I think, for this particular test case, we'd now need the cache file to exist, and write another test for the change made in this PR.

But if the cache file existed then it will throw an error? I pushed a test case to demonstrate this.

Yes, it generally should throw an error, but when we set unlink to throw EROFS, we're simulating the case where the cache file has been removed in the meantime (assuming we want to keep supporting that scenario, as being discussed in #19648 (comment)), in which case it shouldn't throw.

Ah, I see now. We should additionally make sure that the file has been removed if we want to test the code in catch.

I'm not sure if the try-catch is still necessary after this change. It looks like the situations the catch block was intended to address—when the cache file was missing on a writable file system or when it was missing on a read-only file system—are now both handled by the existsSync check.

The first version of this code (in cli-engine.js) was actually a simple if (!options.cache && fs.existsSync(cacheFile)) { fs.unlinkSync(cacheFile); } without try-catch, but has been changed to the try-catch version in #11546, I believe for the reasons explained in #11946 (comment) in a later PR (the original commit is gone, but it seems the comment is under code that was intending to remove try-catch). My understanding of the reasoning is that if it happens that the cache file disappears between two fs commands, this should not throw an error.

My understanding of the reasoning is that if it happens that the cache file disappears between two fs commands, this should not throw an error.

Yes, I also think that's what that comment is saying. I was actually considering that the existsSync check will skip nearly all cases where unlink would currently reject with an error, including, but not limited, to those tested in the try-catch block. So for example existsSync will return false if a user has no permission to read a directory, or if a network drive is not found on Windows, or if an I/O error (e.g. a hardware problem) occurs, etc. By contrast, unlink rejects with different error codes in all these cases. This means that by checking existsSync in advance as it's done in this PR, these cases will no longer produce an error. It seems redundant at this point to test for error codes ENOENT and EROFS specifically in the catch block, when other errors are supposed to be swallowed as well. If a concern is that the file system could change during fs calls then maybe we could repeat the existsSync in the catch block:

			try {
				if (existsSync(cacheFilePath)) {
					await fs.unlink(cacheFilePath);
				}
			} catch (error) {
				if (existsSync(cacheFilePath)) {
					throw error;
				}
			}

My opinion aligns with fasttime's entirely.