SERVER-115373 Reject $type queries on _id field with invalid types (array, regex, undefined) ,add _id check

[vlaualv]

Background & Impact

When users mistakenly query the _id field with invalid types (array, regex, undefined), such as:
db.collection.find({_id: {$type: 'array'}})
db.collection.find({_id: {$type: 4}})This can cause serious performance issues:

• The query planner cannot use the _id index effectively because it cannot determine valid index bounds for types that can never exist （array type）
• This may result in a collection scan (COLLSCAN) instead of an index scan (IXSCAN)
• On large collections, this leads to significant performance degradation and increased resource consumption

Since the _id field can never contain Array, RegEx, or Undefined types (enforced at write time by storage_validation.cpp), such queries are meaningless and will always return empty results while potentially causing full table scans.

Solution

Add parse-time validation to reject $type queries on the _id field when the requested type is invalid. This:

• Fails fast with a clear error message: "The '_id' field cannot be queried by type <typename>"
• Prevents users from accidentally running expensive queries
• Maintains consistency with write-time validation in storage_validation.cpp::storageValidIdField()

Changes

• Added validation in expression_parser.cpp::parseType() to reject invalid types (Array, RegEx, Undefined) for _id field
• Returns InvalidIdField error code
• Added comprehensive unit tests in expression_parser_test.cpp

Test Coverage

Error cases:

• {_id: {$type: 'array'}} / {_id: {$type: 4}}
• {_id: {$type: 'regex'}} / {_id: {$type: 11}}
• {_id: {$type: 'undefined'}} / {_id: {$type: 6}}
• {_id: {$type: ['array', 'objectId']}} (mixed valid/invalid)

Success cases:

• {_id: {$type: 'string'}} / {_id: {$type: 'objectId'}} / {_id: {$type: 'number'}}
• {a: {$type: 'array'}} (non-_id field)
• {_id.a: {$type: 'array'}} (nested path within _id)
• {a._id: {$type: 'array'}} (not top-level _id)

[vlaualv]

https://jira.mongodb.org/browse/SERVER-115373