Adding upstream version 1.16.10.upstream/1.16.10upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1111 insertions, 0 deletions

diff --git a/src/cmd/go/internal/modload/query.go b/src/cmd/go/internal/modload/query.go
new file mode 100644
index 0000000..8affd17
--- /dev/null
+++ b/src/cmd/go/internal/modload/query.go
@@ -0,0 +1,1111 @@
+// 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 modload
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io/fs"
+	"os"
+	pathpkg "path"
+	"path/filepath"
+	"sort"
+	"strings"
+	"sync"
+	"time"
+
+	"cmd/go/internal/cfg"
+	"cmd/go/internal/imports"
+	"cmd/go/internal/modfetch"
+	"cmd/go/internal/search"
+	"cmd/go/internal/str"
+	"cmd/go/internal/trace"
+
+	"golang.org/x/mod/module"
+	"golang.org/x/mod/semver"
+)
+
+// Query looks up a revision of a given module given a version query string.
+// The module must be a complete module path.
+// The version must take one of the following forms:
+//
+// - the literal string "latest", denoting the latest available, allowed
+//   tagged version, with non-prereleases preferred over prereleases.
+//   If there are no tagged versions in the repo, latest returns the most
+//   recent commit.
+// - the literal string "upgrade", equivalent to "latest" except that if
+//   current is a newer version, current will be returned (see below).
+// - the literal string "patch", denoting the latest available tagged version
+//   with the same major and minor number as current (see below).
+// - v1, denoting the latest available tagged version v1.x.x.
+// - v1.2, denoting the latest available tagged version v1.2.x.
+// - v1.2.3, a semantic version string denoting that tagged version.
+// - <v1.2.3, <=v1.2.3, >v1.2.3, >=v1.2.3,
+//   denoting the version closest to the target and satisfying the given operator,
+//   with non-prereleases preferred over prereleases.
+// - a repository commit identifier or tag, denoting that commit.
+//
+// current denotes the currently-selected version of the module; it may be
+// "none" if no version is currently selected, or "" if the currently-selected
+// version is unknown or should not be considered. If query is
+// "upgrade" or "patch", current will be returned if it is a newer
+// semantic version or a chronologically later pseudo-version than the
+// version that would otherwise be chosen. This prevents accidental downgrades
+// from newer pre-release or development versions.
+//
+// The allowed function (which may be nil) is used to filter out unsuitable
+// versions (see AllowedFunc documentation for details). If the query refers to
+// a specific revision (for example, "master"; see IsRevisionQuery), and the
+// revision is disallowed by allowed, Query returns the error. If the query
+// does not refer to a specific revision (for example, "latest"), Query
+// acts as if versions disallowed by allowed do not exist.
+//
+// If path is the path of the main module and the query is "latest",
+// Query returns Target.Version as the version.
+func Query(ctx context.Context, path, query, current string, allowed AllowedFunc) (*modfetch.RevInfo, error) {
+	var info *modfetch.RevInfo
+	err := modfetch.TryProxies(func(proxy string) (err error) {
+		info, err = queryProxy(ctx, proxy, path, query, current, allowed)
+		return err
+	})
+	return info, err
+}
+
+// AllowedFunc is used by Query and other functions to filter out unsuitable
+// versions, for example, those listed in exclude directives in the main
+// module's go.mod file.
+//
+// An AllowedFunc returns an error equivalent to ErrDisallowed for an unsuitable
+// version. Any other error indicates the function was unable to determine
+// whether the version should be allowed, for example, the function was unable
+// to fetch or parse a go.mod file containing retractions. Typically, errors
+// other than ErrDisallowd may be ignored.
+type AllowedFunc func(context.Context, module.Version) error
+
+var errQueryDisabled error = queryDisabledError{}
+
+type queryDisabledError struct{}
+
+func (queryDisabledError) Error() string {
+	if cfg.BuildModReason == "" {
+		return fmt.Sprintf("cannot query module due to -mod=%s", cfg.BuildMod)
+	}
+	return fmt.Sprintf("cannot query module due to -mod=%s\n\t(%s)", cfg.BuildMod, cfg.BuildModReason)
+}
+
+func queryProxy(ctx context.Context, proxy, path, query, current string, allowed AllowedFunc) (*modfetch.RevInfo, error) {
+	ctx, span := trace.StartSpan(ctx, "modload.queryProxy "+path+" "+query)
+	defer span.Done()
+
+	if current != "" && current != "none" && !semver.IsValid(current) {
+		return nil, fmt.Errorf("invalid previous version %q", current)
+	}
+	if cfg.BuildMod == "vendor" {
+		return nil, errQueryDisabled
+	}
+	if allowed == nil {
+		allowed = func(context.Context, module.Version) error { return nil }
+	}
+
+	if path == Target.Path && (query == "upgrade" || query == "patch") {
+		if err := allowed(ctx, Target); err != nil {
+			return nil, fmt.Errorf("internal error: main module version is not allowed: %w", err)
+		}
+		return &modfetch.RevInfo{Version: Target.Version}, nil
+	}
+
+	if path == "std" || path == "cmd" {
+		return nil, fmt.Errorf("can't query specific version (%q) of standard-library module %q", query, path)
+	}
+
+	repo, err := lookupRepo(proxy, path)
+	if err != nil {
+		return nil, err
+	}
+
+	// Parse query to detect parse errors (and possibly handle query)
+	// before any network I/O.
