Modify the placement of the opening brace of trait

Put the opening brace on the next line if

1. putting it one the current line exceeds max width.
2. trait bounds uses multiple lines.

diff --git a/src/items.rs b/src/items.rs
index 2484756fc56aff1b61bd134bc92fdb0bd22051bf..1d02ba653ce62092187423569b3c3e94049d4996 100644 (file)
--- a/src/items.rs
+++ b/src/items.rs
@@ -934,45 +934,45 @@ pub fn format_trait(context: &RewriteContext, item: &ast::Item, offset: Indent)
             )?;
         }
 
-        let where_density =
-            if context.config.indent_style() == IndentStyle::Block && result.is_empty() {
+        // Rewrite where clause.
+        if !generics.where_clause.predicates.is_empty() {
+            let where_density = if context.config.indent_style() == IndentStyle::Block {
                 Density::Compressed
             } else {
                 Density::Tall
             };
 
-        let where_budget = context.budget(last_line_width(&result));
-        let pos_before_where = if type_param_bounds.is_empty() {
-            generics.where_clause.span.lo()
+            let where_budget = context.budget(last_line_width(&result));
+            let pos_before_where = if type_param_bounds.is_empty() {
+                generics.where_clause.span.lo()
+            } else {
+                type_param_bounds[type_param_bounds.len() - 1].span().hi()
+            };
+            let option = WhereClauseOption::snuggled(&generics_str);
+            let where_clause_str = rewrite_where_clause(
+                context,
+                &generics.where_clause,
+                context.config.brace_style(),
+                Shape::legacy(where_budget, offset.block_only()),
+                where_density,
+                "{",
+                None,
+                pos_before_where,
+                option,
+                false,
+            )?;
+            // If the where clause cannot fit on the same line,
+            // put the where clause on a new line
+            if !where_clause_str.contains('\n')
+                && last_line_width(&result) + where_clause_str.len() + offset.width()
+                    > context.config.comment_width()
+            {
+                let width = offset.block_indent + context.config.tab_spaces() - 1;
+                let where_indent = Indent::new(0, width);
+                result.push_str(&where_indent.to_string_with_newline(context.config));
+            }
+            result.push_str(&where_clause_str);
         } else {
-            type_param_bounds[type_param_bounds.len() - 1].span().hi()
-        };
-        let option = WhereClauseOption::snuggled(&generics_str);
-        let where_clause_str = rewrite_where_clause(
-            context,
-            &generics.where_clause,
-            context.config.brace_style(),
-            Shape::legacy(where_budget, offset.block_only()),
-            where_density,
-            "{",
-            None,
-            pos_before_where,
-            option,
-            false,
-        )?;
-        // If the where clause cannot fit on the same line,
-        // put the where clause on a new line
-        if !where_clause_str.contains('\n')
-            && last_line_width(&result) + where_clause_str.len() + offset.width()
-                > context.config.comment_width()
-        {
-            let width = offset.block_indent + context.config.tab_spaces() - 1;
-            let where_indent = Indent::new(0, width);
-            result.push_str(&where_indent.to_string_with_newline(context.config));
-        }
-        result.push_str(&where_clause_str);
-
-        if generics.where_clause.predicates.is_empty() {
             let item_snippet = context.snippet(item.span);
             if let Some(lo) = item_snippet.chars().position(|c| c == '/') {
                 // 1 = `{`
@@ -995,7 +995,9 @@ pub fn format_trait(context: &RewriteContext, item: &ast::Item, offset: Indent)
         }
 
         match context.config.brace_style() {
-            _ if last_line_contains_single_line_comment(&result) => {
+            _ 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));
             }
             BraceStyle::AlwaysNextLine => {
@@ -1003,8 +1005,8 @@ pub fn format_trait(context: &RewriteContext, item: &ast::Item, offset: Indent)
             }
             BraceStyle::PreferSameLine => result.push(' '),
             BraceStyle::SameLineWhere => {
-                if !where_clause_str.is_empty()
-                    && (!trait_items.is_empty() || result.contains('\n'))
+                if result.contains('\n')
+                    || (!generics.where_clause.predicates.is_empty() && !trait_items.is_empty())
                 {
                     result.push_str(&offset.to_string_with_newline(context.config));
                 } else {