How do I detect in a Theia extension whether a document has been modified and saved?

[tsiyona]

We wrote a Theia extension, and we would like to receive an event every time a document (java source file, for example) is modified and saved. Incremental changes before the actual Save are irrelevant for us.
How can we be notified about a code change?

[vince-fugnitto]

@tsiyona you can listen to the onDidSaveTextDocument event (documents are represented by underlying models):

theia/packages/monaco/src/browser/monaco-workspace.ts

Line 85 in 27e6ea7

readonly onDidSaveTextDocument = this.onDidSaveTextDocumentEmitter.event;

From the event you'll have access to the MonacoEditorModel from which you can have special handling for java files as example if that's your use-case.

[tsiyona]

Thank you. Just one more question.
I see that changes I make in the UI via File -> Settings -> Open Preferences are saved in the user preferences.
How do I change the workspace settings? Do I edit the settings file manually, or can it also be done via the UI?

[vince-fugnitto]

@tsiyona when opening the Preferences UI, the default scope is for User. Given that a user has the workspace opened, you can select the Workspace tab to update preferences for the workspace. This will create the .theia/settings.json file if necessary, and add your updated preference. You can also manually edit the settings.json file and it will give you schema, and autocompletion support.

[tsiyona]

Going back to onDidSaveTextDocument event. How can I know what line numbers were changed?

All in all, what I need to know about a modified file is:

1. File new content.
2. File full path.
3. File language (java, for now).
4. Fully qualified name of the class in the changed lines (for *.java files).

What I already have:

• The file content and full path indeed appear in MonacoEditorModel,
• The language I can detect by the file extension, though I see that MonacoEditorModel does include a _languageId member.

What I am still missing:

• The line numbers of the modified lines in the file.
  If I have the file path and the line numbers, I can find the fully qualified name.

[vince-fugnitto]

@tsiyona you'll need to take a look at the API and events to see what might give you the information you require.

• https://eclipse-theia.github.io/theia/docs/next/classes/monaco.monacoworkspace.html

In the case of getting the actual edit content, the save event is likely too late and does not have the information you need for your use-case. You can take a look at the onDidChangeTextDocument event which contains the contentChanges from which you can determine what line was updated (start and end).

Example:

this.monacoWorkspace.onDidChangeTextDocument(editor => {
    // For this example we only care about dirty (unsaved) changes in the document.
    if (editor.model.dirty) {
        const changes = editor.contentChanges;
        changes.forEach(change => {
            if ('range' in change) {
                const range = change.range;
                console.log(`line number: ${range.start.line + 1}`);
            }
        });
    }
});

[tsiyona]

Thank you @vince-fugnitto , in fact, I already implemented listening on onWillSaveTextDocument, however I suspect that I am getting line numbers also for edit changes that were reverted (Ctrl-Z). Apparently this is happening because I did not check the dirty flag.

constructor() {
	this.monacoWorkspace.onWillSaveTextDocument(this.onWillSaveTextDocument);
}

onWillSaveTextDocument = async (willSaveEvent: MonacoTextDocumentWillSaveEvent) => {
	const path = willSaveEvent.textDocument.uri;
	const contentChanges = new Set(willSaveEvent.textDocument.contentChanges.map(v => {return v.range.start.line}));
	const content = willSaveEvent.textDocument.getText();
	const fileExt = path.split('.').pop();

	// use extracted info...
}

Comparing it to your code snippet, I

• should have checked willSaveEvent.textDocument.dirty flag.
• should have also checked if ('range' in change)
• should have added 1 to the line number.

Anyway, I will try using onDidChangeTextDocument.

Thank you!!