+	qm, err := newQueryMatcher(path, query, current, allowed)
+	if (err == nil && qm.canStat) || err == errRevQuery {
+		// Direct lookup of a commit identifier or complete (non-prefix) semantic
+		// version.
+
+		// If the identifier is not a canonical semver tag — including if it's a
+		// semver tag with a +metadata suffix — then modfetch.Stat will populate
+		// info.Version with a suitable pseudo-version.
+		info, err := repo.Stat(query)
+		if err != nil {
+			queryErr := err
+			// The full query doesn't correspond to a tag. If it is a semantic version
+			// with a +metadata suffix, see if there is a tag without that suffix:
+			// semantic versioning defines them to be equivalent.
+			canonicalQuery := module.CanonicalVersion(query)
+			if canonicalQuery != "" && query != canonicalQuery {
+				info, err = repo.Stat(canonicalQuery)
+				if err != nil && !errors.Is(err, fs.ErrNotExist) {
+					return info, err
+				}
+			}
+			if err != nil {
+				return nil, queryErr
+			}
+		}
+		if err := allowed(ctx, module.Version{Path: path, Version: info.Version}); errors.Is(err, ErrDisallowed) {
+			return nil, err
+		}
+		return info, nil
+	} else if err != nil {
+		return nil, err
+	}
+
+	// Load versions and execute query.
+	versions, err := repo.Versions(qm.prefix)
+	if err != nil {
+		return nil, err
+	}
+	releases, prereleases, err := qm.filterVersions(ctx, versions)
+	if err != nil {
+		return nil, err
+	}
+
+	lookup := func(v string) (*modfetch.RevInfo, error) {
+		rev, err := repo.Stat(v)
+		if err != nil {
+			return nil, err
+		}
+
+		if (query == "upgrade" || query == "patch") && modfetch.IsPseudoVersion(current) && !rev.Time.IsZero() {
+			// Don't allow "upgrade" or "patch" to move from a pseudo-version
+			// to a chronologically older version or pseudo-version.
+			//
+			// If the current version is a pseudo-version from an untagged branch, it
+			// may be semantically lower than the "latest" release or the latest
+			// pseudo-version on the main branch. A user on such a version is unlikely
+			// to intend to “upgrade” to a version that already existed at that point
+			// in time.
+			//
+			// We do this only if the current version is a pseudo-version: if the
+			// version is tagged, the author of the dependency module has given us
+			// explicit information about their intended precedence of this version
+			// relative to other versions, and we shouldn't contradict that
+			// information. (For example, v1.0.1 might be a backport of a fix already
+			// incorporated into v1.1.0, in which case v1.0.1 would be chronologically
+			// newer but v1.1.0 is still an “upgrade”; or v1.0.2 might be a revert of
+			// an unsuccessful fix in v1.0.1, in which case the v1.0.2 commit may be
+			// older than the v1.0.1 commit despite the tag itself being newer.)
+			currentTime, err := modfetch.PseudoVersionTime(current)
+			if err == nil && rev.Time.Before(currentTime) {
+				if err := allowed(ctx, module.Version{Path: path, Version: current}); errors.Is(err, ErrDisallowed) {
+					return nil, err
+				}
+				return repo.Stat(current)
+			}
+		}
+
+		return rev, nil
+	}
+
+	if qm.preferLower {
+		if len(releases) > 0 {
+			return lookup(releases[0])
+		}
+		if len(prereleases) > 0 {
+			return lookup(prereleases[0])
+		}
+	} else {
+		if len(releases) > 0 {
+			return lookup(releases[len(releases)-1])
+		}
+		if len(prereleases) > 0 {
+			return lookup(prereleases[len(prereleases)-1])
+		}
+	}
+
+	if qm.mayUseLatest {
+		latest, err := repo.Latest()
+		if err == nil {
+			if qm.allowsVersion(ctx, latest.Version) {
+				return lookup(latest.Version)
+			}
+		} else if !errors.Is(err, fs.ErrNotExist) {
+			return nil, err
+		}
+	}
+
+	if (query == "upgrade" || query == "patch") && current != "" && current != "none" {
+		// "upgrade" and "patch" may stay on the current version if allowed.
+		if err := allowed(ctx, module.Version{Path: path, Version: current}); errors.Is(err, ErrDisallowed) {
+			return nil, err
+		}
+		return lookup(current)
+	}
+
+	return nil, &NoMatchingVersionError{query: query, current: current}
+}
+
+// IsRevisionQuery returns true if vers is a version query that may refer to
+// a particular version or revision in a repository like "v1.0.0", "master",
+// or "0123abcd". IsRevisionQuery returns false if vers is a query that
+// chooses from among available versions like "latest" or ">v1.0.0".
