Add project level git depth setting

Introduce default_git_depth in project's CI/CD settings and set it to
50. Use it if there is no GIT_DEPTH variable specified. Apply this
default only to newly created projects and keep it nil for old ones
in order to not break pipelines that rely on non-shallow clones.

default_git_depth can be updated from CI/CD Settings in the UI, must be
either nil or integer between 0 and 1000 (incl).

Inherit default_git_depth from the origin project when forking projects.

MR pipelines are run on a MR ref (refs/merge-requests/:iid/merge) and it
contains unique commit (i.e. merge commit) which doesn't exist in the
other branch/tags refs. We need to add it cause otherwise it may break
pipelines for old projects that have already enabled Pipelines for merge
results and have git depth 0.

Document new default_git_depth project CI/CD setting

1 files changed, 12 insertions, 6 deletions

diff --git a/app/presenters/ci/build_runner_presenter.rb b/app/presenters/ci/build_runner_presenter.rb
index 6d46e0bf18a..471b6d3b726 100644
--- a/app/presenters/ci/build_runner_presenter.rb
+++ b/app/presenters/ci/build_runner_presenter.rb
@@ -25,14 +25,16 @@ module Ci
     end
 
     def git_depth
-      strong_memoize(:git_depth) do
-        git_depth = variables&.find { |variable| variable[:key] == 'GIT_DEPTH' }&.dig(:value)
-        git_depth.to_i
-      end
+      if git_depth_variable
+        git_depth_variable[:value]
+      else
+        project.default_git_depth
+      end.to_i
     end
 
     def refspecs
       specs = []
+      specs << refspec_for_merge_request_ref if merge_request_ref?
 
       if git_depth > 0
         specs << refspec_for_branch(ref) if branch? || legacy_detached_merge_request_pipeline?
@@ -42,8 +44,6 @@ module Ci
         specs << refspec_for_tag
       end
 
-      specs << refspec_for_merge_request_ref if merge_request_ref?
-
       specs
     end
 
@@ -89,5 +89,11 @@ module Ci
     def refspec_for_merge_request_ref
       "+#{ref}:#{ref}"
     end
+
+    def git_depth_variable
+      strong_memoize(:git_depth_variable) do
+        variables&.find { |variable| variable[:key] == 'GIT_DEPTH' }
+      end
+    end
   end
 end