undeferred

Parameter Swap

undeferred is a go/analysis-based tool that flags suspicious early bindings of named results in a defer call.

It will flag references to a named return value that is passed to the invocation of a defer statement (line 8 below), and references in the body of a deferred function to variables that shadowed a named return outside that defer (line 15 below).

Example messages

Given the following source code example.go:

     1  package example
     2
     3  import (
     4      "errors"
     5  )
     6
     7  func foo() (err error) {
     8      defer errors.Join(err)
     9      return errors.New("foo")
    10  }
    11
    12  func bar() (err error) {
    13      if err := errors.New("bar"); err != nil {
    14          defer func() {
    15              err = nil
    16          }()
    17      }
    18      return
    19  }

undeferred will report the following:

$ undeferred ./...
.../example.go:8:20: defer captures current value of named result 'err'
.../example.go:15:4: defer references shadow of named result 'err'
.../example.go:13:5: shadows named result 'err' referenced in later defer

Usage

Run from source with go run github.com/mutility/undeferred@latest or install with go install github.com/mutility/undeferred@latest and run undeferred from GOPATH/bin.

You can configure behvior at the command line by passing the flags below, or in library use by setting fields on undefer.Analyzer().

Bug reports and feature contributions

undeferred is developed in spare time, so while bug reports and feature contributions are welcomed, it may take a while for them to be reviewed. If possible, try to find a minimal reproduction before reporting a bug. Bugs that are difficult or impossible to reproduce will likely be closed.

All bug fixes will include tests to help ensure no regression; correspondingly all contributions should include such tests.

Mutility Analyzers

undeferred is part of mutility-analyzers.