From 4c3228530f5b3fb62554b9db6755e2651908e589 Mon Sep 17 00:00:00 2001
From: Nick Cameron <ncameron@mozilla.com>
Date: Fri, 22 Apr 2016 11:29:01 +1200
Subject: [PATCH] block indent large closures

somewhat rough around the edges
---
 src/config.rs  |  8 ++++++++
 src/expr.rs    | 14 ++++++++++++--
 src/rewrite.rs |  1 +
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/src/config.rs b/src/config.rs
index 5632e9a925c..846b8a39135 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -188,6 +188,12 @@ impl ConfigType for usize {
     }
 }
 
+impl ConfigType for isize {
+    fn doc_hint() -> String {
+        String::from("<signed integer>")
+    }
+}
+
 impl ConfigType for String {
     fn doc_hint() -> String {
         String::from("<string>")
@@ -384,6 +390,8 @@ create_config! {
     match_block_trailing_comma: bool, false,
         "Put a trailing comma after a block based match arm (non-block arms are not affected)";
     match_wildcard_trailing_comma: bool, true, "Put a trailing comma after a wildcard arm";
+    closure_block_indent_threshold: isize, 4, "How many lines a closure must have before it is \
+                                                block indented. -1 means never use block indent.";
     write_mode: WriteMode, WriteMode::Replace,
         "What Write Mode to use when none is supplied: Replace, Overwrite, Display, Diff, Coverage";
 }
diff --git a/src/expr.rs b/src/expr.rs
index 248cc7e090a..2a6144481ba 100644
--- a/src/expr.rs
+++ b/src/expr.rs
@@ -455,9 +455,19 @@ fn rewrite_closure(capture: ast::CaptureBy,
 
     // We couldn't format the closure body as a single line expression; fall
     // back to block formatting.
-    let body_rewrite = inner_block.rewrite(&context, budget, Indent::empty());
+    let body_rewrite = try_opt!(inner_block.rewrite(&context, budget, Indent::empty()));
 
-    Some(format!("{} {}", prefix, try_opt!(body_rewrite)))
+    let block_threshold = context.config.closure_block_indent_threshold;
+    if block_threshold < 0 || body_rewrite.matches('\n').count() <= block_threshold as usize {
+        return Some(format!("{} {}", prefix, body_rewrite));
+    }
+
+    // The body of the closure is big enough to be block indented, that means we
+    // must re-format.
+    let mut context = context.clone();
+    context.block_indent.alignment = 0;
+    let body_rewrite = try_opt!(inner_block.rewrite(&context, budget, Indent::empty()));
+    Some(format!("{} {}", prefix, body_rewrite))
 }
 
 fn and_one_line(x: Option<String>) -> Option<String> {
diff --git a/src/rewrite.rs b/src/rewrite.rs
index 5ca8d2e8241..247b1df1c3f 100644
--- a/src/rewrite.rs
+++ b/src/rewrite.rs
@@ -27,6 +27,7 @@ pub trait Rewrite {
     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String>;
 }
 
+#[derive(Clone)]
 pub struct RewriteContext<'a> {
     pub parse_session: &'a ParseSess,
     pub codemap: &'a CodeMap,