Adds validation to job length

config/feature_flags/development/ci_validate_job_length.yml

+---
+name: ci_validate_job_length
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/73599
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/344665
+milestone: '14.5'
+type: development
+group: group::pipeline authoring
+default_enabled: true

doc/ci/jobs/index.md

@@ -82,7 +82,7 @@ For example:
 
 ![Pipeline mini graph sorting](img/pipelines_mini_graph_sorting.png)
 
-## Unavailable names for jobs
+## Job name limitations
 
 You can't use these keywords as job names:
 
@@ -96,6 +96,10 @@ You can't use these keywords as job names:
 - `cache`
 - `include`
 
+Job names must be 255 characters or less. [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/342800)
+in GitLab 14.5, [with a feature flag](../../administration/feature_flags.md) named `ci_validate_job_length`.
+Enabled by default. To disable it, ask an administrator to [disable the feature flag](../../administration/feature_flags.md).
+
 ## Group jobs in a pipeline
 
 If you have many similar jobs, your [pipeline graph](../pipelines/index.md#visualize-pipelines) becomes long and hard

lib/gitlab/ci/config/entry/processable.rb

@@ -23,6 +23,7 @@ module Gitlab
               validates :config, presence: true
               validates :name, presence: true
               validates :name, type: Symbol
+              validates :name, length: { maximum: 255 }, if: -> { ::Feature.enabled?(:ci_validate_job_length, default_enabled: :yaml) }
 
               validates :config, disallowed_keys: {
                   in: %i[only except when start_in],

spec/lib/gitlab/ci/config/entry/processable_spec.rb

@@ -33,6 +33,14 @@ RSpec.describe Gitlab::Ci::Config::Entry::Processable do
         end
       end
 
+      context 'when job name is more than 255' do
+        let(:entry) { node_class.new(config, name: ('a' * 256).to_sym) }
+
+        it 'shows a validation error' do
+          expect(entry.errors).to include "job name is too long (maximum is 255 characters)"
+        end
+      end
+
       context 'when job name is empty' do
         let(:entry) { node_class.new(config, name: ''.to_sym) }