switch {
		case strings.HasPrefix(rev, info.Short):
			return fmt.Errorf("revision is longer than canonical (expected %s)", info.Short)
		case strings.HasPrefix(info.Short, rev):
			return fmt.Errorf("revision is shorter than canonical (expected %s)", info.Short)
		default:
			return fmt.Errorf("does not match short name of revision (expected %s)", info.Short)
		}
	}

	t, err := module.PseudoVersionTime(version)

	Tags(ctx context.Context, prefix string) (*Tags, error)

	// Stat returns information about the revision rev.
	// A revision can be any identifier known to the underlying service:
	// commit hash, branch, tag, and so on.
	Stat(ctx context.Context, rev string) (*RevInfo, error)

	// Latest returns the latest revision on the default branch,
	// whatever that means in the underlying implementation.

				"prefix/v3/sub/dir/file.txt": 16,
			},
		},

		{
			repo:   gitrepo1,
			rev:    "aaaaaaaaab",
			subdir: "",
			err:    "unknown revision",
		},
		{
			repo:   hgrepo1,
			rev:    "aaaaaaaaab",
			subdir: "",
			err:    "unknown revision",
		},

		{
			repo:   vgotest1,
			rev:    "submod/v1.0.4",
			subdir: "submod",
			files: map[string]uint64{

		return Status{}, err
	}

	// Skip warning when working directory is set to an older revision.
	if bytes.HasPrefix(outb, []byte("working tree is out of date")) {
		i := bytes.IndexByte(outb, '\n')
		if i < 0 {
			i = len(outb)
		}
		outb = outb[:i]
	}
	uncommitted := len(outb) > 0

	return Status{
		Revision:    rev,
		CommitTime:  commitTime,
		Uncommitted: uncommitted,
	}, nil
}

			if strings.HasPrefix(h, prefix) {
				if hash != "" && hash != h {
					// Hash is an ambiguous hash prefix.
					// More information will not change that.
					return nil, fmt.Errorf("ambiguous revision %s", rev)
				}
				if ref == "" || ref > k { // Break ties deterministically when multiple refs point at same hash.
					ref = k
				}
				rev = h
				hash = h
			}
		}

To avoid ambiguity, Go programs cannot use relative import paths
within a work space.

Remote import paths

Certain import paths also
describe how to obtain the source code for the package using
a revision control system.

A few common code hosting sites have special syntax:

	Bitbucket (Git, Mercurial)

		import "bitbucket.org/user/project"
		import "bitbucket.org/user/project/sub/directory"

// Machine division instructions are slow, so we try to
// compute this division with a multiplication + a few
// other cheap instructions instead.
// (We assume here that c != 0, +/- 1, or +/- 2^i.  Those
// cases are easy to handle in different ways).

// Technique from https://gmplib.org/~tege/divcnst-pldi94.pdf

// First consider unsigned division.
// Our strategy is to precompute 1/c then do

and rsc.io/private/quux.

For fine-grained control over module download and validation, the GONOPROXY
and GONOSUMDB environment variables accept the same kind of glob list
and override GOPRIVATE for the specific decision of whether to use the proxy
and checksum database, respectively.

For example, if a company ran a module proxy serving private modules,
users would configure go using:

	GOPRIVATE=*.corp.example.com

func vendorPkg(vdir, pkg string) {
	src, realPath, _ := modload.Lookup("", false, pkg)
	if src == "" {
		base.Errorf("internal error: no pkg for %s\n", pkg)
		return
	}
	if realPath != pkg {
		// TODO(#26904): Revisit whether this behavior still makes sense.
		// This should actually be impossible today, because the import map is the
		// identity function for packages outside of the standard library.
		//

are dependencies on libraries beyond libc, external linking is likely
to work better. The compilation of a package records the relevant
information to support both linking modes, leaving the decision
to be made when linking the final binary.

Linking Directives

In either linking mode, package-specific directives must be passed
through to cmd/link. These are communicated by writing //go: directives in a