libgo: update to Go 1.11

[official-gcc.git] / libgo / go / cmd / go / internal / modfetch / repo.go

// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package modfetch

import (
        "fmt"
        "os"
        "sort"
        "time"

        "cmd/go/internal/cfg"
        "cmd/go/internal/get"
        "cmd/go/internal/modfetch/codehost"
        "cmd/go/internal/par"
        "cmd/go/internal/semver"
        web "cmd/go/internal/web"
)

const traceRepo = false // trace all repo actions, for debugging

// A Repo represents a repository storing all versions of a single module.
// It must be safe for simultaneous use by multiple goroutines.
type Repo interface {
        // ModulePath returns the module path.
        ModulePath() string

        // Versions lists all known versions with the given prefix.
        // Pseudo-versions are not included.
        // Versions should be returned sorted in semver order
        // (implementations can use SortVersions).
        Versions(prefix string) (tags []string, err 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(rev string) (*RevInfo, error)

        // Latest returns the latest revision on the default branch,
        // whatever that means in the underlying source code repository.
        // It is only used when there are no tagged versions.
        Latest() (*RevInfo, error)

        // GoMod returns the go.mod file for the given version.
        GoMod(version string) (data []byte, err error)

        // Zip downloads a zip file for the given version
        // to a new file in a given temporary directory.
        // It returns the name of the new file.
        // The caller should remove the file when finished with it.
        Zip(version, tmpdir string) (tmpfile string, err error)
}

// A Rev describes a single revision in a module repository.
type RevInfo struct {
        Version string    // version string
        Time    time.Time // commit time

        // These fields are used for Stat of arbitrary rev,
        // but they are not recorded when talking about module versions.
        Name  string `json:"-"` // complete ID in underlying repository
        Short string `json:"-"` // shortened ID, for use in pseudo-version
}

