SERVER-64471 Skip checking prepareUnique on an already unique index during collMod unique conversion

2 files changed, 8 insertions, 19 deletions

diff --git a/jstests/noPassthrough/collmod_index_noop.js b/jstests/noPassthrough/collmod_index_noop.js
index 2e16352bd6e..a769b4d3630 100644
--- a/jstests/noPassthrough/collmod_index_noop.js
+++ b/jstests/noPassthrough/collmod_index_noop.js
@@ -140,8 +140,6 @@ if (collModIndexUniqueEnabled) {
 
     // Validate that if the 'unique' option is specified but is a no-op, the operation as a whole
     // will be a no-op.
-    assert.commandWorked(primaryDB.runCommand(
-        {collMod: collName, index: {keyPattern: {d: 1}, prepareUnique: true}}));
     result = assert.commandWorked(primaryDB.runCommand({
         "collMod": primaryColl.getName(),
         "index": {"name": "d_1", "unique": true},
@@ -149,7 +147,6 @@ if (collModIndexUniqueEnabled) {
     validateResultForCollMod(result, {});
     validateCollModOplogEntryCount({
         "o.index.name": "d_1",
-        "o.index.prepareUnique": {$exists: false},
     },
                                    0);
 
@@ -161,8 +158,6 @@ if (collModIndexUniqueEnabled) {
 
     // Validate that if both the 'hidden' and 'unique' options are specified but the
     // 'hidden' and 'unique' options are no-ops, the operation as a whole will be a no-op.
-    assert.commandWorked(primaryDB.runCommand(
-        {collMod: collName, index: {keyPattern: {e: 1}, prepareUnique: true}}));
     result = assert.commandWorked(primaryDB.runCommand({
         "collMod": primaryColl.getName(),
         "index": {"name": "e_1", "hidden": true, "unique": true},
@@ -170,7 +165,6 @@ if (collModIndexUniqueEnabled) {
     validateResultForCollMod(result, {});
     validateCollModOplogEntryCount({
         "o.index.name": "e_1",
-        "o.index.prepareUnique": {$exists: false},
     },
                                    0);
 
@@ -184,8 +178,6 @@ if (collModIndexUniqueEnabled) {
     // 'unique' option is a no-op, the operation as a whole will NOT be a no-op - instead, it will
     // generate an oplog entry with only 'expireAfterSeconds'. Ditto for the command result returned
     // to the user.
-    assert.commandWorked(primaryDB.runCommand(
-        {collMod: collName, index: {keyPattern: {f: 1}, prepareUnique: true}}));
     result = assert.commandWorked(primaryDB.runCommand({
         "collMod": primaryColl.getName(),
         "index": {"name": "f_1", "expireAfterSeconds": 20, "unique": true},
@@ -209,8 +201,6 @@ if (collModIndexUniqueEnabled) {
     // 'hidden' and 'unique' options are no-ops, the operation as a whole will NOT be a no-op -
     // instead, it will generate an oplog entry with only 'expireAfterSeconds'. Ditto for the
     // command result returned to the user.
-    assert.commandWorked(primaryDB.runCommand(
-        {collMod: collName, index: {keyPattern: {g: 1}, prepareUnique: true}}));
     result = assert.commandWorked(primaryDB.runCommand({
         "collMod": primaryColl.getName(),
         "index": {"name": "g_1", "expireAfterSeconds": 30, "hidden": true, "unique": true},
diff --git a/src/mongo/db/catalog/coll_mod.cpp b/src/mongo/db/catalog/coll_mod.cpp
index 747de3e044a..670dae8ef09 100644
--- a/src/mongo/db/catalog/coll_mod.cpp
+++ b/src/mongo/db/catalog/coll_mod.cpp
@@ -303,23 +303,22 @@ StatusWith<ParsedCollModRequest> parseCollModRequest(OperationContext* opCtx,
             auto indexObjForOplog = indexObj;
 
             if (cmdIndex.getUnique()) {
-                // Disallow one-step unique convertion. The user has to set
-                // 'prepareUnique' to true first.
-                if (!cmrIndex->idx->prepareUnique()) {
-                    return Status(ErrorCodes::InvalidOptions,
-                                  "Cannot make index unique with 'prepareUnique=false'. "
-                                  "Run collMod to set it first.");
-                }
-
                 cmr.numModifications++;
                 if (bool unique = *cmdIndex.getUnique(); !unique) {
                     return Status(ErrorCodes::BadValue, "'Unique: false' option is not supported");
                 }
 
-                // Attempting to converting a unique index should be treated as a no-op.
+                // Attempting to convert a unique index should be treated as a no-op.
                 if (cmrIndex->idx->unique()) {
                     indexObjForOplog = indexObjForOplog.removeField(CollModIndex::kUniqueFieldName);
                 } else {
+                    // Disallow one-step unique convertion. The user has to set
+                    // 'prepareUnique' to true first.
+                    if (!cmrIndex->idx->prepareUnique()) {
+                        return Status(ErrorCodes::InvalidOptions,
+                                      "Cannot make index unique with 'prepareUnique=false'. "
+                                      "Run collMod to set it first.");
+                    }
                     cmrIndex->indexUnique = true;
                 }
             }