cmd/go: restore @latest behavior and support @upgrade in 'go get'

'go get path@latest' may now downgrade a module required at a
pre-release or pseudo-version newer than the latest released
version. This restores the 1.12 behavior and the ability to easily
roll back from a temporary development version.

'go get path@upgrade' is like @latest but will not downgrade.
If no version suffix is specified ('go get path'), @upgrade is
implied.

Fixes #32846

Change-Id: Ibec0628292ab1c484716a5add0950d7a7ee45f47
Reviewed-on: https://go-review.googlesource.com/c/go/+/184440
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

Author: Jay Conrod

src/cmd/go/alldocs.go

@@ -59,12 +59,14 @@ dependency should be removed entirely, downgrading or removing modules
 depending on it as needed.
 
 The version suffix @latest explicitly requests the latest minor release of the
-given path. The suffix @patch requests the latest patch release: if the path
-is already in the build list, the selected version will have the same minor
-version. If the path is not already in the build list, @patch is equivalent
-to @latest. Neither @latest nor @patch will cause 'go get' to downgrade a module
-in the build list if it is required at a newer pre-release version that is
-newer than the latest released version.
+module named by the given path. The suffix @upgrade is like @latest but
+will not downgrade a module if it is already required at a revision or
+pre-release version newer than the latest released version. The suffix
+@patch requests the latest patch release: the latest released version
+with the same major and minor version numbers as the currently required
+version. Like @upgrade, @patch will not downgrade a module already required
+at a newer version. If the path is not already required, @upgrade and @patch
+are equivalent to @latest.
 
 Although get defaults to using the latest version of the module containing
 a named package, it does not use the latest version of that module's
@@ -178,7 +180,7 @@ func (v *upgradeFlag) Set(s string) error {
 		s = ""
 	}
 	if s == "true" {
-		s = "latest"
+		s = "upgrade"
 	}
 	*v = upgradeFlag(s)
 	return nil
@@ -202,8 +204,9 @@ type getArg struct {
 	// if there is no "@"). path specifies the modules or packages to get.
 	path string
 
-	// vers is the part of the argument after "@" (or "" if there is no "@").
-	// vers specifies the module version to get.
+	// vers is the part of the argument after "@" or an implied
+	// "upgrade" or "patch" if there is no "@". vers specifies the
+	// module version to get.
 	vers string
 }
 
@@ -249,7 +252,7 @@ func runGet(cmd *base.Command, args []string) {
 	}
 
 	switch getU {
-	case "", "latest", "patch":
+	case "", "upgrade", "patch":
 		// ok
 	default:
 		base.Fatalf("go get: unknown upgrade flag -u=%s", getU)
@@ -283,11 +286,11 @@ func runGet(cmd *base.Command, args []string) {
 
 	// Parse command-line arguments and report errors. The command-line
 	// arguments are of the form path@version or simply path, with implicit
-	// @latest. path@none is "downgrade away".
+	// @upgrade. path@none is "downgrade away".
 	var gets []getArg
 	var queries []*query
 	for _, arg := range search.CleanPatterns(args) {
-		// Argument is module query path@vers, or else path with implicit @latest.
+		// Argument is path or path@vers.
 		path := arg
 		vers := ""
 		if i := strings.Index(arg, "@"); i >= 0 {
@@ -298,10 +301,14 @@ func runGet(cmd *base.Command, args []string) {
 			continue
 		}
 
-		// If the user runs 'go get -u=patch some/module', update some/module to a
-		// patch release, not a minor version.
-		if vers == "" && getU != "" {
-			vers = string(getU)
+		// If no version suffix is specified, assume @upgrade.
+		// If -u=patch was specified, assume @patch instead.
+		if vers == "" {
+			if getU != "" {
+				vers = string(getU)
+			} else {
+				vers = "upgrade"
+			}
 		}
 
 		gets = append(gets, getArg{raw: arg, path: path, vers: vers})
@@ -358,7 +365,7 @@ func runGet(cmd *base.Command, args []string) {
 			// The argument is a package path.
 			if pkgs := modload.TargetPackages(path); len(pkgs) != 0 {
 				// The path is in the main module. Nothing to query.
-				if vers != "" && vers != "latest" && vers != "patch" {
+				if vers != "upgrade" && vers != "patch" {
 					base.Errorf("go get %s: can't request explicit version of path in main module", arg)
 				}
 				continue
@@ -376,8 +383,8 @@ func runGet(cmd *base.Command, args []string) {
 				continue
 			}
 
