1. Have Existing project that uses fragments 2. Enable compose in build.gradle via

kotlinOptions {
        jvmTarget = '1.8'
        useIR = true
    }
    buildFeatures {
        compose true
        viewBinding true
    }
    composeOptions {
        kotlinCompilerVersion '1.4.20'
        kotlinCompilerExtensionVersion '1.0.0-alpha08'
    }

...

implementation "androidx.compose.runtime:runtime:1.0.0-alpha08"

3. Everything works fine 4. Add

implementation "androidx.compose.ui:ui:1.0.0-alpha08"

5. Every fragment in my app now has a red line on the class name (but still seems to build fine). Hovering over the error says "Class 'MyFragment' is not abstract and does not implement abstract base class member public abstract fun <I : Any!, O : Any!> prepareCall" Ideas?

Try upgrading to latest androidx fragment lib, I think this is due to new on activity result api

@sashjakk that was it. Thank you! I upgraded from the stable version I was at to 1.3.0-beta02 and it went away. phew