Crash for copilot code block

[mjbvz]

🔎 Search Terms

• Copilot

🕗 Version & Regression Information

5.7.0-dev.20240927, not a regression

⏯ Playground Link

No response

💻 Code

Using copilot in VS Code:

1. Add this selection to panel chat https://github.com/microsoft/vscode/blob/d085816005ae61fc8f39b3720b3ec4594b35ecd0/src/vs/base/common/async.ts#L1145-L1278.
2. Have this be your current selection https://github.com/microsoft/vscode/blob/d085816005ae61fc8f39b3720b3ec4594b35ecd0/src/vs/base/test/common/async.test.ts#L1523-L1554
3. As @workspace /tests The last work call has a delay of 51 ms, but I already waited out the throttle delay why is this and how do I fix it.
4. 🐛 The TS Server crashes

🙁 Actual behavior

As the result is streaming back, we get a crash:

Err 55338 [09:24:42.710] Exception on executing command {
  "seq": 18117,
  "type": "request",
  "command": "updateOpen",
  "arguments": {
    "changedFiles": [
      {
        "fileName": "^/vscode-chat-code-block/ts-nul-authority/Users/matb/projects/vscode/src/vs/base/test/common/async.test.ts",
        "textChanges": [
          {
            "newText": "",
            "start": {
              "line": 1503,
              "offset": 1
            },
            "end": {
              "line": 1503,
              "offset": 42
            }
          }
        ]
      }
    ],
    "closedFiles": [],
    "openFiles": []
  }
}:

    Cannot read properties of undefined (reading 'charCount')

    TypeError: Cannot read properties of undefined (reading 'charCount')
        at _LineNode.walk (/Users/matb/projects/vscode/node_modules/typescript/lib/typescript.js:194903:30)
        at _LineIndex.edit (/Users/matb/projects/vscode/node_modules/typescript/lib/typescript.js:194803:17)
        at _ScriptVersionCache._getSnapshot (/Users/matb/projects/vscode/node_modules/typescript/lib/typescript.js:194609:31)
        at _ScriptVersionCache.lineOffsetToPosition (/Users/matb/projects/vscode/node_modules/typescript/lib/typescript.js:194628:17)
        at TextStorage.lineOffsetToPosition (/Users/matb/projects/vscode/node_modules/typescript/lib/typescript.js:184011:22)
        at ScriptInfo.lineOffsetToPosition (/Users/matb/projects/vscode/node_modules/typescript/lib/typescript.js:184319:29)
        at /Users/matb/projects/vscode/node_modules/typescript/lib/typescript.js:191473:40
        at mapDefinedIterator (/Users/matb/projects/vscode/node_modules/typescript/lib/typescript.js:2602:19)
        at mapDefinedIterator.next (<anonymous>)
        at _ProjectService.applyChangesToFile (/Users/matb/projects/vscode/node_modules/typescript/lib/typescript.js:190256:16)

The crash seems to happen during response streaming. During this, code blocks may be updated multiple times and the code in them may not be complete

🙂 Expected behavior

No crash

Additional information about the issue

No response

[sandersn]

This doesn't repro for me on VS Code 1.94, with Typescript built from main and Copilot Chat 0.21.2 with GPT 4o as the model. However, the first response "matched public code so it was blocked". The second response succeeded and didn't crash. o1-preview blocked both a first and second response, but not before streaming considerable amounts of code, also without crashing.

1. What versions of VS Code and Copilot Chat are you using?
2. What model did you use?
3. Do you have public code blocking disabled?

[sandersn]

Looking at the code, it can definitely crash if the children array of the LineNode is empty, which it is upon construction. The crashing line is
let childCharCount = this.children[childIndex].charCount() and childIndex starts at 0.

[mjbvz]

@sandersn I can't reproduce this consistently. I suspect that during streaming of responses, the document ends up in some weird incomplete state that causes this. However even asking the same question again may not trigger this depending on how the code block is streamed to TS