Go - Differens

Go extractor

The Go extractor maps tree-sitter Go CST nodes to canonical concepts. It detects structural changes at the package level: functions, methods, types, and interfaces.

Detected concepts

tree-sitter node type	Canonical concept
`function_declaration`	Function
`method_declaration`	Method
`type_declaration` (struct)	Struct
`type_declaration` (interface)	Interface
`import_declaration`	Import
`var_declaration` (top-level)	Variable
`const_declaration`	Constant
`type_declaration` (other)	Type alias

Example

Two versions of a Go package. The second version extracts a method into a new function:

// old.go
package users

type Store struct {
    db *sql.DB
}

func (s *Store) ValidateEmail(email string) error {
    if !strings.Contains(email, "@") {
        return errors.New("invalid email")
    }
    if len(email) > 254 {
        return errors.New("email too long")
    }
    return nil
}

// new.go
package users

type Store struct {
    db *sql.DB
}

func (s *Store) ValidateEmail(email string) error {
    return validateEmail(email)
}

func validateEmail(email string) error {
    if !strings.Contains(email, "@") {
        return errors.New("invalid email")
    }
    if len(email) > 254 {
        return errors.New("email too long")
    }
    return nil
}

Running differens old.go new.go:

  ~ changed block from `if !strings.Contains(email, "@")…` to `return validateEmail(email)` in function `ValidateEmail`
  + added function `validateEmail`
2 modifications

Known limitations

Implicit interfaces (structural typing) are not tracked. An interface implemented by coincidence is not flagged as a relationship.
Package renames affect import paths; the cross-file correlator handles this when run across the full package.
Cgo blocks are treated as opaque; the extractor does not descend into C preambles.
Generic type parameters (Go 1.18+) are parsed structurally but type parameter renames may not be detected as renames (reported as structural changes).