1 files changed, 357 insertions, 0 deletions
diff --git a/src/cmd/go/internal/modget/query.go b/src/cmd/go/internal/modget/query.go
new file mode 100644
index 0000000..1a5a60f
--- /dev/null
+++ b/src/cmd/go/internal/modget/query.go
@@ -0,0 +1,357 @@
+// Copyright 2020 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 modget
+
+import (
+	"fmt"
+	"path/filepath"
+	"regexp"
+	"strings"
+	"sync"
+
+	"cmd/go/internal/base"
+	"cmd/go/internal/modload"
+	"cmd/go/internal/search"
+	"cmd/go/internal/str"
+
+	"golang.org/x/mod/module"
+)
+
+// A query describes a command-line argument and the modules and/or packages
+// to which that argument may resolve..
+type query struct {
+	// raw is the original argument, to be printed in error messages.
+	raw string
+
+	// rawVersion is the portion of raw corresponding to version, if any
+	rawVersion string
+
+	// pattern is the part of the argument before "@" (or the whole argument
+	// if there is no "@"), which may match either packages (preferred) or
+	// modules (if no matching packages).
+	//
+	// The pattern may also be "-u", for the synthetic query representing the -u
+	// (“upgrade”)flag.
+	pattern string
+
+	// patternIsLocal indicates whether pattern is restricted to match only paths
+	// local to the main module, such as absolute filesystem paths or paths
+	// beginning with './'.
+	//
+	// A local pattern must resolve to one or more packages in the main module.
+	patternIsLocal bool
+
+	// version is the part of the argument after "@", or an implied
+	// "upgrade" or "patch" if there is no "@". version specifies the
+	// module version to get.
+	version string
+
+	// matchWildcard, if non-nil, reports whether pattern, which must be a
+	// wildcard (with the substring "..."), matches the given package or module
+	// path.
+	matchWildcard func(path string) bool
+
+	// canMatchWildcard, if non-nil, reports whether the module with the given
+	// path could lexically contain a package matching pattern, which must be a
+	// wildcard.
+	canMatchWildcardInModule func(mPath string) bool
+
+	// conflict is the first query identified as incompatible with this one.
+	// conflict forces one or more of the modules matching this query to a
+	// version that does not match version.
+	conflict *query
+
+	// candidates is a list of sets of alternatives for a path that matches (or
+	// contains packages that match) the pattern. The query can be resolved by
+	// choosing exactly one alternative from each set in the list.
+	//
+	// A path-literal query results in only one set: the path itself, which
+	// may resolve to either a package path or a module path.
+	//
+	// A wildcard query results in one set for each matching module path, each
+	// module for which the matching version contains at least one matching
+	// package, and (if no other modules match) one candidate set for the pattern
+	// overall if no existing match is identified in the build list.
+	//
+	// A query for pattern "all" results in one set for each package transitively
+	// imported by the main module.
+	//
+	// The special query for the "-u" flag results in one set for each
+	// otherwise-unconstrained package that has available upgrades.
+	candidates   []pathSet
+	candidatesMu sync.Mutex
+
+	// pathSeen ensures that only one pathSet is added to the query per
+	// unique path.
+	pathSeen sync.Map
+
+	// resolved contains the set of modules whose versions have been determined by
+	// this query, in the order in which they were determined.
+	//
+	// The resolver examines the candidate sets for each query, resolving one
+	// module per candidate set in a way that attempts to avoid obvious conflicts
+	// between the versions resolved by different queries.
+	resolved []module.Version
+
+	// matchesPackages is true if the resolved modules provide at least one
+	// package mathcing q.pattern.
+	matchesPackages bool
+}
+
+// A pathSet describes the possible options for resolving a specific path
+// to a package and/or module.
+type pathSet struct {
+	// path is a package (if "all" or "-u" or a non-wildcard) or module (if
+	// wildcard) path that could be resolved by adding any of the modules in this
+	// set. For a wildcard pattern that so far matches no packages, the path is
+	// the wildcard pattern itself.
+	//
+	// Each path must occur only once in a query's candidate sets, and the path is
+	// added implicitly to each pathSet returned to pathOnce.
