Allow empty blocks on one line in more places

In particular if they contain only a single-line comment.

Fixes #493

src/expr.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use std::cmp::Ordering;
+use std::cmp::{Ordering, min};
 use std::borrow::Borrow;
 use std::mem::swap;
 use std::ops::Deref;
@@ -595,9 +595,19 @@ impl Rewrite for ast::Block {
         // width is used only for the single line case: either the empty block `{}`,
         // or an unsafe expression `unsafe { e }`.
 
+        if self.stmts.is_empty() && !block_contains_comment(self, context.codemap) && width >= 2 {
+            return Some("{}".to_owned());
+        }
+
+        // If a block contains only a single-line comment, then leave it on one line.
         let user_str = context.snippet(self.span);
-        if user_str == "{}" && width >= 2 {
-            return Some(user_str);
+        let user_str = user_str.trim();
+        if user_str.starts_with('{') && user_str.ends_with('}') {
+            let comment_str = user_str[1..user_str.len() - 1].trim();
+            if self.stmts.is_empty() && !comment_str.contains('\n') &&
+               !comment_str.starts_with("//") && comment_str.len() + 4 <= width {
+                return Some(format!("{{ {} }}", comment_str));
+            }
         }
 
         let mut visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
@@ -870,11 +880,17 @@ impl<'a> Rewrite for ControlFlow<'a> {
             }
         }
 
-        // This is used only for the empty block case: `{}`.
+        // This is used only for the empty block case: `{}`. So, we use 1 if we know
+        // we should avoid the single line case.
         // 2 = spaces after keyword and condition.
         let block_width = try_opt!(width.checked_sub(label_string.len() + self.keyword.len() +
                                                      extra_offset(&pat_expr_string, inner_offset) +
                                                      2));
+        let block_width = if self.else_block.is_some() || self.nested_if {
+            min(1, block_width)
+        } else {
+            block_width
+        };
 
         let block_str = try_opt!(self.block.rewrite(context, block_width, offset));
 
@@ -949,7 +965,9 @@ impl<'a> Rewrite for ControlFlow<'a> {
                 }
                 _ => {
                     last_in_chain = true;
-                    else_block.rewrite(context, width, offset)
+                    // When rewriting a block, the width is only used for single line
+                    // blocks, passing 1 lets us avoid that.
+                    else_block.rewrite(context, min(1, width), offset)
                 }
             };
 
@@ -1021,8 +1039,8 @@ fn block_contains_comment(block: &ast::Block, codemap: &CodeMap) -> bool {
 // FIXME: incorrectly returns false when comment is contained completely within
 // the expression.
 pub fn is_simple_block(block: &ast::Block, codemap: &CodeMap) -> bool {
-    block.stmts.len() == 1 && stmt_is_expr(&block.stmts[0]) &&
-    !block_contains_comment(block, codemap)
+    (block.stmts.len() == 1 && stmt_is_expr(&block.stmts[0]) &&
+     !block_contains_comment(block, codemap))
 }
 
 /// Checks whether a block contains at most one statement or expression, and no comments.

tests/source/chains-visual.rs

@@ -95,11 +95,11 @@ fn floaters() {
         .bar()
         .baz();
 
-    Foo { x: val } .baz(|| { /*force multiline    */    }) .quux(); 
+    Foo { x: val } .baz(|| { force(); multiline();    }) .quux(); 
 
     Foo { y: i_am_multi_line, z: ok }
         .baz(|| {
-            // force multiline
+            force(); multiline();
         })
         .quux(); 
 

tests/source/chains.rs

@@ -93,11 +93,11 @@ fn floaters() {
         .bar()
         .baz();
 
-    Foo { x: val } .baz(|| { /*force multiline    */    }) .quux(); 
+    Foo { x: val } .baz(|| { force(); multiline();    }) .quux(); 
 
     Foo { y: i_am_multi_line, z: ok }
         .baz(|| {
-            // force multiline
+            force(); multiline();
         })
         .quux(); 
 

tests/target/chains-visual.rs

@@ -105,7 +105,8 @@ fn floaters() {
 
     Foo { x: val }
         .baz(|| {
-            // force multiline
+            force();
+            multiline();
         })
         .quux();
 
@@ -114,7 +115,8 @@ fn floaters() {
         z: ok,
     }
     .baz(|| {
-        // force multiline
+        force();
+        multiline();
     })
     .quux();
 

tests/target/chains.rs

@@ -102,7 +102,8 @@ fn floaters() {
 
     Foo { x: val }
         .baz(|| {
-            // force multiline
+            force();
+            multiline();
         })
         .quux();
 
@@ -111,7 +112,8 @@ fn floaters() {
             z: ok,
         }
         .baz(|| {
-            // force multiline
+            force();
+            multiline();
         })
         .quux();
 

tests/target/expr.rs

@@ -60,8 +60,7 @@ fn foo() -> bool {
         1111 + 2222 {}
 
     if let (some_very_large,
-            tuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuple) = 1 + 2 + 3 {
-    }
+            tuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuple) = 1 + 2 + 3 {}
 
     let test = if true { 5 } else { 3 };
 
@@ -136,12 +135,8 @@ fn baz() {
 fn qux() {
     {}
     // FIXME this one could be done better.
-    {
-        // a block with a comment
-    }
-    {
-
-    }
+    { /* a block with a comment */ }
+    {}
     {
         // A block with a comment.
     }
@@ -293,12 +288,10 @@ fn complex_if_else() {
 fn issue1106() {
     {
         if let hir::ItemEnum(ref enum_def, ref generics) =
-            self.ast_map.expect_item(enum_node_id).node {
-        }
+            self.ast_map.expect_item(enum_node_id).node {}
     }
 
     for entry in WalkDir::new(path)
         .into_iter()
-        .filter_entry(|entry| exclusions.filter_entry(entry)) {
-    }
+        .filter_entry(|entry| exclusions.filter_entry(entry)) {}
 }

tests/target/hard-tabs.rs

@@ -31,8 +31,7 @@ fn main() {
 	let str = "AAAAAAAAAAAAAAaAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAaAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAaAa";
 
 	if let (some_very_large,
-	        tuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuple) = 1 + 2 + 3 {
-	}
+	        tuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuple) = 1 + 2 + 3 {}
 
 	if cond() {
 		something();

tests/target/issue-447.rs

@@ -36,6 +36,5 @@ fn main() {
     let Some(x) = y
     // shouldn't be dropped
     // shouldn't be dropped
-    {
-    }
+    {}
 }

tests/target/match.rs

@@ -78,9 +78,7 @@ fn main() {
     };
 
     match x {
-        y => {
-            // Block with comment. Preserve me.
-        }
+        y => { /*Block with comment. Preserve me.*/ }
         z => {
             stmt();
         }