Renderer freezes / "app not responding" when computing large diffs #32046

Description

Bug Report: Renderer freezes / "app not responding" when computing large diffs

Version: 1.17.4 (regression from 1.15.11)
OS: Windows (x64)
Elevated privileges: Yes (running as Administrator)

Description

After updating from v1.15.11 to v1.17.4, the app becomes unresponsive shortly after startup and shows the Electron "app is not responding" dialog. Relaunching does not help — the freeze occurs consistently.

Root Cause (from exported debug logs)

The renderer thread is blocking indefinitely inside execEditLength / LineDiff.diff when computing a file diff. The call stack from the unresponsive samples in window.log:

at execEditLength (main-whyaYE5k.js:42321)
at LineDiff.diffWithOptionsObj (main-whyaYE5k.js:42370)
at LineDiff.diff (main-whyaYE5k.js:42291)
at diffLines (main-whyaYE5k.js:42521)
at structuredPatch (main-whyaYE5k.js:42559)
at createTwoFilesPatch (main-whyaYE5k.js:42686)
at parseDiffFromFile (main-whyaYE5k.js:44313)
at fileDiffFromContent (session-Li0RE4sZ.js:6706)
at fileDiffFromPatch (session-Li0RE4sZ.js:6640)
at resolveFileDiff (session-Li0RE4sZ.js:6610)

The diff algorithm runs synchronously on the main renderer thread with no timeout or size guard. On large files this causes an O(n²) hang that never resolves, blocking the entire UI.

This appears to be a regression introduced in v1.17.4 — v1.15.11 did not exhibit this behavior, suggesting the diff rendering was made more eager/reactive in this release.

Aggravating factor

Running as Administrator gives OpenCode access to broader directories. The server initializes watchers for all previously opened workspaces simultaneously at startup, including a home directory (C:\Users\<user>). Any large file in those workspaces can trigger the diff computation immediately on load.

Steps to Reproduce

1. Update from v1.15.11 to v1.17.4
2. Have one or more large workspaces (or a home directory) registered as open locations
3. Launch the app — renderer becomes unresponsive within ~30 seconds
4. The "app is not responding" dialog appears; relaunching loops back to step 3

Expected Behavior

Diff computation should either:

• Run off the main thread (Web Worker / background process), or
• Have a file size threshold above which diff rendering is skipped or deferred, or
• Be lazy / on-demand rather than computed reactively on startup

Workaround

Removing large or broad workspaces (especially home directories) from the workspace list reduces the likelihood of triggering the freeze.

Logs

Debug log bundle exported via Export Logs from the unresponsive dialog. Key file: desktop/<timestamp>/window.log — contains 14 unresponsive samples all pointing to the diff call stack above.

Plugins

No response

OpenCode version

1.17.4

Steps to reproduce

No response

Screenshot and/or share link

opencode-debug-20260612T120657.zip

Operating System

No response

Terminal

No response