+func IsRevisionQuery(vers string) bool {
+	if vers == "latest" ||
+		vers == "upgrade" ||
+		vers == "patch" ||
+		strings.HasPrefix(vers, "<") ||
+		strings.HasPrefix(vers, ">") ||
+		(semver.IsValid(vers) && isSemverPrefix(vers)) {
+		return false
+	}
+	return true
+}
+
+// isSemverPrefix reports whether v is a semantic version prefix: v1 or v1.2 (not v1.2.3).
+// The caller is assumed to have checked that semver.IsValid(v) is true.
+func isSemverPrefix(v string) bool {
+	dots := 0
+	for i := 0; i < len(v); i++ {
+		switch v[i] {
+		case '-', '+':
+			return false
+		case '.':
+			dots++
+			if dots >= 2 {
+				return false
+			}
+		}
+	}
+	return true
+}
+
+type queryMatcher struct {
+	path               string
+	prefix             string
+	filter             func(version string) bool
+	allowed            AllowedFunc
+	canStat            bool // if true, the query can be resolved by repo.Stat
+	preferLower        bool // if true, choose the lowest matching version
+	mayUseLatest       bool
+	preferIncompatible bool
+}
+
+var errRevQuery = errors.New("query refers to a non-semver revision")
+
+// newQueryMatcher returns a new queryMatcher that matches the versions
+// specified by the given query on the module with the given path.
+//
+// If the query can only be resolved by statting a non-SemVer revision,
+// newQueryMatcher returns errRevQuery.
+func newQueryMatcher(path string, query, current string, allowed AllowedFunc) (*queryMatcher, error) {
+	badVersion := func(v string) (*queryMatcher, error) {
+		return nil, fmt.Errorf("invalid semantic version %q in range %q", v, query)
+	}
+
+	matchesMajor := func(v string) bool {
+		_, pathMajor, ok := module.SplitPathVersion(path)
+		if !ok {
+			return false
+		}
+		return module.CheckPathMajor(v, pathMajor) == nil
+	}
+
+	qm := &queryMatcher{
+		path:               path,
+		allowed:            allowed,
+		preferIncompatible: strings.HasSuffix(current, "+incompatible"),
+	}
+
+	switch {
+	case query == "latest":
+		qm.mayUseLatest = true
+
+	case query == "upgrade":
+		if current == "" || current == "none" {
+			qm.mayUseLatest = true
+		} else {
+			qm.mayUseLatest = modfetch.IsPseudoVersion(current)
+			qm.filter = func(mv string) bool { return semver.Compare(mv, current) >= 0 }
+		}
+
+	case query == "patch":
+		if current == "none" {
+			return nil, &NoPatchBaseError{path}
+		}
+		if current == "" {
+			qm.mayUseLatest = true
+		} else {
+			qm.mayUseLatest = modfetch.IsPseudoVersion(current)
+			qm.prefix = semver.MajorMinor(current) + "."
+			qm.filter = func(mv string) bool { return semver.Compare(mv, current) >= 0 }
+		}
+
+	case strings.HasPrefix(query, "<="):
+		v := query[len("<="):]
+		if !semver.IsValid(v) {
+			return badVersion(v)
+		}
+		if isSemverPrefix(v) {
+			// Refuse to say whether <=v1.2 allows v1.2.3 (remember, @v1.2 might mean v1.2.3).
+			return nil, fmt.Errorf("ambiguous semantic version %q in range %q", v, query)
+		}
+		qm.filter = func(mv string) bool { return semver.Compare(mv, v) <= 0 }
+		if !matchesMajor(v) {
+			qm.preferIncompatible = true
+		}
+
+	case strings.HasPrefix(query, "<"):
+		v := query[len("<"):]
+		if !semver.IsValid(v) {
+			return badVersion(v)
+		}
+		qm.filter = func(mv string) bool { return semver.Compare(mv, v) < 0 }
+		if !matchesMajor(v) {
+			qm.preferIncompatible = true
+		}
+
+	case strings.HasPrefix(query, ">="):
+		v := query[len(">="):]
+		if !semver.IsValid(v) {
+			return badVersion(v)
+		}
+		qm.filter = func(mv string) bool { return semver.Compare(mv, v) >= 0 }
+		qm.preferLower = true
+		if !matchesMajor(v) {
+			qm.preferIncompatible = true
+		}
+
+	case strings.HasPrefix(query, ">"):
+		v := query[len(">"):]
+		if !semver.IsValid(v) {
+			return badVersion(v)
+		}
+		if isSemverPrefix(v) {
+			// Refuse to say whether >v1.2 allows v1.2.3 (remember, @v1.2 might mean v1.2.3).
+			return nil, fmt.Errorf("ambiguous semantic version %q in range %q", v, query)
+		}
+		qm.filter = func(mv string) bool { return semver.Compare(mv, v) > 0 }
+		qm.preferLower = true
+		if !matchesMajor(v) {
+			qm.preferIncompatible = true
+		}
+
+	case semver.IsValid(query):
+		if isSemverPrefix(query) {
+			qm.prefix = query + "."
