microsoft / microsoft/vscode-java-debug

Cannot check array[0].lengh variable in debugger

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Description

Hi everyone.

I have an issue when trying to debug a program that contains 2D array. If I try to put breakpoints checking for array[0].length, it fails with:

Breakpoint condition 'array[0].length > 0' error: Cannot evaluate because of compilation error(s): length cannot be resolved or is not a field.

After somme diggining, it seems that the debugger considers the array[0] object as a double:

Breakpoint condition 'array[0][0] == 0' error: Cannot evaluate because of compilation error(s): The type of the expression must be an array type but it resolved to double.

Do you have any idea on how to solve this?

Thanks

Nicolas

Environment
  • Operating System: Ubuntu 22.04.3 LTS
  • JDK version:
openjdk 19.0.2 2023-01-17
OpenJDK Runtime Environment (build 19.0.2+7-Ubuntu-0ubuntu322.04)
OpenJDK 64-Bit Server VM (build 19.0.2+7-Ubuntu-0ubuntu322.04, mixed mode, sharing)
  • Visual Studio Code version:
Version: 1.81.1
Commit: 6c3e3dba23e8fadc360aed75ce363ba185c49794
Date: 2023-08-09T22:18:39.991Z
Electron: 22.3.18
ElectronBuildId: 22689846
Chromium: 108.0.5359.215
Node.js: 16.17.1
V8: 10.8.168.25-electron.0
OS: Linux x64 6.2.0-26-generic snap
  • Java extension version: Java Extension Pack (v0.25.13)
  • Java Debugger extension version: v0.53.0
Steps To Reproduce
  1. Add in Watch array.length
  2. Add in Watch array[0].length
  3. Add coniditional breakpoint in line 15: array[0].length > 0
Current Result
Breakpoint condition 'array[0].length > 0' error: Cannot evaluate because of compilation error(s): length cannot be resolved or is not a field.

Screenshot from 2023-08-24 12-53-09

Expected Result

Debugger should stop on breakpoint without error

Files

Code source: TestDebugger.java.txt
Log file:
client.log.2023-08-24.txt

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by running the attached TestDebugger.java.txt reproduction in VS Code and inspect client.log.2023-08-24.txt alongside the debugger expression-evaluation behavior for array.length and array[0].length. Done means watch expressions and the conditional breakpoint involving array[0].length evaluate without errors.

Written by the indexing model from the issue text.

Assessment

Tech stack
java, typescript, vscode
Domain
devtools
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
45/100

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