Fix missing struct field separators under certain conditions

src/vertical.rs

@@ -160,8 +160,18 @@ pub(crate) fn rewrite_with_alignment<T: AlignedItem>(
     };
     let init_span = mk_sp(span.lo(), init_last_pos);
     let one_line_width = if rest.is_empty() { one_line_width } else { 0 };
-    let result =
-        rewrite_aligned_items_inner(context, init, init_span, shape.indent, one_line_width)?;
+
+    // if another group follows, we must force a separator
+    let force_separator = !rest.is_empty();
+
+    let result = rewrite_aligned_items_inner(
+        context,
+        init,
+        init_span,
+        shape.indent,
+        one_line_width,
+        force_separator,
+    )?;
     if rest.is_empty() {
         Some(result + spaces)
     } else {
@@ -201,6 +211,7 @@ fn rewrite_aligned_items_inner<T: AlignedItem>(
     span: Span,
     offset: Indent,
     one_line_width: usize,
+    force_trailing_separator: bool,
 ) -> Option<String> {
     // 1 = ","
     let item_shape = Shape::indented(offset, context.config).sub_width(1)?;
@@ -246,9 +257,15 @@ fn rewrite_aligned_items_inner<T: AlignedItem>(
             });
     }
 
+    let separator_tactic = if force_trailing_separator {
+        SeparatorTactic::Always
+    } else {
+        context.config.trailing_comma()
+    };
+
     let fmt = ListFormatting::new(item_shape, context.config)
         .tactic(tactic)
-        .trailing_separator(context.config.trailing_comma())
+        .trailing_separator(separator_tactic)
         .preserve_newline(true);
     write_list(&items, &fmt)
 }

tests/source/issue-4791/buggy.rs

@@ -0,0 +1,14 @@
+// rustfmt-struct_field_align_threshold: 30
+// rustfmt-trailing_comma: Never
+
+struct Foo {
+    group_a: u8,
+
+    group_b: u8,
+}
+
+struct Bar {
+    group_a: u8,
+
+    group_b: u8
+}

tests/source/issue-4791/trailing_comma.rs

@@ -0,0 +1,14 @@
+// rustfmt-struct_field_align_threshold: 30
+// rustfmt-trailing_comma: Always
+
+struct Foo {
+    group_a: u8,
+
+    group_b: u8
+}
+
+struct Bar {
+    group_a: u8,
+
+    group_b: u8,
+}

tests/target/issue-4791/buggy.rs

@@ -0,0 +1,14 @@
+// rustfmt-struct_field_align_threshold: 30
+// rustfmt-trailing_comma: Never
+
+struct Foo {
+    group_a: u8,
+
+    group_b: u8
+}
+
+struct Bar {
+    group_a: u8,
+
+    group_b: u8
+}