-			// If we're querying "latest" or "patch", we need to know the current
-			// version of the module. For "latest", we want to avoid accidentally
+			// If we're querying "upgrade" or "patch", we need to know the current
+			// version of the module. For "upgrade", we want to avoid accidentally
 			// downgrading from a newer prerelease. For "patch", we need to query
 			// the correct minor version.
 			// Here, we check if "path" is the name of a module in the build list
@@ -736,10 +743,6 @@ func getQuery(path, vers string, prevM module.Version, forceModulePath bool) (mo
 		base.Fatalf("go get: internal error: prevM may be set if and only if forceModulePath is set")
 	}
 
-	if vers == "" || vers == "patch" && prevM.Version == "" {
-		vers = "latest"
-	}
-
 	if forceModulePath || !strings.Contains(path, "...") {
 		if path == modload.Target.Path {
 			if vers != "latest" {
@@ -893,9 +896,10 @@ func (u *upgrader) Upgrade(m module.Version) (module.Version, error) {
 	// which may return a pseudoversion for the latest commit.
 	// Query "latest" returns the newest tagged version or the newest
 	// prerelease version if there are no non-prereleases, or repo.Latest
-	// if there aren't any tagged versions. Since we're providing the previous
-	// version, Query will confirm the latest version is actually newer
-	// and will return the current version if not.
+	// if there aren't any tagged versions.
+	// If we're querying "upgrade" or "patch", Query will compare the current
+	// version against the chosen version and will return the current version
+	// if it is newer.
 	info, err := modload.Query(m.Path, string(getU), m.Version, modload.Allowed)
 	if err != nil {
 		// Report error but return m, to let version selection continue.

src/cmd/go/internal/modget/get.go

@@ -79,7 +79,7 @@ func addUpdate(m *modinfo.ModulePublic) {
 		return
 	}
 
-	if info, err := Query(m.Path, "latest", m.Version, Allowed); err == nil && semver.Compare(info.Version, m.Version) > 0 {
+	if info, err := Query(m.Path, "upgrade", m.Version, Allowed); err == nil && semver.Compare(info.Version, m.Version) > 0 {
 		m.Update = &modinfo.ModulePublic{
 			Path:    m.Path,
 			Version: info.Version,

src/cmd/go/internal/modload/build.go

@@ -28,9 +28,10 @@ import (
 //   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. If current is "",
-//   "patch" is equivalent to "latest".
+//   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.
@@ -39,11 +40,12 @@ import (
 //   with non-prereleases preferred over prereleases.
 // - a repository commit identifier or tag, denoting that commit.
 //
-// current is optional, denoting the current version of the module.
-// If query is "latest" or "patch", current will be returned if it is a newer
-// semantic version or if it is a chronologically later pseudoversion. This
-// prevents accidental downgrades from newer prerelease or development
-// versions.
+// current denotes the current version of the module; it may be "" if the
+// current 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.
 //
 // If the allowed function is non-nil, Query excludes any versions for which
 // allowed returns false.
@@ -81,6 +83,10 @@ func queryProxy(proxy, path, query, current string, allowed func(module.Version)
 		ok = allowed
 		mayUseLatest = true
 
+	case query == "upgrade":
+		ok = allowed
+		mayUseLatest = true
+
 	case query == "patch":
 		if current == "" {
 			ok = allowed
@@ -202,9 +208,9 @@ func queryProxy(proxy, path, query, current string, allowed func(module.Version)
 			return nil, err
 		}
 
-		// For "latest" and "patch", make sure we don't accidentally downgrade
+		// For "upgrade" and "patch", make sure we don't accidentally downgrade
 		// from a newer prerelease or from a chronologically newer pseudoversion.
-		if current != "" && (query == "latest" || query == "patch") {
+		if current != "" && (query == "upgrade" || query == "patch") {
 			currentTime, err := modfetch.PseudoVersionTime(current)
 			if semver.Compare(rev.Version, current) < 0 || (err == nil && rev.Time.Before(currentTime)) {
 				return repo.Stat(current)

src/cmd/go/internal/modload/query.go

@@ -4,13 +4,19 @@ env GO111MODULE=on
 # @patch and @latest within the main module refer to the current version.
 # The main module won't be upgraded, but missing dependencies will be added.
 cp go.mod.orig go.mod
-go get -d rsc.io/x@latest
+go get -d rsc.io/x
+grep 'rsc.io/quote v1.5.2' go.mod
+go get -d rsc.io/x@upgrade
 grep 'rsc.io/quote v1.5.2' go.mod
 cp go.mod.orig go.mod
 go get -d rsc.io/x@patch
 grep 'rsc.io/quote v1.5.2' go.mod
 cp go.mod.orig go.mod
 
