Format trait aliases

src/items.rs

@@ -1087,6 +1087,22 @@ pub fn format_trait(context: &RewriteContext, item: &ast::Item, offset: Indent)
     }
 }
 
+pub fn format_trait_alias(
+    context: &RewriteContext,
+    ident: ast::Ident,
+    generics: &ast::Generics,
+    ty_param_bounds: &ast::TyParamBounds,
+    shape: Shape,
+) -> Option<String> {
+    let alias = ident.name.as_str();
+    // 6 = "trait ", 2 = " ="
+    let g_shape = shape.offset_left(6 + alias.len())?.sub_width(2)?;
+    let generics_str = rewrite_generics(context, generics, g_shape, generics.span)?;
+    let lhs = format!("trait {}{} =", alias, generics_str);
+    // 1 = ";"
+    rewrite_assign_rhs(context, lhs, ty_param_bounds, shape.sub_width(1)?).map(|s| s + ";")
+}
+
 fn format_unit_struct(context: &RewriteContext, p: &StructParts, offset: Indent) -> Option<String> {
     let header_str = format_header(p.prefix, p.ident, p.vis);
     let generics_str = if let Some(generics) = p.generics {

src/visitor.rs

@@ -22,8 +22,8 @@ use comment::{combine_strs_with_missing_comments, contains_comment, remove_trail
               CodeCharKind, CommentCodeSlices, FindUncommented};
 use comment::rewrite_comment;
 use config::{BraceStyle, Config};
-use items::{format_impl, format_trait, rewrite_associated_impl_type, rewrite_associated_type,
-            rewrite_type_alias, FnSig, StaticParts, StructParts};
+use items::{format_impl, format_trait, format_trait_alias, rewrite_associated_impl_type,
+            rewrite_associated_type, rewrite_type_alias, FnSig, StaticParts, StructParts};
 use lists::{itemize_list, write_list, DefinitiveListTactic, ListFormatting, SeparatorPlace,
             SeparatorTactic};
 use macros::{rewrite_macro, MacroPosition};
@@ -373,9 +373,16 @@ impl<'b, 'a: 'b> FmtVisitor<'a> {
                 let rw = format_trait(&self.get_context(), item, self.block_indent);
                 self.push_rewrite(item.span, rw);
             }
-            ast::ItemKind::TraitAlias(..) => {
-                // FIXME: #2283.
-                self.push_rewrite(item.span, None);
+            ast::ItemKind::TraitAlias(ref generics, ref ty_param_bounds) => {
+                let shape = Shape::indented(self.block_indent, self.config);
+                let rw = format_trait_alias(
+                    &self.get_context(),
+                    item.ident,
+                    generics,
+                    ty_param_bounds,
+                    shape,
+                );
+                self.push_rewrite(item.span, rw);
             }
             ast::ItemKind::ExternCrate(_) => {
                 let rw = rewrite_extern_crate(&self.get_context(), item);