Support different tabbing of function args

(Although, frankly anything other than visual is deeply wrong).

src/config.rs

@@ -90,6 +90,7 @@ create_config! {
     fn_return_indent: ReturnIndent,
     fn_args_paren_newline: bool,
     fn_args_layout: Density,
+    fn_arg_indent: BlockIndentStyle,
     struct_trailing_comma: SeparatorTactic,
     struct_lit_trailing_comma: SeparatorTactic,
     struct_lit_style: StructLitStyle,
@@ -115,6 +116,7 @@ impl Default for Config {
             fn_return_indent: ReturnIndent::WithArgs,
             fn_args_paren_newline: true,
             fn_args_layout: Density::Tall,
+            fn_arg_indent: BlockIndentStyle::Visual,
             struct_trailing_comma: SeparatorTactic::Vertical,
             struct_lit_trailing_comma: SeparatorTactic::Vertical,
             struct_lit_style: StructLitStyle::BlockIndent,

src/items.rs

@@ -18,7 +18,7 @@ use expr::rewrite_assign_rhs;
 use comment::FindUncommented;
 use visitor::FmtVisitor;
 use rewrite::Rewrite;
-use config::Config;
+use config::{Config, BlockIndentStyle};
 
 use syntax::{ast, abi};
 use syntax::codemap::{self, Span, BytePos};
@@ -237,6 +237,7 @@ impl<'a> FmtVisitor<'a> {
                                            explicit_self,
                                            one_line_budget,
                                            multi_line_budget,
+                                           indent,
                                            arg_indent,
                                            args_span));
         result.push(')');
@@ -293,6 +294,7 @@ impl<'a> FmtVisitor<'a> {
                     explicit_self: Option<&ast::ExplicitSelf>,
                     one_line_budget: usize,
                     multi_line_budget: usize,
+                    indent: usize,
                     arg_indent: usize,
                     span: Span)
                     -> String {
@@ -341,11 +343,17 @@ impl<'a> FmtVisitor<'a> {
             item.item = arg;
         }
 
+        let indent = match self.config.fn_arg_indent {
+            BlockIndentStyle::Inherit => indent,
+            BlockIndentStyle::Tabbed => indent + self.config.tab_spaces,
+            BlockIndentStyle::Visual => arg_indent,
+        };
+
         let fmt = ListFormatting {
             tactic: self.config.fn_args_layout.to_list_tactic(),
             separator: ",",
             trailing_separator: SeparatorTactic::Never,
-            indent: arg_indent,
+            indent: indent,
             h_width: one_line_budget,
             v_width: multi_line_budget,
             ends_with_newline: false,

tests/config/small_tabs.toml

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