From 4d50e7c7606efca32bd937a4c60772a616fdbc33 Mon Sep 17 00:00:00 2001
From: mujpao <mujpao@gmail.com>
Date: Mon, 1 Nov 2021 23:13:30 -0700
Subject: [PATCH] Put empty trait braces on same line if possible

---
 src/items.rs                                  | 15 ++++--
 tests/source/empty-item-single-line-false.rs  | 46 +++++++++++++++++++
 .../item-brace-style-always-next-line.rs      | 35 ++++++++++++++
 tests/target/empty-item-single-line-false.rs  | 41 +++++++++++++++++
 .../item-brace-style-always-next-line.rs      | 29 ++++++++++++
 5 files changed, 163 insertions(+), 3 deletions(-)
 create mode 100644 tests/source/empty-item-single-line-false.rs
 create mode 100644 tests/target/empty-item-single-line-false.rs

diff --git a/src/items.rs b/src/items.rs
index 1c7899b3ac3..e37a1b69658 100644
--- a/src/items.rs
+++ b/src/items.rs
@@ -1122,12 +1122,24 @@ pub(crate) fn format_trait(
             }
         }
 
+        let block_span = mk_sp(generics.where_clause.span.hi(), item.span.hi());
+        let snippet = context.snippet(block_span);
+        let open_pos = snippet.find_uncommented("{")? + 1;
+
         match context.config.brace_style() {
             _ if last_line_contains_single_line_comment(&result)
                 || last_line_width(&result) + 2 > context.budget(offset.width()) =>
             {
                 result.push_str(&offset.to_string_with_newline(context.config));
             }
+            _ if context.config.empty_item_single_line()
+                && trait_items.is_empty()
+                && !result.contains('\n')
+                && !contains_comment(&snippet[open_pos..]) =>
+            {
+                result.push_str(" {}");
+                return Some(result);
+            }
             BraceStyle::AlwaysNextLine => {
                 result.push_str(&offset.to_string_with_newline(context.config));
             }
@@ -1144,9 +1156,6 @@ pub(crate) fn format_trait(
         }
         result.push('{');
 
-        let block_span = mk_sp(generics.where_clause.span.hi(), item.span.hi());
-        let snippet = context.snippet(block_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..]) {
diff --git a/tests/source/empty-item-single-line-false.rs b/tests/source/empty-item-single-line-false.rs
new file mode 100644
index 00000000000..20c5bc83b46
--- /dev/null
+++ b/tests/source/empty-item-single-line-false.rs
@@ -0,0 +1,46 @@
+// rustfmt-brace_style: AlwaysNextLine
+// rustfmt-empty_item_single_line: false
+
+fn function()
+{
+
+}
+
+struct Struct
+{
+
+}
+
+enum Enum
+{
+
+}
+
+trait Trait
+{
+
+}
+
+impl<T> Trait for T
+{
+
+}
+
+trait Trait2<T>
+where
+    T: Copy + Display + Write + Read + FromStr, {}
+
+trait Trait3<T>
+where
+    T: Something
+        + SomethingElse
+        + Sync
+        + Send
+        + Display
+        + Debug
+        + Copy
+        + Hash
+        + Debug
+        + Display
+        + Write
+        + Read, {}
diff --git a/tests/source/item-brace-style-always-next-line.rs b/tests/source/item-brace-style-always-next-line.rs
index 38094d67a77..0fb6405120a 100644
--- a/tests/source/item-brace-style-always-next-line.rs
+++ b/tests/source/item-brace-style-always-next-line.rs
@@ -27,3 +27,38 @@ mod M {
 
     struct D<T> where T: Copy {}
 }
+
+
+fn function()
+{
+
+}
+
+trait Trait
+{
+
+}
+
+impl<T> Trait for T
+{
+
+}
+
+trait Trait2<T>
+where
+    T: Copy + Display + Write + Read + FromStr, {}
+
+trait Trait3<T>
+where
+    T: Something
+        + SomethingElse
+        + Sync
+        + Send
+        + Display
+        + Debug
+        + Copy
+        + Hash
+        + Debug
+        + Display
+        + Write
+        + Read, {}
diff --git a/tests/target/empty-item-single-line-false.rs b/tests/target/empty-item-single-line-false.rs
new file mode 100644
index 00000000000..bf7f70e7c43
--- /dev/null
+++ b/tests/target/empty-item-single-line-false.rs
@@ -0,0 +1,41 @@
+// rustfmt-brace_style: AlwaysNextLine
+// rustfmt-empty_item_single_line: false
+
+fn function()
+{
+}
+
+struct Struct {}
+
+enum Enum {}
+
+trait Trait
+{
+}
+
+impl<T> Trait for T
+{
+}
+
+trait Trait2<T>
+where
+    T: Copy + Display + Write + Read + FromStr,
+{
+}
+
+trait Trait3<T>
+where
+    T: Something
+        + SomethingElse
+        + Sync
+        + Send
+        + Display
+        + Debug
+        + Copy
+        + Hash
+        + Debug
+        + Display
+        + Write
+        + Read,
+{
+}
diff --git a/tests/target/item-brace-style-always-next-line.rs b/tests/target/item-brace-style-always-next-line.rs
index 531ac598683..4935fac04f1 100644
--- a/tests/target/item-brace-style-always-next-line.rs
+++ b/tests/target/item-brace-style-always-next-line.rs
@@ -40,3 +40,32 @@ mod M
     where
         T: Copy, {}
 }
+
+fn function() {}
+
+trait Trait {}
+
+impl<T> Trait for T {}
+
+trait Trait2<T>
+where
+    T: Copy + Display + Write + Read + FromStr,
+{
+}
+
+trait Trait3<T>
+where
+    T: Something
+        + SomethingElse
+        + Sync
+        + Send
+        + Display
+        + Debug
+        + Copy
+        + Hash
+        + Debug
+        + Display
+        + Write
+        + Read,
+{
+}