Stale error decorations

[ulugbekna]

Type: Bug

Not sure how to repro but I get stale errors quite often.

The command "Update everything" doesn't fix it. 🤔

Extension version: 3.26.0
VS Code version: Code - Insiders 1.105.0-insider (588279f5b77b10bc41f3f8bb864350814e3823f4, 2025-09-26T05:05:03.410Z)
OS version: Darwin arm64 24.6.0
Modes:

System Info

Item	Value
CPUs	Apple M1 Pro (8 x 2400)
GPU Status	2d_canvas: enabled direct_rendering_display_compositor: disabled_off_ok gpu_compositing: enabled multiple_raster_threads: enabled_on opengl: enabled_on rasterization: enabled raw_draw: disabled_off_ok skia_graphite: enabled_on trees_in_viz: disabled_off video_decode: enabled video_encode: enabled webgl: enabled webgl2: enabled webgpu: enabled webnn: disabled_off
Load (avg)	16, 12, 14
Memory (System)	32.00GB (0.15GB free)
Process Argv	--log info --log github.vscode-pull-request-github=debug --log github.copilot-chat=trace --crash-reporter-id 3184aec0-4b31-4764-bfb0-162155975430 --log info --log github.vscode-pull-request-github=debug --log github.copilot-chat=trace --crash-reporter-id 3184aec0-4b31-4764-bfb0-162155975430
Screen Reader	no
VM	0%

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[usernamehw]

I think in the past this was usually a delay problem (When it's not zero like: "errorLens.delay": 1000,).

Unclear what can be done without the steps to reproduce.

[Crzyrndm]

This can be reliably reproduced with the Nordic nRF Connect Extension nordic-semiconductor.nrf-connect-extension-pack.
Any error that is highlighted after a Build remains if the file compiles with no warnings or errors

Valid

Stale

The underlining updates when a new build is initialised but the highlighting remains

LSP warnings/errors are correctly handled, it's only the diagnostics that are generated by the build action (which retain their underlining until a rebuild) that see this issue

[ulugbekna]

Reproduced with a throwaway provider; Nordic is not required.

The prototype uses a task problem matcher plus a separate same-host diagnostic on the same URI:

1. A task reports an error while the file is closed.
2. The file is opened and a local diagnostic is published.
3. A clean task clears the native task marker.
4. languages.getDiagnostics(uri) and an Error Lens-style refresh are inspected.

Results:

• VS Code 1.105.0: the removed task diagnostic remains in getDiagnostics() and is redrawn by a manual refresh.
• VS Code 1.133.0: the same stale diagnostic remains, so the bug is still present in current stable.
• Error Lens 3.28.0 on VS Code 1.133.0: after Error Lens: Update Everything, Error Lens: Copy Problem Message on the stale line still returns the removed task message.
• This reproduces with the default errorLens.delay: 0, so delay is not required.

This confirms the upstream diagnostics-mirror failure tracked by microsoft/vscode#256118. The narrow candidate fix is microsoft/vscode#290278, which forwards empty foreign-marker updates and removes cleared mirror entries.

There is no reliable Error Lens-only automatic fix using stable APIs: both diagnostic events and languages.getDiagnostics() come from the stale mirror, while task marker ownership/status is not exposed. Task-lifecycle heuristics could hide valid build warnings. Keeping this issue open until the VS Code fix ships and is verified against the prototype.