Heuristic max width for function calls

src/config.rs

@@ -215,9 +215,11 @@ macro_rules! create_config {
 
 create_config! {
     max_width: usize, "Maximum width of each line",
-    ideal_width: usize, "Ideal width of each line",
-    leeway: usize, "Leeway of line width",
+    ideal_width: usize, "Ideal width of each line (only used for comments)",
+    leeway: usize, "Leeway of line width (deprecated)",
     tab_spaces: usize, "Number of spaces per tab",
+    list_width: usize, "Maximum width in a struct literal or function \
+                        call before faling back to vertical formatting",
     newline_style: NewlineStyle, "Unix or Windows line endings",
     fn_brace_style: BraceStyle, "Brace style for functions",
     fn_return_indent: ReturnIndent, "Location of return type in function declaration",
@@ -256,6 +258,7 @@ impl Default for Config {
             ideal_width: 80,
             leeway: 5,
             tab_spaces: 4,
+            list_width: 50,
             newline_style: NewlineStyle::Unix,
             fn_brace_style: BraceStyle::SameLineWhere,
             fn_return_indent: ReturnIndent::WithArgs,

src/items.rs

@@ -948,7 +948,7 @@ impl<'a> FmtVisitor<'a> {
             item.item = ty;
         }
 
-        let fmt = ListFormatting::for_fn(h_budget, offset, self.config);
+        let fmt = ListFormatting::for_item(h_budget, offset, self.config);
         let list_str = try_opt!(write_list(&items, &fmt));
 
         Some(format!("<{}>", list_str))

src/lists.rs

@@ -26,6 +26,8 @@ pub enum ListTactic {
     Horizontal,
     // Try Horizontal layout, if that fails then vertical
     HorizontalVertical,
+    // HorizontalVertical with a soft limit.
+    LimitedHorizontalVertical(usize),
     // Pack as many items as possible per row over (possibly) many rows.
     Mixed,
 }
@@ -59,6 +61,19 @@ pub struct ListFormatting<'a> {
 
 impl<'a> ListFormatting<'a> {
     pub fn for_fn(width: usize, offset: Indent, config: &'a Config) -> ListFormatting<'a> {
+        ListFormatting {
+            tactic: ListTactic::LimitedHorizontalVertical(config.list_width),
+            separator: ",",
+            trailing_separator: SeparatorTactic::Never,
+            indent: offset,
+            h_width: width,
+            v_width: width,
+            ends_with_newline: false,
+            config: config,
+        }
+    }
+
+    pub fn for_item(width: usize, offset: Indent, config: &'a Config) -> ListFormatting<'a> {
         ListFormatting {
             tactic: ListTactic::HorizontalVertical,
             separator: ",",
@@ -118,6 +133,13 @@ pub fn write_list<'b>(items: &[ListItem], formatting: &ListFormatting<'b>) -> Op
     let fits_single = total_width + total_sep_len <= formatting.h_width;
 
     // Check if we need to fallback from horizontal listing, if possible.
+    if let ListTactic::LimitedHorizontalVertical(limit) = tactic {
+        if total_width > limit {
+            tactic = ListTactic::Vertical;
+        } else {
+            tactic = ListTactic::HorizontalVertical;
+        }
+    }
     if tactic == ListTactic::HorizontalVertical {
         debug!("write_list: total_width: {}, total_sep_len: {}, h_width: {}",
                total_width,

src/types.rs

@@ -230,7 +230,7 @@ fn rewrite_segment(segment: &ast::PathSegment,
                                      list_lo,
                                      span_hi);
 
-            let fmt = ListFormatting::for_fn(list_width, offset + extra_offset, context.config);
+            let fmt = ListFormatting::for_item(list_width, offset + extra_offset, context.config);
             let list_str = try_opt!(write_list(&items.collect::<Vec<_>>(), &fmt));
 
             // Update position of last bracket.