Remove empty list imports

Author: marcusklaas

src/imports.rs

@@ -15,8 +15,6 @@ use syntax::ast;
 use syntax::parse::token;
 use syntax::print::pprust;
 
-
-// TODO remove empty lists (if they're even possible)
 // TODO (some day) remove unused imports, expand globs, compress many single imports into a list import
 
 fn rewrite_single_use_list(path_str: String, vpi: ast::PathListItem, vis: &str) -> String {
@@ -40,22 +38,25 @@ fn rewrite_single_use_list(path_str: String, vpi: ast::PathListItem, vis: &str)
 
 impl<'a> FmtVisitor<'a> {
     // Basically just pretty prints a multi-item import.
+    // Returns None when the import can be removed.
     pub fn rewrite_use_list(&mut self,
                             block_indent: usize,
                             one_line_budget: usize, // excluding indentation
                             multi_line_budget: usize,
                             path: &ast::Path,
                             path_list: &[ast::PathListItem],
-                            visibility: ast::Visibility) -> String {
+                            visibility: ast::Visibility) -> Option<String> {
         let path_str = pprust::path_to_string(path);
 
         let vis = match visibility {
             ast::Public => "pub ",
             _ => ""
         };
 
-        if path_list.len() == 1 {
-            return rewrite_single_use_list(path_str, path_list[0], vis);
+        match path_list.len() {
+            0 => return None,
+            1 => return Some(rewrite_single_use_list(path_str, path_list[0], vis)),
+            _ => ()
         }
 
         // 2 = ::
@@ -110,10 +111,10 @@ impl<'a> FmtVisitor<'a> {
                 ast::PathListItem_::PathListMod{ .. } => None,
             }
         })).collect();
-        if path_str.len() == 0 {
+        Some(if path_str.len() == 0 {
             format!("{}use {{{}}};", vis, write_list(&items, &fmt))
         } else {
             format!("{}use {}::{{{}}};", vis, path_str, write_list(&items, &fmt))
-        }
+        })
     }
 }

src/visitor.rs

@@ -152,19 +152,30 @@ impl<'a, 'v> visit::Visitor<'v> for FmtVisitor<'a> {
 
         match item.node {
             ast::Item_::ItemUse(ref vp) => {
-                self.format_missing_with_indent(item.span.lo);
                 match vp.node {
                     ast::ViewPath_::ViewPathList(ref path, ref path_list) => {
                         let block_indent = self.block_indent;
                         let one_line_budget = config!(max_width) - block_indent;
                         let multi_line_budget = config!(ideal_width) - block_indent;
-                        let new_str = self.rewrite_use_list(block_indent,
-                                                            one_line_budget,
-                                                            multi_line_budget,
-                                                            path,
-                                                            path_list,
-                                                            item.vis);
-                        self.changes.push_str_span(item.span, &new_str);
+                        let formatted = self.rewrite_use_list(block_indent,
+                                                              one_line_budget,
+                                                              multi_line_budget,
+                                                              path,
+                                                              path_list,
+                                                              item.vis);
+
+                        if let Some(new_str) = formatted {
+                            self.format_missing_with_indent(item.span.lo);
+                            self.changes.push_str_span(item.span, &new_str);
+                        } else {
+                            // Format up to last newline
+                            let span = codemap::mk_sp(self.last_pos, item.span.lo);
+                            let span_end = match self.snippet(span).rfind('\n') {
+                                Some(offset) => self.last_pos + BytePos(offset as u32),
+                                None => item.span.lo
+                            };
+                            self.format_missing(span_end);
+                        }
                         self.last_pos = item.span.hi;
                     }
                     ast::ViewPath_::ViewPathGlob(_) => {