> ## Documentation Index
> Fetch the complete documentation index at: https://differens.ossl.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Go

> Semantic diffing for Go

## 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:

```go theme={null}
// 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
}
```

```go theme={null}
// 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).