FileSystemWatcher reports incorrect sequence of events on MacOS

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#113,945 1 comment 2 reactions 0 assignees View on GitHub

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
45/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
csharp

Research direction

Start with FileSystemWatcher and dotnet-watch, then follow the reproduction details in dotnet/sdk issue 47912 to reproduce the macOS event ordering. Investigate why the Updated event arrives before Added, and verify completion when dotnet-watch reports Added, Updated, then Deleted consistently on macOS without changing the Windows or Linux behavior.

Written by the indexing model from the issue text.

Description

area-System.IO
Description

dotnet-watch uses FileSystemWatcher to watch for changes in source files.

In some scenarios on MacOS donet-watch receives the following sequence of events:

File Updated
File Added
File Deleted

i.e. the file was updated before it was added.

We don't see this behavior on Windows or Linux.

Reproduction Steps

See https://github.com/dotnet/sdk/issues/47912

Expected behavior

Following sequence of events reported by dotnet-watch:

dotnet watch ⌚ Added  '/xxx/Blazor9/wwwroot/app.css~'.
dotnet watch ⌚ Updated  '/xxx/Blazor9/wwwroot/app.css~'.
dotnet watch ⌚ Deleted '/xxx/Blazor9/wwwroot/app.css~'.
Actual behavior

Following sequence of events reported by dotnet-watch:

dotnet watch ⌚ Updated  '/xxx/Blazor9/wwwroot/app.css~'.
dotnet watch ⌚ Added  '/xxx/Blazor9/wwwroot/app.css~'.
dotnet watch ⌚ Deleted '/xxx/Blazor9/wwwroot/app.css~'.
Regression?

No response

Known Workarounds

No response

Configuration

No response

Other information

No response

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