| go/build | Package build gathers information about Go packages. |
| go/internal/gccgoimporter | Package gccgoimporter implements Import for gccgo-generated object files. |
| go/internal/gcimporter | Package gcimporter implements Import for gc-generated object files. |
| go/internal/srcimporter | Package srcimporter implements importing directly from source files rather than installed packages. |
| go/token | Package token defines constants representing the lexical tokens of the Go programming language and basic operations on tokens (printing, predicates). |
| go/types | Package types declares the data types and implements the algorithms for type-checking of Go packages. |
| io | Package io provides basic interfaces to I/O primitives. |
| runtime | Package runtime contains operations that interact with Go's runtime system, such as functions to control goroutines. |