// Re: module paths, import paths, repository roots, and lookups
//
// A module is a collection of Go packages stored in a file tree
// with a go.mod file at the root of the tree.
// The go.mod defines the module path, which is the import path
// corresponding to the root of the file tree.
// The import path of a directory within that file tree is the module path
// joined with the name of the subdirectory relative to the root.
//
// For example, the module with path rsc.io/qr corresponds to the
// file tree in the repository https://github.com/rsc/qr.
// That file tree has a go.mod that says "module rsc.io/qr".
// The package in the root directory has import path "rsc.io/qr".
// The package in the gf256 subdirectory has import path "rsc.io/qr/gf256".
// In this example, "rsc.io/qr" is both a module path and an import path.
// But "rsc.io/qr/gf256" is only an import path, not a module path:
// it names an importable package, but not a module.
//
// As a special case to incorporate code written before modules were
// introduced, if a path p resolves using the pre-module "go get" lookup
// to the root of a source code repository without a go.mod file,
// that repository is treated as if it had a go.mod in its root directory
// declaring module path p. (The go.mod is further considered to
// contain requirements corresponding to any legacy version
// tracking format such as Gopkg.lock, vendor/vendor.conf, and so on.)
//
// The presentation so far ignores the fact that a source code repository
// has many different versions of a file tree, and those versions may
// differ in whether a particular go.mod exists and what it contains.
// In fact there is a well-defined mapping only from a module path, version
// pair - often written path@version - to a particular file tree.
// For example rsc.io/qr@v0.1.0 depends on the "implicit go.mod at root of
// repository" rule, while rsc.io/qr@v0.2.0 has an explicit go.mod.
// Because the "go get" import paths rsc.io/qr and github.com/rsc/qr
// both redirect to the Git repository https://github.com/rsc/qr,
// github.com/rsc/qr@v0.1.0 is the same file tree as rsc.io/qr@v0.1.0
// but a different module (a different name). In contrast, since v0.2.0
// of that repository has an explicit go.mod that declares path rsc.io/qr,
// github.com/rsc/qr@v0.2.0 is an invalid module path, version pair.
// Before modules, import comments would have had the same effect.
//
// The set of import paths associated with a given module path is
// clearly not fixed: at the least, new directories with new import paths
// can always be added. But another potential operation is to split a
// subtree out of a module into its own module. If done carefully,
// this operation can be done while preserving compatibility for clients.
// For example, suppose that we want to split rsc.io/qr/gf256 into its
// own module, so that there would be two modules rsc.io/qr and rsc.io/qr/gf256.
// Then we can simultaneously issue rsc.io/qr v0.3.0 (dropping the gf256 subdirectory)
// and rsc.io/qr/gf256 v0.1.0, including in their respective go.mod
// cyclic requirements pointing at each other: rsc.io/qr v0.3.0 requires
// rsc.io/qr/gf256 v0.1.0 and vice versa. Then a build can be
// using an older rsc.io/qr module that includes the gf256 package, but if
// it adds a requirement on either the newer rsc.io/qr or the newer
// rsc.io/qr/gf256 module, it will automatically add the requirement
// on the complementary half, ensuring both that rsc.io/qr/gf256 is
// available for importing by the build and also that it is only defined
// by a single module. The gf256 package could move back into the
// original by another simultaneous release of rsc.io/qr v0.4.0 including
// the gf256 subdirectory and an rsc.io/qr/gf256 v0.2.0 with no code
// in its root directory, along with a new requirement cycle.
// The ability to shift module boundaries in this way is expected to be
// important in large-scale program refactorings, similar to the ones
// described in https://talks.golang.org/2016/refactor.article.
//
// The possibility of shifting module boundaries reemphasizes
// that you must know both the module path and its version
// to determine the set of packages provided directly by that module.
//
// On top of all this, it is possible for a single code repository
// to contain multiple modules, either in branches or subdirectories,
// as a limited kind of monorepo. For example rsc.io/qr/v2,
// the v2.x.x continuation of rsc.io/qr, is expected to be found
// in v2-tagged commits in https://github.com/rsc/qr, either
// in the root or in a v2 subdirectory, disambiguated by go.mod.
// Again the precise file tree corresponding to a module
// depends on which version we are considering.
//
// It is also possible for the underlying repository to change over time,
// without changing the module path. If I copy the github repo over
// to https://bitbucket.org/rsc/qr and update https://rsc.io/qr?go-get=1,
// then clients of all versions should start fetching from bitbucket
// instead of github. That is, in contrast to the exact file tree,
// the location of the source code repository associated with a module path
// does not depend on the module version. (This is by design, as the whole
// point of these redirects is to allow package authors to establish a stable
// name that can be updated as code moves from one service to another.)
//
// All of this is important background for the lookup APIs defined in this
// file.
//
// The Lookup function takes a module path and returns a Repo representing
// that module path. Lookup can do only a little with the path alone.
// It can check that the path is well-formed (see semver.CheckPath)
// and it can check that the path can be resolved to a target repository.
// To avoid version control access except when absolutely necessary,
// Lookup does not attempt to connect to the repository itself.
//
// The Import function takes an import path found in source code and
// determines which module to add to the requirement list to satisfy
// that import. It checks successive truncations of the import path
// to determine possible modules and stops when it finds a module
// in which the latest version satisfies the import path.
//
// The ImportRepoRev function is a variant of Import which is limited
// to code in a source code repository at a particular revision identifier
// (usually a commit hash or source code repository tag, not necessarily
// a module version).
// ImportRepoRev is used when converting legacy dependency requirements
// from older systems into go.mod files. Those older systems worked
// at either package or repository granularity, and most of the time they
// recorded commit hashes, not tagged versions.

var lookupCache par.Cache

// Lookup returns the module with the given module path.
// A successful return does not guarantee that the module
// has any defined versions.
func Lookup(path string) (Repo, error) {
        if traceRepo {
                defer logCall("Lookup(%q)", path)()
        }

        type cached struct {
                r   Repo
                err error
        }
        c := lookupCache.Do(path, func() interface{} {
                r, err := lookup(path)
                if err == nil {
                        if traceRepo {
                                r = newLoggingRepo(r)
                        }
                        r = newCachingRepo(r)
                }
                return cached{r, err}
        }).(cached)

        return c.r, c.err
}

// lookup returns the module with the given module path.
func lookup(path string) (r Repo, err error) {
        if cfg.BuildMod == "vendor" {
                return nil, fmt.Errorf("module lookup disabled by -mod=%s", cfg.BuildMod)
        }
        if proxyURL == "off" {
                return nil, fmt.Errorf("module lookup disabled by GOPROXY=%s", proxyURL)
        }
        if proxyURL != "" && proxyURL != "direct" {
                return lookupProxy(path)
        }

        security := web.Secure
        if get.Insecure {
                security = web.Insecure
        }
        rr, err := get.RepoRootForImportPath(path, get.PreferMod, security)
        if err != nil {
                // We don't know where to find code for a module with this path.
                return nil, err
        }

