I manually tested on Korean, Japanese, and Chinese IME, and found that only when using Korean IME, the CEditSessionUpdateCompositionString::_MakeInterimString function is called. (so far as I have checked)

Meanwhile, in Korean, the maximum number of interim character is 1, so the values of lStartResult and lEndResult are always 0.
So I changed code to not throw an exception when lEndResult value is 0.

However, I don't know the background of this code being written this way, so I'm not sure if my changes won't cause problems when typing in Japanese and Chinese.

@miniksa @leonMSFT Could you help me with this?

@MycroftKang, thank you for taking a look at this. I really appreciate it. I'm out of the office, though, until January 4th. My plan is to dig through the code history then and make sure that this shouldn't cause a problem. Thank you in advance for your patience!

@msftbot make sure @miniksa signs off on this

Hello @zadjii-msft!

Because you've given me some instructions on how to help merge this pull request, I'll be modifying my merge approach. Here's how I understand your requirements for merging this pull request:

• I'll only merge this pull request if it's approved by @miniksa

If this doesn't seem right to you, you can tell me to cancel these instructions and use the auto-merge policy that has been configured for this repository. Try telling me "forget everything I just told you".

OK. I did the history search. It looks like it was always rejecting anything that wasn't 1 for this particular check back through the v1 conhost. However, the v1 conhost also had a bit of divergence for Chinese, Japanese, and Korean right up at the top that went down 4 different mechanisms that I had unified way back in something like 2015 because they were 95% the same. It could be that I made this mistake in the unification of the interfaces but that code is a bit harder to analyze.

However, on looking at how it's used and operates, I'm fine with it just switching to not throwing the error since it appears to resolve Korean and doesn't appear to immediately impact Chinese or Japanese. If something comes up as fall out later, I think we can further work it out at that time.

Automerge off. @DHowett is going to check this against UNIVERSAL WUBI before commit.

Woops. He'll check it after the fact.

Validated. Thanks again for the fix.

@miniksa @DHowett Can you tell me when this PR with the bug fix related to Korean IME will be officially released? I'm currently using Windows 10 21H1, but found this bug still exists... 😕

This turned into OS PR !5568527, which made it to co_release in February, so I believe this only made it to Windows 11 builds. Looks like 10.0.21313 or above, but I think that just means "Windows 11"