+			// Do not allow the query "v1.2" to match versions lower than "v1.2.0",
+			// such as prereleases for that version. (https://golang.org/issue/31972)
+			qm.filter = func(mv string) bool { return semver.Compare(mv, query) >= 0 }
+		} else {
+			qm.canStat = true
+			qm.filter = func(mv string) bool { return semver.Compare(mv, query) == 0 }
+			qm.prefix = semver.Canonical(query)
+		}
+		if !matchesMajor(query) {
+			qm.preferIncompatible = true
+		}
+
+	default:
+		return nil, errRevQuery
+	}
+
+	return qm, nil
+}
+
+// allowsVersion reports whether version v is allowed by the prefix, filter, and
+// AllowedFunc of qm.
+func (qm *queryMatcher) allowsVersion(ctx context.Context, v string) bool {
+	if qm.prefix != "" && !strings.HasPrefix(v, qm.prefix) {
+		return false
+	}
+	if qm.filter != nil && !qm.filter(v) {
+		return false
+	}
+	if qm.allowed != nil {
+		if err := qm.allowed(ctx, module.Version{Path: qm.path, Version: v}); errors.Is(err, ErrDisallowed) {
+			return false
+		}
+	}
+	return true
+}
+
+// filterVersions classifies versions into releases and pre-releases, filtering
+// out:
+// 	1. versions that do not satisfy the 'allowed' predicate, and
+// 	2. "+incompatible" versions, if a compatible one satisfies the predicate
+// 	   and the incompatible version is not preferred.
+//
+// If the allowed predicate returns an error not equivalent to ErrDisallowed,
+// filterVersions returns that error.
+func (qm *queryMatcher) filterVersions(ctx context.Context, versions []string) (releases, prereleases []string, err error) {
+	needIncompatible := qm.preferIncompatible
+
+	var lastCompatible string
+	for _, v := range versions {
+		if !qm.allowsVersion(ctx, v) {
+			continue
+		}
+
+		if !needIncompatible {
+			// We're not yet sure whether we need to include +incomptaible versions.
+			// Keep track of the last compatible version we've seen, and use the
+			// presence (or absence) of a go.mod file in that version to decide: a
+			// go.mod file implies that the module author is supporting modules at a
+			// compatible version (and we should ignore +incompatible versions unless
+			// requested explicitly), while a lack of go.mod file implies the
+			// potential for legacy (pre-modules) versioning without semantic import
+			// paths (and thus *with* +incompatible versions).
+			//
+			// This isn't strictly accurate if the latest compatible version has been
+			// replaced by a local file path, because we do not allow file-path
+			// replacements without a go.mod file: the user would have needed to add
+			// one. However, replacing the last compatible version while
+			// simultaneously expecting to upgrade implicitly to a +incompatible
+			// version seems like an extreme enough corner case to ignore for now.
+
+			if !strings.HasSuffix(v, "+incompatible") {
+				lastCompatible = v
+			} else if lastCompatible != "" {
+				// If the latest compatible version is allowed and has a go.mod file,
+				// ignore any version with a higher (+incompatible) major version. (See
+				// https://golang.org/issue/34165.) Note that we even prefer a
+				// compatible pre-release over an incompatible release.
+				ok, err := versionHasGoMod(ctx, module.Version{Path: qm.path, Version: lastCompatible})
+				if err != nil {
+					return nil, nil, err
+				}
+				if ok {
+					// The last compatible version has a go.mod file, so that's the
+					// highest version we're willing to consider. Don't bother even
+					// looking at higher versions, because they're all +incompatible from
+					// here onward.
+					break
+				}
+
+				// No acceptable compatible release has a go.mod file, so the versioning
+				// for the module might not be module-aware, and we should respect
+				// legacy major-version tags.
+				needIncompatible = true
+			}
+		}
+
+		if semver.Prerelease(v) != "" {
+			prereleases = append(prereleases, v)
+		} else {
+			releases = append(releases, v)
+		}
+	}
+
+	return releases, prereleases, nil
+}
+
+type QueryResult struct {
+	Mod      module.Version
+	Rev      *modfetch.RevInfo
+	Packages []string
+}
+
+// QueryPackages is like QueryPattern, but requires that the pattern match at
+// least one package and omits the non-package result (if any).
+func QueryPackages(ctx context.Context, pattern, query string, current func(string) string, allowed AllowedFunc) ([]QueryResult, error) {
+	pkgMods, modOnly, err := QueryPattern(ctx, pattern, query, current, allowed)
+
+	if len(pkgMods) == 0 && err == nil {
+		return nil, &PackageNotInModuleError{
+			Mod:         modOnly.Mod,
+			Replacement: Replacement(modOnly.Mod),
+			Query:       query,
+			Pattern:     pattern,
+		}
+	}
+
+	return pkgMods, err
+}
+
+// QueryPattern looks up the module(s) containing at least one package matching
+// the given pattern at the given version. The results are sorted by module path
+// length in descending order. If any proxy provides a non-empty set of candidate
+// modules, no further proxies are tried.
+//
+// For wildcard patterns, QueryPattern looks in modules with package paths up to
+// the first "..." in the pattern. For the pattern "example.com/a/b.../c",
+// QueryPattern would consider prefixes of "example.com/a".
+//
+// If any matching package is in the main module, QueryPattern considers only
+// the main module and only the version "latest", without checking for other
+// possible modules.
+//
+// QueryPattern always returns at least one QueryResult (which may be only
+// modOnly) or a non-nil error.
