Support where predicates on the same line

src/config.rs

@@ -92,6 +92,7 @@ create_config! {
     fn_args_layout: Density,
     fn_arg_indent: BlockIndentStyle,
     where_indent: BlockIndentStyle, // Visual will be treated like Tabbed
+    where_layout: ListTactic,
     generics_indent: BlockIndentStyle,
     struct_trailing_comma: SeparatorTactic,
     struct_lit_trailing_comma: SeparatorTactic,
@@ -120,6 +121,7 @@ impl Default for Config {
             fn_args_layout: Density::Tall,
             fn_arg_indent: BlockIndentStyle::Visual,
             where_indent: BlockIndentStyle::Tabbed,
+            where_layout: ListTactic::Vertical,
             generics_indent: BlockIndentStyle::Visual,
             struct_trailing_comma: SeparatorTactic::Vertical,
             struct_lit_trailing_comma: SeparatorTactic::Vertical,

src/items.rs

@@ -823,7 +823,7 @@ impl<'a> FmtVisitor<'a> {
                                  span_end);
 
         let fmt = ListFormatting {
-            tactic: ListTactic::Vertical,
+            tactic: self.config.where_layout,
             separator: ",",
             trailing_separator: SeparatorTactic::Never,
             indent: offset,

src/lists.rs

@@ -28,6 +28,8 @@ pub enum ListTactic {
     Mixed,
 }
 
+impl_enum_decodable!(ListTactic, Vertical, Horizontal, HorizontalVertical, Mixed);
+
 #[derive(Eq, PartialEq, Debug, Copy, Clone)]
 pub enum SeparatorTactic {
     Always,

tests/config/small_tabs.toml

@@ -9,6 +9,7 @@ fn_args_paren_newline = true
 fn_args_layout = "Tall"
 fn_arg_indent = "Visual"
 where_indent = "Tabbed"
+where_layout = "Vertical"
 generics_indent = "Visual"
 struct_trailing_comma = "Vertical"
 struct_lit_trailing_comma = "Vertical"

tests/source/fn-custom-2.rs

@@ -1,6 +1,7 @@
 // rustfmt-fn_arg_indent: Inherit
 // rustfmt-generics_indent: Tabbed
 // rustfmt-where_indent: Inherit
+// rustfmt-where_layout: Mixed
 // Test different indents.
 
 fn foo(a: Aaaaaaaaaaaaaaa, b: Bbbbbbbbbbbbbbbb, c: Ccccccccccccccccc, d: Ddddddddddddddddddddddddd, e: Eeeeeeeeeeeeeeeeeee) {
@@ -15,6 +16,10 @@ fn baz() where X: TTTTTTTT {
     baz();
 }
 
+fn qux() where X: TTTTTTTTTTTTTTTTTTTTTTTTTTTT, X: TTTTTTTTTTTTTTTTTTTTTTTTTTTT, X: TTTTTTTTTTTTTTTTTTTTTTTTTTTT, X: TTTTTTTTTTTTTTTTTTTTTTTTTTTT {
+    baz();
+}
+
 impl Foo {
     fn foo(self, a: Aaaaaaaaaaaaaaa, b: Bbbbbbbbbbbbbbbb, c: Ccccccccccccccccc, d: Ddddddddddddddddddddddddd, e: Eeeeeeeeeeeeeeeeeee) {
         foo();

tests/source/fn-custom-3.rs

@@ -1,5 +1,6 @@
 // rustfmt-fn_arg_indent: Tabbed
 // rustfmt-generics_indent: Inherit
+// rustfmt-where_layout: HorizontalVertical
 // Test different indents.
 
 fn foo(a: Aaaaaaaaaaaaaaa, b: Bbbbbbbbbbbbbbbb, c: Ccccccccccccccccc, d: Ddddddddddddddddddddddddd, e: Eeeeeeeeeeeeeeeeeee) {
@@ -10,6 +11,14 @@ fn bar<'a: 'bbbbbbbbbbbbbbbbbbbbbbbbbbb, TTTTTTTTTTTTT, UUUUUUUUUUUUUUUUUUUU: WW
     bar();
 }
 
+fn qux() where X: TTTTTTTTTTTTTTTTTTTTTTTTTTTT, X: TTTTTTTTTTTTTTTTTTTTTTTTTTTT {
+    baz();
+}
+
+fn qux() where X: TTTTTTTTTTTTTTTTTTTTTTTTTTTT, X: TTTTTTTTTTTTTTTTTTTTTTTTTTTT, X: TTTTTTTTTTTTTTTTTTTTTTTTTTTT, X: TTTTTTTTTTTTTTTTTTTTTTTTTTTT {
+    baz();
+}
+
 impl Foo {
     fn foo(self, a: Aaaaaaaaaaaaaaa, b: Bbbbbbbbbbbbbbbb, c: Ccccccccccccccccc, d: Ddddddddddddddddddddddddd, e: Eeeeeeeeeeeeeeeeeee) {
         foo();

tests/target/fn-custom-2.rs

@@ -1,6 +1,7 @@
 // rustfmt-fn_arg_indent: Inherit
 // rustfmt-generics_indent: Tabbed
 // rustfmt-where_indent: Inherit
+// rustfmt-where_layout: Mixed
 // Test different indents.
 
 fn foo(a: Aaaaaaaaaaaaaaa,
@@ -24,6 +25,13 @@ where X: TTTTTTTT
     baz();
 }
 
+fn qux()
+where X: TTTTTTTTTTTTTTTTTTTTTTTTTTTT, X: TTTTTTTTTTTTTTTTTTTTTTTTTTTT,
+      X: TTTTTTTTTTTTTTTTTTTTTTTTTTTT, X: TTTTTTTTTTTTTTTTTTTTTTTTTTTT
+{
+    baz();
+}
+
 impl Foo {
     fn foo(self,
     a: Aaaaaaaaaaaaaaa,

tests/target/fn-custom-3.rs

@@ -1,5 +1,6 @@
 // rustfmt-fn_arg_indent: Tabbed
 // rustfmt-generics_indent: Inherit
+// rustfmt-where_layout: HorizontalVertical
 // Test different indents.
 
 fn foo(a: Aaaaaaaaaaaaaaa,
@@ -17,6 +18,21 @@ UUUUUUUUUUUUUUUUUUUU: WWWWWWWWWWWWWWWWWWWWWWWW>
     bar();
 }
 
+fn qux()
+    where X: TTTTTTTTTTTTTTTTTTTTTTTTTTTT, X: TTTTTTTTTTTTTTTTTTTTTTTTTTTT
+{
+    baz();
+}
+
+fn qux()
+    where X: TTTTTTTTTTTTTTTTTTTTTTTTTTTT,
+          X: TTTTTTTTTTTTTTTTTTTTTTTTTTTT,
+          X: TTTTTTTTTTTTTTTTTTTTTTTTTTTT,
+          X: TTTTTTTTTTTTTTTTTTTTTTTTTTTT
+{
+    baz();
+}
+
 impl Foo {
     fn foo(self,
         a: Aaaaaaaaaaaaaaa,