SERVER-60209 Add option of persisting old multiversion constants after upgrade

3 files changed, 28 insertions, 4 deletions

diff --git a/buildscripts/resmokelib/multiversionconstants.py b/buildscripts/resmokelib/multiversionconstants.py
index 6055e771c24..0ff3b42b56f 100644
--- a/buildscripts/resmokelib/multiversionconstants.py
+++ b/buildscripts/resmokelib/multiversionconstants.py
@@ -111,6 +111,7 @@ def calculate_fcv_constants():
     fcvs = list(map(Version, fcvs))
     lts = releases_yml['longTermSupportReleases']
     lts = list(map(Version, lts))
+    lower_bound_override = releases_yml.get('generateFCVLowerBoundOverride')
 
     mongo_version_yml_file.close()
     releases_yml_file.close()
@@ -121,8 +122,13 @@ def calculate_fcv_constants():
     # Highest LTS release less than latest.
     last_lts = lts[bisect_left(lts, latest) - 1]
 
-    # All FCVs greater than last LTS, up to latest.
-    requires_fcv_tag_list = fcvs[bisect_right(fcvs, last_lts):bisect_right(fcvs, latest)]
+    # Normally, this list includes all FCVs greater than last LTS, up to latest.
+    # However, if we have 'generateFCVLowerBoundOverride' set in releases.yml, we will
+    # extend the lower bound to also include the prevous value of lastLTS.
+    lts_cutoff = last_lts
+    if lower_bound_override is not None:
+        lts_cutoff = Version(lower_bound_override)
+    requires_fcv_tag_list = fcvs[bisect_right(fcvs, lts_cutoff):bisect_right(fcvs, latest)]
 
     # All FCVs less than latest.
     fcvs_less_than_latest = fcvs[:bisect_left(fcvs, latest)]
@@ -165,7 +171,7 @@ LAST_LTS_MONGOS_BINARY = "mongos-" + LAST_LTS_BIN_VERSION
 
 REQUIRES_FCV_TAG_LATEST = tag_str(fcv_constants.latest)
 
-# Generate tags for all FCVS in (lastLTS, latest].
+# Generate tags for all FCVS in (lastLTS, latest], or (lowerBoundOverride, latest] if requested.
 # All multiversion tests should be run with these tags excluded.
 REQUIRES_FCV_TAG = ",".join([tag_str(fcv) for fcv in fcv_constants.requires_fcv_tag_list])
 
diff --git a/src/mongo/util/version/releases.h.tpl b/src/mongo/util/version/releases.h.tpl
index f006eed1ed1..701266bc71f 100644
--- a/src/mongo/util/version/releases.h.tpl
+++ b/src/mongo/util/version/releases.h.tpl
@@ -56,10 +56,15 @@
 #set mvc_doc = yaml.safe_load(mvc_file)
 #set mvc_fcvs = mvc_doc['featureCompatibilityVersions']
 #set mvc_majors = mvc_doc['longTermSupportReleases']
+#set mvc_lower_bound_override = mvc_doc.get('generateFCVLowerBoundOverride')
 ##
 ## Transform strings to versions.
 #set global fcvs = list(map(Version, mvc_fcvs))
 #set majors = list(map(Version, mvc_majors))
+#set global lower_bound_override = None
+#if mvc_lower_bound_override is not None:
+  #set global lower_bound_override = Version(mvc_lower_bound_override)
+#end if
 
 #set global latest = Version(re.match(r'^[0-9]+\.[0-9]+', $mongo_version).group(0))
 ## Highest release less than latest.
@@ -84,6 +89,12 @@ namespace mongo::multiversion {
 fcvs = self.getVar('fcvs')
 last_lts, last_continuous, latest = self.getVar('last_lts'), self.getVar('last_continuous'), self.getVar('latest')
 generic_fcvs = self.getVar('generic_fcvs')
+lower_bound_override = self.getVar('lower_bound_override')
+
+# Will also generate an older set of constants if requested in releases.yml.
+lts_cutoff = last_lts
+if lower_bound_override is not None:
+    lts_cutoff = lower_bound_override
 
 # The 'latest' version must be one of the versions listed in releases.yml.
 assert(latest in fcvs)
@@ -100,7 +111,7 @@ fcv_list = []
 # A list of (FCV enum name, FCV string) tuples for all the transitioning FCV values.
 transition_fcvs = []
 
-for fcv_x in fcvs[bisect_left(fcvs, last_lts):bisect_right(fcvs, latest)]:
+for fcv_x in fcvs[bisect_left(fcvs, lts_cutoff):bisect_right(fcvs, latest)]:
     fcv_list.append((self.fcv_cpp_name(fcv_x), self.dotted(fcv_x)))
     if fcv_x in generic_fcvs.values():
         up_transitions = []
diff --git a/src/mongo/util/version/releases.yml b/src/mongo/util/version/releases.yml
index f5725052a2c..ca829d039c9 100644
--- a/src/mongo/util/version/releases.yml
+++ b/src/mongo/util/version/releases.yml
@@ -23,3 +23,10 @@ longTermSupportReleases:
   - "4.2"
   - "4.4"
   - "5.0"
+
+# Optional.
+# Using this special override extends FCV constant generation down to the previous value of
+# lastLTS. This is intended to ease the transition to a new lastLTS by extending the lifetime
+# of those older constants, so that they can be removed at a more convenient time.
+# For example, we can set this to "5.0" when releasing "6.0".
+# generateFCVLowerBoundOverride: "4.4"