From c6401f1cd9ac36b63cd0ee077239fe4828ef1ec0 Mon Sep 17 00:00:00 2001
From: Thomas Reynolds <me@tdreyno.com>
Date: Sun, 10 Jan 2016 17:14:41 -0800
Subject: [PATCH] Fixes #1716

---
 CHANGELOG.md                                     |  1 +
 middleman-core/features/clean_build.feature      | 16 ++++++++++++++++
 middleman-core/lib/middleman-core/application.rb |  2 ++
 middleman-core/lib/middleman-core/builder.rb     | 10 +++++++---
 4 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index b0e80a88..370a5e81 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,7 @@ master
 * Fix new extension template
 * Don't parse frontmatter on ignored files.
 * Fix displaying frontmatter on `/__middleman/sitemap`
+* Add `skip_build_clean` config which when set to a block, will avoid removing non-generated paths from build, like .git #1716
 
 # 4.0.0
 
diff --git a/middleman-core/features/clean_build.feature b/middleman-core/features/clean_build.feature
index eaa9942e..60c18578 100644
--- a/middleman-core/features/clean_build.feature
+++ b/middleman-core/features/clean_build.feature
@@ -16,6 +16,22 @@ Feature: Build Clean
       | build/should_be_ignored3.html |
     And the file "build/index.html" should contain "Comment in layout"
 
+  Scenario: Clean build has a whitelist
+    Given a fixture app "clean-app"
+    When a file named "build/.test" with:
+      """
+      Hello
+      """
+    When a file named "config.rb" with:
+      """
+      set :skip_build_clean do |path|
+        path =~ /\.test/
+      end
+      """
+    Given a built app at "clean-app"
+    Then the following files should exist:
+      | build/.test         |
+
   Scenario: Clean build an app with newly ignored files and a nested output directory
     Given a fixture app "clean-nested-app"
     When a file named "config.rb" with:
diff --git a/middleman-core/lib/middleman-core/application.rb b/middleman-core/lib/middleman-core/application.rb
index 5818548b..4efca949 100644
--- a/middleman-core/lib/middleman-core/application.rb
+++ b/middleman-core/lib/middleman-core/application.rb
@@ -191,6 +191,8 @@ module Middleman
       yaml: [%w(--- ---), %w(--- ...)]
     }, 'Allowed frontmatter delimiters'
 
+    define_setting :skip_build_clean, proc { |p| [/\.git/].any? { |r| r.match(p) } }, 'Whether some paths should not be removed during a clean build.'
+
     define_setting :watcher_disable, false, 'If the Listen watcher should not run'
     define_setting :watcher_force_polling, false, 'If the Listen watcher should run in polling mode'
     define_setting :watcher_latency, nil, 'The Listen watcher latency'
diff --git a/middleman-core/lib/middleman-core/builder.rb b/middleman-core/lib/middleman-core/builder.rb
index 4166dcf5..02feb15b 100644
--- a/middleman-core/lib/middleman-core/builder.rb
+++ b/middleman-core/lib/middleman-core/builder.rb
@@ -58,7 +58,7 @@ module Middleman
       prerender_css
       output_files
 
-      clean if @cleaning
+      clean! if @cleaning
 
       ::Middleman::Profiling.report('build')
 
@@ -219,8 +219,12 @@ module Middleman
 
     # Remove files which were not built in this cycle
     Contract ArrayOf[Pathname]
-    def clean
-      @to_clean.each do |f|
+    def clean!
+      to_remove = @to_clean.reject do |f|
+        app.config[:skip_build_clean].call(f.to_s)
+      end
+
+      to_remove.each do |f|
         FileUtils.rm(f)
         trigger(:deleted, f)
       end