Merge pull request rust-lang#3100 from topecongiro/issue-3092

Fix poor formatting of empty trait with generic bounds

Author: nrc

src/expr.rs

@@ -1937,7 +1937,9 @@ fn shape_from_rhs_tactic(
     rhs_tactic: RhsTactics,
 ) -> Option<Shape> {
     match rhs_tactic {
-        RhsTactics::ForceNextLineWithoutIndent => Some(shape.with_max_width(context.config)),
+        RhsTactics::ForceNextLineWithoutIndent => shape
+            .with_max_width(context.config)
+            .sub_width(shape.indent.width()),
         RhsTactics::Default => {
             Shape::indented(shape.indent.block_indent(context.config), context.config)
                 .sub_width(shape.rhs_overhead(context.config))

src/items.rs

@@ -1121,6 +1121,7 @@ pub fn format_trait(context: &RewriteContext, item: &ast::Item, offset: Indent)
 
         let snippet = context.snippet(item.span);
         let open_pos = snippet.find_uncommented("{")? + 1;
+        let outer_indent_str = offset.block_only().to_string_with_newline(context.config);
 
         if !trait_items.is_empty() || contains_comment(&snippet[open_pos..]) {
             let mut visitor = FmtVisitor::from_context(context);
@@ -1134,13 +1135,12 @@ pub fn format_trait(context: &RewriteContext, item: &ast::Item, offset: Indent)
             visitor.format_missing(item.span.hi() - BytePos(1));
 
             let inner_indent_str = visitor.block_indent.to_string_with_newline(context.config);
-            let outer_indent_str = offset.block_only().to_string_with_newline(context.config);
 
             result.push_str(&inner_indent_str);
             result.push_str(visitor.buffer.to_string().trim());
             result.push_str(&outer_indent_str);
         } else if result.contains('\n') {
-            result.push('\n');
+            result.push_str(&outer_indent_str);
         }
 
         result.push('}');

tests/source/trait.rs

@@ -106,3 +106,12 @@ trait Foo<'a> {
 impl<'a> Foo<'a> for i32 {
     type Bar<  'a  > = i32;
 }
+
+// #3092
+pub mod test {
+    pub trait ATraitWithALooongName {}
+    pub trait ATrait
+        :ATraitWithALooongName + ATraitWithALooongName + ATraitWithALooongName + ATraitWithALooongName
+{
+}
+}

tests/target/trait.rs

@@ -144,3 +144,15 @@ trait Foo<'a> {
 impl<'a> Foo<'a> for i32 {
     type Bar<'a> = i32;
 }
+
+// #3092
+pub mod test {
+    pub trait ATraitWithALooongName {}
+    pub trait ATrait:
+        ATraitWithALooongName
+        + ATraitWithALooongName
+        + ATraitWithALooongName
+        + ATraitWithALooongName
+    {
+    }
+}