Set language of a text document in a VSCode extension

Since VSCode 1.28 (September 2018), it's also possible to set the language mode for a document after it has been created using languages.setTextDocumentLanguage():

Set (and change) the language that is associated with the given document.

Note that calling this function will trigger the onDidCloseTextDocument event followed by the onDidOpenTextDocument event.

Here's a simple example that opens a document containing {} and sets the language to JSON:

vscode.workspace.openTextDocument({content: "{}"}).then(document => {
    vscode.window.showTextDocument(document);
    vscode.languages.setTextDocumentLanguage(document, "json");
});

I found a solution by myself:

let options: Object = {
  content: string,
  language: "sql"
};

vscode.workspace.openTextDocument(options).then(doc => {
  vscode.window.showTextDocument(doc, vscode.ViewColumn.One);
}, err => {
  vscode.window.showErrorMessage(err);
});

A solution when using TextDocumentContentProvider seems not to be possible.

The commit with my change