+	path string
+
+	// pkgMods is a set of zero or more modules, each of which contains the
+	// package with the indicated path. Due to the requirement that imports be
+	// unambiguous, only one such module can be in the build list, and all others
+	// must be excluded.
+	pkgMods []module.Version
+
+	// mod is either the zero Version, or a module that does not contain any
+	// packages matching the query but for which the module path itself
+	// matches the query pattern.
+	//
+	// We track this module separately from pkgMods because, all else equal, we
+	// prefer to match a query to a package rather than just a module. Also,
+	// unlike the modules in pkgMods, this module does not inherently exclude
+	// any other module in pkgMods.
+	mod module.Version
+
+	err error
+}
+
+// errSet returns a pathSet containing the given error.
+func errSet(err error) pathSet { return pathSet{err: err} }
+
+// newQuery returns a new query parsed from the raw argument,
+// which must be either path or path@version.
+func newQuery(raw string) (*query, error) {
+	pattern := raw
+	rawVers := ""
+	if i := strings.Index(raw, "@"); i >= 0 {
+		pattern, rawVers = raw[:i], raw[i+1:]
+		if strings.Contains(rawVers, "@") || rawVers == "" {
+			return nil, fmt.Errorf("invalid module version syntax %q", raw)
+		}
+	}
+
+	// If no version suffix is specified, assume @upgrade.
+	// If -u=patch was specified, assume @patch instead.
+	version := rawVers
+	if version == "" {
+		if getU.version == "" {
+			version = "upgrade"
+		} else {
+			version = getU.version
+		}
+	}
+
+	q := &query{
+		raw:            raw,
+		rawVersion:     rawVers,
+		pattern:        pattern,
+		patternIsLocal: filepath.IsAbs(pattern) || search.IsRelativePath(pattern),
+		version:        version,
+	}
+	if strings.Contains(q.pattern, "...") {
+		q.matchWildcard = search.MatchPattern(q.pattern)
+		q.canMatchWildcardInModule = search.TreeCanMatchPattern(q.pattern)
+	}
+	if err := q.validate(); err != nil {
+		return q, err
+	}
+	return q, nil
+}
+
+// validate reports a non-nil error if q is not sensible and well-formed.
+func (q *query) validate() error {
+	if q.patternIsLocal {
+		if q.rawVersion != "" {
+			return fmt.Errorf("can't request explicit version %q of path %q in main module", q.rawVersion, q.pattern)
+		}
+		return nil
+	}
+
+	if q.pattern == "all" {
+		// If there is no main module, "all" is not meaningful.
+		if !modload.HasModRoot() {
+			return fmt.Errorf(`cannot match "all": %v`, modload.ErrNoModRoot)
+		}
+		if !versionOkForMainModule(q.version) {
+			// TODO(bcmills): "all@none" seems like a totally reasonable way to
+			// request that we remove all module requirements, leaving only the main
+			// module and standard library. Perhaps we should implement that someday.
+			return &modload.QueryMatchesMainModuleError{
+				Pattern: q.pattern,
+				Query:   q.version,
+			}
+		}
+	}
+
+	if search.IsMetaPackage(q.pattern) && q.pattern != "all" {
+		if q.pattern != q.raw {
+			return fmt.Errorf("can't request explicit version of standard-library pattern %q", q.pattern)
+		}
+	}
+
+	return nil
+}
+
+// String returns the original argument from which q was parsed.
+func (q *query) String() string { return q.raw }
+
+// ResolvedString returns a string describing m as a resolved match for q.
+func (q *query) ResolvedString(m module.Version) string {
+	if m.Path != q.pattern {
+		if m.Version != q.version {
+			return fmt.Sprintf("%v (matching %s@%s)", m, q.pattern, q.version)
+		}
+		return fmt.Sprintf("%v (matching %v)", m, q)
+	}
+	if m.Version != q.version {
+		return fmt.Sprintf("%s@%s (%s)", q.pattern, q.version, m.Version)
+	}
+	return q.String()
+}
+
+// isWildcard reports whether q is a pattern that can match multiple paths.
+func (q *query) isWildcard() bool {
+	return q.matchWildcard != nil || (q.patternIsLocal && strings.Contains(q.pattern, "..."))
+}
+
+// matchesPath reports whether the given path matches q.pattern.
