Version: 1.102.0
OS: Windows_NT x64 10.0.19045

Source: #245092 (comment)

Steps to Reproduce:

git clone https://github.com/n-gist/getDiagnostics-test.git

If need, install go-to-problem-1.0.0.vsix for testing vscode.languages.getDiagnostics() output, which logs to output channel named getDiagnostics() test, code:

// Ctrl+F8
const showCounters = () => {
	for (const d of vscode.languages.getDiagnostics()) {
		channel.appendLine(`${d[1].length}, ${d[0].toString()}`)
	}
}

// Shift+F8
const showContent = () => {
	for (const d of vscode.languages.getDiagnostics()) {
		channel.appendLine(`(${d[1].length}) ${d[0].toString()}:`)
		for (const e of d[1]) channel.appendLine(JSON.stringify(e))
		channel.appendLine('')
	}
}

1. Start tsc: watch task
2. Open file src/main.ts
3. getDiagnostics() outputs 6 entries for main.ts. Expected: 3

Note: entries coming from task differs from extension ones. Their range.start and range.end equals. Not sure if this is an issue, or thats just how problem matchers work, giving only one, starting position