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This gets a lot more frustrating the more error branches we might have and especially if one needs to add/remove result values. Hence I use this pattern to DRY it up:
Obviously it's a bit gross but it has some good things going:
it reads nice "return with error"
it centralizes adding that error prefix to where the function name itself is and adding any necessary dummy result values such as an empty struct or a possible nil pointer.
if you add/remove result values there's only one additional centralized error handling place to change them to
Problem
Ok finally we get to the problem..
unparam detects that the func stored in withErr the first param is always nil:
main.go:10:30: readDateFromFile$1 - result 0 (time.Time) is always nil
Warning
But only if there's a defer statement, see the repro case below..
Repro
Save as main.go:
package main
import (
"fmt""os""time"
)
funcreadDateFromFile() (time.Time, error) {
withErr:=func(errerror) (time.Time, error) {
return time.Time{}, fmt.Errorf("readDateFromFile: %w", err)
}
dateStr, err:=os.ReadFile("file-that-has-timestamp-as-content.txt")
iferr!=nil {
returnwithErr(err)
}
deferfunc() { /* curiously, this defer is needed for the lint to flag the above `withErr()` */ }()
date, err:=time.Parse(time.RFC3339, string(dateStr))
iferr!=nil {
returnwithErr(err)
}
returndate, nil
}
funcmain () {
_, _=readDateFromFile()
}
And runtime environment from Dockerfile:
FROM golang:1.23.1
RUN go install mvdan.cc/unparam@latest
WORKDIR /workdir
Then run it:
$ docker build -t repro .
$ docker run --rm -it -v "$(pwd):/workdir" repro
$ unparam main.gomain.go:10:30: readDateFromFile$1 - result 0 (time.Time) is always nil
Background
(exotic = I "invented" it myself, haven't seen it used in the wild.)
What the pattern is? Suppose I have a function that reads file content and parses it as timestamp:
This gets a lot more frustrating the more error branches we might have and especially if one needs to add/remove result values. Hence I use this pattern to DRY it up:
Obviously it's a bit gross but it has some good things going:
Problem
Ok finally we get to the problem..
unparam detects that the func stored in
withErrthe first param is always nil:Warning
But only if there's a defer statement, see the repro case below..
Repro
Save as
main.go:And runtime environment from
Dockerfile:Then run it: