8 files changed, 138 insertions, 2 deletions
diff --git a/buildscripts/resmokeconfig/suites/feature_flag_multiversion.yml b/buildscripts/resmokeconfig/suites/feature_flag_multiversion.yml
new file mode 100644
index 00000000000..86d66750a49
--- /dev/null
+++ b/buildscripts/resmokeconfig/suites/feature_flag_multiversion.yml
@@ -0,0 +1,13 @@
+# This test suite only includes run_feature_flag_multiversion_test.js as this test should only be
+# run on build variants that have the featureFlagToaster and featureFlagSpoon feature flags enabled.
+test_kind: js_test
+
+selector:
+  roots:
+  - jstests/multiVersion/genericSetFCVUsage/run_feature_flag_multiversion_test.js
+
+# Multiversion tests start their own mongod's.
+executor:
+  config:
+    shell_options:
+      nodb: ''
diff --git a/buildscripts/resmokeconfig/suites/multiversion.yml b/buildscripts/resmokeconfig/suites/multiversion.yml
index 2dd6305b139..bb1ec6b7023 100644
--- a/buildscripts/resmokeconfig/suites/multiversion.yml
+++ b/buildscripts/resmokeconfig/suites/multiversion.yml
@@ -17,6 +17,9 @@ selector:
   # TODO SERVER-42919: recent work on the ReplicaSetMonitor means that mongoS no longer crashes when
   # it attempts to connect to an upgraded mongoD. Un-blacklist when SERVER-42919 fixes this issue.
   - jstests/multiVersion/genericSetFCVUsage/crash_mongos_against_upgraded_cluster.js
+  exclude_with_any_tags:
+  - featureFlagToaster
+  - featureFlagSpoon
 
 # Multiversion tests start their own mongod's.
 executor:
diff --git a/buildscripts/resmokeconfig/suites/multiversion_auth.yml b/buildscripts/resmokeconfig/suites/multiversion_auth.yml
index b1935a79edc..ba2f80dfab6 100644
--- a/buildscripts/resmokeconfig/suites/multiversion_auth.yml
+++ b/buildscripts/resmokeconfig/suites/multiversion_auth.yml
@@ -21,6 +21,9 @@ selector:
   # TODO SERVER-42919: recent work on the ReplicaSetMonitor means that mongoS no longer crashes when
   # it attempts to connect to an upgraded mongoD. Un-blacklist when SERVER-42919 fixes this issue.
   - jstests/multiVersion/genericSetFCVUsage/crash_mongos_against_upgraded_cluster.js
+  exclude_with_any_tags:
+  - featureFlagToaster
+  - featureFlagSpoon
 
 # Multiversion tests start their own mongod's.
 executor:
diff --git a/etc/evergreen.yml b/etc/evergreen.yml
index b0c08f8dd60..6a8abfbdb24 100644
--- a/etc/evergreen.yml
+++ b/etc/evergreen.yml
@@ -6163,6 +6163,17 @@ tasks:
       use_multiversion: /data/multiversion
       fallback_num_sub_suites: 1
 
