Version 2.4.1 extension crash

[igorpupkinable]

Given the following in the Docker file:

RUN --mount=type=secret,id=registry-pat,env=REGISTRY_PAT \
    --mount=type=secret,id=registry-username,env=REGISTRY_USERNAME \
    echo -e "$YARN_REGISTRY:username=$REGISTRY_USERNAME\n$YARN_REGISTRY:_password=$(echo -n $REGISTRY_PAT | base64 --wrap=0)" > .npmrc

comment the last line during debugging session, i.e. # echo -e ...

Experience extension crash:

TypeError: Cannot read properties of undefined (reading 'getRange')
    at Cg.getHeredocs (/[REDACTED]/.vscode/extensions/ms-azuretools.vscode-containers-2.4.1/dist/dockerfile-language-server-nodejs/lib/server.js:56:96)
    at Cg.getHeredocs (/[REDACTED]/.vscode/extensions/ms-azuretools.vscode-containers-2.4.1/dist/dockerfile-language-server-nodejs/lib/server.js:76:5086)
    at Validator.getHeredocLines (/[REDACTED]/.vscode/extensions/ms-azuretools.vscode-containers-2.4.1/dist/dockerfile-language-server-nodejs/lib/server.js:91:6128)
    at Validator.validateInstruction (/[REDACTED]/.vscode/extensions/ms-azuretools.vscode-containers-2.4.1/dist/dockerfile-language-server-nodejs/lib/server.js:91:6764)
    at Validator.validate (/[REDACTED]/.vscode/extensions/ms-azuretools.vscode-containers-2.4.1/dist/dockerfile-language-server-nodejs/lib/server.js:91:5631)
    at Object.validate (/[REDACTED]/.vscode/extensions/ms-azuretools.vscode-containers-2.4.1/dist/dockerfile-language-server-nodejs/lib/server.js:91:45615)
    at t.validate (/[REDACTED]/.vscode/extensions/ms-azuretools.vscode-containers-2.4.1/dist/dockerfile-language-server-nodejs/lib/server.js:192:4569)
    at /[REDACTED]/.vscode/extensions/ms-azuretools.vscode-containers-2.4.1/dist/dockerfile-language-server-nodejs/lib/server.js:192:11460

Node.js v22.22.1
[Error - 14:21:46] Server process exited with code 1.
[Error - 14:21:46] The Dockerfile Language Server server crashed 5 times in the last 3 minutes. The server will not be restarted. See the output for more information.

I understand this is due to trailing backslash on the previous line, but ideally extension should be capable of recovering from such failures while developer is removing trailing slash.

At the moment the workaround is to remove trailing slash, then go to Extensions and disable/enable the extension.

[rcjsuen]

Hi, thanks for the bug report. I wasn't able to reproduce this. If you put this in your Dockerfile it crashes immediately?

RUN --mount=type=secret,id=registry-pat,env=REGISTRY_PAT \
    --mount=type=secret,id=registry-username,env=REGISTRY_USERNAME \
    # echo -e "$YARN_REGISTRY:username=$REGISTRY_USERNAME\n$YARN_REGISTRY:_password=$(echo -n $REGISTRY_PAT | base64 --wrap=0)" > .npmrc

[igorpupkinable]

Hi, thanks for the bug report. I wasn't able to reproduce this. If you put this in your Dockerfile it crashes immediately?

RUN --mount=type=secret,id=registry-pat,env=REGISTRY_PAT
--mount=type=secret,id=registry-username,env=REGISTRY_USERNAME
# echo -e "$YARN_REGISTRY:username=$REGISTRY_USERNAME\n$YARN_REGISTRY:_password=$(echo -n $REGISTRY_PAT | base64 --wrap=0)" > .npmrc

Scenario 1:

1. So I did save these 3 lines as test.dockerfile with both Container Tools and Docker extensions disabled.
2. Reopened the file.
3. Enabled Container Tools extension > OK.
4. Enabled Docker extension > Crash

Scenario 2:

1. Create new text file (Ctrl+N)
2. Select Dockerfile language mode
3. Paste these 3 lines > OK
4. Save file as test2.dockerfile > Crash

**VS Code**
name:      code
summary:   Code editing. Redefined.
publisher: Visual Studio Code (vscode✓)
store-url: https://snapcraft.io/code
...
snap-id:      Ht0aUHi7ofh9Fbwh6m7jUN2pAy6kzBiu
tracking:     latest/stable
refresh-date: 3 days ago
channels:
  latest/stable:    41dd792b 2026-04-08 (233) 379MB classic
...
installed:          41dd792b            (233) 379MB classic

**Extensions:**
Identifier ms-azuretools.vscode-containers
Version 2.4.1
Last Updated 3 days ago

Identifier ms-azuretools.vscode-docker
Version 2.0.0
Last Updated 3 days ago

[rcjsuen]

@bwateratmsft I can't reproduce this. I tried installing Microsoft's 2.0.0 Docker extension and couldn't reproduce it either... 🤔

[bwateratmsft]

I'll give it a shot this week sometime. Just got back from vacation so still catching up on things...

[igorpupkinable]

@rcjsuen thank you for trying.
@bwateratmsft just to be sure I did the following again:

1. Disable All Installed Extensions
2. Close and re-open VS Code
3. Save these 3 lines as test.dockerfile
4. Enabled Container Tools or Docker extension
5. Immediate crash with TypeError: Cannot read properties of undefined (reading 'getRange') as before.

I can wipe .vscode and reinstall snap to start from scratch but I am not sure it will make any difference.

[rcjsuen]

@igorpupkinable It still doesn't happen with me. We are probably missing something subtle.

1. Disable the extension.
2. Create a simple Dockerfile with FROM scratch. Close it.
3. Open your settings.json file.
4. Add "dockerfile-langserver.trace.server": "verbose" as an entry.
5. Open the simple Dockerfile created in 2.
6. Re-enable the extension.
7. Open Output pane. From the dropdown, find "Dockerfile Language Server".
8. Confirm that there is output.
9. Open the buggy Dockerfile.
10. Confirm that it crashes and then share the full logs.

Edit: Missed a step...

[igorpupkinable]

@rcjsuen please find full log attached.

Dockerfile Language Server.log

[rcjsuen]

Thanks, Igor. I am able to reproduce the issue now. The key thing was that there needed to be a newline after the 3 lines. I was only creating the Dockerfile with three suspected lines. Once I hit Enter and created another line it crashed for me. :)

[rcjsuen]

Created rcjsuen/dockerfile-ast#123 for this issue.

[igorpupkinable]

@rcjsuen sorry for the confusion. I have Files: Insert Final Newline enabled. Who would have thought :)))