From 1043a6d866ce290b6140acdcff287189cdaa2642 Mon Sep 17 00:00:00 2001
From: Dillon Welch <daw0328@gmail.com>
Date: Mon, 23 Oct 2017 17:34:53 -0700
Subject: [PATCH 1/2] Rewrite old attribute mapping to save many object
 allocations
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Stringifying the keys of a hash can be done without allocating many
arrays like the previous approach did.

```ruby
begin
  require "bundler/inline"
rescue LoadError => e
  $stderr.puts "Bundler version 1.10 or later is required. Please update
                your Bundler"
  raise e
end

gemfile(true) do
  source "https://rubygems.org"

  gem "benchmark-ips"
end

def allocate_count
  GC.disable
  before = ObjectSpace.count_objects
  yield
  after = ObjectSpace.count_objects
  after.each { |k,v| after[k] = v - before[k] }
  after[:T_HASH] -= 1 # probe effect - we created the before hash.
  GC.enable
  result = after.reject { |k,v| v == 0 }
  GC.start
  result
end

@old = {a: :b, c: :d, e: :f}

def master_version
  Hash[@old.map { |k, v| [k.to_s, v] }]
end

def fast_version
  result = {}
  @old.each { |k, v| result[k.to_s] = v }
end

puts "master_version"
puts allocate_count { 1000.times { master_version } }
puts "fast_version"
puts allocate_count { 1000.times { fast_version } }

Benchmark.ips do |x|
  x.report("master_version") { master_version }
  x.report("fast_version")     { fast_version }
  x.compare!
end
```

```ruby
master_version
{:FREE=>-14768, :T_STRING=>6054, :T_ARRAY=>7000, :T_HASH=>1000, :T_IMEMO=>1000}
fast_version
{:FREE=>-7001, :T_STRING=>6000, :T_HASH=>1000}
Warming up --------------------------------------
      master_version    38.137k i/100ms
        fast_version    50.133k i/100ms
Calculating -------------------------------------
      master_version    451.898k (±19.2%) i/s -      2.174M in   5.002186s
        fast_version    633.579k (±19.4%) i/s -      3.058M in   5.019391s

Comparison:
        fast_version:   633578.7 i/s
      master_version:   451897.6 i/s - same-ish: difference falls within error
```
---
 lib/haml/buffer.rb | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/haml/buffer.rb b/lib/haml/buffer.rb
index 81a4e853b0..8fd92bbc4e 100644
--- a/lib/haml/buffer.rb
+++ b/lib/haml/buffer.rb
@@ -132,7 +132,9 @@ def adjust_tabs(tab_change)
     def attributes(class_id, obj_ref, *attributes_hashes)
       attributes = class_id
       attributes_hashes.each do |old|
-        AttributeBuilder.merge_attributes!(attributes, Hash[old.map {|k, v| [k.to_s, v]}])
+        result = {}
+        old.each { |k, v| result[k.to_s] = v }
+        AttributeBuilder.merge_attributes!(attributes, result)
       end
       AttributeBuilder.merge_attributes!(attributes, parse_object_ref(obj_ref)) if obj_ref
       AttributeBuilder.build_attributes(

From 3bba45257a3ad8cca068924281719955ac05abf6 Mon Sep 17 00:00:00 2001
From: Dillon Welch <daw0328@gmail.com>
Date: Wed, 25 Oct 2017 17:11:07 -0700
Subject: [PATCH 2/2] CHANGELOG.md note

---
 CHANGELOG.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e08c9dd70c..2525d76df7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,6 @@
 # Haml Changelog
 
+* Performance/memory usage improvement in `lib/haml/buffer.rb` [#963](https://github.com/haml/haml/pull/963) (thanks [Dillon Welch](https://github.com/oniofchaos))
 * Add erubis to gemspec so that `benchmark.rb` works [#964](https://github.com/haml/haml/pull/964) (thanks [Dillon Welch](https://github.com/oniofchaos))
 
 ## 5.0.4