tests/target/issue-4791/issue_4928.rs

@@ -0,0 +1,70 @@
+// rustfmt-brace_style: SameLineWhere
+// rustfmt-comment_width: 100
+// rustfmt-edition: 2018
+// rustfmt-fn_args_layout: Compressed
+// rustfmt-hard_tabs: false
+// rustfmt-match_block_trailing_comma: true
+// rustfmt-max_width: 100
+// rustfmt-merge_derives: false
+// rustfmt-newline_style: Unix
+// rustfmt-normalize_doc_attributes: true
+// rustfmt-overflow_delimited_expr: true
+// rustfmt-reorder_imports: false
+// rustfmt-reorder_modules: true
+// rustfmt-struct_field_align_threshold: 20
+// rustfmt-tab_spaces: 4
+// rustfmt-trailing_comma: Never
+// rustfmt-use_small_heuristics: Max
+// rustfmt-use_try_shorthand: true
+// rustfmt-wrap_comments: true
+
+/// Lorem ipsum dolor sit amet.
+#[repr(C)]
+#[derive(Debug, Default, Copy, Clone, PartialEq, Eq)]
+pub struct BufferAttr {
+    /* NOTE: Blah blah blah blah blah. */
+    /// Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt
+    /// ut labore et dolore magna aliqua. Morbi quis commodo odio aenean sed adipiscing. Nunc
+    /// congue nisi vitae suscipit tellus mauris a. Consectetur adipiscing elit pellentesque
+    /// habitant morbi tristique senectus.
+    pub foo: u32,
+
+    /// Elit eget gravida cum sociis natoque penatibus et magnis dis. Consequat semper viverra nam
+    /// libero. Accumsan in nisl nisi scelerisque eu. Pellentesque id nibh tortor id aliquet. Sed
+    /// velit dignissim sodales ut. Facilisis sed odio morbi quis commodo odio aenean sed. Et
+    /// ultrices neque ornare aenean euismod elementum. Condimentum lacinia quis vel eros donec ac
+    /// odio tempor.
+    ///
+    /// Lacinia at quis risus sed vulputate odio ut enim. Etiam erat velit scelerisque in dictum.
+    /// Nibh tellus molestie nunc non blandit massa enim nec. Nascetur ridiculus mus mauris vitae.
+    pub bar: u32,
+
+    /// Mi proin sed libero enim sed faucibus turpis. Amet consectetur adipiscing elit duis
+    /// tristique sollicitudin nibh sit amet. Congue quisque egestas diam in arcu cursus euismod
+    /// quis viverra. Cum sociis natoque penatibus et magnis dis parturient montes. Enim sit amet
+    /// venenatis urna cursus eget nunc scelerisque viverra. Cras semper auctor neque vitae tempus
+    /// quam pellentesque. Tortor posuere ac ut consequat semper viverra nam libero justo. Vitae
+    /// auctor eu augue ut lectus arcu bibendum at. Faucibus vitae aliquet nec ullamcorper sit amet
+    /// risus nullam. Maecenas accumsan lacus vel facilisis volutpat. Arcu non odio euismod
+    /// lacinia.
+    ///
+    /// [`FooBar::beep()`]: crate::foobar::FooBar::beep
+    /// [`FooBar::boop()`]: crate::foobar::FooBar::boop
+    /// [`foobar::BazBaq::BEEP_BOOP`]: crate::foobar::BazBaq::BEEP_BOOP
+    pub baz: u32,
+
+    /// Eu consequat ac felis donec et odio pellentesque diam. Ut eu sem integer vitae justo eget.
+    /// Consequat ac felis donec et odio pellentesque diam volutpat.
+    pub baq: u32,
+
+    /// Amet consectetur adipiscing elit pellentesque habitant. Ut morbi tincidunt augue interdum
+    /// velit euismod in pellentesque. Imperdiet sed euismod nisi porta lorem. Nec tincidunt
+    /// praesent semper feugiat. Facilisis leo vel fringilla est. Egestas diam in arcu cursus
+    /// euismod quis viverra. Sagittis eu volutpat odio facilisis mauris sit amet. Posuere morbi
+    /// leo urna molestie at.
+    ///
+    /// Pretium aenean pharetra magna ac. Nisl condimentum id venenatis a condimentum vitae. Semper
+    /// quis lectus nulla at volutpat diam ut venenatis tellus. Egestas tellus rutrum tellus
+    /// pellentesque eu tincidunt tortor aliquam.
+    pub foobar: u32
+}

tests/target/issue-4791/no_trailing_comma.rs

@@ -0,0 +1,8 @@
+// rustfmt-struct_field_align_threshold: 0
+// rustfmt-trailing_comma: Never
+
+pub struct Baz {
+    group_a: u8,
+
+    group_b: u8
+}

tests/target/issue-4791/trailing_comma.rs

@@ -0,0 +1,14 @@
+// rustfmt-struct_field_align_threshold: 30
+// rustfmt-trailing_comma: Always
+
+struct Foo {
+    group_a: u8,
+
+    group_b: u8,
+}
+
+struct Bar {
+    group_a: u8,
+
+    group_b: u8,
+}