Controlled TextInput doesn't work most of the time

[acoates-ms]

Fixes #7638.

JS was not providing the mostRecentEventCount back to native. So in TextInputShadowNode::SetText, this condition would never be true, m_mostRecentEventCount == m_nativeEventCount, so any updated text value coming from JS would always be ignored.

Microsoft Reviewers: Open in CodeFlow

[NickGerleman]

Wow this one is nasty...

Are we still actively investing in adding UI tests to RNTester examples?

[rectified95]

@NickGerleman Yes, it's still on my to-do list.

[rectified95]

@acoates-ms the m_mostRecentEventCount == m_nativeEventCount condition currently works for the live rewrite scenario in RNTester,

<TextInput
  onChangeText={text => {
    text = text.replace(/ /g, '_');
    this.setState({text});
  }}
  value={this.state.text}
/>

where m_mostRecentEventCount gets updated due to the setTextAndSelection command coming from JS. Can you check this still works after this change?

[acoates-ms]

@rectified95 yes that example seems to work with these changes.

[ghost]

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[NickGerleman]

@NickGerleman Yes, it's still on my to-do list.

I think test coverage will have to be a bit of a group effort. We just have too much untested code to do otherwise.

I think it would be valuable if we started adding coverage when fixing native control bugs. I think we're at the point where the framework should allow testing the sort of scenario this PR addresses without too much burden.

[NickGerleman]

OTOH there's definitely been times in the past where I felt like adding too scope (adding tests) would make a fix take too long for me to take on.

Maybe we can do something to reduce that initial barrier.