goref

Goref

Goref is a Go package that analyzes a set of Go programs, starting from one or more main packages, and computes the inverse of the cross-package identifier usage graph. In other words, it indexes your Go code and tells you where an exported identifier is used. It can answer questions such as:

• Where is this type instantiated?
• Where is this function called?
• Where are all the references to this identifier?
• What types implement this interface?
• What interfaces are implemented by this type?

Usage

Goref, unlike guru relies in pre-indexing code to make searches faster. Guru is very convenient when developing in a modest-sized codebase, but calls like guru callers -scope ... are very slow and use a lot of memory. Instead, goref indexes code once and lets you search it quickly.

As a library

Goref can be used as a library, see its godoc for usage information.

With ElasticSearch

Goref can also be used to index code into ElasticSearch. This is currently a Work-In-Progress. The binary for this is at elasticsearch/main/main for lack of a good name until now. Usage is:

./main
  --version 42    # version of the code being indexed
  --include_tests # or --noinclude_tests to avoid indexing [XTests](https://godoc.org/golang.org/x/tools/go/loader#hdr-CONCEPTS_AND_TERMINOLOGY)
  --elasticsearch_url http://localhost:9200
  --elasticsearch_user user
  --elasticsearch_password hunter2
  github.com/korfuri/goref
  your/awesome/pacakge

This always imports dependencies recursively.

Code versioning

When code is indexed, the concept of "version" is critical. Since code is a living thing, indexes of code must be versioned. Since the code we index lives in many repositories, we can't use the repositories' history as a versioning tool.

So versions have to be provided to the index externally. It's recommended to keep a global, monotonically increasing counter for this. Every time you go get one or more packages, that counter should be incremented. The counter is an int64, so an elegant way to do this is to use the time.Time() at which you last sync'd your entire Go tree.

Note that the goref PackageGraph is not version-aware: it will only load one version of any given package. The version is purely meant for later indexing after the graph has been initialized and references have been created.

If you'll be doing operations to a completely immutable tree of packages (typically, your PackageGraph remains in memory and is never serialized to disk, and you don't go get or git pull while loading packages), you can just set the version to a fixed number and ignore that.

Goref is (obviously) not safe to use if you concurrently update the code while it's analyzing it.

Vendoring and goref

Vendored packages are treated as separate packages in goref. There is no support to deduplicate github.com/foo/bar and github.com/baz/qux/vendor/foo/bar. This follows the go tool's philosophy on that question.

Similarly, code mirrors such as gopkg.in are not considered in any specific way by goref. github.com/foo/bar and gopkg.in/foo/bar.v42 are treated as different packages even if they are identical.

Types of references

Currently, goref provides the following kinds of references, defined in reftype.go:

• Import represents an import of a package by a file. Since a package doesn't exist in a single position, there will be a Ref from the importing file to each file in the imported package.
• Call represents a call of a function by another function.
• Instantiation are generated for composite literals.
• Implementation represent a reference from a type implementing an interface to that interface.
• Extension represent a reference from interface A to interface B if interface A is a superset of interface B.
• Reference is the default enum value, used if goref can't figure out what kind of reference is used but detects that a package depends on an identifier in another package.