cmd/go/internal/gover: add new Go version package

Clean up Go version comparison.

CL 494436 added an ad hoc version comparison for the toolchain switch.

There are also other version comparisons scattered throughout the code,
assuming that using semver.Compare with a "v" prefix gives the right answer.
As we start to allow versions like "go 1.21rc1" in the go.mod file,
those comparisons will not work properly.

A future CL will need to inject Go versions into semver for use with MVS,
so do what Bryan suggested in the review of CL 494436 and rewrite the
comparison in terms of that conversion.

For #57001.

Change-Id: Ia1d441f1bc259874c6c1b3b9349bdf9823a707d4
Reviewed-on: https://go-review.googlesource.com/c/go/+/496735
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>

1 files changed, 9 insertions, 9 deletions

diff --git a/src/cmd/go/internal/modload/load.go b/src/cmd/go/internal/modload/load.go
index 550f837da08..d917b5defed 100644
--- a/src/cmd/go/internal/modload/load.go
+++ b/src/cmd/go/internal/modload/load.go
@@ -113,6 +113,7 @@ import (
 	"cmd/go/internal/base"
 	"cmd/go/internal/cfg"
 	"cmd/go/internal/fsys"
+	"cmd/go/internal/gover"
 	"cmd/go/internal/imports"
 	"cmd/go/internal/modfetch"
 	"cmd/go/internal/modindex"
@@ -122,7 +123,6 @@ import (
 	"cmd/go/internal/str"
 
 	"golang.org/x/mod/module"
-	"golang.org/x/mod/semver"
 )
 
 // loaded is the most recently-used package loader.
@@ -992,15 +992,15 @@ func loadFromRoots(ctx context.Context, params loaderParams) *loader {
 	if ld.GoVersion == "" {
 		ld.GoVersion = MainModules.GoVersion()
 
-		if ld.Tidy && versionLess(LatestGoVersion(), ld.GoVersion) {
-			ld.errorf("go: go.mod file indicates go %s, but maximum version supported by tidy is %s\n", ld.GoVersion, LatestGoVersion())
+		if ld.Tidy && versionLess(gover.Local(), ld.GoVersion) {
+			ld.errorf("go: go.mod file indicates go %s, but maximum version supported by tidy is %s\n", ld.GoVersion, gover.Local())
 			base.ExitIfErrors()
 		}
 	}
 
 	if ld.Tidy {
 		if ld.TidyCompatibleVersion == "" {
-			ld.TidyCompatibleVersion = priorGoVersion(ld.GoVersion)
+			ld.TidyCompatibleVersion = gover.Prev(ld.GoVersion)
 		} else if versionLess(ld.GoVersion, ld.TidyCompatibleVersion) {
 			// Each version of the Go toolchain knows how to interpret go.mod and
 			// go.sum files produced by all previous versions, so a compatibility
@@ -1008,12 +1008,12 @@ func loadFromRoots(ctx context.Context, params loaderParams) *loader {
 			ld.TidyCompatibleVersion = ld.GoVersion
 		}
 
-		if semver.Compare("v"+ld.GoVersion, tidyGoModSumVersionV) < 0 {
+		if gover.Compare(ld.GoVersion, tidyGoModSumVersion) < 0 {
 			ld.skipImportModFiles = true
 		}
 	}
 
-	if semver.Compare("v"+ld.GoVersion, narrowAllVersionV) < 0 && !ld.UseVendorAll {
+	if gover.Compare(ld.GoVersion, narrowAllVersion) < 0 && !ld.UseVendorAll {
 		// The module's go version explicitly predates the change in "all" for graph
 		// pruning, so continue to use the older interpretation.
 		ld.allClosesOverTests = true
@@ -1201,7 +1201,7 @@ func loadFromRoots(ctx context.Context, params loaderParams) *loader {
 			// Add importer go version information to import errors of standard
 			// library packages arising from newer releases.
 			if importer := pkg.stack; importer != nil {
-				if v, ok := rawGoVersion.Load(importer.mod); ok && versionLess(LatestGoVersion(), v.(string)) {
+				if v, ok := rawGoVersion.Load(importer.mod); ok && versionLess(gover.Local(), v.(string)) {
 					stdErr.importerGoVersion = v.(string)
 				}
 			}
@@ -1226,7 +1226,7 @@ func loadFromRoots(ctx context.Context, params loaderParams) *loader {
 // versionLess returns whether a < b according to semantic version precedence.
 // Both strings are interpreted as go version strings, e.g. "1.19".
 func versionLess(a, b string) bool {
-	return semver.Compare("v"+a, "v"+b) < 0
+	return gover.Compare(a, b) < 0
 }
 
 // updateRequirements ensures that ld.requirements is consistent with the
@@ -1903,7 +1903,7 @@ func (ld *loader) checkTidyCompatibility(ctx context.Context, rs *Requirements)
 		}
 
 		compatFlag := ""
-		if ld.TidyCompatibleVersion != priorGoVersion(ld.GoVersion) {
+		if ld.TidyCompatibleVersion != gover.Prev(ld.GoVersion) {
 			compatFlag = " -compat=" + ld.TidyCompatibleVersion
 		}
 		if suggestUpgrade {