"File name too long" error occurs when diagnostic reports are created for factories with a long enough package + name combo

[JoelWilcox]

Description

This error specifically happens when the reports destination has been set and a report is attempted to be created for a provider factory where "provider-factory-$factoryFqName" exceeds the file name length. We run into this in instances where we've generated a binding container from a custom-annotated inner class of another class, but it could also occur with a source file with sufficiently long package + class name combination.

Self-contained Reproducer

PR coming shortly with a test to cover this and incremental fix, but here's an example that causes the failure:

package com.squareup.feature.featureflags

interface FeatureFlag

object RealProductionLoremIpsumFunctionalityFeatureFlagWrapper {
  @ContributesFeatureFlag
  object AllowLoremIpsumFunctionalitySemiLongNameFeatureFlag : FeatureFlag
}

package anvil.register.featureflags.com.squareup.feature.featureflags

// In this example, this binding container would normally be Anvil- or KSP-generated code based on the above feature flag and a custom contribution annotation
@BindingContainer
@ContributesTo(scope = AppScope::class)
public object RealProductionLoremIpsumFunctionalityFeatureFlagWrapper_AllowLoremIpsumFunctionalitySemiLongNameFeatureFlag {
  @Provides
  @IntoSet
  public fun providesAllowLoremIpsumFunctionalitySemiLongNameFeatureFlag(): FeatureFlag = RealProductionLoremIpsumFunctionalityFeatureFlagWrapper.AllowLoremIpsumFunctionalitySemiLongNameFeatureFlag
}

Metro version

0.7.2

Context

No response