Option to pack fn args on fewer lines

Author: Nick Cameron

src/config.rs

@@ -11,7 +11,7 @@
 extern crate toml;
 
 use {NewlineStyle, BraceStyle, ReturnIndent, StructLitStyle};
-use lists::SeparatorTactic;
+use lists::{SeparatorTactic, ListTactic};
 use issues::ReportTactic;
 
 #[derive(Copy, Clone, Eq, PartialEq, Debug)]
@@ -26,6 +26,25 @@ pub enum BlockIndentStyle {
 
 impl_enum_decodable!(BlockIndentStyle, Inherit, Tabbed, Visual);
 
+#[derive(Copy, Clone, Eq, PartialEq, Debug)]
+pub enum Density {
+    // Fit as much on one line as possible.
+    Compressed,
+    // Use more lines.
+    Tall,
+}
+
+impl_enum_decodable!(Density, Compressed, Tall);
+
+impl Density {
+    pub fn to_list_tactic(self) -> ListTactic {
+        match self {
+            Density::Compressed => ListTactic::Mixed,
+            Density::Tall => ListTactic::HorizontalVertical,
+        }
+    }
+}
+
 macro_rules! create_config {
     ($($i:ident: $ty:ty),+ $(,)*) => (
         #[derive(RustcDecodable, Clone)]
@@ -70,6 +89,7 @@ create_config! {
     fn_brace_style: BraceStyle,
     fn_return_indent: ReturnIndent,
     fn_args_paren_newline: bool,
+    fn_args_layout: Density,
     struct_trailing_comma: SeparatorTactic,
     struct_lit_trailing_comma: SeparatorTactic,
     struct_lit_style: StructLitStyle,
@@ -94,6 +114,7 @@ impl Default for Config {
             fn_brace_style: BraceStyle::SameLineWhere,
             fn_return_indent: ReturnIndent::WithArgs,
             fn_args_paren_newline: true,
+            fn_args_layout: Density::Tall,
             struct_trailing_comma: SeparatorTactic::Vertical,
             struct_lit_trailing_comma: SeparatorTactic::Vertical,
             struct_lit_style: StructLitStyle::BlockIndent,

src/items.rs

@@ -342,7 +342,7 @@ impl<'a> FmtVisitor<'a> {
         }
 
         let fmt = ListFormatting {
-            tactic: ListTactic::HorizontalVertical,
+            tactic: self.config.fn_args_layout.to_list_tactic(),
             separator: ",",
             trailing_separator: SeparatorTactic::Never,
             indent: arg_indent,

tests/config/small_tabs.toml

@@ -6,6 +6,7 @@ newline_style = "Unix"
 fn_brace_style = "SameLineWhere"
 fn_return_indent = "WithArgs"
 fn_args_paren_newline = true
+fn_args_layout = "Tall"
 struct_trailing_comma = "Vertical"
 struct_lit_trailing_comma = "Vertical"
 struct_lit_style = "BlockIndent"

tests/source/fn-custom.rs

@@ -0,0 +1,13 @@
+// rustfmt-fn_args_layout: Compressed
+// Test some of the ways function signatures can be customised.
+
+// Test compressed layout of args.
+fn foo(a: Aaaaaaaaaaaaaaa, b: Bbbbbbbbbbbbbbbb, c: Ccccccccccccccccc, d: Ddddddddddddddddddddddddd, e: Eeeeeeeeeeeeeeeeeee) {
+    foo();
+}
+
+impl Foo {
+    fn foo(self, a: Aaaaaaaaaaaaaaa, b: Bbbbbbbbbbbbbbbb, c: Ccccccccccccccccc, d: Ddddddddddddddddddddddddd, e: Eeeeeeeeeeeeeeeeeee) {
+        foo();
+    }    
+}

tests/target/fn-custom.rs

@@ -0,0 +1,15 @@
+// rustfmt-fn_args_layout: Compressed
+// Test some of the ways function signatures can be customised.
+
+// Test compressed layout of args.
+fn foo(a: Aaaaaaaaaaaaaaa, b: Bbbbbbbbbbbbbbbb, c: Ccccccccccccccccc,
+       d: Ddddddddddddddddddddddddd, e: Eeeeeeeeeeeeeeeeeee) {
+    foo();
+}
+
+impl Foo {
+    fn foo(self, a: Aaaaaaaaaaaaaaa, b: Bbbbbbbbbbbbbbbb, c: Ccccccccccccccccc,
+           d: Ddddddddddddddddddddddddd, e: Eeeeeeeeeeeeeeeeeee) {
+        foo();
+    }
+}