Unknown statement syntax when running swiftc with new 5.7 syntax source file

[liuyang1520]

Describe the bug
Got unknown statement syntax when running swiftc with new 5.7 syntax source file, for parsing the syntax tree into JSON.

Steps To Reproduce
Steps to reproduce the behavior:

1. Create a new Swift app in the Xcode
2. Write a simple function with the new 5.7 if let syntax

    func testExample() throws {
        let app = XCUIApplication()
        app.launch()
        
        var name: String? = "Linda"
        
        if let name {
            print("Hello, \(name)!")
        }
    }

3. Run swiftc -frontend -emit-syntax test-swift-appUITests/test_swift_appUITests.swift
4. See the error:

test-swift-appUITests/test_swift_appUITests.swift:32:9: error: unknown statement syntax exists in the source
        if let name {
        ^

Expected behavior
Should get the correct JSON output without error.

Screenshots

Environment (please fill out the following information)

• OS: macOS 12.5.1
• Xcode Version/Tag/Branch: Version 14.1 (14B47b)
• Swiftc

swift-driver version: 1.62.15 Apple Swift version 5.7.1 (swiftlang-5.7.1.135.3 clang-1400.0.29.51)
Target: arm64-apple-macosx12.0

Additional context
Add any other context about the problem here.

[shreyanshp]

@AnthonyLatsis just a query, should this be raised on https://github.com/apple/swift-driver instead?

[AnthonyLatsis]

Nah, this looks like a SE-0345 plumbing oversight in libSwiftSyntax.

cc @calda

[shreyanshp]

Thank you so much for your response @AnthonyLatsis

Yeah we moved to latest syntax and now emit-syntax is breaking for us

@calda , @AnthonyLatsis let me know if you need any help or any more information to get this fixed please 🙇

[AnthonyLatsis]

@shreyanshp I am going to close this as not planned because it turns out the -emit-syntax flag is being removed (see #62145 (comment)). swift-syntax is validated against the legacy parser, so it won’t have this issue.