Clarification of the meaning of '?' in a request

[tromey]

We got a bug report against the gdb DAP implementation. You can see the thread here: https://sourceware.org/pipermail/gdb/2024-January/051056.html

The bug seems to be that the client in this case sends:

{"arguments": null, "command": "configurationDone", "seq": 2, "type":  "request"}

My question is -- is this valid? The configurationDone request does say:

interface ConfigurationDoneRequest extends Request {
  command: 'configurationDone';

  arguments?: ConfigurationDoneArguments;
}

However, the real meaning of the ? does not seem to be spelled out anywhere. Is null an allowable value here? I wrote the gdb adapter to assume that optional values would simply be omitted -- but it's no problem to change if null is valid.

I think it would be good to be explicit about this.

[connor4312]

No, this is not valid. The point of truth for DAP is its JSON schema. In JSON schema, null is not a valid replacement for optional object properties. You can test this in any JSON scheme validator by trying to validate {"foo":null} with a schema like.

{
    "$schema": "http://json-schema.org/draft-04/schema#",
    "type":"object",
    "properties": { "foo": { "type": "string" } }
}

(It is also not a valid replacement for optional object properties in TypeScript, which is how the interfaces are shown on the specification page)

This is a bug in the client.