[Proposal] Adding Support for Custom GraphQL Types and Resolvers in Firebase Data Connect

[1amageek]

Description

This PR adds support for custom scalar types and resolvers in Firebase Data Connect. The implementation includes:

1. Schema configuration

• Added customTypes and resolvers fields to SchemaYaml interface
• Added validation for custom type definitions and resolver functions
• Updated schema YAML parser to support the new fields

2. Emulator Integration

• Added new endpoints to configure custom types and resolvers in the emulator
• Added validation layer for custom type and resolver configurations
• Implemented error handling for configuration failures

3. Known Limitation
   Currently, there's an issue with the emulator binary where it returns an error when using custom scalar types:

Does not support customized scalar type: [Type]

This is a limitation in the current emulator binary and will require updates to the emulator itself to fully support custom types.

Example Configuration:

schema:
  source: "./schema"
  datasource:
    postgresql:
      database: "mydb"
      cloudSql:
        instanceId: "instance-id"
  customTypes:
    Time:
      sqlType: "time"
      graphqlType: "String"
      serialize: "(time) => time.toISOString().split('T')[1]"
      parseValue: "(value) => new Date(`1970-01-01T${value}`)"
  resolvers:
    "Query.currentTime": "(parent, args, context) => new Date().toISOString()"

GraphQL Schema Usage:

scalar Time

type Sample @table(name: "Samples") {
  time: Time
}

Scenarios Tested

Note: The current PR only includes tests in validate.spec.ts. Additional testing, particularly for emulator integration, is recommended.

Sample Commands