A linter that suggests interface types
Latest commit 588bd99 Dec 15, 2016 @shurcooL shurcooL committed with README: Skip /vendor/ folders in usage example.
This is a better default usage example. Most people want to run the tool
on code they control, not vendored code that cannot be modified.

Updates #27.
Fixes #29.



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A linter that suggests interface types. In other words, it warns about the usage of types that are more specific than necessary.

go get -u github.com/mvdan/interfacer/cmd/interfacer


func ProcessInput(f *os.File) error {
        b, err := ioutil.ReadAll(f)
        if err != nil {
                return err
        return processBytes(b)
$ interfacer $(go list ./... | grep -v /vendor/)
foo.go:10:19: f can be io.Reader

Basic idea

This package relies on go/types for the heavy lifting: name resolution, constant folding and type inference. It also uses go/loader to resolve the packages specified by import paths.

It inspects the parameters of your functions to see if they fit an interface type that is less specific than the current type.

The example above illustrates this point. Overly specific interfaces also trigger a warning - if f were an io.ReadCloser, the same message would appear.

It suggests interface types defined both in std and in your packages.

False positives

To avoid false positives, it never does any suggestions on functions that may be implementing an interface method or a named function type.

It also skips parameters passed by value (excluding pointers and interfaces) on unexported functions, since that would introduce extra allocations where they are usually not worth the tradeoff.

Suppressing warnings

If a suggestion is technically correct but doesn't make sense, you can still suppress the warning by mentioning the type in the function name:

func ProcessInputFile(f *os.File) error {
    // use as an io.Reader