectetur adipiscing elit. Donec a diam lectus. Sed sit
-        // amet ipsum mauris. Maecenas congue ligula ac quam viverra nec consectetur ante
-        // hendrerit. Donec et mollis dolor.
+        // amet ipsum mauris. Maecenas congue ligula ac quam viverra nec consectetur ante hendrerit.
+        // Donec et mollis dolor.
         first:  item(),
         // Praesent et diam eget libero egestas mattis sit amet vitae augue.
         // Nam tincidunt congue enim, ut porta lorem lacinia consectetur.

tests/target/issue_6180.rs

@@ -0,0 +1,19 @@
+// rustfmt-wrap_comments: true
+// rustfmt-comment_width: 100
+
+pub struct Foo {
+    // This line has 99 characters ...............................................................9
+    pub foo: u8,
+
+    // This line has 100 characters ...............................................................9
+    pub bar: u8,
+
+    // This line has 101 characters
+    // ................................................................9
+    pub baz: u8,
+}
+
+pub mod foo {
+    // This line has 100 characters ...............................................................9
+    pub fn foo() {}
+}