i18n select-ICU generates two units in xlf

I’m submitting a…

[ ] Regression (a behavior that used to work and stopped working in a new release)
[x] Bug report  
[ ] Performance issue
[ ] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead see https://github.com/angular/angular/blob/master/CONTRIBUTING.md#question
[ ] Other... Please describe:

Current behavior

ng xi18n creates two units for select-icu expression. Given html template:

              <span i18n="@@testLabel">
                {variable, select, aLabel {Label for A}}
              </span>

ng xi18n --i18n-format=xlf creates:

      <trans-unit id="testLabel" datatype="html">
        <source>
                <x id="ICU" equiv-text="{variable, select, aLabel {...}}"/>
              </source>
        <context-group purpose="location">
          <context context-type="sourcefile">app/shared/statistics/statistics.component.html</context>
          <context context-type="linenumber">23</context>
        </context-group>
      </trans-unit>
      <trans-unit id="b4645e675b21d80d80ff7669e6c6ac8a84bab9cd" datatype="html">
        <source>{VAR_SELECT, select, aLabel {Label for A} }</source>
        <context-group purpose="location">
          <context context-type="sourcefile">app/shared/statistics/statistics.component.html</context>
          <context context-type="linenumber">24</context>
        </context-group>
      </trans-unit>

also ng xi18n --i18n-format=xlf2 creates:

    <unit id="testLabel">
      <notes>
        <note category="location">app/shared/statistics/statistics.component.html:23,25</note>
      </notes>
      <segment>
        <source>
                <ph id="0" equiv="ICU" disp="{variable, select, aLabel {...}}"/>
              </source>
      </segment>
    </unit>
    <unit id="5433920347450028630">
      <notes>
        <note category="location">app/shared/statistics/statistics.component.html:24</note>
      </notes>
      <segment>
        <source>{VAR_SELECT, select, aLabel {Label for A} }</source>
      </segment>
    </unit>

First unit has correct id but sourse doesnt contain test to translate and (i think) is useless. Second unit has correct text, but id is generated.

Expected behavior

ng xi18n would create only one unit with correct id and source containing text to translate. like:

    <unit id="testLabel">
      <notes>
        <note category="location">app/shared/statistics/statistics.component.html:24</note>
      </notes>
      <segment>
        <source>{VAR_SELECT, select, aLabel {Label for A} }</source>
      </segment>
    </unit>

Minimal reproduction of the problem with instructions

What is the motivation / use case for changing the behavior?

First unit doesn’t contain text to translate, therefore it leads to confusion for translator.

Environment

ng -v

Angular CLI: 6.1.5
Node: 10.5.0
OS: win32 x64
Angular: 6.1.6

Angular version: 6.1.6


Browser:
- [ ] Chrome (desktop) version XX
- [ ] Chrome (Android) version XX
- [ ] Chrome (iOS) version XX
- [ ] Firefox version XX
- [ ] Safari (desktop) version XX
- [ ] Safari (iOS) version XX
- [ ] IE version XX
- [ ] Edge version XX
 
For Tooling issues:
- Node version: XX  
- Platform:  

Others:

[ocombe]

It’s because the compiler will extract the ICU expression separately. With ivy we will have a new approach where the ICU expression stays in the main extracted message

[AndrewKushnir]

FYI, closing this ticket as a duplicate of #39551.