4 files changed, 89 insertions, 2 deletions
diff --git a/lib/gitlab/ci/build/policy/changes.rb b/lib/gitlab/ci/build/policy/changes.rb
new file mode 100644
index 00000000000..7bf51519752
--- /dev/null
+++ b/lib/gitlab/ci/build/policy/changes.rb
@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Ci
+    module Build
+      module Policy
+        class Changes < Policy::Specification
+          def initialize(globs)
+            @globs = Array(globs)
+          end
+
+          def satisfied_by?(pipeline, seed)
+            return true unless pipeline.branch_updated?
+
+            pipeline.modified_paths.any? do |path|
+              @globs.any? do |glob|
+                File.fnmatch?(glob, path, File::FNM_PATHNAME | File::FNM_DOTMATCH)
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/ci/config/entry/policy.rb b/lib/gitlab/ci/config/entry/policy.rb
index 09e8e52b60f..c92562f8c85 100644
--- a/lib/gitlab/ci/config/entry/policy.rb
+++ b/lib/gitlab/ci/config/entry/policy.rb
@@ -25,17 +25,19 @@ module Gitlab
             include Entry::Validatable
             include Entry::Attributable
 
-            attributes :refs, :kubernetes, :variables
+            ALLOWED_KEYS = %i[refs kubernetes variables changes].freeze
+            attributes :refs, :kubernetes, :variables, :changes
 
             validations do
               validates :config, presence: true
-              validates :config, allowed_keys: %i[refs kubernetes variables]
+              validates :config, allowed_keys: ALLOWED_KEYS
               validate :variables_expressions_syntax
 
               with_options allow_nil: true do
                 validates :refs, array_of_strings_or_regexps: true
                 validates :kubernetes, allowed_values: %w[active]
                 validates :variables, array_of_strings: true
+                validates :changes, array_of_strings: true
               end
 
               def variables_expressions_syntax
diff --git a/lib/gitlab/git/diff_stats_collection.rb b/lib/gitlab/git/diff_stats_collection.rb
index d4033f56387..998c41497a2 100644
--- a/lib/gitlab/git/diff_stats_collection.rb
+++ b/lib/gitlab/git/diff_stats_collection.rb
@@ -18,6 +18,10 @@ module Gitlab
         indexed_by_path[path]
       end
 
+      def paths
+        @collection.map(&:path)
+      end
+
       private
 
       def indexed_by_path
diff --git a/lib/gitlab/git/push.rb b/lib/gitlab/git/push.rb
new file mode 100644
index 00000000000..7c1309721fd
--- /dev/null
+++ b/lib/gitlab/git/push.rb
@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Git
+    class Push
+      include Gitlab::Utils::StrongMemoize
+
+      attr_reader :oldrev, :newrev
+
+      def initialize(project, oldrev, newrev, ref)
+        @project = project
+        @oldrev = oldrev.presence || Gitlab::Git::BLANK_SHA
+        @newrev = newrev.presence || Gitlab::Git::BLANK_SHA
+        @ref = ref
+      end
+
+      def branch_name
+        strong_memoize(:branch_name) do
+          Gitlab::Git.branch_name(@ref)
+        end
+      end
+
+      def branch_added?
+        Gitlab::Git.blank_ref?(@oldrev)
+      end
+
+      def branch_removed?
+        Gitlab::Git.blank_ref?(@newrev)
+      end
+
+      def branch_updated?
+        branch_push? && !branch_added? && !branch_removed?
+      end
+
+      def force_push?
+        Gitlab::Checks::ForcePush.force_push?(@project, @oldrev, @newrev)
+      end
+
+      def branch_push?
+        strong_memoize(:branch_push) do
+          Gitlab::Git.branch_ref?(@ref)
+        end
+      end
+
+      def modified_paths
+        unless branch_updated?
+          raise ArgumentError, 'Unable to calculate modified paths!'
+        end
+
+        strong_memoize(:modified_paths) do
+          @project.repository.diff_stats(@oldrev, @newrev).paths
+        end
+      end
+    end
+  end
+end