IssueTracker

Same issue.

Try this:
Roll back to AS-C3.
Set gradle back to '...:3.6.0-alpha03'. (The issue is caused by this, I think.)
Clean project.


I'm sure an update will fix it.

Same issue.

Successfully downgraded projects to use AS3.6C3

RG

Same issue here, downgrading to AS3.6C3 works OK

New project does not produce this kind of error, will try to drill down to what dependency will break it.

Have drilled down and found that the error occures on

dependencies {
...
   implementation 'androidx.constraintlayout:constraintlayout:2.0.0-beta2'
...
}

tested with following alphas and betas

"alpha3": OK
"alpha4": Fail
"alpha5": Fail

"beta1": Fail
"beta2": Fail

This was a simple test, have not tested thoroughly with a more complex test yet.

-> Solution : Downgrade 'androidx.constraintlayout:constraintlayout:2.0.0-xxx' to 'androidx.constraintlayout:constraintlayout:2.0.0-alpha3'

RG

Great catch! rolling back to 'androidx.constraintlayout:constraintlayout:2.0.0-alpha3' enables to keep using 3.6.0-alpha04 android gradle plugin

Thank you for your feedback. Team may reach out for more feedback in reproducing or triaging this issue.

Unfortunately, alpha3 is also failing for me, see also https://issuetracker.google.com/issues/121395935
Alpha2 is working for me.

seems related to https://b.corp.google.com/issues/136107435

FWIW I can confirm reverting to alpha3 fixes the issue for me.  Going all the way back to a2 wasn't necessary.

I think this is related to the change in AAPT2 where it became stricter about defining attr resources in styleables. Before you could define a new attribute under a declare styleable without giving its format, and now you have to explicitly define it as its own resource (if I understood correctly). Ryan, can you confirm? Is there perhaps a way to relax this if there are a lot of libraries that are already depending on this 'lazy' way of defining attrs? (I will check with the constraint layout folks separately to fix it on their side)

This change in aapt2 was made because aapt(1) also required that one either explicitly defines the attribute separately (with or without a format) or one specifies the format on the attribute within the declare-styleable.
aapt2 did not require this at first and allowed for declare-styleable attributes defined without a format to create new attribute resources.

There is not a way to relax this currently with aapt2 but depending on how Gradle invokes aapt2, it may be possible to work around this issue by defining each missing attribute resource within the application resource directory.
<attr name="flow_horizontalSeparator" />
<attr name="flow_verticalSeparator" />
...

I don't really understand this comment

> but depending on how Gradle invokes aapt2

AGP defines how Gradle invokes the aapt2 tool.

@15 What Ryan is suggesting is that if we notice that there are attributes without definitions we can automatically add them during resource merging. While it would solve our problem short term, this wouldn't work long term as it wouldn't work in the namespaced world. The proper solution would be to fix the libraries (constraintlayout and possibly other libraries out there), but it might be difficult to track them all down.
As a temporary workaround you can add the missing attributes yourself to your values file, for example:
"error: resource attr/flow_verticalSeparator not found" -> add "<attr name="flow_verticalSeparator"/>" into src/main/res/values/attrs.xml

Confirmed this is an issue with constraint layout 2.2.0-alpha4. Either downgrade to an older version of the library or add these to your app's src/main/res/values/attrs.xml:
<resources>
        <attr name="motionProgress"/>
        <attr name="motionTarget"/>
        <attr name="layout_marginBottom"/>
        <attr name="motionPathRotate"/>
        <attr name="duration"/>
</resources>

John, could you take a look? I tried to look at the current sources on cs/ but I couldn't find this. These attributes appear in constraint layout 2.0.0-alpha4 (and alpha5) in AAR's res/values/values.xml.