Issue 2506

src/types.rs

@@ -616,7 +616,18 @@ impl Rewrite for ast::TraitRef {
 impl Rewrite for ast::Ty {
     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
         match self.node {
-            ast::TyKind::TraitObject(ref bounds, ..) => bounds.rewrite(context, shape),
+            ast::TyKind::TraitObject(ref bounds, tobj_syntax) => {
+                // we have to consider 'dyn' keyword is used or not!!!
+                let is_dyn = tobj_syntax == ast::TraitObjectSyntax::Dyn;
+                // 4 is length of 'dyn '
+                let shape = if is_dyn { shape.offset_left(4)? } else { shape };
+                let res = bounds.rewrite(context, shape)?;
+                if is_dyn {
+                    Some(format!("dyn {}", res))
+                } else {
+                    Some(res)
+                }
+            }
             ast::TyKind::Ptr(ref mt) => {
                 let prefix = match mt.mutbl {
                     Mutability::Mutable => "*mut ",

tests/source/issue-2506.rs

@@ -0,0 +1,16 @@
+#![feature(dyn_trait)]
+fn main() {
+    // checks rustfmt doesn't remove dyn
+    trait MyTrait {
+        fn method(&self) -> u64;
+    }
+    fn f1(a: Box<dyn MyTrait>) {}
+
+    // checks if line wrap works correctly
+    trait Very_______________________Long__________________Name____________________Trait {
+        fn method(&self) -> u64;
+    }
+
+    fn f2(a: Box<dyn Very_______________________Long__________________Name____________________Trait+ 'static,>) {}
+
+}

tests/target/issue-2506.rs

@@ -0,0 +1,22 @@
+#![feature(dyn_trait)]
+fn main() {
+    // checks rustfmt doesn't remove dyn
+    trait MyTrait {
+        fn method(&self) -> u64;
+    }
+    fn f1(a: Box<dyn MyTrait>) {}
+
+    // checks if line wrap works correctly
+    trait Very_______________________Long__________________Name____________________Trait
+         {
+        fn method(&self) -> u64;
+    }
+
+    fn f2(
+        a: Box<
+            dyn Very_______________________Long__________________Name____________________Trait
+                + 'static,
+        >,
+    ) {
+    }
+}