SERVER-65024 Fix the uniqueness constraint handling for foreground index builds

(cherry picked from commit 5985d757ddc2645fb1b5df88f78abf6b9a833452)

4 files changed, 55 insertions, 9 deletions

diff --git a/jstests/noPassthroughWithMongod/reindex_duplicate_keys.js b/jstests/noPassthroughWithMongod/reindex_duplicate_keys.js
new file mode 100644
index 00000000000..aa4a363a72a
--- /dev/null
+++ b/jstests/noPassthroughWithMongod/reindex_duplicate_keys.js
@@ -0,0 +1,46 @@
+/**
+ * Tests that reIndex command fails with duplicate key error when there are duplicates in the
+ * collection.
+ */
+
+(function() {
+"use strict";
+
+const collNamePrefix = "reindex_duplicate_keys_";
+let count = 0;
+
+// Bypasses DuplicateKey insertion error for testing via failpoint.
+let addDuplicateDocumentsToCol = function(db, coll, doc) {
+    jsTestLog("Inserts documents without index entries.");
+    assert.commandWorked(
+        db.adminCommand({configureFailPoint: "skipIndexNewRecords", mode: "alwaysOn"}));
+
+    assert.commandWorked(coll.insert(doc));
+    assert.commandWorked(coll.insert(doc));
+
+    assert.commandWorked(db.adminCommand({configureFailPoint: "skipIndexNewRecords", mode: "off"}));
+};
+
+let runTest = function(doc) {
+    const collName = collNamePrefix + count++;
+    const coll = db.getCollection(collName);
+    coll.drop();
+
+    // Makes sure to create the _id index.
+    assert.commandWorked(db.createCollection(collName));
+    if (doc) {
+        assert.commandWorked(coll.createIndex(doc, {unique: true}));
+    } else {
+        doc = {_id: 1};
+    }
+
+    // Inserts two violating documents without indexing them.
+    addDuplicateDocumentsToCol(db, coll, doc);
+
+    // Checks reIndex command fails with duplicate key error.
+    assert.commandFailedWithCode(coll.reIndex(), ErrorCodes.DuplicateKey);
+};
+
+runTest();
+runTest({a: 1});
+})();
\ No newline at end of file
diff --git a/src/mongo/db/catalog/index_catalog.h b/src/mongo/db/catalog/index_catalog.h
index c07d386fec9..9f5b431d990 100644
--- a/src/mongo/db/catalog/index_catalog.h
+++ b/src/mongo/db/catalog/index_catalog.h
@@ -67,7 +67,7 @@ enum class IndexBuildMethod {
      */
     kHybrid,
     /**
-     * Perform a collection scan to dump all keys into the exteral sorter, then into the index.
+     * Perform a collection scan to dump all keys into the external sorter, then into the index.
      * During this process, callers guarantee that no writes will be accepted on this collection.
      */
     kForeground,
diff --git a/src/mongo/db/catalog/multi_index_block.cpp b/src/mongo/db/catalog/multi_index_block.cpp
index 8cbfbe535d0..e389a181478 100644
--- a/src/mongo/db/catalog/multi_index_block.cpp
+++ b/src/mongo/db/catalog/multi_index_block.cpp
@@ -304,9 +304,12 @@ StatusWith<std::vector<BSONObj>> MultiIndexBlock::init(
             collection->getIndexCatalog()->prepareInsertDeleteOptions(
                 opCtx, collection->ns(), descriptor, &index.options);
 
-            // Index builds always relax constraints and check for violations at commit-time.
+            // Foreground index builds have to check for duplicates. Other index builds can relax
+            // constraints and check for violations at commit-time.
             index.options.getKeysMode = IndexAccessMethod::GetKeysMode::kRelaxConstraints;
-            index.options.dupsAllowed = true;
+            index.options.dupsAllowed = _method == IndexBuildMethod::kForeground
+                ? !descriptor->unique() || _ignoreUnique
+                : true;
             index.options.fromIndexBuilder = true;
 
             LOGV2(20384,
diff --git a/src/mongo/db/catalog/multi_index_block.h b/src/mongo/db/catalog/multi_index_block.h
index 211cc52373d..471c8ae861f 100644
--- a/src/mongo/db/catalog/multi_index_block.h
+++ b/src/mongo/db/catalog/multi_index_block.h
@@ -82,12 +82,9 @@ public:
     ~MultiIndexBlock();
 
     /**
-     * By default we enforce the 'unique' flag in specs when building an index by failing.
-     * If this is called before init(), we will ignore unique violations. This has no effect if
-     * no specs are unique.
-     *
-     * If this is called, any 'dupRecords' set passed to dumpInsertsFromBulk() will never be
-     * filled.
+     * When this is called:
+     * For hybrid index builds, the index interceptor will not track duplicates.
+     * For foreground index builds, the uniqueness constraint will be relaxed.
      */
     void ignoreUniqueConstraint();