From a63ae913dfbb3813256144e52ae1063ac59edba4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nicol=C3=B2=20Rebughini?= <nicolo.rebughini@pm.me>
Date: Mon, 20 Mar 2023 17:32:42 +0100
Subject: [PATCH] Do not allocate the first path character in asset helper
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

In asset heavy views, the asset_path helper might be called a lot of
times. When checking the first character of the source element with []
we allocate a string each time just to check it against ?/.

By using String#start_with? we can avoid this step and go a bit faster.

This is the code I used to measure the change:

```

require "bundler/inline"

ROOT_STRING = '/'
TEST_PATH = "/some/path"

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

  gem "benchmark-ips"
end

Benchmark.ips do |x|
  x.report("source[0]") do
   TEST_PATH[0] != ROOT_STRING
  end

  x.report("source.start_with?") do
   TEST_PATH.start_with?(ROOT_STRING)
  end

  x.compare!
end
```

Warming up --------------------------------------
           source[0]   905.322k i/100ms
  source.start_with?     1.541M i/100ms
Calculating -------------------------------------
           source[0]      9.012M (± 0.7%) i/s -     45.266M in   5.022969s
  source.start_with?     15.395M (± 0.4%) i/s -     77.030M in   5.003691s

Comparison:
  source.start_with?: 15394807.0 i/s
           source[0]:  9012304.9 i/s - 1.71x  slower
---
 actionview/lib/action_view/helpers/asset_url_helper.rb | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/actionview/lib/action_view/helpers/asset_url_helper.rb b/actionview/lib/action_view/helpers/asset_url_helper.rb
index 72ca5fe04f..6ee75f580c 100644
--- a/actionview/lib/action_view/helpers/asset_url_helper.rb
+++ b/actionview/lib/action_view/helpers/asset_url_helper.rb
@@ -196,7 +196,7 @@ def asset_path(source, options = {})
           source = "#{source}#{extname}"
         end
 
-        if source[0] != ?/
+        unless source.start_with?(?/)
           if options[:skip_pipeline]
             source = public_compute_asset_path(source, options)
           else