SERVER-37058: Update with numeric field names inside an array can cause validation to fail

3 files changed, 75 insertions, 1 deletions

diff --git a/jstests/core/update_numeric_field_name.js b/jstests/core/update_numeric_field_name.js
new file mode 100644
index 00000000000..bc165a7ca78
--- /dev/null
+++ b/jstests/core/update_numeric_field_name.js
@@ -0,0 +1,29 @@
+// Test that update operations correctly fail if they violate the "ambiguous field name in array"
+// constraint for indexes. This is designed to reproduce SERVER-37058.
+(function() {
+    "use strict";
+
+    const coll = db.coll;
+    coll.drop();
+
+    assert.writeOK(coll.insert({_id: 0, 'a': [{}]}));
+    assert.commandWorked(coll.createIndex({'a.0.c': 1}));
+
+    // Attempt to insert a field name '0'. The first '0' refers to the first element of the array
+    // 'a'.
+    assert.writeErrorWithCode(coll.update({_id: 0}, {$set: {'a.0.0': 1}}), 16746);
+
+    // Verify that the indexes were not affected.
+    let res = assert.commandWorked(coll.validate(true));
+    assert(res.valid, tojson(res));
+
+    assert.writeErrorWithCode(coll.update({_id: 0}, {$set: {'a.0.0.b': 1}}), 16746);
+    res = assert.commandWorked(coll.validate(true));
+    assert(res.valid, tojson(res));
+
+    // An update which does not violate the ambiguous field name in array constraint should succeed.
+    assert.writeOK(coll.update({_id: 0}, {$set: {'a.1.b.0.0': 1}}));
+
+    res = assert.commandWorked(coll.validate(true));
+    assert(res.valid, tojson(res));
+})();
diff --git a/src/mongo/db/update_index_data.cpp b/src/mongo/db/update_index_data.cpp
index 2b1144d40a3..ade76f0c50d 100644
--- a/src/mongo/db/update_index_data.cpp
+++ b/src/mongo/db/update_index_data.cpp
@@ -149,12 +149,35 @@ bool getCanonicalIndexField(StringData fullName, string* out) {
             while (j + 1 < fullName.size() && isdigit(fullName[j + 1]))
                 j++;
 
-            if (j + 1 == fullName.size() || fullName[j + 1] == '.') {
+            if (j + 1 == fullName.size()) {
                 // only digits found, skip forward
                 i = j;
                 modified = true;
                 continue;
             }
+
+            // Check for consecutive digits separated by a period.
+            if (fullName[j + 1] == '.') {
+                // Peek ahead to see if the next set of characters are also numeric.
+                size_t k = j + 2;
+                while (k < fullName.size() && isdigit(fullName[k])) {
+                    k++;
+                }
+
+                // The second set of digits may end at the end of the path or a '.'.
+                if (k == fullName.size() || fullName[k] == '.') {
+                    // Found consecutive numerical path components. Since this implies a numeric
+                    // field name, return the prefix as the canonical index field. This is meant to
+                    // fix SERVER-37058.
+                    modified = true;
+                    break;
+                }
+
+                // Only one numerical path component, skip forward.
+                i = j;
+                modified = true;
+                continue;
+            }
         }
 
         buf << c;
diff --git a/src/mongo/db/update_index_data_test.cpp b/src/mongo/db/update_index_data_test.cpp
index 167cb632ab1..f01f495ed1f 100644
--- a/src/mongo/db/update_index_data_test.cpp
+++ b/src/mongo/db/update_index_data_test.cpp
@@ -126,4 +126,26 @@ TEST(UpdateIndexDataTest, getCanonicalIndexField1) {
 
     ASSERT_FALSE(getCanonicalIndexField("a.", &x));
 }
+
+TEST(UpdateIndexDataTest, CanonicalIndexFieldForConsecutiveDigits) {
+    std::string indexField;
+
+    ASSERT_TRUE(getCanonicalIndexField("a.0.0", &indexField));
+    ASSERT_EQ(indexField, "a");
+
+    ASSERT_TRUE(getCanonicalIndexField("a.55.01", &indexField));
+    ASSERT_EQ(indexField, "a");
+
+    ASSERT_TRUE(getCanonicalIndexField("a.0.0.b.1", &indexField));
+    ASSERT_EQ(indexField, "a");
+
+    ASSERT_TRUE(getCanonicalIndexField("a.0b.1", &indexField));
+    ASSERT_EQ(indexField, "a.0b");
+
+    ASSERT_TRUE(getCanonicalIndexField("a.0.b.1.2", &indexField));
+    ASSERT_EQ(indexField, "a.b");
+
+    ASSERT_TRUE(getCanonicalIndexField("a.0.11b", &indexField));
+    ASSERT_EQ(indexField, "a.11b");
+}
 }