is declared by more than one NgModule.
You can't declare a component in more than 1 module.
If both modules need it, you need to declare/export your component in a third
module and imports this one in abc & def.
@NgModule({
imports: [ MainModule ]
})
export class AbcModule { }
@NgModule({
imports: [ MainModule ]
})
export class DefModule { }
@NgModule({
declarations: [ CommonMod ],
exports: [ CommonMod ]
})
export class MainModule { }