+func QueryPattern(ctx context.Context, pattern, query string, current func(string) string, allowed AllowedFunc) (pkgMods []QueryResult, modOnly *QueryResult, err error) {
+	ctx, span := trace.StartSpan(ctx, "modload.QueryPattern "+pattern+" "+query)
+	defer span.Done()
+
+	base := pattern
+
+	firstError := func(m *search.Match) error {
+		if len(m.Errs) == 0 {
+			return nil
+		}
+		return m.Errs[0]
+	}
+
+	var match func(mod module.Version, root string, isLocal bool) *search.Match
+	matchPattern := search.MatchPattern(pattern)
+
+	if i := strings.Index(pattern, "..."); i >= 0 {
+		base = pathpkg.Dir(pattern[:i+3])
+		if base == "." {
+			return nil, nil, &WildcardInFirstElementError{Pattern: pattern, Query: query}
+		}
+		match = func(mod module.Version, root string, isLocal bool) *search.Match {
+			m := search.NewMatch(pattern)
+			matchPackages(ctx, m, imports.AnyTags(), omitStd, []module.Version{mod})
+			return m
+		}
+	} else {
+		match = func(mod module.Version, root string, isLocal bool) *search.Match {
+			m := search.NewMatch(pattern)
+			prefix := mod.Path
+			if mod == Target {
+				prefix = targetPrefix
+			}
+			if _, ok, err := dirInModule(pattern, prefix, root, isLocal); err != nil {
+				m.AddError(err)
+			} else if ok {
+				m.Pkgs = []string{pattern}
+			}
+			return m
+		}
+	}
+
+	var queryMatchesMainModule bool
+	if HasModRoot() {
+		m := match(Target, modRoot, true)
+		if len(m.Pkgs) > 0 {
+			if query != "upgrade" && query != "patch" {
+				return nil, nil, &QueryMatchesPackagesInMainModuleError{
+					Pattern:  pattern,
+					Query:    query,
+					Packages: m.Pkgs,
+				}
+			}
+			if err := allowed(ctx, Target); err != nil {
+				return nil, nil, fmt.Errorf("internal error: package %s is in the main module (%s), but version is not allowed: %w", pattern, Target.Path, err)
+			}
+			return []QueryResult{{
+				Mod:      Target,
+				Rev:      &modfetch.RevInfo{Version: Target.Version},
+				Packages: m.Pkgs,
+			}}, nil, nil
+		}
+		if err := firstError(m); err != nil {
+			return nil, nil, err
+		}
+
+		if matchPattern(Target.Path) {
+			queryMatchesMainModule = true
+		}
+
+		if (query == "upgrade" || query == "patch") && queryMatchesMainModule {
+			if err := allowed(ctx, Target); err == nil {
+				modOnly = &QueryResult{
+					Mod: Target,
+					Rev: &modfetch.RevInfo{Version: Target.Version},
+				}
+			}
+		}
+	}
+
+	var (
+		results          []QueryResult
+		candidateModules = modulePrefixesExcludingTarget(base)
+	)
+	if len(candidateModules) == 0 {
+		if modOnly != nil {
+			return nil, modOnly, nil
+		} else if queryMatchesMainModule {
+			return nil, nil, &QueryMatchesMainModuleError{
+				Pattern: pattern,
+				Query:   query,
+			}
+		} else {
+			return nil, nil, &PackageNotInModuleError{
+				Mod:     Target,
+				Query:   query,
+				Pattern: pattern,
+			}
+		}
+	}
+
+	err = modfetch.TryProxies(func(proxy string) error {
+		queryModule := func(ctx context.Context, path string) (r QueryResult, err error) {
+			ctx, span := trace.StartSpan(ctx, "modload.QueryPattern.queryModule ["+proxy+"] "+path)
+			defer span.Done()
+
+			pathCurrent := current(path)
+			r.Mod.Path = path
+			r.Rev, err = queryProxy(ctx, proxy, path, query, pathCurrent, allowed)
+			if err != nil {
+				return r, err
+			}
+			r.Mod.Version = r.Rev.Version
+			needSum := true
+			root, isLocal, err := fetch(ctx, r.Mod, needSum)
+			if err != nil {
+				return r, err
+			}
+			m := match(r.Mod, root, isLocal)
+			r.Packages = m.Pkgs
+			if len(r.Packages) == 0 && !matchPattern(path) {
+				if err := firstError(m); err != nil {
+					return r, err
+				}
+				return r, &PackageNotInModuleError{
+					Mod:         r.Mod,
+					Replacement: Replacement(r.Mod),
+					Query:       query,
+					Pattern:     pattern,
+				}
+			}
+			return r, nil
+		}
+
+		allResults, err := queryPrefixModules(ctx, candidateModules, queryModule)
+		results = allResults[:0]
+		for _, r := range allResults {
+			if len(r.Packages) == 0 {
+				modOnly = &r
+			} else {
+				results = append(results, r)
+			}
+		}
+		return err
+	})
+
+	if queryMatchesMainModule && len(results) == 0 && modOnly == nil && errors.Is(err, fs.ErrNotExist) {
+		return nil, nil, &QueryMatchesMainModuleError{
+			Pattern: pattern,
+			Query:   query,
+		}
+	}
+	return results[:len(results):len(results)], modOnly, err
+}
+
+// modulePrefixesExcludingTarget returns all prefixes of path that may plausibly
+// exist as a module, excluding targetPrefix but otherwise including path
+// itself, sorted by descending length.
