[analyzer] False positives for discarded_futures when passing future-returning function call as an argument

[RemcoSchrijver]

Issue encountered while using austerity package, when passing a future function as parameter it wrongfully marks it as an discared_future issue, an example using flutter is provided below. For background on the issue already raised with austerity see this issue.

Looking at the priorities file this should be marked as a p2 issue, as mentioned in the other thread this is fixed by ignoring the rule for this line. I also did not find any other issues on this fact.

An example of code generating a false positive would be:

Future<String> getValue() async {
  await Future.delayed(Duration(seconds: 3));
  return 'Woolha';
}

FutureBuilder<String>(
  future: getValue(),
  builder: (
    BuildContext context,
    AsyncSnapshot<String> snapshot,
    ) {
      print(snapshot.connectionState);
      if (snapshot.connectionState == ConnectionState.waiting) {
        return CircularProgressIndicator();
      } else if (snapshot.connectionState == ConnectionState.done) {
      if (snapshot.hasError) {
         return const Text('Error');
       } else if (snapshot.hasData) {
         return Text(snapshot.data);
       } else {
         return const Text('Empty data');
       }
     } else {
       return Text('State: ${snapshot.connectionState}');
     }
  },
)

[MelbourneDeveloper]

@RemcoSchrijver, this has been an issue for me as well. There are situations when you need to return a future in a non-async scenario, and this is one. It means that we have to ignore the linter in a lot of places.