undeferred

README

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().

Flag	Field	Meaning
-exact	ExactTypeOnly	Suppress reports of mismatched parameters of mismatching types
-gen	IncludeGeneratedFiles	Include reports from generated files

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.

Documentation

Overview

Package main hosts the undeferred analyzer undefer.Analyzer()