+func modulePrefixesExcludingTarget(path string) []string {
+	prefixes := make([]string, 0, strings.Count(path, "/")+1)
+
+	for {
+		if path != targetPrefix {
+			if _, _, ok := module.SplitPathVersion(path); ok {
+				prefixes = append(prefixes, path)
+			}
+		}
+
+		j := strings.LastIndexByte(path, '/')
+		if j < 0 {
+			break
+		}
+		path = path[:j]
+	}
+
+	return prefixes
+}
+
+func queryPrefixModules(ctx context.Context, candidateModules []string, queryModule func(ctx context.Context, path string) (QueryResult, error)) (found []QueryResult, err error) {
+	ctx, span := trace.StartSpan(ctx, "modload.queryPrefixModules")
+	defer span.Done()
+
+	// If the path we're attempting is not in the module cache and we don't have a
+	// fetch result cached either, we'll end up making a (potentially slow)
+	// request to the proxy or (often even slower) the origin server.
+	// To minimize latency, execute all of those requests in parallel.
+	type result struct {
+		QueryResult
+		err error
+	}
+	results := make([]result, len(candidateModules))
+	var wg sync.WaitGroup
+	wg.Add(len(candidateModules))
+	for i, p := range candidateModules {
+		ctx := trace.StartGoroutine(ctx)
+		go func(p string, r *result) {
+			r.QueryResult, r.err = queryModule(ctx, p)
+			wg.Done()
+		}(p, &results[i])
+	}
+	wg.Wait()
+
+	// Classify the results. In case of failure, identify the error that the user
+	// is most likely to find helpful: the most useful class of error at the
+	// longest matching path.
+	var (
+		noPackage   *PackageNotInModuleError
+		noVersion   *NoMatchingVersionError
+		noPatchBase *NoPatchBaseError
+		notExistErr error
+	)
+	for _, r := range results {
+		switch rErr := r.err.(type) {
+		case nil:
+			found = append(found, r.QueryResult)
+		case *PackageNotInModuleError:
+			// Given the option, prefer to attribute “package not in module”
+			// to modules other than the main one.
+			if noPackage == nil || noPackage.Mod == Target {
+				noPackage = rErr
+			}
+		case *NoMatchingVersionError:
+			if noVersion == nil {
+				noVersion = rErr
+			}
+		case *NoPatchBaseError:
+			if noPatchBase == nil {
+				noPatchBase = rErr
+			}
+		default:
+			if errors.Is(rErr, fs.ErrNotExist) {
+				if notExistErr == nil {
+					notExistErr = rErr
+				}
+			} else if err == nil {
+				if len(found) > 0 || noPackage != nil {
+					// golang.org/issue/34094: If we have already found a module that
+					// could potentially contain the target package, ignore unclassified
+					// errors for modules with shorter paths.
+
+					// golang.org/issue/34383 is a special case of this: if we have
+					// already found example.com/foo/v2@v2.0.0 with a matching go.mod
+					// file, ignore the error from example.com/foo@v2.0.0.
+				} else {
+					err = r.err
+				}
+			}
+		}
+	}
+
+	// TODO(#26232): If len(found) == 0 and some of the errors are 4xx HTTP
+	// codes, have the auth package recheck the failed paths.
+	// If we obtain new credentials for any of them, re-run the above loop.
+
+	if len(found) == 0 && err == nil {
+		switch {
+		case noPackage != nil:
+			err = noPackage
+		case noVersion != nil:
+			err = noVersion
+		case noPatchBase != nil:
+			err = noPatchBase
+		case notExistErr != nil:
+			err = notExistErr
+		default:
+			panic("queryPrefixModules: no modules found, but no error detected")
+		}
+	}
+
+	return found, err
+}
+
+// A NoMatchingVersionError indicates that Query found a module at the requested
+// path, but not at any versions satisfying the query string and allow-function.
+//
+// NOTE: NoMatchingVersionError MUST NOT implement Is(fs.ErrNotExist).
+//
+// If the module came from a proxy, that proxy had to return a successful status
+// code for the versions it knows about, and thus did not have the opportunity
+// to return a non-400 status code to suppress fallback.
+type NoMatchingVersionError struct {
+	query, current string
+}
+
+func (e *NoMatchingVersionError) Error() string {
+	currentSuffix := ""
+	if (e.query == "upgrade" || e.query == "patch") && e.current != "" && e.current != "none" {
+		currentSuffix = fmt.Sprintf(" (current version is %s)", e.current)
+	}
+	return fmt.Sprintf("no matching versions for query %q", e.query) + currentSuffix
+}
+
+// A NoPatchBaseError indicates that Query was called with the query "patch"
+// but with a current version of "" or "none".
+type NoPatchBaseError struct {
+	path string
+}
+
+func (e *NoPatchBaseError) Error() string {
+	return fmt.Sprintf(`can't query version "patch" of module %s: no existing version is required`, e.path)
+}
+
+// A WildcardInFirstElementError indicates that a pattern passed to QueryPattern
+// had a wildcard in its first path element, and therefore had no pattern-prefix
+// modules to search in.
