Swift scripts in VSC update errors and warnings only after running

[F1248]

I was asked to move swiftlang/vscode-swift#1908 here.

Swift version

swiftlang-6.2.3.3.2

Platform

macOS Tahoe 26.1 (25B78)

Editor

Visual Studio Code 1.106.0 with Swift extension 2.12.0

Description

Starting with version 2.4.0, warnings and errors in Swift scripts (standalone files) only update after running the Swift: Run Swift Script command but not after the file is modified or saved. In version 2.2.0, they update immediately when the file is modified.

Steps to Reproduce

1. Create a new file Test.swift
2. Write some Swift code to the file that produces an error or warning, then save the file

let x: Int = "" // expected error: `Cannot convert value of type 'String' to specified type 'Int'`

3. The error only appears after running Swift: Run Swift Script
4. Replace "" with 0, then save the file again
5. The error only disappears after running Swift: Run Swift Script again