Add CI variable for repository languages

Expose repository languages as a CI variable for use during CI.

app/models/project.rb

@@ -1811,6 +1811,7 @@ class Project < ApplicationRecord
       .append(key: 'CI_PROJECT_NAMESPACE', value: namespace.full_path)
       .append(key: 'CI_PROJECT_URL', value: web_url)
       .append(key: 'CI_PROJECT_VISIBILITY', value: visibility)
+      .append(key: 'CI_PROJECT_REPOSITORY_LANGUAGES', value: repository_languages.map(&:name).join(',').downcase)
       .concat(pages_variables)
       .concat(container_registry_variables)
       .concat(auto_devops_variables)

doc/ci/variables/predefined_variables.md

@@ -88,6 +88,7 @@ future GitLab releases.**
 | `CI_PROJECT_PATH_SLUG`                  | 9.3    | all    | `$CI_PROJECT_PATH` lowercased and with everything except `0-9` and `a-z` replaced with `-`. Use in URLs and domain names. |
 | `CI_PROJECT_URL`                        | 8.10   | 0.5    | The HTTP(S) address to access project |
 | `CI_PROJECT_VISIBILITY`                 | 10.3   | all    | The project visibility (internal, private, public) |
+| `CI_PROJECT_REPOSITORY_LANGUAGES`       | 12.3   | all    | Comma-separated, lowercased list of the languages used in the repository (e.g. `ruby,javascript,html,css`) |
 | `CI_COMMIT_REF_PROTECTED`                      | 11.11  | all    | If the job is running on a protected branch |
 | `CI_REGISTRY`                           | 8.10   | 0.5    | If the Container Registry is enabled it returns the address of GitLab's Container Registry |
 | `CI_REGISTRY_IMAGE`                     | 8.10   | 0.5    | If the Container Registry is enabled for the project it returns the address of the registry tied to the specific project |

ee/changelogs/unreleased/rf-ci-project-langs-var.yml

+---
+title: Add CI variable for repository languages
+merge_request: 16477
+author:
+type: other

spec/models/ci/build_spec.rb

@@ -2215,6 +2215,7 @@ describe Ci::Build do
           { key: 'CI_PROJECT_NAMESPACE', value: project.namespace.full_path, public: true, masked: false },
           { key: 'CI_PROJECT_URL', value: project.web_url, public: true, masked: false },
           { key: 'CI_PROJECT_VISIBILITY', value: 'private', public: true, masked: false },
+          { key: 'CI_PROJECT_REPOSITORY_LANGUAGES', value: project.repository_languages.map(&:name).join(',').downcase, public: true, masked: false },
           { key: 'CI_PAGES_DOMAIN', value: Gitlab.config.pages.host, public: true, masked: false },
           { key: 'CI_PAGES_URL', value: project.pages_url, public: true, masked: false },
           { key: 'CI_API_V4_URL', value: 'http://localhost/api/v4', public: true, masked: false },