cmd/go: omit new 'vendor/modules.txt' annotations if the go version is 1.13 or lower

Updates #33848

Change-Id: I887d78179d467030f4177d1834ccefee28a55c8a
Reviewed-on: https://go-review.googlesource.com/c/go/+/201257
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

src/cmd/go/internal/modcmd/vendor.go

@@ -19,6 +19,7 @@ import (
 	"cmd/go/internal/imports"
 	"cmd/go/internal/modload"
 	"cmd/go/internal/module"
+	"cmd/go/internal/semver"
 )
 
 var cmdVendor = &base.Command{
@@ -59,9 +60,16 @@ func runVendor(cmd *base.Command, args []string) {
 		modpkgs[m] = append(modpkgs[m], pkg)
 	}
 
+	includeAllReplacements := false
 	isExplicit := map[module.Version]bool{}
-	for _, r := range modload.ModFile().Require {
-		isExplicit[r.Mod] = true
+	if gv := modload.ModFile().Go; gv != nil && semver.Compare("v"+gv.Version, "v1.14") >= 0 {
+		// If the Go version is at least 1.14, annotate all explicit 'require' and
+		// 'replace' targets found in the go.mod file so that we can perform a
+		// stronger consistency check when -mod=vendor is set.
+		for _, r := range modload.ModFile().Require {
+			isExplicit[r.Mod] = true
+		}
+		includeAllReplacements = true
 	}
 
 	var buf bytes.Buffer
@@ -89,20 +97,22 @@ func runVendor(cmd *base.Command, args []string) {
 		}
 	}
 
-	// Record unused and wildcard replacements at the end of the modules.txt file:
-	// without access to the complete build list, the consumer of the vendor
-	// directory can't otherwise determine that those replacements had no effect.
-	for _, r := range modload.ModFile().Replace {
-		if len(modpkgs[r.Old]) > 0 {
-			// We we already recorded this replacement in the entry for the replaced
-			// module with the packages it provides.
-			continue
-		}
+	if includeAllReplacements {
+		// Record unused and wildcard replacements at the end of the modules.txt file:
+		// without access to the complete build list, the consumer of the vendor
+		// directory can't otherwise determine that those replacements had no effect.
+		for _, r := range modload.ModFile().Replace {
+			if len(modpkgs[r.Old]) > 0 {
+				// We we already recorded this replacement in the entry for the replaced
+				// module with the packages it provides.
+				continue
+			}
 
-		line := moduleLine(r.Old, r.New)
-		buf.WriteString(line)
-		if cfg.BuildV {
-			os.Stderr.WriteString(line)
+			line := moduleLine(r.Old, r.New)
+			buf.WriteString(line)
+			if cfg.BuildV {
+				os.Stderr.WriteString(line)
+			}
 		}
 	}
 

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

@@ -6,6 +6,7 @@ env GO111MODULE=on
 
 cd $WORK/auto
 cp go.mod go.mod.orig
+cp $WORK/modules-1.13.txt $WORK/auto/modules.txt
 
 # An explicit -mod=vendor should force use of the vendor directory.
 env GOFLAGS=-mod=vendor
@@ -145,19 +146,23 @@ stderr '^go: inconsistent vendoring in '$WORK/auto':$'
 stderr '^\texample.com/printversion@v1.0.0: is explicitly required in go.mod, but vendor/modules.txt indicates example.com/printversion@v1.1.0$'
 stderr '\n\nrun .go mod vendor. to sync, or use -mod=mod or -mod=readonly to ignore the vendor directory$'
 
-# 'go mod vendor' should write a 1.14 vendor/modules.txt even if
-# the go version is still 1.13.
+# If the go version is still 1.13, 'go mod vendor' should write a
+# matching vendor/modules.txt containing the corrected 1.13 data.
 go mod vendor
-cmp $WORK/modules-1.14.txt vendor/modules.txt
+cmp $WORK/modules-1.13.txt vendor/modules.txt
 
 go list -mod=vendor -f {{.Dir}} -tags tools all
 stdout '^'$WORK'[/\\]auto$'
 stdout '^'$WORK'[/\\]auto[/\\]vendor[/\\]example.com[/\\]printversion$'
 stdout '^'$WORK'[/\\]auto[/\\]vendor[/\\]example.com[/\\]version$'
 
-# When the version is upgraded to 1.14, -mod=vendor should kick in
-# automatically and succeed.
+# When the version is upgraded to 1.14, 'go mod vendor' should write a
+# vendor/modules.txt with the updated 1.14 annotations.
 go mod edit -go=1.14
+go mod vendor
+cmp $WORK/modules-1.14.txt vendor/modules.txt
+
+# Then, -mod=vendor should kick in automatically and succeed.
 go list -f {{.Dir}} -tags tools all
 stdout '^'$WORK'[/\\]auto$'
 stdout '^'$WORK'[/\\]auto[/\\]vendor[/\\]example.com[/\\]printversion$'
@@ -203,7 +208,7 @@ example.com/printversion
 example.com/version
 # example.com/unused => nonexistent.example.com/unused v1.0.0-whatever
 # example.com/version v1.2.0 => nonexistent.example.com/version v1.2.0
--- $WORK/auto/vendor/modules.txt --
+-- $WORK/modules-1.13.txt --
 # example.com/printversion v1.0.0
 example.com/printversion
 # example.com/version v1.0.0 => ./replacement-version