        if rr.VCS == "mod" {
                // Fetch module from proxy with base URL rr.Repo.
                return newProxyRepo(rr.Repo, path)
        }

        code, err := lookupCodeRepo(rr)
        if err != nil {
                return nil, err
        }
        return newCodeRepo(code, rr.Root, path)
}

func lookupCodeRepo(rr *get.RepoRoot) (codehost.Repo, error) {
        code, err := codehost.NewRepo(rr.VCS, rr.Repo)
        if err != nil {
                if _, ok := err.(*codehost.VCSError); ok {
                        return nil, err
                }
                return nil, fmt.Errorf("lookup %s: %v", rr.Root, err)
        }
        return code, nil
}

// ImportRepoRev returns the module and version to use to access
// the given import path loaded from the source code repository that
// the original "go get" would have used, at the specific repository revision
// (typically a commit hash, but possibly also a source control tag).
func ImportRepoRev(path, rev string) (Repo, *RevInfo, error) {
        if cfg.BuildMod == "vendor" || cfg.BuildMod == "readonly" {
                return nil, nil, fmt.Errorf("repo version lookup disabled by -mod=%s", cfg.BuildMod)
        }

        // Note: Because we are converting a code reference from a legacy
        // version control system, we ignore meta tags about modules
        // and use only direct source control entries (get.IgnoreMod).
        security := web.Secure
        if get.Insecure {
                security = web.Insecure
        }
        rr, err := get.RepoRootForImportPath(path, get.IgnoreMod, security)
        if err != nil {
                return nil, nil, err
        }

        code, err := lookupCodeRepo(rr)
        if err != nil {
                return nil, nil, err
        }

        revInfo, err := code.Stat(rev)
        if err != nil {
                return nil, nil, err
        }

        // TODO: Look in repo to find path, check for go.mod files.
        // For now we're just assuming rr.Root is the module path,
        // which is true in the absence of go.mod files.

        repo, err := newCodeRepo(code, rr.Root, rr.Root)
        if err != nil {
                return nil, nil, err
        }

        info, err := repo.(*codeRepo).convert(revInfo, "")
        if err != nil {
                return nil, nil, err
        }
        return repo, info, nil
}

func SortVersions(list []string) {
        sort.Slice(list, func(i, j int) bool {
                cmp := semver.Compare(list[i], list[j])
                if cmp != 0 {
                        return cmp < 0
                }
                return list[i] < list[j]
        })
}

// A loggingRepo is a wrapper around an underlying Repo
// that prints a log message at the start and end of each call.
// It can be inserted when debugging.
type loggingRepo struct {
        r Repo
}

func newLoggingRepo(r Repo) *loggingRepo {
        return &loggingRepo{r}
}

// logCall prints a log message using format and args and then
// also returns a function that will print the same message again,
// along with the elapsed time.
// Typical usage is:
//
//      defer logCall("hello %s", arg)()
//
// Note the final ().
func logCall(format string, args ...interface{}) func() {
        start := time.Now()
        fmt.Fprintf(os.Stderr, "+++ %s\n", fmt.Sprintf(format, args...))
        return func() {
                fmt.Fprintf(os.Stderr, "%.3fs %s\n", time.Since(start).Seconds(), fmt.Sprintf(format, args...))
        }
}

func (l *loggingRepo) ModulePath() string {
        return l.r.ModulePath()
}

func (l *loggingRepo) Versions(prefix string) (tags []string, err error) {
        defer logCall("Repo[%s]: Versions(%q)", l.r.ModulePath(), prefix)()
        return l.r.Versions(prefix)
}

func (l *loggingRepo) Stat(rev string) (*RevInfo, error) {
        defer logCall("Repo[%s]: Stat(%q)", l.r.ModulePath(), rev)()
        return l.r.Stat(rev)
}

func (l *loggingRepo) Latest() (*RevInfo, error) {
        defer logCall("Repo[%s]: Latest()", l.r.ModulePath())()
        return l.r.Latest()
}

func (l *loggingRepo) GoMod(version string) ([]byte, error) {
        defer logCall("Repo[%s]: GoMod(%q)", l.r.ModulePath(), version)()
        return l.r.GoMod(version)
}

func (l *loggingRepo) Zip(version, tmpdir string) (string, error) {
        defer logCall("Repo[%s]: Zip(%q, %q)", l.r.ModulePath(), version, tmpdir)()
        return l.r.Zip(version, tmpdir)
}