+# The main module cannot be updated to @latest, which is a specific version.
+! go get -d rsc.io/x@latest
+stderr '^go get rsc.io/x@latest: can.t request explicit version of path in main module$'
+
 # The main module cannot be updated to a specific version.
 ! go get rsc.io/x@v0.1.0
 stderr '^go get rsc.io/x@v0.1.0: can.t request explicit version of path in main module$'

src/cmd/go/testdata/script/mod_get_main.txt

@@ -10,11 +10,11 @@ grep 'require rsc.io/quote' go.mod
 
 cp go.mod.orig go.mod
 ! go get -d rsc.io/quote/x...
-stderr 'go get rsc.io/quote/x...: module rsc.io/quote@latest \(v1.5.2\) found, but does not contain packages matching rsc.io/quote/x...'
+stderr 'go get rsc.io/quote/x...: module rsc.io/quote@upgrade \(v1.5.2\) found, but does not contain packages matching rsc.io/quote/x...'
 ! grep 'require rsc.io/quote' go.mod
 
 ! go get -d rsc.io/quote/x/...
-stderr 'go get rsc.io/quote/x/...: module rsc.io/quote@latest \(v1.5.2\) found, but does not contain packages matching rsc.io/quote/x/...'
+stderr 'go get rsc.io/quote/x/...: module rsc.io/quote@upgrade \(v1.5.2\) found, but does not contain packages matching rsc.io/quote/x/...'
 ! grep 'require rsc.io/quote' go.mod
 
 # If a pattern matches no packages within a module, the module should not

src/cmd/go/testdata/script/mod_get_patterns.txt

@@ -17,7 +17,7 @@ stderr 'ReadZip not implemented for svn'
 # reasonable message instead of a panic.
 ! go get -d vcs-test.golang.org/svn/nonexistent.svn
 ! stderr panic
-stderr 'go get vcs-test.golang.org/svn/nonexistent.svn: no matching versions for query "latest"'
+stderr 'go get vcs-test.golang.org/svn/nonexistent.svn: no matching versions for query "upgrade"'
 
 -- go.mod --
 module golang/go/issues/28943/main

src/cmd/go/testdata/script/mod_get_svn.txt

@@ -9,18 +9,33 @@ env GO111MODULE=on
 # The v0.1.1 pseudo-version is semantically higher than the latest tag.
 # The v0.0.0 pseudo-version is chronologically newer.
 
-# 'get -u' should not downgrade to the (lower) tagged version.
+# Start at v0.1.1-0.20190429073117-b5426c86b553
 go get -d example.com/pseudoupgrade@b5426c8
+go list -m -u all
+stdout '^example.com/pseudoupgrade v0.1.1-0.20190429073117-b5426c86b553$'
+
+# 'get -u' should not downgrade to the (lower) tagged version.
 go get -d -u
 go list -m -u all
 stdout '^example.com/pseudoupgrade v0.1.1-0.20190429073117-b5426c86b553$'
 
-# 'get example.com/pseudoupgrade@latest' should not downgrade to
-# the (lower) tagged version.
-go get -d example.com/pseudoupgrade@latest
+# 'get example.com/pseudoupgrade@upgrade' should not downgrade.
+go get -d example.com/pseudoupgrade@upgrade
 go list -m all
 stdout '^example.com/pseudoupgrade v0.1.1-0.20190429073117-b5426c86b553$'
 
+# 'get example.com/pseudoupgrade' should not downgrade.
+# This is equivalent to 'get example.com/pseudoupgrade@upgrade'.
+go get -d example.com/pseudoupgrade
+go list -m all
+stdout '^example.com/pseudoupgrade v0.1.1-0.20190429073117-b5426c86b553$'
+
+# 'get example.com/pseudoupgrade@latest' should downgrade.
+# @latest should not consider the current version.
+go get -d example.com/pseudoupgrade@latest
+go list -m all
+stdout '^example.com/pseudoupgrade v0.1.0$'
+
 # We should observe the same behavior with the newer pseudo-version.
 go get -d example.com/pseudoupgrade@v0.0.0-20190430073000-30950c05d534
 
@@ -29,12 +44,21 @@ go get -d -u
 go list -m -u all
 stdout '^example.com/pseudoupgrade v0.0.0-20190430073000-30950c05d534$'
 
-# 'get example.com/pseudoupgrade@latest' should not downgrade to the
-# chronologically older tagged version.
-go get -d example.com/pseudoupgrade@latest
+# 'get example.com/pseudoupgrade@upgrade should not downgrade.
+go get -d example.com/pseudoupgrade@upgrade
 go list -m -u all
 stdout '^example.com/pseudoupgrade v0.0.0-20190430073000-30950c05d534$'
 
+# 'get example.com/pseudoupgrade' should not downgrade.
+go get -d example.com/pseudoupgrade
+go list -m -u all
+stdout '^example.com/pseudoupgrade v0.0.0-20190430073000-30950c05d534$'
+
+# 'get example.com/pseudoupgrade@latest' should downgrade.
+go get -d example.com/pseudoupgrade@latest
+go list -m -u all
+stdout '^example.com/pseudoupgrade v0.1.0$'
+
 -- go.mod --
 module x