VS Code: How to access debug variables from within extension? - visual-studio-code

Question

I am writing an extension for visual studio code where I want to evaluate the current variables of a javascript debug session. These variables are normally shown when one have open the debug pane under the section VARIABLES. See the attached screenshot.
I want to get access to these variables when the user right clicks the editor, but I don't know how.
My current extension setting for this is like that: in the package.json I have registered a menu contribution along with a command:
"contributes": {
"menus": {
"editor/context": [{
"command": "extension.showVariables",
"group": "navigation"
}]
}
}
In my extension.ts I register the command like that:
export function activate(context: vscode.ExtensionContext) {
let disposable = vscode.commands.registerCommand('extension.showVariables', () => {
// TODO: let variables = vscode.debug.activeDebugSession.variables.toString();
vscode.window.showInformationMessage(variables);
});
}
I have tried to get them through vscode.debug.activeDebugSession but there is no API for variables here. I also tried to register an event handler for vscode.debug.onDidReceiveDebugSessionCustomEvent but I can't figure out where to search for the debug variables.
Is it even possible to access these variables in an vs extension or do I need to implement my own debugger?

Answer 1

I have managed to get access to the local variables although this is not a general solution - it may only work in a single threaded debugger. If you know any better way, please answer or comment.
Say, the debugger breaks in a method that has a local variable car.
To get the value of car, I am using the customRequest method on the active debug session:
const session = vscode.debug.activeDebugSession;
const response = await session.customRequest('evaluate', { expression: 'car', frameId: frameId });
const car = response.result;
To get the frameId, I use another call of customRequest:
const session = vscode.debug.activeDebugSession;
const response = await session.customRequest('stackTrace', { threadId: 1 })
const frameId = response.stackFrames[0].id;
To get a real car object (not a string representation) in my extension, I pass "JSON.stringify(car)" as expression in the evaluate customRequest. Then, I can use JSON.parse(response.result).
To get all scopes, stacks and variables, have a look at the
Debug Session API and the specification of the DebugProtocol.

Answer 2

You have to talk to the debug adapter using the debug adapter protocol directly using vscode.debug.activeDebugSession.customRequest(command: string, args?: any) (Ref)
This function receives 2 parameters: command and args. Check out this resource to find all possible values of those parameters. One example is the 'evaluate' command that Michael Hilus uses in his answer:
If you want to get the variables in a multi threaded debug session, you must do these requests in this order
Threads Request: Get the thread ids
StackTrace Request: Get the frame ids
Scopes Request: Get the variablesReference
Variables Request: Finally, get the variable names with their values. If a variable is an object you might want to use Variables Request again with the variablesReference of the variable with an object value.
PS: It's kind of hard to find what you want in the DAP specification, so here is a tip:
Go to the 'Types' section in the right menu and find what you want. For instance, Breakpoints.
Ctrl+F and search ': Breakpoint'
Take a look at all matches in the response section of each request.
In the case of variablesReference I had to search variablesReference: number to find it in the responses of Evaluate Request, Scope (type) and Variable (also type).