+type WildcardInFirstElementError struct {
+	Pattern string
+	Query   string
+}
+
+func (e *WildcardInFirstElementError) Error() string {
+	return fmt.Sprintf("no modules to query for %s@%s because first path element contains a wildcard", e.Pattern, e.Query)
+}
+
+// A PackageNotInModuleError indicates that QueryPattern found a candidate
+// module at the requested version, but that module did not contain any packages
+// matching the requested pattern.
+//
+// NOTE: PackageNotInModuleError MUST NOT implement Is(fs.ErrNotExist).
+//
+// If the module came from a proxy, that proxy had to return a successful status
+// code for the versions it knows about, and thus did not have the opportunity
+// to return a non-400 status code to suppress fallback.
+type PackageNotInModuleError struct {
+	Mod         module.Version
+	Replacement module.Version
+	Query       string
+	Pattern     string
+}
+
+func (e *PackageNotInModuleError) Error() string {
+	if e.Mod == Target {
+		if strings.Contains(e.Pattern, "...") {
+			return fmt.Sprintf("main module (%s) does not contain packages matching %s", Target.Path, e.Pattern)
+		}
+		return fmt.Sprintf("main module (%s) does not contain package %s", Target.Path, e.Pattern)
+	}
+
+	found := ""
+	if r := e.Replacement; r.Path != "" {
+		replacement := r.Path
+		if r.Version != "" {
+			replacement = fmt.Sprintf("%s@%s", r.Path, r.Version)
+		}
+		if e.Query == e.Mod.Version {
+			found = fmt.Sprintf(" (replaced by %s)", replacement)
+		} else {
+			found = fmt.Sprintf(" (%s, replaced by %s)", e.Mod.Version, replacement)
+		}
+	} else if e.Query != e.Mod.Version {
+		found = fmt.Sprintf(" (%s)", e.Mod.Version)
+	}
+
+	if strings.Contains(e.Pattern, "...") {
+		return fmt.Sprintf("module %s@%s found%s, but does not contain packages matching %s", e.Mod.Path, e.Query, found, e.Pattern)
+	}
+	return fmt.Sprintf("module %s@%s found%s, but does not contain package %s", e.Mod.Path, e.Query, found, e.Pattern)
+}
+
+func (e *PackageNotInModuleError) ImportPath() string {
+	if !strings.Contains(e.Pattern, "...") {
+		return e.Pattern
+	}
+	return ""
+}
+
+// ModuleHasRootPackage returns whether module m contains a package m.Path.
+func ModuleHasRootPackage(ctx context.Context, m module.Version) (bool, error) {
+	needSum := false
+	root, isLocal, err := fetch(ctx, m, needSum)
+	if err != nil {
+		return false, err
+	}
+	_, ok, err := dirInModule(m.Path, m.Path, root, isLocal)
+	return ok, err
+}
+
+func versionHasGoMod(ctx context.Context, m module.Version) (bool, error) {
+	needSum := false
+	root, _, err := fetch(ctx, m, needSum)
+	if err != nil {
+		return false, err
+	}
+	fi, err := os.Stat(filepath.Join(root, "go.mod"))
+	return err == nil && !fi.IsDir(), nil
+}
+
+// A versionRepo is a subset of modfetch.Repo that can report information about
+// available versions, but cannot fetch specific source files.
+type versionRepo interface {
+	ModulePath() string
+	Versions(prefix string) ([]string, error)
+	Stat(rev string) (*modfetch.RevInfo, error)
+	Latest() (*modfetch.RevInfo, error)
+}
+
+var _ versionRepo = modfetch.Repo(nil)
+
+func lookupRepo(proxy, path string) (repo versionRepo, err error) {
+	err = module.CheckPath(path)
+	if err == nil {
+		repo = modfetch.Lookup(proxy, path)
+	} else {
+		repo = emptyRepo{path: path, err: err}
+	}
+
+	if index == nil {
+		return repo, err
+	}
+	if _, ok := index.highestReplaced[path]; !ok {
+		return repo, err
+	}
+
+	return &replacementRepo{repo: repo}, nil
+}
+
+// An emptyRepo is a versionRepo that contains no versions.
+type emptyRepo struct {
+	path string
+	err  error
+}
+
+var _ versionRepo = emptyRepo{}
+
+func (er emptyRepo) ModulePath() string                         { return er.path }
+func (er emptyRepo) Versions(prefix string) ([]string, error)   { return nil, nil }
+func (er emptyRepo) Stat(rev string) (*modfetch.RevInfo, error) { return nil, er.err }
+func (er emptyRepo) Latest() (*modfetch.RevInfo, error)         { return nil, er.err }
+
+// A replacementRepo augments a versionRepo to include the replacement versions
+// (if any) found in the main module's go.mod file.
+//
+// A replacementRepo suppresses "not found" errors for otherwise-nonexistent
+// modules, so a replacementRepo should only be constructed for a module that
+// actually has one or more valid replacements.