+func (q *query) matchesPath(path string) bool {
+	if q.matchWildcard != nil {
+		return q.matchWildcard(path)
+	}
+	return path == q.pattern
+}
+
+// canMatchInModule reports whether the given module path can potentially
+// contain q.pattern.
+func (q *query) canMatchInModule(mPath string) bool {
+	if q.canMatchWildcardInModule != nil {
+		return q.canMatchWildcardInModule(mPath)
+	}
+	return str.HasPathPrefix(q.pattern, mPath)
+}
+
+// pathOnce invokes f to generate the pathSet for the given path,
+// if one is still needed.
+//
+// Note that, unlike sync.Once, pathOnce does not guarantee that a concurrent
+// call to f for the given path has completed on return.
+//
+// pathOnce is safe for concurrent use by multiple goroutines, but note that
+// multiple concurrent calls will result in the sets being added in
+// nondeterministic order.
+func (q *query) pathOnce(path string, f func() pathSet) {
+	if _, dup := q.pathSeen.LoadOrStore(path, nil); dup {
+		return
+	}
+
+	cs := f()
+
+	if len(cs.pkgMods) > 0 || cs.mod != (module.Version{}) || cs.err != nil {
+		cs.path = path
+		q.candidatesMu.Lock()
+		q.candidates = append(q.candidates, cs)
+		q.candidatesMu.Unlock()
+	}
+}
+
+// reportError logs err concisely using base.Errorf.
+func reportError(q *query, err error) {
+	errStr := err.Error()
+
+	// If err already mentions all of the relevant parts of q, just log err to
+	// reduce stutter. Otherwise, log both q and err.
+	//
+	// TODO(bcmills): Use errors.As to unpack these errors instead of parsing
+	// strings with regular expressions.
+
+	patternRE := regexp.MustCompile("(?m)(?:[ \t(\"`]|^)" + regexp.QuoteMeta(q.pattern) + "(?:[ @:;)\"`]|$)")
+	if patternRE.MatchString(errStr) {
+		if q.rawVersion == "" {
+			base.Errorf("go get: %s", errStr)
+			return
+		}
+
+		versionRE := regexp.MustCompile("(?m)(?:[ @(\"`]|^)" + regexp.QuoteMeta(q.version) + "(?:[ :;)\"`]|$)")
+		if versionRE.MatchString(errStr) {
+			base.Errorf("go get: %s", errStr)
+			return
+		}
+	}
+
+	if qs := q.String(); qs != "" {
+		base.Errorf("go get %s: %s", qs, errStr)
+	} else {
+		base.Errorf("go get: %s", errStr)
+	}
+}
+
+func reportConflict(pq *query, m module.Version, conflict versionReason) {
+	if pq.conflict != nil {
+		// We've already reported a conflict for the proposed query.
+		// Don't report it again, even if it has other conflicts.
+		return
+	}
+	pq.conflict = conflict.reason
+
+	proposed := versionReason{
+		version: m.Version,
+		reason:  pq,
+	}
+	if pq.isWildcard() && !conflict.reason.isWildcard() {
+		// Prefer to report the specific path first and the wildcard second.
+		proposed, conflict = conflict, proposed
+	}
+	reportError(pq, &conflictError{
+		mPath:    m.Path,
+		proposed: proposed,
+		conflict: conflict,
+	})
+}
+
+type conflictError struct {
+	mPath    string
+	proposed versionReason
+	conflict versionReason
+}
+
+func (e *conflictError) Error() string {
+	argStr := func(q *query, v string) string {
+		if v != q.version {
+			return fmt.Sprintf("%s@%s (%s)", q.pattern, q.version, v)
+		}
+		return q.String()
+	}
+
+	pq := e.proposed.reason
+	rq := e.conflict.reason
+	modDetail := ""
+	if e.mPath != pq.pattern {
+		modDetail = fmt.Sprintf("for module %s, ", e.mPath)
+	}
+
+	return fmt.Sprintf("%s%s conflicts with %s",
+		modDetail,
+		argStr(pq, e.proposed.version),
+		argStr(rq, e.conflict.version))
+}
+
+func versionOkForMainModule(version string) bool {
+	return version == "upgrade" || version == "patch"
+}