Duplicate task configs to test all supported Bazel LTS releases (#1858)

For each task, if bazel version is not specified, duplicate the task for
each supported Bazel LTS releases.

Users can override the bazel version in the presubmit.yml file
explicitly to bypass this duplication.

Relevant discussion and changes:
- bazelbuild/bazel-central-registry#1332
- bazelbuild/bazel-central-registry#1373
- bazel-contrib/rules-template#105

buildkite/bazel-central-registry/bcr_presubmit.py

@@ -445,6 +445,22 @@ def upload_jobs_to_pipeline(pipeline_steps):
     )
 
 
+def duplicate_configs_for_supported_bazel_lts_releases(task_configs):
+    # For each task, if bazel version is not specified, duplicate the task for each supported Bazel LTS releases.
+    BAZEL_LTS = [("7.x", ":seven:"), ("6.x", ":six:")] # the second element is the emoji name
+    new_task_configs = {}
+    for task_name, task_config in task_configs.items():
+        if "bazel" in task_config:
+            new_task_configs[task_name] = task_config
+        else:
+            for bazel_version, emoji in BAZEL_LTS:
+                new_task_config = task_config.copy()
+                new_task_config["bazel"] = bazel_version
+                new_task_config["name"] = task_config["name"] + " (:bazel: " + emoji + ")"
+                new_task_configs[task_name + "_" + bazel_version] = new_task_config
+    return new_task_configs
+
+
 def main(argv=None):
     if argv is None:
         argv = sys.argv[1:]
@@ -473,9 +489,11 @@ def main(argv=None):
         pipeline_steps = []
         for module_name, module_version in modules:
             configs = get_task_config(module_name, module_version)
-            add_presubmit_jobs(module_name, module_version, configs.get("tasks", {}), pipeline_steps)
+            task_configs = duplicate_configs_for_supported_bazel_lts_releases(configs.get("tasks", {}))
+            add_presubmit_jobs(module_name, module_version, task_configs, pipeline_steps)
             configs = get_test_module_task_config(module_name, module_version)
-            add_presubmit_jobs(module_name, module_version, configs.get("tasks", {}), pipeline_steps, is_test_module=True)
+            task_configs = duplicate_configs_for_supported_bazel_lts_releases(configs.get("tasks", {}))
+            add_presubmit_jobs(module_name, module_version, task_configs, pipeline_steps, is_test_module=True)
         if should_wait_bcr_maintainer_review(modules) and pipeline_steps:
             pipeline_steps = [{"block": "Wait on BCR maintainer review", "blocked_state": "running"}] + pipeline_steps
         upload_jobs_to_pipeline(pipeline_steps)