+type replacementRepo struct {
+	repo versionRepo
+}
+
+var _ versionRepo = (*replacementRepo)(nil)
+
+func (rr *replacementRepo) ModulePath() string { return rr.repo.ModulePath() }
+
+// Versions returns the versions from rr.repo augmented with any matching
+// replacement versions.
+func (rr *replacementRepo) Versions(prefix string) ([]string, error) {
+	repoVersions, err := rr.repo.Versions(prefix)
+	if err != nil && !errors.Is(err, os.ErrNotExist) {
+		return nil, err
+	}
+
+	versions := repoVersions
+	if index != nil && len(index.replace) > 0 {
+		path := rr.ModulePath()
+		for m, _ := range index.replace {
+			if m.Path == path && strings.HasPrefix(m.Version, prefix) && m.Version != "" && !modfetch.IsPseudoVersion(m.Version) {
+				versions = append(versions, m.Version)
+			}
+		}
+	}
+
+	if len(versions) == len(repoVersions) { // No replacement versions added.
+		return versions, nil
+	}
+
+	sort.Slice(versions, func(i, j int) bool {
+		return semver.Compare(versions[i], versions[j]) < 0
+	})
+	str.Uniq(&versions)
+	return versions, nil
+}
+
+func (rr *replacementRepo) Stat(rev string) (*modfetch.RevInfo, error) {
+	info, err := rr.repo.Stat(rev)
+	if err == nil || index == nil || len(index.replace) == 0 {
+		return info, err
+	}
+
+	v := module.CanonicalVersion(rev)
+	if v != rev {
+		// The replacements in the go.mod file list only canonical semantic versions,
+		// so a non-canonical version can't possibly have a replacement.
+		return info, err
+	}
+
+	path := rr.ModulePath()
+	_, pathMajor, ok := module.SplitPathVersion(path)
+	if ok && pathMajor == "" {
+		if err := module.CheckPathMajor(v, pathMajor); err != nil && semver.Build(v) == "" {
+			v += "+incompatible"
+		}
+	}
+
+	if r := Replacement(module.Version{Path: path, Version: v}); r.Path == "" {
+		return info, err
+	}
+	return rr.replacementStat(v)
+}
+
+func (rr *replacementRepo) Latest() (*modfetch.RevInfo, error) {
+	info, err := rr.repo.Latest()
+
+	if index != nil {
+		path := rr.ModulePath()
+		if v, ok := index.highestReplaced[path]; ok {
+			if v == "" {
+				// The only replacement is a wildcard that doesn't specify a version, so
+				// synthesize a pseudo-version with an appropriate major version and a
+				// timestamp below any real timestamp. That way, if the main module is
+				// used from within some other module, the user will be able to upgrade
+				// the requirement to any real version they choose.
+				if _, pathMajor, ok := module.SplitPathVersion(path); ok && len(pathMajor) > 0 {
+					v = modfetch.PseudoVersion(pathMajor[1:], "", time.Time{}, "000000000000")
+				} else {
+					v = modfetch.PseudoVersion("v0", "", time.Time{}, "000000000000")
+				}
+			}
+
+			if err != nil || semver.Compare(v, info.Version) > 0 {
+				return rr.replacementStat(v)
+			}
+		}
+	}
+
+	return info, err
+}
+
+func (rr *replacementRepo) replacementStat(v string) (*modfetch.RevInfo, error) {
+	rev := &modfetch.RevInfo{Version: v}
+	if modfetch.IsPseudoVersion(v) {
+		rev.Time, _ = modfetch.PseudoVersionTime(v)
+		rev.Short, _ = modfetch.PseudoVersionRev(v)
+	}
+	return rev, nil
+}
+
+// A QueryMatchesMainModuleError indicates that a query requests
+// a version of the main module that cannot be satisfied.
+// (The main module's version cannot be changed.)
+type QueryMatchesMainModuleError struct {
+	Pattern string
+	Query   string
+}
+
+func (e *QueryMatchesMainModuleError) Error() string {
+	if e.Pattern == Target.Path {
+		return fmt.Sprintf("can't request version %q of the main module (%s)", e.Query, e.Pattern)
+	}
+
+	return fmt.Sprintf("can't request version %q of pattern %q that includes the main module (%s)", e.Query, e.Pattern, Target.Path)
+}
+
+// A QueryMatchesPackagesInMainModuleError indicates that a query cannot be
+// satisfied because it matches one or more packages found in the main module.
+type QueryMatchesPackagesInMainModuleError struct {
+	Pattern  string
+	Query    string
+	Packages []string
+}
+
+func (e *QueryMatchesPackagesInMainModuleError) Error() string {
+	if len(e.Packages) > 1 {
+		return fmt.Sprintf("pattern %s matches %d packages in the main module, so can't request version %s", e.Pattern, len(e.Packages), e.Query)
+	}
+
+	if search.IsMetaPackage(e.Pattern) || strings.Contains(e.Pattern, "...") {
+		return fmt.Sprintf("pattern %s matches package %s in the main module, so can't request version %s", e.Pattern, e.Packages[0], e.Query)
+	}
+
+	return fmt.Sprintf("package %s is in the main module, so can't request version %s", e.Packages[0], e.Query)
+}