+# Tests the runFeatureFlagMultiversionTest helper.
+# This requires the 'featureFlagToaster' and 'featureFlagSpoon' parameters to be set to true on
+# build variants that enable this task.
+- name: feature_flag_multiversion_gen
+  commands:
+  - func: "generate resmoke tasks"
+    vars:
+      resmoke_args: "--storageEngine=wiredTiger"
+      use_multiversion: /data/multiversion
+      fallback_num_sub_suites: 1
+
 - name: unittest_shell_hang_analyzer_gen
   commands:
   - func: "generate resmoke tasks"
@@ -10429,7 +10440,7 @@ buildvariants:
     burn_in_tag_buildvariants: enterprise-rhel-62-64-bit-majority-read-concern-off enterprise-rhel-62-64-bit-inmem linux-64-duroff enterprise-rhel-62-64-bit-multiversion
     num_scons_link_jobs_available: 0.99
     test_flags: >-
-        --mongodSetParameters="{featureFlagTimeseriesCollection: true}"
+        --mongodSetParameters="{featureFlagTimeseriesCollection: true, featureFlagToaster: true, featureFlagSpoon: true}"
   tasks:
   - name: compile_parallel_TG
     distros:
@@ -10454,6 +10465,7 @@ buildvariants:
     - rhel62-large
   - name: disk_wiredtiger
   - name: .encrypt
+  - name: feature_flag_multiversion_gen
   - name: idl_tests
   - name: initial_sync_fuzzer_gen
   - name: .integration
diff --git a/jstests/multiVersion/genericSetFCVUsage/run_feature_flag_multiversion_test.js b/jstests/multiVersion/genericSetFCVUsage/run_feature_flag_multiversion_test.js
new file mode 100644
index 00000000000..41d8d9ba898
--- /dev/null
+++ b/jstests/multiVersion/genericSetFCVUsage/run_feature_flag_multiversion_test.js
@@ -0,0 +1,61 @@
+/**
+ * Tests the behavior of the 'runFeatureFlagMultiversionTest' helper.
+ * This test requires that the featureFlagToaster and featureFlagSpoon parameters to be enabled and
+ * the featureFlagFryer parameter to be disabled.
+ *
+ * Add test tags for the feature flags depended on by this test.
+ * @tags: [featureFlagToaster, featureFlagSpoon]
+ */
+
+(function() {
+'use strict';
+
+let numLastLTSRuns = 0;
+let numLastContRuns = 0;
+
+function runTest(downgradeFCV) {
+    let name = "feature_flag_test";
+    let nodes = {n0: {binVersion: "latest"}};
+    let rst = new ReplSetTest({name: name, nodes: nodes});
+    rst.startSet();
+    rst.initiate();
+
+    let primary = rst.getPrimary();
+    let adminDB = primary.getDB("admin");
+    assert.commandWorked(adminDB.adminCommand({setFeatureCompatibilityVersion: downgradeFCV}));
+    checkFCV(adminDB, downgradeFCV);
+    if (downgradeFCV === lastLTSFCV) {
+        numLastLTSRuns++;
+    } else {
+        numLastContRuns++;
+    }
+    rst.stopSet();
+}
+
+try {
+    // We expect the test run to fail when using a non-existent feature flag.
+    runFeatureFlagMultiversionTest("nonExistentFeatureFlag", runTest);
+} catch (error) {
+}
+
+// No tests should have been run when a non-existent feature flag is passed in.
+assert.eq(numLastLTSRuns, 0);
+assert.eq(numLastContRuns, 0);
+
+// No tests should have been run when a disabled feature flag is passed in.
+runFeatureFlagMultiversionTest("featureFlagFryer", runTest);
+assert.eq(numLastLTSRuns, 0);
+assert.eq(numLastContRuns, 0);
+
+// Pass in a feature flag that is slated for release in the latest version. This should run against
+// both the last-lts and last-continuous FCV.
+runFeatureFlagMultiversionTest("featureFlagToaster", runTest);
+assert.eq(numLastLTSRuns, 1);
+assert.eq(numLastContRuns, 1);
+
+// Pass in a feature flag that was released in an older version. This should only run against the
+// last-lts FCV.
+runFeatureFlagMultiversionTest("featureFlagSpoon", runTest);
+assert.eq(numLastLTSRuns, 2);
+assert.eq(numLastContRuns, 1);
+})();
+\ No newline at end of file
diff --git a/src/mongo/idl/SConscript b/src/mongo/idl/SConscript
index 92f99142b64..6ec8319fa38 100644
--- a/src/mongo/idl/SConscript
+++ b/src/mongo/idl/SConscript
@@ -32,6 +32,7 @@ env.Library(
     target='feature_flag',
     source=[
         'feature_flag.cpp',
+        'feature_flag_test.idl',
     ],
     LIBDEPS=[
         '$BUILD_DIR/mongo/base',
@@ -54,7 +55,6 @@ env.CppUnitTest(
         'server_parameter_with_storage_test.cpp',
         'config_option_no_init_test.idl',
         'config_option_test.idl',
-        'feature_flag_test.idl',
         'server_parameter_specialized_test.idl',
         'server_parameter_with_storage_test.idl',
         'unittest.idl',
diff --git a/src/mongo/idl/feature_flag_test.idl b/src/mongo/idl/feature_flag_test.idl
index fc76119c208..2bbc4a1378d 100644
--- a/src/mongo/idl/feature_flag_test.idl
+++ b/src/mongo/idl/feature_flag_test.idl
@@ -35,6 +35,11 @@ feature_flags:
       cpp_varname: gFeatureFlagToaster
       default: false
 
+    featureFlagFryer:
+      description: "Create a feature flag"
+      cpp_varname: gFeatureFlagFryer
+      default: false
+
     featureFlagBlender:
       description: "Create a feature flag"
       cpp_varname: gFeatureFlagBlender
diff --git a/src/mongo/shell/feature_compatibility_version.js b/src/mongo/shell/feature_compatibility_version.js
index 6e95a30ba4c..fd4ea3250c2 100644
--- a/src/mongo/shell/feature_compatibility_version.js
+++ b/src/mongo/shell/feature_compatibility_version.js
@@ -91,3 +91,42 @@ function removeFCVDocument(adminDB) {
     assert.commandWorked(res, "failed to list collections");
     assert.eq(newUUID, res.cursor.firstBatch[0].info.uuid);
 }
+
+/**
+ * Runs 'testFunc' with the last-lts FCV as an argument. If 'featureFlag' has a release version
+ * equal to the latest FCV, 'testFunc' will also be run a second time but with last-continuous FCV
+ * as the argument.
+ *
+ * If featureFlag does not exist in the server, throw an error.
+ * If featureFlag is not enabled, return without running 'testFunct'.
+ *
+ * 'testFunc' is expected to be a function that accepts a valid downgrade FCV as input.
+ */
+function runFeatureFlagMultiversionTest(featureFlag, testFunc) {
+    jsTestLog("Running standalone to gather parameter info about featureFlag: " + featureFlag);
+    // Spin up a standalone to check the release version of 'featureFlag'.
+    let standalone = MongoRunner.runMongod();
+    let adminDB = standalone.getDB("admin");
+    let res;
+    try {
+        res = assert.commandWorked(adminDB.runCommand({getParameter: 1, [featureFlag]: 1}),
+                                   "Failed to call getParameter on feature flag: " + featureFlag);
+    } finally {
+        MongoRunner.stopMongod(standalone);
+    }
+
+    if (res && !res[featureFlag]["value"]) {
+        jsTestLog("Feature flag: " + featureFlag + " is not enabled. Skipping test.");
+        return;
+    }
+
+    jsTestLog("Running testFunc with last-lts FCV.");
+    testFunc(lastLTSFCV);
+    if (res && res[featureFlag].hasOwnProperty("version") &&
+        MongoRunner.compareBinVersions(res[featureFlag]["version"].toString(), "latest") === 0) {
+        // The feature associated with 'featureFlag' will be released in the latest FCV. We should
+        // also run upgrade/downgrade behavior against the last-continuous FCV.
+        jsTestLog("Running testFunc with last-continuous FCV.");
+        testFunc(lastContinuousFCV);
+    }
+}