CALM Preview shows blank pane after upgrading to VSCode 1.116

[jimthompson5802]

Bug Report

Steps to Reproduce:

1. Upgrade VSCode IDE to version 1.116.
2. Open a CALM architecture file in the VSCode IDE.
3. Request a preview of the architecture (open CALM Preview pane).

Expected Result:

The CALM Preview pane renders a visualization of the architecture.

Actual Result:

The CALM Preview pane opens but displays no visualization — the pane is blank.

Environment:

• VSCode: 1.116
• calm-cli: 1.37.0
• CALM Tool Extension: 0.5.0
• OS: Darwin Mac 24.6.0 (Darwin Kernel Version 24.6.0)

Additional Context:

The issue appears to be a regression introduced by the VSCode 1.116 upgrade. The preview pane opens without error but renders nothing. No error messages or stack traces observed at time of filing.

With VSCode 1.115, CALM preview works as expected.

Falling back to VSCode 1.115 allows the CALM Tool functionality to work.

[jimthompson5802]

If it helps, here is the CALM Tool Output log from VSCode 1.116
calm-tool-log-preview-error.md

[jimthompson5802]

Additional debugging data. I'm attaching a screenshare video illustrating the issue and a series of actions I took to debug the problem that eventually led to displaying the CALM Preview. Series of actions:

1. Open CALM architecture file
2. Issue Command CALM: Open Preview
3. Issue Command Preferences: Configure Runtime Arguments
4. Close the Editor pane that covered the CALM Preview area for configuring runtime arguments

At this point the CALM Preview Pane which was previously blank now display the architecture visualization.

Current hypothesis: It seems like the event to show the CALM Preview at the beginning is not recognized. However, when the editor pane that "overlaid" the CALM Preview is closed, the event to dislay the preview is recognized.

CALM-Preview-Issue-VSCode-1-116-Issue.mov

[jimthompson5802]

Noticed this in the Web Developer console

[jimthompson5802]

Uninstalled and reinstalled CALM Tool 0.5.0. No change in symptoms, initial CALM Preview pane is still blank.

FWIW...there are other ways to get the CALM Preview Pane to eventually display. One is by moving the pane to a different Editor Group and the other is by covering and uncovering it with the Terminal. This video demonstrates these two methods.

CALM-Preview-Issue-VSCode-1-116-other-workarounds.mov

[jimthompson5802]

Yet Another Data Point

Create a simple VSCode extension in an attempt to recreate the symptoms. I was able to recreate the symptom of a "blank" webview panel when first created and then displays correctly if the panel is covered then uncovered. Then used a coding agent to find root cause and recommend a fix, which, at least in this case, addressed the symptom. Here is the test scenario:

---

• Installed version 0.0.4 of the extension
• Run command to display a webview panel, which is initially blank
• Cover and uncover the panel, at this point the webview panel display correctly

---

• Install version 0.0.5 of the extension, which contains coding agent recommendation for a fix, and restart extensions
• Run command to display webeview panel, which displays correctly.

Here is the video of the above test

CALM-Preview-Issue-VSCode-1-116-possible-fix.mov

Diagnose Blank First Paint In Hello World Webview Test Extension

Notes:

1. Cited module and line numbers are to contents in a separate test repo and not architecture-as-code repo.
2. Other than similarity of symptoms, I'm not clear if the solution recommended below applies to this issue.

Summary

The most likely root cause is in the panel lifecycle code, not the HTML. In showHelloWorld.ts, a newly created webview panel is already shown by createWebviewPanel, but the handler immediately calls panel.reveal(...) again at line 95. That extra reveal is unnecessary and is the best explanation for the “blank until another pane covers/uncovers it” behavior: it looks like a first-paint/repaint timing issue triggered by an extra visibility/layout transition.

The markup in renderHelloWorldWebview.ts is self-contained, uses only inline CSS, and both unit and integration tests pass, so this does not look like a CSP, resource-loading, or runtime exception problem. VS Code’s own webview guidance also shows reveal() for reusing an existing panel, not for a brand-new one: https://code.visualstudio.com/api/extension-guides/webview

Recommendation

• Change the command flow so reveal() is only called when reusing an existing panel.
• For a brand-new panel:
  • create it
  • set panel.title
  • set panel.webview.html
  • do not call reveal() Line 95 was commented out for the fix.
• Keep column selection logic, but simplify it if possible to the documented pattern based on the active editor column plus a fallback.
• Do not use retainContextWhenHidden as the primary fix; this symptom is happening on initial display, not hidden-state restoration.

Test Plan

• Manual: first invocation of Show Hello World should paint immediately with no need to overlap/uncover the editor.
• Manual: second invocation should reuse the same panel and still paint correctly.
• Manual: switch away and back to the webview tab to confirm it restores normally.
• Automated: add a unit test around the handler to assert reveal() is not called on first creation and is only called on reuse.

Assumptions

• This diagnosis assumes the repro is on desktop VS Code on macOS, matching the screenshot behavior.
• If the blank-first-paint issue still happens after removing the unconditional reveal(), the remaining root cause is likely an upstream VS Code/Electron repaint bug rather than this extension’s HTML. In that case, validate on the latest Stable vs Insiders build and capture Webview DevTools / window logs before filing upstream.

[LeighFinegold]

@jimthompson5802 - can take a look. Maybe being blind, but did you attach the calm document you running it on?

[jimthompson5802]

@LeighFinegold If you're asking did I have a CALM JSON file open when I requested a Preview, the answer is "Yes.". See the video in this post: #2361 (comment)

[javaChip56]

I can confirm this same issue occurs on Windows VSCode 1.116 as well.

Somehow forcing the layout in my vscode settings.json allowed me to load the preview.

[LeighFinegold]

@jimthompson5802 - my ask was can you attach a known calm document that fails, but @javaChip56 I guess is saying that all files are failing since the upgrade to vscode 1.116

[jimthompson5802]

@LeighFinegold yes...CALM Tool Preview of any CALM architecture fails in VSCode 1.116 when the Preview Panel is first opened. However, if the "blank" panel is covered and uncovered or the panel moves from one Editor group to another, the visualizations appears. So under the cover, the generated content seems to be OK. It is just the initial rendering does not display the content.

Here are three that all fail:

• First Architecture from the Beginner Learning Tutorial: my-first-architecture.json

• Ecommerce Site from the Intermedidate Learning Tutorial: ecommerce-platform.json

• TraderX: trading-system.architecture.json

There is no "blank panel" issue with VSCode 1.115.